Hydroboost Braking System

[circleD]

There are several threads bit when people just put info and questions in the middle of an old topic its hard to find.
Luckily its just the front you really need to bled and not the long rear ones.
My advice is bled them test them and bled them again. Its cheap insurance to bled to much than think you're good.
But yes the new cylinders will have some air pockets that take time to bled.

[DaveVA78Chieftain]

Hydroboost based system bleeding is the same as a normal brake system.  You can use 2 person pressure bleed, 1 person bleeder kit, gravity bleed or pressure bleed.  For 1 or 2 person bleed, perform initial bleed with engine off.  Then perform it once more with engine running (increases pressure at each wheel).

You said binding - One common issue is rubber brake hose failure.  A piece of hose brakes loose inside the rubber hose and acts like a flapper valve.   While it allows fluid to flow past the flapper when you press on the brake, it does not allow the fluid to flow back to the MC when you release the brake resulting in the caliper not releasing (brake binding).

Dave

[circleD]

And those hose part #s should be in Dave's Hydo Boost thread. It takes a lot of reading but you learn more than you want.

[DaveVA78Chieftain]

Different hoses for different applications. 
Most of the Dodge info is on my website. 
For Chevy, both Wagner and Raybestos list the hoses (Dodge too).

[Rickf1985]

If you are sure it is the front section of the master cylinder that is empty it is going to take a lot of fluid to fill those two calipers. Probably close to two quarts. The front brakes are the chamber closest to the hydrobooster and the rear are the farthest away. Even though you only did the front brakes once you get fluid to the calipers and out the bleeders it would be a good idea to bleed the rears also since this unit sounds like it has been sitting for a while. That will assure you that you have any moisture contaminated fluid out of the system. Another thing is that when you are bleeding, and yes the procedure is the same, try NOT to push the pedal all the way to the floor. On an old master cylinder the piston does not usually go very far down in the bore when working correctly. This leads to crud and rust forming in the bore closer to the bottom of the travel. Now if you push the pedal all the way down you are pushing those piston cups through all pf that crap in the bore. Sometimes it does nothing and sometimes you end up with a leaking master cylinder. I just try to err on the safe side.

[Cowinthfog]

Thank you guys for your ideas and help. After some more trouble shooting I discovered the right front line had collapsed internally, even though it looked fine. It blocked the line so well, that the previous owners just drove it until the all the brake material was gone and it wore most of the way through the pad backing plate! D:oH!  Yikes. It's all better now, and the system bled fine, of course, once the blocked line was replaced. Am I correct in understanding that the brakes do not use the same fluid as the power steering system? I have wondered because of how the two systems appear so closely tied together. Anyway, the Hydro Boost page and your help are VERY appreciated. I am getting it ready for it's first trip with us to a family reunion in the Blackfoot area, from Mount Vernon, WA, so excited! Thanks,


Josh

[eXodus]

Brake System Brake Fluid,
Hydroboost Unit with Powersteering, Powersteering fluid, ATF something

[boogie_man]

I just went through this with my 86 Chieftain. While replacing the leaking power steering lines and had the left front wheel and splash shield off, we checked the master cylinder and the rear chamber was really low as the brake feel was kind of "soft" and I double pumped brakes to stop and even the dash light started coming on.  I found and bought a new reservoir thru O'reilly's for like 70.00 bucks so figured change it and won't have to deal with a 30 year old part again.  Bench bled that unit and installed it and did the 2 man pump and bleed at all 4 corners and WOW, what a huge improvement !!  Used brake fluid for that and GM power steering fluid for p/s reservoir but the p/s pump kept buzzing, sounded like some fords do.  We then lifted the nose up and cranked the steering to full lock with engine off and let it sit for 1 hour each side, then topped off all fluids and fired it all back up to find she has that hydro-boost "hiss" sound.   Working perfectly now    

[eXodus]

my power steering needed about 300 miles to get all air out. so keep checking the next couple of trips.


and check you hydroboost unit regular now, mine started leaking a couple of weeks after getting new fluids. had to replace it...

[DaveVA78Chieftain]

squeals a lot - as in fan belt squeal when the belt is loose from being stretched?

The power steering pump is also used to pressurize the hydroboost.

[Rickf1985]

The belt is probably glazed and will not grip the pulleys.

[DaveVA78Chieftain]

I agree with Rick as far as the squeal is concerned.

it has plenty of fluids in it

Just curious, both sides of the master cylinder were full (you did not have to add fluid)?

[Rickf1985]

I just went back a couple posts and saw the pedal to the floor post. That would not be a symptom of a slipping belt, that would be a symptom of a bad master cylinder or a broken brake line or wheel cylinder. Second Dave's question, are both sides of the master cylinder full?

[Rickf1985]

The belt slipping will NOT cause the pedal to go to the floor. If the hydroboost is not working then the pedal will by high and very hard to push. If it is going to the floor then either the master cylinder went out, they do not usually just go out like that, or you have a massive amount of air in the system. IF the pedal goes to the floor and you have not had to add fluid then the only other thing it can be is the master cylinder. What you describe with the belt squealing when you hit the brake pedal tells me the hydroboost is working and the belt is bad or loose. OR, the power steering pump pulley or the crankshaft pulley are extremely worn from slipping belts. If that is the case then no matter how tight you get the belt it will slip until the offending pulleys are replaced.

