Well, i looked at every section of this forum and none covered my vehicle so i guess this is right place to post, if not i am sure someone will correct me.
Hello everyone. Hope i am in the right area. Could not find a mechanical discussion so i ended up here.
Now my current issue is the brakes.
This unit is a 1983 Holiday Rambler with the CHEVY P30 chassis. It has the HYDROBOOST brake system on it .
Nothing was wrong with the system when i started , i just wanted it all to be new. (lesson here... if not broke... don't fix) lol. So I replaced the entire braking system, hydrobooster, master cylinder, portioning block etc. , pads, calipers, lines power steering pump.
At first the system seemed to work for the first 5 miles but then i noticed the engine was dragging down. Note here that engine was warmed up to normal engine temp.
Then i realised it was the brakes applying themselves and the peddle was hard as a rock and all the way up so when i put my foot on the peddle is was no play in it. All six wheels heated up and started smoking so i know something is bad wrong. I had to remove the retuirn line on the booster and let the PS fluid out before i could move the thing. So with the fluid low as it was the PS pump could not build up pressure to lock the brakes , but i was able to drive it back home. (PS was really growling on turns and braking)
This brake system 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. Return lines are clear and new and no kinks.
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 main master cylinder to engage the tag axel master cylinder and that will engage the tag axel brakes.
Anyway, maybe someone out there has had the same issue and can help me locate the trouble maker. lol
Thanks for any help.

 

there may be an adjustment for the brake pedal push rod into the master cylinder. if not adjusted correctly, the brakes will self apply during a test drive. the m/c replenishing and compensation ports are closed off by the pushrod being to tight. every brake application pushes more fluid into the system. as the fluid heats up and expands from dragging brakes the condition get worse the longer you drive....the fluid needs to be able to move back into the reservoir when the pedal is release to disengage the brakes.


you may need some free play in the adjustment...either that or you got a wrong part is my guess.

 

Thanks for the reply. I am at my wits end on this thing and no end in sight!!
Here is what i have done so far.
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.
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.
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.
Thanks, CR

 

there should be a spec for brake pedal free play. this is measureable. Only one thing applies the brakes and that is through the m/c. all the other stuff just assists brake app. I would check pedal free play and if its ok, I might try putting the old mc back in.


what gm chassis is this built on? year?

 

Did you ever find a solution to your problem? I have a G 30 and we are convinced it’s bad geometry. The hydroboost is the wrong size and we can’t find one that fits

But I’m looking for any solution that doesn’t involve a custom-built booster arm

 

Did you follow the instructions of master cylinder about pre-bleeding it? Just a wild guess!

 

What year is the G30, where did you look for a replacement that knows what is the correct unit for your vehicle?
How was it determined to be the Hydroboost unit? They rarely gave much trouble..

 

disconnect the booster arm from the brake pedal, the brakes dont lock up, wheels spin

reconnect the arm, start the engine, brakes immediately lock up

i posted details here
https://chevroletforum.com/forum/exp...nt-fit-106752/