seeking a mentor. Dual Hydrovac to Hydroboost brake conversion

[mytoolman]

I have been searching for the best way to convert the BRAKES in my 1973 Superior that sits atop a Dodge M400/RM500 Chassis from dual hydrovac to HYDRO BOOST.

I came across an impressive web site SWEETING PERFORMANCE on the Web.  (The site shows he has a shop out of Huntington Beach California if the info posted is to be trusted). The site claims they modify Bosch Hydro booster's to be as close to a "plug and play conversion" to replace Hydro Vac's as there is. Since I found his web site impressive, I started my conversation with Matt Sweeting.

Sadly, The only thing that Matt Sweeting has done was to see if I will go along in his efforts to have me GIFT him $960.00.

I had high hopes.  I interviewed others about this conversion, I learned that they had done something with hydro boosters to accomplish decent brake results for about a third less money.  I elected to go with a more expensive option and instead results get excellent results. I did not want to be one who had to report " It stops on a dime BUT the brake pedal is pretty touchy" or something similar that I had heard from others who did this all on their own.

I will tell you Mr Matt Sweeting knows all the correct things to ask and tell about this conversion I am seeking to do.
He easily convinced me to part with my money in hopes of having a excellently functioning, mostly plug and play, hydro boost power brake system to replace the dual hydra vac currently in my 1973 Superior Motor Coach that sits on a Dodge M400/RM500 Chassis.

Where Mr Sweeting fails is in his ability to actually get you a hydro booster at all it seems.

I have a chain of 19 emails. He responded each time except to the last two from me which were only written Sunday morning so he has not had a chance to answer. We have also had 2 additional phone calls to go along with the original where I was convinced to proceed.

It doesnt matter anymore if he does or doesnt answer.  I called Costco Citi Bank Visa and reported this transaction as an apparent scam. They have credited my $960 back to me even though they still formally have to investigate themselves and actually contact him for his side in this saga.

Im sure they will find in my favor. Searching the BBB and other such ways a consumer can vent shows Mr Sweeting has a history of non performance once he has achieved his goal of having you pay to build a system. He is apparently very proficient at doing nothing other than take your payment.

i will mention Mr Sweeting is not shy to respond harshly to anyone who claims he is a scammer on line. His retorts sound very convincing that the consumer is somehow the problem.

I paid for him to build me a unit that should have been in my hands in February. He still hasnt produced it. My recent request for a progress report had him move the goal post forward another 4 weeks. Its debatable if he has moved the goal post forward 3 or 4 times from his all his email replies. This last email stating 5 more weeks had my alarm bells blaring.

After his last email response to delay again, I searched the net for what others had experienced and my story was told over and over again. Most said they had given up and just lost their money. Im not sure how they paid but I know Costco's Citi Bank Visa really protects its card holder about the best in the industry so Im confident I will prevail with getting my money back.

Meanwhile I still have no functioning brakes in my rig.

I learned Sweeting uses a Bosch booster so I will be contacting Bosch. I learned he asked about the diameter of my original factory master cylinder to determine what Bosch hydro booster would mimic the pressure that the old system should produce when everything is functioning as designed. I learned he didnt have "the uncommon" 7/8 diameter clevis eye hole to give me that my old system uses. The clevis acts as the pedal movement adjustment at the end of the master cylinder push rod and is where the brake pedal mounts up.

Sweeting said he was going to make something happen with a 9/16th diameter clevis eye hole that are common. Its my guess he was going to have me enlarge the hole in the end of the brake pedal lever to 9/16" and supply the larger bolt also so the brake pedal assembly and the master cylinder adjustment rod would attach.

If anyone has successfully converted one of these M400/RM500 with Dual Hydro Vac , Front Disc Brakes and rear 14" rear drum brakes to instead use a hydro boost system,  Im all ears to find out what to do....Please help me here. I have lost a lot of valuable time waiting for Mr Sweeting to produce.

I WILL get this accomplished. I just want to do it as soon as possible and having to learn every nuance of how to get a successful result could take a fair amount of time. If you have already done it I will get things handled so much faster. thanks for reading and of course for any pearls you may offer.

ALSO---if Dave is listening...I know that Superior went to Hydro Boost in 1978 so a listing of the hydro boost parts they used for that model would be helpful. I see the extensive listing of brake parts for Superiors he has put together for hydro vac type rigs but did not see the hydro boost information listed....

