Brake Problems 1983 Holiday Rambler Chevy Chassis

Hello everyone. Hope i am in the right area. Could not find a mechanical discussion so i ended up here.
Last issue i had was electrical and you folks solved that issue in chic time. Thanks again.
Now my current issue is the brakes.
I replaced the entire braking system, hydra booster, master cylinder, portioning block etc.
At first the system was perfect and operated as it should.
Then all of a sudden i was driving along and the the brakes started applying themselves, the peddle did not move tho. All six wheels heated up and started smoking so i figured i had a master cylinder issue?
Anyway, maybe someone out there has had the same issue and can help me locate the trouble maker. lol
Thanks for any help.

Did a quick search on hydroboost brakes applying themselves, lots of hits on work truck and 4X4 forums. Hydroboost is used on diesel pick ups and is an upgrade to some 4X4 guys. If it was one or two wheels it could be internally failed brake hoses or loose wheel bearings. You say all four wheels and that could be a power steering return hose, from hydroboost, restriction. Yours is a real early system so don't pay any attention to references to "rotten green switches", yours is likely all mechanical with no electronics, my 1993 Chevy P30 Bounder is all mechanical. There is a guy out there, username "oldusedbear", with lots of info on Hydroboost/autopark, he is agreeable to email help, and has some write ups on line.

Bill

Thanks for the reply and information. Yes, mine is all mechanical and no auto park stuff. All hoses of any type were replaced and i just finished checking them again for kinks etc. None found. I did find a small write up about the return line being kinked which would allow a buildup in the booster. However, i found no restrictions of any kind anywhere.
Yes, all SIX wheels were engaged and hot as fire when i stopped. The tag axel operates off an independent hydraulic over vacuum booster system that just applies to the tag axel itself. That vacuum booster is activated when the brake pedel is pushed causing brake fluid from the master cylinder to engage the rear master cylinder and that will engage the tag axel brakes. Crazy system as i see it.lol.
Where do i find that "oldusedbear" fellow?

Oldusedbear can be found by putting his user name in hydroboost brake search terms. Since you have no auto park you can also just google hydroboost brake problems and find numerous hits from truck forums. Join one that has a lot of activity and find a guru to help you. If you did the work thats been done so far yourself, a knowledgable guru will be able to help you sort it out because you apparently know how to use a wrench.

Bill

If the throw rod from the brake pedal to the master cylinder is too long it can cause the problem you describe.  Maybe when you changed everything you didn't notice the tight fit.  What happens is the master cyl does not fully return and prevents complete return of the pressurized brake fluid. 

You are right about that litte rod between the booster and mastercylinder. However on this one that little rod is not adjustable. I did notice however that while both ends were rounded , one end had a raised section right behind the ball. Never knew which went to what side so i guessed and it seemed to work OK.
NOW, for the big revelation!! I believe i solved my own problem!! Yaaaa. lol gona break my arm.
I had dismantled the entire components of the engine all at once and then 1 year later i re assembled it all with new parts.
Upon reinstalling the PS pump i believe i had switched the return lines for the power steering box and the hydro booster?? So today i switched them back and went for a test drive and it worked fine. I will go for long drive tomorrow and verify that was the problem.
I guess my question is about those return lines...just what is the difference in them? They are both the same size and less than an inch apart on the pump. Could it be there is some sort of check valve in one or the other of the lines?
Again, Thank you all for the input.

OK everyone, i am back to the drawing board again!!. It has been awhile since i brought this up and have just stopped on it cause i was so disgusted with it i wanted to just forget it.
Here is the update, I thought i had the problem fixed by switching the return lines on the gear box and the booster, BUT all that did was releive the pressure and lower the fluid level in the PS unit. So when i refilled the unit it started doing the same thing, LOCKING THE BRAKES UP AFTER ABOUT 2 MILES OF DRIVING.
I have perused every web forum (many of them) i can find and while some answers are similar to my problem none of them are exact. Furthermore all the solutions i have seen are something i already done.
Here is what i have done so far since my last post and i am really up against a wall.
1) Replaced the new booster with another new booster.
2) the rod between the MC and booster is fixed in length and is from the old system and there is no binding or excess there. The rod length and the distance between the ms and booster are exact. so no extra play or push there.
3) Took the high pressure valve out of new PS and found it to be defective in that it was not installed properly and the set screw was almost conpletely out of its seat. I was actually getting about 600 PSI.
4) Took high pressure valve and spacers out of old pump and put them in the new pump and with the spacer it is supposed to produce 1100 PSI, according to the spec sheet.
5) bled entire brake system and pedal then jumped from almost on the floor to about 3/4 way up. That is where it should be.
6) Was confident i had it fixed and then went for test drive and within three miles (everything was then warmed up) brakes locked up and i never touched the brake pedal just as before. Stopped and cut engine off and pumped brakes and was able to go about 1/2 mile and they would lock up again without me ever touching the pedal. Took some time to get back home.LOL
Don't know where to go to from here.
Tracing it all backwards there is just nothing else left: new booster, new MC, new PS pump, lines and pads and everything else in line. I have asked some local mechanics about it and they just kinda of shrug and say they don't know.
Thanks for any input and i know this is getting old but i am stuck.

