brake upgrade question

[gimpstang]

I recently started putting my 89 XR back together after three years of sitting. I upgraded the brakes both front and rear (pbr front, t-bird rears) but forgot to gut the proportioning valve. When I was bleeding the brakes, the fronts seemed to bleed fine, but the rears are really spongy but, more importantly, the fronts won't release. When I apply the brakes, the fronts will clamp but won't let go on either side. The rears won't t clamp at all. The pedal also feels "different" when bleeding the rears vs the fronts. Are all these issues related to the proportioning valve or is there something else going on?

On a good note, she started up first time and idles like a dream.

[Mike McCreight]

Matt!
Gotta rotate the rear calipers around the rotor towards the front of the car, so that the bleeder screws are above the brake hose inlets.
Just pull the bolts out from the adapters where they thread into the caliper brackets.
I can't see the valve being too much of an issue, UNLESS the rear of the car is way up in the air. It's not really a proportioning valve, more of a low-tech anti-lock, reduces flow to the rear brakes when the car is under hard braking.
Let us know how i works out. (I got your Email...)

[gimpstang]

Would not rotating the calipers cause the fronts to stick?

[aviatorpa23]

If the fronts are staying "locked" or not releasing - something else is going on. If these are rebuilt PBRs the should apply and release without a problem. If there calipers are from previous owner/car residing in a wrecking yard, well ..... Next, maybe look at the master cyl. However gut the proportioning valve once the XR is road ready. You will be impressed with the stopping ability!!

[gimpstang]

yes they are staying clamped even after i release the brake pedal. however, if I open the bleeder screw, the pressure reduces and the calipers releases.

[aviatorpa23]

Obviously line pressure is being held - I would look upstream - master cyl. the attached from Ehow.com on trouble shooting master cylinders ... Clogged Ports and Leaks

The visual inspection begins with a look at the master cylinder. Any wetness near the rear of the master cylinder at the booster needs a closer look. Remove the master cylinder retaining nuts, and check for fluid between the cylinder and the booster. Any fluid here indicates a leaking master cylinder, and a replacement will be needed.
If no external leaks are found, clean and remove the reservoir cap. Check the fluid level and condition. Then have a partner push the brake pedal as you observe the fluid. When the pedal is released, a spurt of fluid should be observed in the reservoir. No spurt of fluid indicates a clogged replenish port, and the only repair is a new cylinder. Unless the fluid can release into the master cylinder reservoir when the pedal is released, the pressure cannot be relieved and will hold the brakes on only partially. Another check for this is to apply the brake, released it and open the bleeder screw. A clogged vent or replenish port will cause fluid to spurt out of the bleeder.

[gimpstang]

darn. I was afraid you were gonna say it was the master cylinder.

[DSPXR4ti]

Do you have pic's of your master cyl set up, or is it just stock?

Some of the Tbird master cyl. have a residual valve which will hold pressure to the front or rear calipers base on how you have it plumed.

But it does sound like a master cyl.

Ben

[gimpstang]

Its stock. I was going to see how the brakes felt on track before deciding on upgrading the MC.

[jkxr4ti]

I think it sounds more likely to be a master cylinder especially if its both fronts but dont rule out collapsed or clogged flex lines, especially if its been sitting a few years.