[Smeds]

I'm sorry to read this, as I have a 1971 Travco with dual hydrovac that I am considering the same conversion, or possibly the more expensive air-hydraulic conversion.  I think mine sits on the M375, but it most definitely has dual hydrovacs, and I believe 1.75" master.  Hopefully this resolves positively for you!  I'm wondering now which direction I should go!!

[DaveVA78Chieftain]

I need to ask a basic question first to confirm M500 (RM400) chassis.  Do you have 17.5" tires or 19.5" tires?

17.5" = RM400 (M350) chassis with 12" x 3" rear brakes
19.5" = RM500 (M400) chassis with 15" x 4" rear brakes

Also do you have Bendix Twinplex (2 wheel cylinders / wheel) or Bendix Duo-Servo (1 wheel Cylinder / Wheel) rear brakes.

[mytoolman]

I have a RM500 (M400) Dodge Chassis 1973 Superior 2200 Motor coach. It has front Disc Brakes with 15"x4" rear drum brakes. EACH DRUM has TWO WHEEL CYLINDERS that operate the shoes inside the drum. It is a TWIN PLEX system with Dual HYDRO VAC(2) frame mounted units. It uses ONE SINGLE MASTER CYLINDER. This Lone master cylinder is mounted under the floor where the driver sits. The Master is a dual chamber type master cylinder to split the circuits.  The Wheels that my rig came from the factory with originally are still on my rig and they are the 19.5 diameter with the 5x8 lug pattern version. My rig has the 440 engine and 727 transmission.

[DaveVA78Chieftain]

I feel your frustration regarding the situation with SWEETING PERFORMANCE.  This is the first I have heard of them so know nothing about them. I will try to help the best I can but I have never done anything like this.  I usually just try to support stock setups.  With that said,

Note: Information I am showing is pulled directly from the 73 - 75 Dodge Motorhome service manual (with 74-75 Supplement).  Dodge P/N info is pulled directly from the 69 - 77 Dodge Motorhome Service Manual.  Additionally, Superior purchased the chassis from Dodge based on the size and length configurations of the RV body they wanted to build on top of it.  All this is Dodge products note Superior.

I show your current configuration here.

The configuration you desire to upgrade to is here.

Specifications

I will have to finish this later today (have to take wife to doctors appointment) but wanted to pass that info on for now.

Dave

[mytoolman]

Thanks Dave...I see that the hydro booster is no longer available....Is it a fair assumption that if I were to somehow come across a doner M500 rig from 1976-80 that was equipped as a hydro boost brake system that i could exchange what I have for what the doner would have to offer to end up with my brakes being hydro boosted?

It looks like the master cylinder in each of these has a 1-1/4" (1.25") bore and a 1-19/32"(1.59") stroke so if I could find a system from some other donor that had the same specs/characteristics I could fashion up some mounting brackets, and get hoses made to make it happen....

additionally Mr Sweeting had mentioned in our earliest conversation that he would be sourcing a Bosch Hydro Booster so if I could learn what the specs were for what was in the hydroboosted units from 76-80 maybe Bosch could supply one of theirs that would work the same.... Even better Maybe Bosch could cross over the part number from the original Dodge part number to what they have....

additionally....while my RM500 has DUAL HYDRO VAC(2) Units  that are frame mounted it only has a SINGLE MASTER CYLINDER. If I am reading this sheet correctly the spec sheet curiously lists my rig as having TWO MASTER CYLINDERS AND MINE CLEARLY HAS ONLY ever HAD ONE.

[DaveVA78Chieftain]

Actually your current setup has 3 master cylinders.  The main one attached to the Brake pedal and one attached to each booster (Hydro-VAc Booster).  The vacuum can of each Hydovac unit operates the associated master cylinder. When bleeding this type of system you have to bleed the brake pedal one first, then each of the hydro-vac master cylinders, then the rear wheel cylinders and lastly the front calipers. Air in the lines at any point will result in poor braking because the air can be compressed rather than transferring the applied force to the calipers/Wheel cylinders.  Air in the lines could be the root cause of your brake problems.

As the the 75 & later Hydroboost diagram I pointed to indicates, Dodge used the DUO-SERVO brakes on the Hydroboost vs the Twinplex brakes on your setup.  I have no clue what the impact of that is.

Let me do some research online to see if I can find a Hydroboost unit.

[DaveVA78Chieftain]

First, if you haven't already you need the to purchase the 3 volume 69 to 75 Dodge Service Manual set from the site store.  The service manual has the hydro-boost info in it for the M400 - M500 chassis set.  The parts manual covers 1969 thru 1977 which will be immensely helpful in identifying the needed parts.
Depending on year model of donor vehicle, you can also purchase 76-77 Service manual. Not sure if there is anything in it that is not in the 69 - 75 service manual.  Please understand that 98% of the ref info on my website was generated from those manuals.  All I did was try to organize all the information for a each configuration such that it was easily accessible from  one spot. Easy to do via links on a web site but impossible in a paper manual.