[Rickf1985]

You need to bench bleed the master cylinder, it will usually come with the fittings needed to do that. If you do not bench bleed it you take the chance of trapping air in it and then you will have a hell of a time bleeding it even with help. Once it is bled on the bench install it and hook up the lines and what I would do is go to the right rear and open the bleeder. Fluid should start coming out, open it a good three or four turns and then just sit there and start at it and eventually you should see a few bubbles come out followed by cleaner fluid. The rear is technically done but I always like to go do the left rear also. This one should not produce any bubbles since the main line to the rear was already bled out but you can get clean fluid through this line also. And you never know, there may have been air in there from the failed mater cylinder. Then go to the right front and do the same thing, open the bleeder until the air stops or you get clean fluid and then the left front. At that point you should have good solid brakes, assuming the master cylinder was the problem and it sounds like it is. If for some reason you still have a spongy pedal then you can either do the gravity bleed over again or get someone to push the pedal.

[Jonbbrew]

I just found out I have Hydrovac not Hydro boost. Big difference I guess is troubleshooting...

[EldoradoBill]

Helpful write-up; thank you!


I replaced my Hydroboost last weekend (the brakes would apply and not release if you depressed the pedal while turning the wheel!!!) and I'd like to add a couple notes to anyone replacing theirs: First the actual R&R is much more straight-forward than you would think at first read. Just a bunch of nuts and bolts (of which most are locking which means they fight you every turn off and on!) the large nut holding the unit to the bracket is a bear to get off, you will need to start it with a BFH and chisel especially when you forget to remove the locking ring first  W%  then assemble the booster with bracket to the frame just snug before final tightening so it lines up smoothly. Check the free-play of pedal to booster and booster to master cylinder before assembling so you can make corrections on the bench/ground first.

[BigBad9902]

I have a 1988 Jamboree Rallye sitting on a Chevy C30 frame, and the rear brakes kept locking up on me. I replaced all hoses front and back, E-Brake cable, rear drums and shoes, front rotors, calipers and pads and also the proportioning valve. Thought it was all fixed only to find out now that the front calipers are sticking still. The driver side more so than the passenger, but none the less sticking. Could I have ruined the caliper by getting it so hot, (it actually discolored the caliper it got so hot), or could it maybe be something in the Master Cylinder? I have thoroughly bled the system and have zero air in it, so I just don't know. The Hydroboost and MC are about the only things I did not replace. Thanks for any help.

[Rickf1985]

I have never seen a caliper got hot enough to discolor without burning the seals out of it. It is possible that the seals hardened but the fact that both sides are hanging and you have not replaced the master cylinder makes me think more along the lines of a bad master cylinder. Since you have already replaced 90% of the brake system it would only make sense to finish the job and do the master cylinder also. And I would replace the front calipers again if they got that hot. The hydroboost can hold the brakes on but the pedal will not be returning to the top if it is so you will know if that is happening. And if the calipers have gotten that hot be sure to flush the fluid out with fresh fluid.

[BigBad9902]

Ok, found out that the MC was actually replaced, it was the Hydrobooster that had not been replaced yet. I ordered the new one and the brake pedal rod was about 2 inches shorter on the new one so looking for the right one now. Is there any adjustment built into the Hydroboost, and if so, where?

[Rickf1985]

You need a gap in the rad between the booster and the master. That may have been the problem before. The gap is very small though. If you have the right master and the right booster the gap should be correct. It is possible that you do not have the right master cylinder. Who knows what happened before you got it? If you have a friendly parts store maybe they can get you the right one so you can compare the distances from flange to piston on each master cylinder. If you do in fact have the right one they can just send the new one back.

[EldoradoBill]

I had to reuse the  pushrod from the old unit in the rebuilt hydroboost unit; the rebuild didn't come with one.


Bill

[cook elandan]

I have an issue with my 1989 Winnebago Elandan Chevy 454 unit. When I turn the steering wheel in either direction the brake pedal goes down on its own and will come back up when steering wheel is re-centered.  The steering wheel is hard to turn and will only turn about quarter turn in either direction. I am in my driveway and going forward or backwards the brake stops the motor home but still hard steering. When turning the steering wheel the engine does loose rpm's.  power steering fluid is full.  Any thoughts.  Thanks.

[Rickf1985]

It sort of sounds like you have a restriction in the return line after the hydroboost but you should have two return lines, one from the steering box and one from the Hydroboost going back to separate fittings on the pump. This would normally prevent what you are describing. Could you verify that you have two returns to the steering pump? If you do you will have three lines on the pump, if you only have one return you will have two lines. The return lines are held on with a hose clamp and the pressure line is a screwed in connection.

[cook elandan]

Rick, yes i have the two return lines, one pressure line and the fill line.  I guess i could remove the return line and make sure that fluid flows.