disc brakes with hydroboost dragging

[GYShah]

Hey guys

I have a hydrooboost brake system with 4 disc brakes and a new power steering pump

most of the time, things are great, nice even braking

however, on occassion, the brakes just start dragging and make the bronco completely undrivable until the engine cools down

Ive noticed it happens almost invariably if Ive been driving the engine a little hot for awhile usually in traffic and having to do some stop and go braking

seems to be the rears not the fronts
proportioning valve seems ok

just drove it daily for 3 weeks with a new steering pump and no problem and then it happens again last night (in traffic)

Is it too much heat on the master cylinder or somewhere along the hydraulic lines to the back brakes?

I need some suggestions, please.
Thanks!

 

[rmiller747]

Hey guys

I have a hydrooboost brake system with 4 disc brakes and a new power steering pump

most of the time, things are great, nice even braking

however, on occassion, the brakes just start dragging and make the bronco completely undrivable until the engine cools down

Ive noticed it happens almost invariably if Ive been driving the engine a little hot for awhile usually in traffic and having to do some stop and go braking

seems to be the rears not the fronts
proportioning valve seems ok


just drove it daily for 3 weeks with a new steering pump and no problem and then it happens again last night (in traffic)

Is it too much heat on the master cylinder or somewhere along the hydraulic lines to the back brakes?

I need some suggestions, please.
Thanks!

I had a similar issue. Have 4 wheel discs and hydro boost as well. my brakes were just dragging but never locked up. I had to install a proportioning valve (I used the bleed tool for the valve). Prior had the stock set up. And then had to bleed and bleed and bleed the brakes (GM discs).

Just my experience, not sure if it relates or not.

 

[GYShah]

thanks!
I do have a proportioning valve and this seems to distribute the braking evenly most of the time

But this problem is VERY intermittent and just catastrophic as far as driveablity until the engine cools

I have to think its related to engine heat or something else being overheated

 

[Apogee]

It sounds like you're building residual pressure to the rear brakes. Most commonly, this is caused by inadequate free play between the pedal pushrod and booster or booster and MC. If you loosen the MC when the issue occurs, do the rear brakes release? If so, then you've found your problem.

 

[TOFIC]

What master cylinder?? some masters are dual purpose units, disc/drum and disc/disc.
if it is new check the documentation that came with it. I doubt it is pedal drag as that would affect both brakes not just the rears.

 

[GYShah]

Chevy discs and Chevy master cylinder with a disc/disc setup

 

[GYShah]

Is it possible the master cylinder (which is just above the headers) is heating up too much?

 

[Apogee]

Is it possible the master cylinder (which is just above the headers) is heating up too much?

Is it too hot to touch? If so, then yes, it's probably too hot. If not, then probably not.

 

[TOFIC]

Chevy discs and Chevy master cylinder with a disc/disc setup

what HB unit??? a Astro unit maybe??

 

[brbuilder]

Had the same/similar problem. Installed a couple washers between the the HB unit and the MC. Quick easy way to check if the problem is the length of the rod from the MC to HB being just a little too long.

 

[GYShah]

So it turns out there was resistance in the return line from the hydroboost to the pump. I had read this was possible but couldn't find any kinks in the return hose so I thought it wasn't the problem.
I took the metal fitting off the hydroboost to check it and saw that it had been fitted with another metal piece to form a 90 degree elbow. I presume this was to let the return hose follow a less angled path back to the pump.
However, when the 2 metal fittings were screwed together, the threads themselves inside the elbow formed a bottleneck!!
So I simply removed the second fitting and attached the return hose directly to the first.
No elbow..no resistance in the return line..no fluid buildup in the hydroboost..and no more drag!!!

 

[toddz69]

Good to hear! Amazing the little things we find sometimes...

Todd Z.