Hello everyone. Hope i am in the right area. Could not find a mechanical discussion so i ended up here.
Last issue i had was electrical and you folks solved that issue in chic time. Thanks again.
Now my current issue is the brakes.
I replaced the entire braking system, hydra booster, master cylinder, portioning block etc.
At first the system was perfect and operated as it should.
Then all of a sudden i was driving along and the the brakes started applying themselves, the peddle did not move tho. All six wheels heated up and started smoking so i figured i had  master cylinder issue?    Did do everything flex hoses calipers front do you have disc on rear or wheel cylinders? I'm trying to get a grip on this. Unusual for sure.

Did you have contamination in the fluid?

I flushed the entire system in the beginning and the fluid was clear from the beginning so i am pretty sure there was no problem there. Matter of fact as i may have mentioned before, there was nothing wrong with the system to begin with,  I just wanted to make it all new again. The lesson here is, IF IT IS NOT BROKE DO NOT FIX IT. I will forever remember that lesson. lol
Thanks, CR

All parts match perfect? something may be wrong? mismatched? I think a part # run down may be necessary. Wish I had a simple solution. XL parts a/c delco, may need a jobber, they don,t sell to the public.

There are two things I'd check. First, even new hoses can fail internally.  The return hose is the suspect there, either collapsing or plugged by dirt or other.  Second, you're about down to a mechanical stop of some kind on the brake pedal. Since this seems temperature related, that would be less likely.

Final thought. Have you checked the proportioning valve between the two brake systems? I can't envision how it would cause the problem you describe, but?

Final, final thought. There must be a valve or switch that controls the boost pump, could it be sticking?

Just grasping straws here but....

I keep coming back to the rrturn circuit

Ernie

Hotdawg22 said:

The tag axel operates off an independent hydraulic over vacuum booster system that just applies to the tag axel itself. That vacuum booster is activated when the brake pedel is pushed causing brake fluid from the master cylinder to engage the rear master cylinder and that will engage the tag axel brakes. Crazy system as i see it.lol.
Where do i find that "oldusedbear" fellow?

Click to expand...

Look at your tag axle brake system, possibly plumbed or wired wrong? Search for schematics online for your set up. I have found that most mechanics eyes just glaze over when questioned about Hydroboost brakes. The lesson learned is "don't take something apart and walk away for any length of time. Finish it while your memory is fresh."

Bill

Check that the brake pedal has some "play" so as not to be too tight to the booster. The pedal may not be retracting far enough. Something could be hanging it up or return spring isn't good and some brake pushrods are adjustable for length. Replacement booster may have slightly different dimension.

I couldn't determine if you replaced the flexible hoses to the calipers or not.  While the problem seems to be hydroboost related it may be a flow restriction.  I have seen hoses pinched shut from rust inside the steel hose supports.  It can take considerable time for the pressure to subside and braking to cease.  Just a thought, I don't know your exact system.

Thanks for all the reply's/suggestions. I have replaced the flex hoses but i would have to rule them out because of all the wheels locking up. If one or two wheels locked up...it would most likely be the flex lines.
This is most definitely a case where the brakes are being applied internally and since i replaced the booster again and fixed the high pressure relief valve in the pump, it almost has to be pressure restriction related. 
Ernie, i too am leaning heavily towards that return line, even tho it is brand new the symptom's of a plugged return line are there. I will once again replace it with a new one. The proportioning valve is new and if it malfunctions, it only affects the front brakes OR the back but not all the brakes at the same time.
I have no hair left so i can't pull any more out, lol.

Being the problem is all the wheels, I'd be looking at the master cylinder. How hard is it to get to the lines going to the master cylinder? You might try taking a line loose after the lockup and see if it releases the brakes. I had a 80 Itasca that had a bad master cylinder and it would not release the front brakes after you stepped on the pedal for quite awhile. I went through the same thing, replacing calipers, hoses, ect. It was the master cylinder. Did you buy new or rebuilt? Mine was pretty hard to get to.

Food for thought, When it happenes start cracking a line or bleeder. If pressure is there it should fly out of there like a foots on the pedal. Start at the master.

Given the fact that the brakes are locked up, cracking a bleeder will relieve the pressure and free up all the wheels . But as soon as it starts rolling again pressure starts building up again.
The MC and booster were a pain to get to so when i did all this work i cut out that fender well shield and reshaped it and installed it with fender bolts and fastners so i can remove it all in 5 minutes. So once that shield is removed the MC is right there and accessable.
But, i am ruling the MC out cause as the pressure builds up in the booster it actually gets high enough to make the wiper move when i apply the brake pedal. The wipers are hydraulic and operate from the PS pump, just like the booster.
Thanks to all and still looking.

That sounds like the booster is causing the problem but why? Not sure. The booster is the assist you to brake, but not brake for you.