For reference, a plus is that you can use a 76 - 78 M400, M500, or M600 donor vehicle for 99% of the front end section parts. That helps your parts search immensely.  Because of the differences between a Hydro-Vac setup and Hydro-Boost you are going to pulling most everything out of the donor vehicle.

A. Master Cylinder (also available on EBAY) Grab the donor one also as there maybe a residual valve in the rear axle port.
B. Booster - I simply do not know if Cardone can rebuild a booster in time before your planned trip -
C. Mounting hardware, hoses, brackets, pedal mechanism, etc.
D. Combination Metering Valve / Brake Warning Switch - There is a Residual Valve on the rear of the metering valve to maintain light hydraulic pressure in the rear wheel drum brake hydraulic system to keep the wheel cylinder piston cups sealed against the piston bore during "off brake" periods.
E. You will have to make a many new brake lines.  Not as complex as a Hydro-Vac but still a lot of lines.

As I said before, I am clueless about how the system will react to a Twinplex vs DUO-SERVO rear brake system.
Front brakes should be ok as the same components were used on M400/M500/M600 systems.

I do not know if a 76 & later M500/M600 15" x 4" duo-servo rear brake system will bolt up to a Twinplex based axle.  cannot use a 75 M500 axle as it's also Twinplex.  Cant use a any M400 rear axle cause it's based on 12" x 3" brakes even though the front end booster/Master Cylinders are the same on M400/M500/M600.

Again, the Dodge manuals provide 98% of the info you need so they are well worth the purchase.
Read over the material on my web site for your new and old configuration so that you understand what everything does.

One last point, you may want to bleed the current system, all 3 master cylinders then each wheel before you do anything. That may solve all your brake problems and save yo9u lots of time and money.

Dave

[mytoolman]

Wow. You have obviously taken the time and effort to really consider what I am asking about. it is extremely rare that I find another who will consider from A-Z what I want and then answer me in complete sentences that flow so the answer will not leave me wondering about some points being talked about if " he meant this or did he mean that." In those situations of this of that, I do of course ask for clarification but it still isnt the same to help solve the concern and often answers still are not offered well. A well written guide where the small nuances are mentioned and detailed are so important to actually having success. Added to that I am a snob for sentences and paragraphs written correctly including having words used and spelled properly....What I am saying is thank you. If you have noticed my posts are usually on subjects that others are also considering. I do my very best to also go from A-Z to make sure the reader can accomplish the same task I have been involved with and NOT have to reinvent the wheel like I mostly might have had to do.... All of those prior words written could be summarized in just saying THANK YOU.

I am considering this conversion because I am not happy to be held hostage by parts availability or suppliers who wont be forth coming about the information they have so the best way to obtain needed parts can be achieved. I also realize our hobby involves mostly folks on limited incomes who have nostalgic hopes . I want to help them do that. Finding out that parts could have been purchased for half the price elsewhere if only the correct information were actually freely available is hard to swallow for most people who are owners of these rigs when they find out they could have. I contend that many become demoralized when they realize they cant get things handled without just plain paying for the information that in most other similar vehicle related situations is offered for free.

Originally I just wanted my brake system to work as it was originally designed. It has become increasingly clear how hard and unlikely it is that this type of hydrovac brake system will ever be durable and as cost effective to have for the way I will use my rig. I also really dont like the fact that rebuilt parts dont seem to hold up to the test of time today. I dont have the stomach, have endless energy or funds to repeat repairs when parts fail just after the warranty period etc. Specifically I am speaking to how frail rebuilt hydro vacs seem to be today.

  As time has gone on and it has been a long, long time now...maybe 5 years if I really think about it, since I started messing with getting a functional brake system. Most of that time was me getting motivated then having life or a parts road block get in the way form having a nice, relatively fast repair or solution. I am currently highly motivated to get excellent, reliable and "typically" functioning brakes... my motivation is much more that anytime in the past.

It is now VERY clear from your last post that there is NO real data for doing what I am seeking regarding my idea to convert from Hydrovac to Hydroboost since I have the Twin Plex rear brake system on my rig. There is much I dont know(yet) concerning the actual engineering. You bring up good points such as your question asking if some pressure must be held on the rear brake components such as wheel cylinders to have seamlessly, "typically" functioning brakes.

