Brake question (pulls left under hard braking)

[ejp]

The short: I've been searching around, and think that I have a basic idea of what my problem might be - but am wondering how I can test the brake master on my '88 before throwing more money at parts.

The long: I bought an '88 Carrera this summer and have been doing some brake work on it. The front pads and rotors were toast when I bought the car, and the left front wheel would lock before any others would (and it seemed that I should have significantly more braking ability before lockup). I've been overhauling the brakes on my '88 over the past few weekends. I did the pads (EBC YellowStuff), rotors (Zimmerman coated), and flexible lines (SS) up front.

The car pulled to the left under any kind of braking. I had earlier noticed that the dust boots on the passenger side rotor were completely shredded and one of the pistons did not seem to move as smoothly as it should. I didn't have time to rebuild the caliper, so I just pulled it and replaced it with a new one. It is much, much better. However, under hard braking, the car still pulls to the left. Also, the left wheel will lock before the others every time (and I know that this car should have more stopping power).

When I tried using a Power Bleeder to bleed the brakes, the reservoir would not hold pressure. I saw no indication of fluid leaking out of the reservoir, master, at the caliper, or at any of the front hard/soft line junctions. At the speed that the power bleeder is losing pressure, if there were a fluid leak, I suspect that I should be able to see the fluid level dropping at the reservoir. I tried two different Power Bleeder caps and even tested the caps by placing my thumb over the hole - it held pressure. Rather than fussing with the Power Bleeder, I phoned a friend to pump the pedal and promptly ordered a MityVac. The pedal has a firm feel to it, and I am certain that the brake system is properly bled.

This suggests one of three possible issues:
1. Broken brake reservoir (most likely, but I can't see how this would cause the car to pull to the left under braking)
2. Bad MC (this would likely cause braking performance issues - but is the Power Bleeder pressure issue even related, and if so, why no fluid loss?)
3. Some sort of vacuum issue with the power assist (again, Power Bleeder pressure issue is unlikely related and could be throwing me off...and would this result in the car pulling to the left?)

So the question is: what should I look for/test before I R&R the brake master cylinder? Is there anything else that I've overlooked (e.g. bad driver's side caliper, needs a corner balance, etc)?

[dshepp806]

Hopefully you clamped off the drain (overflow) line at the MC, right?

Air can be a killer,..so I always bang my calipers (etc.) with a small rubber mallet to dislodge any small air bubbles that may lodge.

Of course, you want to be sure to install the calipers in the correct position......hard to believe, but I've heard of a few people doing it

Doyle

[ejp]

Originally Posted by dshepp806

Hopefully you clamped off the drain (overflow) line at the MC, right?

Air can be a killer,..so I always bang my calipers (etc.) with a small rubber mallet to dislodge any small air bubbles that may lodge.

Of course, you want to be sure to install the calipers in the correct position......hard to believe, but I've heard of a few people doing it

Doyle

Umm...clamped the overflow line? *sigh* - That's where that other line does, and explains why the power bleeder wasn't holding pressure. D'oh - my first 911, and I'm a little embarrassed by that oversight .

The rotors were definitely installed on the correct side (with the bleeder nipple up). I'm pretty sure that my power bleeder oversight notwithstanding, the brakes were properly bled, and the reservoir is most likely fine. Remember that the left lockup issue existed before I ever touched the system. What else could I have missed, and how can I test before just replacing parts (e.g. if it's an MC problem)?

[midnight911]

i had similar issue but for some stupid reason. the driver side tire was low on pressure. those hard side wall tire runs like run-flats. i did alignment, wheel bearing, brake rebuild, etc before checking the tire pressure...doh...

also, caster inconsistency contributes to similar symptom.

[ejp]

Originally Posted by midnight911

i had similar issue but for some stupid reason. the driver side tire was low on pressure. those hard side wall tire runs like run-flats. i did alignment, wheel bearing, brake rebuild, etc before checking the tire pressure...doh...

also, caster inconsistency contributes to similar symptom.

I regularly check my tire pressure, but I do need to get the alignment re-done. It was aligned and lowered after replacing f/r shocks and struts...but I believe that the new shocks will settle, and needs to be corner balanced and thus aligned again.

Perhaps I should do this before throwing more money at the brakes.

[joe88911]

was this ever resolved?