Converting to hydroboost

[cs641]

I have a Landau motorhome on a Dodge chassis with the factory hydro-vac brakes. I'd like to convert to hydroboost. Any of you guys done this conversion? If so what words of wisdom could you offer and what parts did you use?


Many thanks!

[khantroll]

Hi Cs641, which Dodge chassis is under it? That will determine how difficult it will be. I'm planning it on mine, but it's not easy on a non-8 lug chassis.


Thanks!

[Froggy1936]

In your computors search box type hydroboost install there is a lot of info incl complete install instuctions  Good luck its a lot of work !  Frank

[Rickf1985]

The biggest problem is do you have a way of mechanically mounting the Hydroboost so that the linkage will work from the brake pedal? The wheel lugs make no difference, the wheel cylinder size has to match the whatever the Hydroboost came off of within an eight inch one way or the other or you will have too much pedal travel or not enough travel. Otherwise you will need to change the wheel cylinder size and the the only way I would do that is if I were going up in size. Plus you have to get a hydroboost from an older truck that used rear drum brakes. Or you are going to be doing a lot of cross referencing to find the right master cylinder that will fit the booster and be sized correctly for your system.

To put it more simply, the hydroboost is nothing more than the assist unit for the master cylinder. You need first to figure out how to mount the hydroboost unit and then you have to figure out what master cylinder is going to work with first, your wheel cylinder size and configuration, disc or drum and second it has to fit the hydroboost unit.

You have a lot of research to do.

[cs641]

Thanks for the info. I have a 5 lug (unknown model) chassis and I noticed today the brake master cylinder is rear facing. I agree that the biggest challenge ahead is the mounting to make the linkage(s) work.


I have done a lot of searching already and not finding too much in regards to what I'm looking to do. I have done the conversion on a pickup truck but that's a lot less complicated than this beast. Basically trying to figure out what a good donor vehicle is if there's a specific one that is preferred or not preferred.


One thing I'm wondering is if an adjustable proportioning valve would help any if I got my HB unit from an all disc vehicle.

[Rickf1985]

The master cylinder is different for disc brakes due to the ratio of the piston sizes.

[khantroll]

Hi Rick,


The reason I asked about lugs was to find out which chassis he had. Converting to hydroboost on an m375 is different the converting to hydroboost on an m400.


I don't have my manuals in front of me at the moment, so I'm not sure which if any other chassis besides the m375 and the early m500 that use the 5 lug on 8 inch bolt pattern.


CS641, does your unit currently have front disc brakes? That might narrow it down. At any rate, there isn't a good "donor vehicle" for most of this. Most of the parts can be purchased brand new, but they cross reference to all kinds of applications. Dave's website: http://dave78chieftain.com/ gives you all the info you need to know about what brakes you currently have and the hydroboost versions that may have replaced them (most units changed to Hydrovac at some point).


As for your question about proportioning valves, I plan to use a universal one from summit.

[Rickf1985]

Get a disc brake rear out of a newer vehicle and then you do not need a prop valve as long as you have discs in the front. You will need a disc/disc master due to the extra volume needed by the calipers and you will have to match the master cylinder piston size to the caliper piston size to get the correct ration to keep pedal travel within spec.

[khantroll]

Rick,

Can you shed some light on that for me? All of the disc conversions I have seen (mostly on Jeeps) utilize a prop valve whether they are done with an axle swap or adapter kits. Does it just rely on the fluid dynamics of the brake fluid to execute different amounts of force between the front and rear?

Thanks!

[Rickf1985]

A proportioning valve limits pressure to the rear brakes in a panic stop and on trucks is usually mounted on the frame above the rear axle with a height sensing arm going to the axle. There are some prop valves mounted inline on the frame and some mounted in the outlet of the master cylinder. I think what you are looking at on the Motorhomes is a combination valve which has two functions. It holds off the front brakes long enough for the rear brake shoes to make contact with the drums on a disc/drum setup and it also incorporates the brake warning light which warns of there is a loss of pressure in the front or rear of the system.

This is NOT a prop valve. You need to find out which you have before building a system. The prop valve is supposed to keep the rear wheels from locking before the front. Personally I am not sure that can even happen in one of these monsters. Hm? W%

If it were me building the brake system I would find a 80s GM P30 with rear discs and get all of the brake stuff off of that and go with that. That way you have all matching components. The rear should bolt in with maybe some modifications on spring location. The front will be the challenge adapting the rotors and calipers. If it were easy everyone would do it. Hm? W%

[DaveVA78Chieftain]

A little ref info from the Dodge MH Service manual:
http://dave78chieftain.com/ControlValves.html

A little more ref info: http://www.rpmautodover.com/mccv.htm

[cs641]

Thanks for the info, I've been away from the computer.


I have the M500 chassis with disc front, drum rear. 5 lug.