 I was probably being Pollyannaish in thinking I could completely interchange the later Dodge Hydroboost system into my slightly earlier rig and have immediate success.

 Im pretty stubborn about doing this conversion so I will be learning all I can. I am sure many questions will arise that hopefully can be answered without too much effort. i could stand to have an engineer or two from Bendix, Wagner and Bosch to have help here. Although I have ALSO had limited success when I have had such people involved with other projects. Often ego's etc can get in the way and hinder the final result from happening smoothly with this highly educated type of person. Its hard to know what you dont know until you realize that there is a question about that....

I am willing to do some trial and error stuff that will very likely be necessary since the hard data is not available...trial and error will be after all we know has been thought over...I want the most excellent brakes operation to happen in this rig just like I want it for every vehicle I would be in or those that are around me on the road also....

[DaveVA78Chieftain]

I just looked at the 78 - 81 Parts book. It says the M500/M600 still used 15" x 4" Twinplex brakes even though service manuals say they used DUO-SERVO brakes.  I suspect that all M500/M600 used Twinplex brakes so I doubt that is going to be a difference for you.

[mytoolman]

I just looked at the 78 - 81 Parts book. It says the M500/M600 still used 15" x 4" Twinplex brakes even though service manuals say they used DUO-SERVO brakes.  I suspect that all M500/M600 used Twinplex brakes so I doubt that is going to be a difference for you.

It is EXCELLENT that  M500/M600 from 1976-1981 used the SAME 15" x 4" TWINPLEX brakes for the rear AND the same ROTOR and Calipers also that are also on my earlier 1973 rig. I will now feel very comfortable about putting the effort into duplicating what was on these later models and expect 100 percent success. I was always concerned when I read your information that my rear brake system was super limited and thought parts were going to be very hard to get (they are hard to get) but now that pressure is relieved some since the years it was actually used extends an additional 8 years longer than I thought. I guess you too just learned that the twinplex stuff goes on these later models, that seemed to always be a question you had also...

I Dont have a 1976-81 parts book..... can you give me the MANUFACTURER'S Name (A) and the PART NUMBER (B) for EACH of these THREE 1976-81 M500/M600 parts??
 1. Master Cylinder:

1A.)__________________________              1B.) ____________________________

2. Hydro BOOSTER

2A.) ______________________________        2B.) ____________________________________

3. Rear Brake wheel cylinder "PRE BRAKE" PRESSURE applying VALVE"

3A) ______________________________________________________         3B) ________________________________________________

I spoke to Bosch and they said with the manufacturer name AND the part number they would be able to cross reference to one of their name brand HYDRO BOOSTER units.

[DaveVA78Chieftain]

1. Most all of the information you asked about is listed on the bottom half of my 76 & Later M500 Configuration page.

2. In the lower section of page 5-19 (pdf page 49) of the 69-77 Dodge MH Parts Manual is the note "Vendor Cross Reference - Booster Cylinders". Dodge Hydro-boost P/N 4031352 crosses to Bendix P/N 2770004.  Please note this booster was used on both GM and Dodge products.

3. Not exactly sure what you mean by

3. Rear Brake wheel cylinder "PRE BRAKE" PRESSURE applying VALVE"

.  However is that the 117psi Metering Valve (PSI Cut-in) value at the bottom of Dodge Motorhome Brake Reference Data

4. As far as rear wheel cylinders are concerned if you need them, you have to physically look at yours to see which one you have (1 3/8" or 1 1/2" bore).  Both are still available. Looking at online pictures the rubber seal end caps appear to be different for each version.

[mytoolman]

1. Most all of the information you asked about is listed on the bottom half of my 76 & Later M500 Configuration page.

2. In the lower section of page 5-19 (pdf page 49) of the 69-77 Dodge MH Parts Manual is the note "Vendor Cross Reference - Booster Cylinders". Dodge Hydro-boost P/N 4031352 crosses to Bendix P/N 2770004.  Please note this booster was used on both GM and Dodge products.

3. Not exactly sure what you mean by

3. Rear Brake wheel cylinder "PRE BRAKE" PRESSURE applying VALVE"

.  However is that the 117psi Metering Valve (PSI Cut-in) value at the bottom of Dodge Motorhome Brake Reference Data Yes I meant what you have now educated me is a "117psi Metering (Cut In) Valve". I of course will need to find one of these Metering Cut in Valves or something aftermarket that will provide the same function/result.

