What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Brakes holding

U-711ipmc

U-711ipmc

1/2 ton status
 Premium
Joined
Jan 28, 2013
Posts
175
Reaction score
12
Location
Boyd, TEXAS
I need help!

1988 Suburban on tons, LS swapped with PSC pump and reservoir and ram, hydroboost brakes, Stock Dana 60 front brakes, Rear dana 70HD with aftermarket Disc brakes with e-brake (similar to ruffstuff rear calipers).

Problem: When I press the brake pedal down it stays down and the brakes stay engaged. They eventually come back up. Pedal push rod is in and spring is hooked up.

I have cleaned and lubed all calipers and slide pieces and pins. E-brake portion is fully disengaged. I am stumped. Hydrobooster needs replacing? Any thoughts on what to check?
 
Last edited:
When you pull it back, is it free moving or in a bind? Were they working before this problem? Motor on or off when it happens?
 
Pull the pedal back? Nothing.

On and off.

And as far as working before.... hahaha the vacuum brakes worked fine.

I’m going to check the push rod between the booster and master cylinder in the morning
 
Ok so checked the rod length between the booster and mc. It seems to be correct by what info I could find online.

I hate to throw 200$ at a booster and it not be it.
 
Is there an ABS module in this system. Sounds like there is a restriction in the brake hydraulics. I don't know what a hydroboost would if the power hydraulics were reversed.
 
No abs. After dealing with this crap all day...I’m finding that when it’s running it is pushing the booster piston against the mc. So I’m assuming it’s the booster. I’ve checked my routing of the return lines as some forum said that was the issue t’ing together. But I don’t have t’s, and the cooler is off of the gear box return not the brake booster return.
 
I'd try loosening the master cylinder mounting nuts next time the brakes start dragging or lock up--if that releases them,then the push rod does not have enough "free play" between the booster & master cylinder--as the brake fluid heats up and expands the brakes apply themselves and the return port in the master cylinder will be blocked by the piston,so the fluid cant return to the fluid chamber..
 
diesel4me said:
I'd try loosening the master cylinder mounting nuts next time the brakes start dragging or lock up--if that releases them,then the push rod does not have enough "free play" between the booster & master cylinder--as the brake fluid heats up and expands the brakes apply themselves and the return port in the master cylinder will be blocked by the piston,so the fluid cant return to the fluid chamber..
Click to expand...

A over full brake fluid lvl can also cuase the brakes to drag when hot. I don't believe this is your issue.
 
I’m going to try and replace the booster. It shouldn’t be applying pressure once it’s warmed up. It’s the shortest rod I have. And by all accounts online it’s correct.

The master cylinder level is between the half and full mark.
 
I agree you should try a spacer between the master and booster just to verify that rod isn't too long. This also lets you move things around a bit in case they aren't aligned quite right.

You should also look for mechanical binding in the pedal and linkage. The pedal bolt may be too tight, the pedal rod could be off-angle causing some rubbing with the grommet or something could be physically hitting. I had a similar problem when I first went hydroboost and it was the end of a pedal bolt rubbing on the steering column.

Which brake pedal are you using? If you're using the vacuum booster pedal, that could be putting the pedal rod at the wrong angle. I assume you've looked through the sticky thread at the top of the Garage forum and know all this stuff.

I've also heard that having air in the system can cause slow pedal return, but the HB is usually easy to bleed.

How does the pedal act when the engine isn't running?
 
Yes I have read the sticky here numerous times and many other forums.
I purchased a new reman booster last night and threw it on this morning before the rain started. So I have yet to road test it. It seems to return a lot stronger than the old one did. I bled it per the psc instructions. Lifting the front end etc.

The pedal is a hydro pedal.

I’m hoping this thing is fixed. Will update later.
 
New booster fixed the sticking brakes! Finally was able to test drive it this afternoon and it did great. Much more responsive, better feel. I hate that it wasn't simple to figure out. or at least simple to me. Thanks everyone for the ideas.
 
My friend had a 1 ton cube van at his shop with hydroboost that had a weird issue--sometimes when the driver went to take a left turn,the brakes applied themselves,like a ghost was stepping on the pedal!.:eek1:....once you turned the steering wheel straight again,the brake pedal would come back up and the brakes would release..

Didn't do it all the time,but often enough to make using the van quite hazardous,especially since it was a delivery vehicle driven by several different drivers..the owner decided to sell it "as-is" rather than throw more money at it,it had high miles--he said he felt it was haunted,and didn't want it in the fleet any more..
 
You must log in or register to reply here.

Latest Posts

Top Bottom