Rear brakes locking up

[panteramatt]

So I installed the chevy front disc brake conversion and power booster a while ago on the wifes bronco. The pedal always seems hard to push although it stopped good. Well the booster valve was bad from the get go. Replaced it and its a LOT stronger but the rear brakes lock up pretty easy. It has the correct master cylinder. DO I have to remove the h block?

 

[nvrstuk]

Need more info as there are many variables.

What Chev conv?

What vac booster?

What is the "correct" m/c? Bore dia

Disc brakes rear or drum?

 

[Oldtimer]

The "H" block came with drum/drum brakes.
It was replaced with a combination (metering/proportioning/differential) valve that came with disc/drum brakes.

 

[panteramatt]

Need more info as there are many variables.

What Chev conv?

What vac booster?

What is the "correct" m/c? Bore dia

Disc brakes rear or drum?

Honestly I did this years ago and can not remember. I.ordered everything from one of these bronco supporters but dont remember who. It has drum rear.

 

[Broncobowsher]

Master cylinders often, but not always, have illogical port orientation. Front port runs rear brakes, rear port runs front brakes. But not every master cylinder follows this. Your "correct" master may be plumbed wrong. With unknown parts, it will only be an unknown.

Are the rear brakes 10" or 11"?

What front pads? If you have a set of used, glazed over, hard "lifetime" pads in the front and a fresh set of grippy rear shoes, the rear will want to lock first as the front isn't doing much. There are so many more variables in a brake system.

 

[nvrstuk]

Cheap fix for a system that isn't designed properly (meaning not designed from the factory or by a competent"brake" engineer" is to install an adjustable proportioning valve in the rear brake line. What this does is reduce the pressure to the rear drums and prevents premature lockup.

In a nutshell, drum brakes require less pressure to work effectively than discs do.

When you apply the SAME pressure from the mc to the frt disc brakes and the rear drum brakes you have two major issues: # 1 is the rear drums don't take as much pressure to "lock up" as you are pushing hard on the pedal to slow down as a disc does & #2 is weight bias shift as the vehicle's rear weight is transferred to the front & it is easier to lock the rear brakes since the rear axle doesn't have as much weight on it.

Installing an adj proportional valve allows you to "dial back" the pressure to the rear to prevent premature rear lockup.

They can work extremely well for retrofitting vehicles that were never designed with discs, installation of much more efficient &/or larger disc rotors/pads, larger boosters, trying to have more efficient brakes since you/we are running tires that are 50% larger diameter tires & might weigh 2-2 1/2 times as much... heavier rotating mass is much harder to slow down, etc, etc. So many variables.

 

[ntsqd]

Picture(s) of the m/c & its plumbing, and of the H block could help with narrowing down what you have.

 

[panteramatt]

Picture(s) of the m/c & its plumbing, and of the H block could help with narrowing down what you have.

I will check on the plumbing as soon as I get home and take a pic of the H block

 

[ntsqd]

Master cyl too. Ideally we could see how it is plumbed to the H block.

 

[panteramatt]

Master cyl too. Ideally we could see how it is plumbed to the H block.

you got it

 

[panteramatt]

Welp, cant figure out how to post a Pic. Anyway, the lines are ran correctly

 

[Broncobowsher]

Welp, cant figure out how to post a Pic. Anyway, the lines are ran correctly

How do you know? Just because they fit doesn't mean they are ran correctly.

 

[panteramatt]

Welp, cant figure out how to post a Pic. Anyway, the lines are ran correctly

How do you know? Just because they fit doesn't mean they are ran correctly.

Because the front port on the master cylinder runs to the rear brakes and vice versa. Is that not correct?

 

[panteramatt]

And the master is for front disc rear drum

 

[bmc69]

Cheap fix for a system that isn't designed properly (meaning not designed from the factory or by a competent"brake" engineer" is to install an adjustable proportioning valve in the rear brake line. What this does is reduce the pressure to the rear drums and prevents premature lockup.

In a nutshell, drum brakes require less pressure to work effectively than discs do.

I installed one of those on my trail rig and it worked the charm. 39.5 IROKS, hydroboost. Rear wheels locked up too quickly before installing and adjusting the inline valve to rear brakes.

 

[bax]

What Bill said. do that.

 

[Shimmy]

am i missing something? is the a proportioning valve installed?

 

[panteramatt]

No there is no propertioning valve

 

[Shimmy]

No there is no propertioning valve

if you changed from a stock setup a proportioning valve is necessary. i'd put one in, adjust and go from there.

 

[Dude 713]

I had the same trouble when I did my brakes. Finley figured out that the calipers were too tight in the bracket, took the grinder and opened things up a little bit and they work great now.