 I will look at your extensive Brake Reference Data Pages to determine who the Manufacturer is and what the part number is. The person I spoke to at Bosch seemed genuinely interested in my project and was willing to help if I could provide the very most basic information....ie a manufacturer and part number.

4. As far as rear wheel cylinders are concerned if you need them, you have to physically look at yours to see which one you have (1 3/8" or 1 1/2" bore).  Both are still available. Looking at online pictures the rubber seal end caps appear to be different for each version. I HAVE ALREADY REPLACED THE REAR WHEEL CYLINDERS that was done 2 years back so there is no need to deal with that. I even learned a technique to duplicate the crazy bends the steel brake lines that tie the two wheel cylinders together have so new steel lines are in my rig.  I also did the front calipers, new flex hoses etc at that same time. Additionally 8 months ago I replaced the MAIN master cylinder with a brand new one. I basically decided then when the brakes were still NOT functioning well, pumping up. grabbing and not releasing that  I was not going to give this original system any more of my time or money. I gave up after I bought a power bleeder and tried bleeding every bleeder front to back and back to front with no positive result.

 The expensive long lengths of pressure hose need replacement and both Hydro vacs and their master cylinder assemblies have not been touched yet so I am quitting on this original short lived in Dodge's history system in favor of the Hydro Boost system Dodge went to instead on the following models. Its my guess they too figured this particular Hydro vac idea was too troublesome to continue using in subsequent manufacturing of these medium duty truck chassis'  way back when....

[mytoolman]

1. Most all of the information you asked about is listed on the bottom half of my 76 & Later M500 Configuration page.

2. In the lower section of page 5-19 (pdf page 49) of the 69-77 Dodge MH Parts Manual is the note "Vendor Cross Reference - Booster Cylinders". Dodge Hydro-boost P/N 4031352 crosses to Bendix P/N 2770004.  Please note this booster was used on both GM and Dodge products.

3. Not exactly sure what you mean by

3. Rear Brake wheel cylinder "PRE BRAKE" PRESSURE applying VALVE"

.  However is that the 117psi Metering Valve (PSI Cut-in) value at the bottom of Dodge Motorhome Brake Reference Data Yes I meant what you have now educated me is a "117psi Metering (Cut In) Valve". I of course will need to find one of these Metering Cut in Valves or something aftermarket that will provide the same function/result.

 I will look at your extensive Brake Reference Data Pages to determine who the Manufacturer is and what the part number is for the MASTER CYLINDER since I still dont know that I appreciate it a bunch that you have kindly given me the BOOSTER INFO. The person I spoke to at Bosch seemed genuinely interested in my project and was (very) willing to help if I could provide the very most basic information....ie a manufacturer and part number.

4. As far as rear wheel cylinders are concerned if you need them, you have to physically look at yours to see which one you have (1 3/8" or 1 1/2" bore).  Both are still available. Looking at online pictures the rubber seal end caps appear to be different for each version. I HAVE ALREADY REPLACED THE REAR WHEEL CYLINDERS that was done 2 years back so there is no need to deal with that. I even learned a technique to duplicate the crazy bends the steel brake lines that tie the two wheel cylinders together have so new steel lines are in my rig.  I also did the front calipers, new flex hoses etc at that same time. Additionally 8 months ago I replaced the MAIN master cylinder with a brand new one. I basically decided then when the brakes were still NOT functioning well that I was quiting on this system. They were, pumping up. grabbing and not releasing and I had done extensive bleeding.   I was not going to give this original system any more of my time or money. I gave up after I bought a power bleeder and tried bleeding every bleeder front to back and back to front with no positive result.

 The expensive long lengths of pressure hose need replacement and both Hydro vacs and their master cylinder assemblies have not been touched yet so I am quitting on this original, short lived in Dodge's history, system in favor of the Hydro Boost system Dodge went to instead on the models they built that came after mine. Its my guess they too figured this particular dual Hydro vac idea was too troublesome to continue using in subsequent manufacturing of these medium duty truck chassis'  way back when....

[DaveVA78Chieftain]

I of course will need to find one of these Metering Cut in Valves or something aftermarket that will provide the same function/result.

I am guessing that you mean proportioning valve.  There are aftermarket adjustable brake proportioning valve.  My understanding is the front disc brakes require around 1500-2000 psi of pressure where the rear drum brakes will lock up around 600 psi.  So, the proportioning valve reduces the rear system pressure so the breaks do not lock up.

[DaveVA78Chieftain]

This video goes over the basics of what you are doing.  Includes some basic diagrams as well as a proportional and adaption.

[mytoolman]

I of course will need to find one of these Metering Cut in Valves or something aftermarket that will provide the same function/result.

