Installed new Hydrobooster, now my brakes are locked up

[TylerT]

Got the new unit on, then took it for a test drive. Brakes worked much better, and no more leak. I shut it off to go get my wife, came out and started it up. It wouldn't back down the driveway. It won't go forward or backward, the brakes are locked on. What in the world have I done?

 

[TylerT]

Okay, I let it cool off for about 30 mins. Went back out and drove it around about 1/2 a mile. The further I drove, the tighter the brakes got, and eventually I had to turn on my hazards and just roll stop signs cause I knew the brakes were locking again. Pulled into my driveway, stopped, and then tried to reverse. Sure enough, brakes are locked up. This is driving me crazy.

 

[RustBuket]

Sounds like some sort of check valve is sticking or something?

 

[TylerT]

I'm in a world of trouble then, cause I didn't even know brakes had check valves.

 

[k20]

Hey man, just saw this online, may be worth a shot, what pushrod did you use? According to this post on another forum I found http://www.woodalls.com/forums/Index.cfm/fuseaction/thread/tid/14208598.cfm If its adjusted too long they will drag, and if you reuse the one from the non-hydro, they will drag. Wortha shot.

 

[DieselDan]

Sorry to say, but sounds like you got a bad hydrabooster.

I had one of mine start dragging a few years ago. First I thought I had a driveline problem (vibration) . 'Course it didn't help that it was about -20F at the time and I was running to work. After I figured out the brakes were dragging ("Damn, that rotor's HOT!") I found that if I turned the engine off, pumped the brakes a few times to relieve the accumilator pressure, the brakes release; at least until I had to use the again

I swapped the booster out and got rolling again. I tried to dismantle the booster to why it stopped but ran out of time and patience

 

[TylerT]

Come on yall, I need some help. Anyone else?

 

[diesel4me]

Hmmmm...

I had the same thing happen to me after I swapped a rebuilt master cylinder on a truck of mine once (vacuum assist brakes though,gas engine)...I found out the pushrod "seat" in the piston on the new master was not as deep as the old one was,and as a result there was no "free play" thats needed to prevent the brakes from being "held on" after the brake fluid heats up and expanded..you should be able to move the pedal at least 1/8 to 1/4" before any contact is felt with the master cylinder,or the brakes will lock up after driving a few miles,and not release until the fliud cools again..

I don't know much about hydroboost though,even though my 82 K20 has it because its a diesel..but I assume the same thing applies to a hydroboost,if there isn't any "free play" between the master cylinder and whatever pushes against the piston in it(its a pushrod on the vacuum brakes,and some have an adjustment nut so you can lenghten or shorten it)...I ended up trading the master cylinder in for one that matched my old one exactly--I think the first one was boxed wrong... ..nothing like doing a job twice,and having to bleed it again too! hope this helps you out.

 

[TylerT]

Thank all of you guys so much. I'm about ready to give up, but I'm not gonna. Soon as I throw my papers and take me a little nap afterward, I'm gonna get this thing fixed.

 

[diesel4me]

try this..

I should have added this..when my truck screwed up that way,a mechanic told me to drive my truck far enough to get the brakes to drag,and then loosen the 2 bolts or nuts holding the master cylinder on right away,then see if the truck rolls freely--if it does,then its the pushrod adjustment thats too "tight" and there isn't enough free play !..but I'd think just "feelling" the brake pedal for any free play would do the same thing too.. --

I did as he said--my brake pedal had no free play after 5 miles and it started smelling like burning brakes,but after I backed the 2 nuts off several turns that held the master cylinder on,I was able to push the truck easily.-(I drove it home slowly that way,but I don't reccomend doing it!)--.thats when I removed it and went back to the parts store for another one that matched my old one..good thing my "core" was still at the store to match up!

 

[TylerT]

Thanks a million guys. Fixed it this morning. Something rang a bell when I read this thread. During the course of throwing 500 Sunday papers, I had a lot of time to think. And my thoughts closely matched the responses I got on here. I took the master cylinder off, sure enough, there was no room for the pushrod, it was it contact with the thing that it pushes. I found the spacer that came with the booster, that I thought I didn't need since the old one didn't have that spacer on it, and put it on. No more locking brakes. Thanks again for saving me from taking it to a brake shop.

 

[diesel4me]

Saved yourself some dough!...

Glad you found the problem! I bet a shop would have raped you to figure that one out! ..they probably would have just did what you did (put that spacer back on) and tell you they had to do all kinds of work,replace the hydroboost,etc..either that or they would have ripped their hair out trying to figure out the problem,and charged accordingly..after replacing things that didn't need to be..

This is why I prefer fixing my own vehicles,unless I know I'm going to screw it up because I'm not qualified--I leave the late model EFI vehicles to the experts who have all the scanners and computer tech..but I don't send my older GM truck out to a garage very often,if ever..( quite often my friend who fixes late model vehicles calls ME when he has an older GM truck that has him bamboozled!--but I'd never attempt to fix my 95 Contour myself! ).