I am guessing that you mean proportioning valve.  There are aftermarket adjustable brake proportioning valve.  My understanding is the front disc brakes require around 1500-2000 psi of pressure where the rear drum brakes will lock up around 600 psi.  So, the proportioning valve reduces the rear system pressure so the breaks do not lock up.

No I dont seem to be communicating properly. The valve I was asking who the manufacturer is and what the part number is is the one mentioned in an earlier post to me that you called a CUT IN VALVE. You wrote that its job is to KEEP PRESSURE on the rear wheel cylinder cups so that the rear brakes will react sooner since with it in action there is always some pressure on the wheel cylinder cups (117psi??)

Since you have mentioned it....Is the metering valve(proportioning valve) different in the later hydro boosted M500-M600 than what my 1973 M500 uses? I of course would could save a lot of time and effort to learn who manufactured it and also the related  part number if you have that also..

If you have the info at your finger tips, I am finding it confusing to determine the info I need from all the info you have in your data spec sheets...I have a mild dyslexia and enough ADHD to create issues with processing info sometimes. If I absolutely must use the published info I will get one of my friends to go thru everything with me to figure it all out. If you can oblige me: I need the Manufacturer and part number for the Master cylinder, the Cut in Valve, and the metering valve for the 1976-81 M500 since everything in those years used Hydro boost.

Additionally I did a Goggle search on what you have mentioned is the Bendix Cross Over for the Dodge Hydro Booster for those 1976-81 M500/M600 models (Dodge P/N 4031352) and found that the part number you reference as the Bendix Cross , namely 2770004, ONLY crosses to A REPAIR KIT for an unknown model of Hydro Booster, NOT AN ACTUAL HYDRO BOOSTER. So far in my limited effort to go any deeper I have not found what Hydro Booster part number that repair kit would repair or what GM or Dodge vehicle that applies to either..

[DaveVA78Chieftain]

1. The mfg of the chassis is Dodge so the original P/N's are Dodge P/N's.  The first column of the parts section is the Dodge P/N column on page 76 & Later M500 Configuration.  Each column going across is the cross reference P/N of that item for the aftermarket mfg if I had the info at that time.

2. You said you planned on finding a parts vehicle so I told you to grab all parts such as the combination valve/brake warning switch.  That switch is no longer manufactured so only available used.  For hydro-boost, the residual valve is installed on the output of that switch.  My guess is that it also acts as the proportioning valve also.

Otherwise, unless the Bosch rep has an alternative suggestion, you have to forgo the combo valve/residual valve and just use an aftermarket adjustable proportioning valve in order to reduce the rear brake pressure.

3. You said the Bosch rep would help you cross reference the Bendix P/N to a Bosch P/N which is your best option.  I gave you that info already.  Bendix no longer makes this hydro-boost unit.  The rebuild mfgs no longer have cores in stock to rebuild with.  If you find a donor vehicle you can send in the old unit to be rebuilt if it needs to be done.  I did see in the Precision Rebuilders book that Bendix P/N 2770004 crosses to P/N 2771173 which fits not only your application but several GM applications.

[mytoolman]

1. The mfg of the chassis is Dodge so the original P/N's are Dodge P/N's.  The first column of the parts section is the Dodge P/N column on page 76 & Later M500 Configuration.  Each column going across is the cross reference P/N of that item for the aftermarket mfg if I had the info at that time.

2. You said you planned on finding a parts vehicle so I told you to grab all parts such as the combination valve/brake warning switch.  That switch is no longer manufactured so only available used.  For hydro-boost, the residual valve is installed on the output of that switch.  My guess is that it also acts as the proportioning valve also.

Otherwise, unless the Bosch rep has an alternative suggestion, you have to forgo the combo valve/residual valve and just use an aftermarket adjustable proportioning valve in order to reduce the rear brake pressure.

3. You said the Bosch rep would help you cross reference the Bendix P/N to a Bosch P/N which is your best option.  I gave you that info already.  Bendix no longer makes this hydro-boost unit.  The rebuild mfgs no longer have cores in stock to rebuild with.  If you find a donor vehicle you can send in the old unit to be rebuilt if it needs to be done.  I did see in the Precision Rebuilders book that Bendix P/N 2770004 crosses to P/N 2771173 which fits not only your application but several GM applications.

So far I have not found a  hydro boosted, Front disc REAR DRUM donor.  Hydro Boost Donor's with rear DISC are common but the ones Ive found are  no larger than a Chevy 2500 so far. Am I wrong to think a 2500 brake system would be too small for the M500 twin plex?  Will a master cylinder and hydro booster from a Disc front AND DISC REAR set up even work at all plugged into  a Disc and DRUM set up ?

I know that FORD BUILT A E350 DIESEL POWERED van in 1998 that was front disc and 12 inch rear DRUM that was hydro boosted. They are rare though. Im not sure if that would work anyway since it only has a 12 inch rear drums not the large 15 inch like mine do.

I own a 2002 Ford E550 van cutaway truck that is 7.3 Powerstroke Diesel powered. It has FOUR WHEEL DISC BRAKE and HYDRO BOOST. If its no concern that the M500 is Drum and my E550's components  are 4 wheel disc I could copy  my e550 hydro boost system for the m500....the million dollar question is will the 4 wheel disc stuff work in the M500 disc drum set up ??

[eXodus]

Will a master cylinder and hydro booster from a Disc front AND DISC REAR set up even work at all plugged into  a Disc and DRUM set up ?

Yes it will. I've replaced my Chevy front Disc + Rear drum  Hydroboost unit with a 2011  GMC Diesel LMZ   Disc/Disc Hydroboost unit which is rated for 32.000lbs.

The hydroboost only creates force in one direction - it couldn't care less if you have 4 drums  2/2 or 4 discs.

The magic happens within the Master Cylinder and the Proportion Valve.   

I got lucky by just replacing the booster with a more powerful one - I didn't touch the Master and the proportioning valve and my Disc/Drum setup works perfect , the brake distance is way lower and pushing the pedal is soo easy.  But I read stories that this might end up with a touchy pedal.

If your pedal is too responsive after putting in the hydroboost - you may need to reduce the diameter of your master cylinder - that gives you more travel and such more control.   But try to drive it for a couple of days.   You might be just got used to having to use an high amount effort to break. 


Be aware - I got a Chevy P30  I don't know how much of this translates to a Dodge double booster setup.

[RockwoodMike]

Just to throw myself into the mix of all this..What if you go Frankenstein and use other manufacturer's brake systems..

I have a 73 D22 that I am building with that duel hydrovac system..Also I have a Ryder moving van (yellow box van) that has similar load ratings on the axles..Disc fronts..drum rears (duel rears) and all it has is a single vacuum master cylinder..When I had it running(rebuilding the motor right now) it would stop easily even when loaded with all my tools in the back..

The booster..master cylinder and proportioning valve are readily available..

This yellow van is a 94 E350 on a RV chassis. 

[mytoolman]

Will a master cylinder and hydro booster from a Disc front AND DISC REAR set up even work at all plugged into  a Disc and DRUM set up ?

Yes it will. I've replaced my Chevy front Disc + Rear drum  Hydroboost unit with a 2011  GMC Diesel LMZ   Disc/Disc Hydroboost unit which is rated for 32.000lbs.

The hydroboost only creates force in one direction - it couldn't care less if you have 4 drums  2/2 or 4 discs.

The magic happens within the Master Cylinder and the Proportion Valve.   

I got lucky by just replacing the booster with a more powerful one - I didn't touch the Master and the proportioning valve and my Disc/Drum setup works perfect , the brake distance is way lower and pushing the pedal is soo easy.  But I read stories that this might end up with a touchy pedal.

If your pedal is too responsive after putting in the hydroboost - you may need to reduce the diameter of your master cylinder - that gives you more travel and such more control.   But try to drive it for a couple of days.   You might be just got used to having to use an high amount effort to break. 


Be aware - I got a Chevy P30  I don't know how much of this translates to a Dodge double booster setup.

This is great information....thank you. I am currently waiting for a hydrobooster hose kit to arrive from Summit racing and then I will be fast at work to get the hydrobooster  I have chosen from a 2000 Chevy 3500 Diesel powered truck to fit in place. I have a master cylinder that has had about 100 brake attempts on it in place under the floor boards of my rig that I will use if it will give me the brake feel I am seeking.

I consulted with Steve Bush of Bush Power Brakes National City. Im not exactly why I neglected seeking his expertise in this project earlier. I did business with him 8 years ago when I he rebuilt the hydrovac in my 1955 Ford C600 that I use as my mobile tool store. He did an excellent job. I guess I was concerned he wouldnt like me to alter what the factory originally did and did not ask him for his opinion until a few days ago. Steve has owned his business for 46 years. He is 74 years old. He looks fit etc but is showing his age. He is from a time and an upbringing that matches mine so he has integrity. He nixed my idea of an "Electric" booster. He said "The Electric unit will be too expensive for the size of unit you need for an RV....now if we were talking the typical size electric that work in the custom made resto mods or hot rods I do then electric is wonderful...its a very clean result."

He too said trial and error is what will determine the master cylinder my rig will end up with. I hope my nearly brand new one I installed a year ago now will provide the brake feel and stopping performance I am seeking. I havent had the brakes act in a reasonable fashion EVER for my entire ownership of this rig so things like its "proportional" valve(sometimes called a metering valve?) and how they will react are unknowns too.

I am hopeful for an excellent result....the first time around...Im long over-due for a nice easy fix for once...

[mytoolman]

Just to throw myself into the mix of all this..What if you go Frankenstein and use other manufacturer's brake systems..

I have a 73 D22 that I am building with that duel hydrovac system..Also I have a Ryder moving van (yellow box van) that has similar load ratings on the axles..Disc fronts..drum rears (duel rears) and all it has is a single vacuum master cylinder..When I had it running(rebuilding the motor right now) it would stop easily even when loaded with all my tools in the back..

The booster..master cylinder and proportioning valve are readily available..

This yellow van is a 94 E350 on a RV chassis. 

thanks...my current brake pedal goes through the floor and its mastercylinder is right under the floor board where the driver sits. I know a hydrobooster/master cylinder will fit that same area right there under the floor board almost like it is made for it. The diameter of a hydrovac type unit like you have pictured would need a bunch of fabrication work to find a way into my rig.

 I think I have found the correct components to go hydroboost. 74 year old Steve Bush of Bush Power Brake's National City was kind enough to give me 10 minutes of his time Wednesday and told me what components to get and what to expect. He said even his almost 50 years of experience would mandate trial and error to be sure any given bore size master would have results I will be ok with. He suggested that I start with the master cylinder currently in place on my rig since it is new anyway and see what happens. If there is too much travel then a larger bore size will have to happen. If the pedal is to short and touchy then a smaller size bored master cylinder will have to be tried....Im hopeful what I have now for a master cylinder will be what works.

[mytoolman]

Just to throw myself into the mix of all this..What if you go Frankenstein and use other manufacturer's brake systems..

I have a 73 D22 that I am building with that duel hydrovac system..Also I have a Ryder moving van (yellow box van) that has similar load ratings on the axles..Disc fronts..drum rears (duel rears) and all it has is a single vacuum master cylinder..When I had it running(rebuilding the motor right now) it would stop easily even when loaded with all my tools in the back..

The booster..master cylinder and proportioning valve are readily available..

This yellow van is a 94 E350 on a RV chassis. 

thanks...my current brake pedal goes through the floor and its mastercylinder is right under the floor board where the driver sits. I know a hydrobooster/master cylinder will fit that same area right there under the floor board almost like it is made for it. The diameter of a hydrovac type unit like you have pictured would need a bunch of fabrication work to find a way into my rig.

 I think I have found the correct components to go hydroboost. 74 year old Steve Bush of Bush Power Brake's National City was kind enough to give me 10 minutes of his time Wednesday and told me what components to get and what to expect. He said even his almost 50 years of experience would mandate trial and error to be sure any given bore size master would have results I will be ok with. He suggested that I start with the master cylinder currently in place on my rig since it is new anyway and see what happens. If there is too much travel then a larger bore size will have to happen. If the pedal is to short and touchy then a smaller size bored master cylinder will have to be tried....Im hopeful what I have now for a master cylinder will be what works. Steve said a hydrobooster from a 1995 GM 3500 DIESEL Powered truck coupled with my current master cylinder should be good for my 1973 Rig that has a Dodge M500 chassis. In fact he said I will have way better brakes then it ever had since they will stop well and all the parts problems of the diaphram etc failures and general durability factors these old hydrovac's are prone to will not be a issue  any longer...

[eXodus]

I think I have found the correct components to go hydroboost. 74 year old Steve Bush of Bush Power Brake's National City was kind enough to give me 10 minutes of his time Wednesday and told me what components to get and what to expect. He said even his almost 50 years of experience would mandate trial and error to be sure any given bore size master would have results I will be ok with. He suggested that I start with the master cylinder currently in place on my rig since it is new anyway and see what happens. If there is too much travel then a larger bore size will have to happen. If the pedal is to short and touchy then a smaller size bored master cylinder will have to be tried....Im hopeful what I have now for a master cylinder will be what works.

That's what I did - just swap the booster and tested it.  Same Master Cylinder as before - much better performance. 

Give yourself a little time to test.