Van

Did you do my last test? To try and narrow down which side... which brake pad is getting "pushed back"?

jeeper31

Yes i did and the pads on both sides were in there pretty tight. There was no side to side movement. when I put my finger between the edge of the pad and the hub of the rotor I was able to push the pad out on the passenger side. i really didn't check the other side as I had decided to bring to the mechanic.

I did raise the car and turn the wheel with either the left front or the right front on the ground adn the pedal did press lower in BOTH situations.

Bringing it back the mechanic in about an hour.

Van

You recently changed the front wheel bearings, right?

Is it possible that you used the wrong parts? It sounds to me like you're getting flexing between the hub and the spindle.... wheel bearings are the only connecting part here.

I would suggest getting a fresh set of wheel bearings (and seal) and do that job again.

jeeper31

Definately used the right parts.

Van

I didn't mean that as a slight against you or anything... I meant it as a potential manufacturing error, or perhaps parts that were mislabeled from the factory.

As I see it, we know:
-a side load on the wheels causes the front brake rotor to "flex" or move in relation to the caliper and there-by causing the caliper pistions to move inward, which then requires extra brake pedal travel to move the brake pads back against the brake rotor.

By process of elimination (through replacement) we know it's not:
-the rotors
-faulty brake bleeding
-Loose caliper mounting bolts (because the calipers had to come off to change rotors)

So... potentials are:
-rotor connection to the hub (held in place by the wheel studs... is there any problem here? Do the lugnuts torque up properly?)
-hub flexing (hubs do fail, but usually catestrophically, and it is unlikely that both hubs are flexing...)
-hub connection to spindle (via wheel bearings)
-spindle flexing (again, unlikely both are flexing)

I know it sounds silly throwing more new parts at this thing, but because the wheel bearings were recently replaced, they stick out in my mind as a large variable.

Sometimes you get junk new parts -- a few years ago, I rebuilt my engine to "freshen it up" and I replaced all sorts of parts that were still functioning. I get it all together, she starts right up, I'm happy, and then the engine starts to overheat -- the $40 BRAND NEW thermostat was NFG (no fu-king good). I had to put the old one back in....

jeeper31

Van - Didn't think that was a slight at all. Sorry you thought I did. Short response was becasue I was driving and on my blackberry. I really appreaciate the help.

Came home from mechanic and he admittied he is puzzled. have to bring it in again and leave it.

I got home and thought again that I would narrrow it down to one side. Just thew the jack under the right side and raised car until right wheel was off the ground. Turned wheels left to right and brake pedal was lower upon pressing it. Did same thing with raising left side and at first it felt like the pedal was ok and then it happened.

I am beginning to think that there is nothing wrong and that is how low the pedal should be. Then I talk myself out of that when I just go around a curve and the pedal lowers again. At times it is startling cause the brakes dont engage where I think they should.

Van

I believe something is wrong... My car doesn't behave like that -- well, it did once, but I had a rear wheel bearing that went out! After hard right cornering, the pedal would sink way down... and then on the 2nd pump it would be back to normal.

I'm sorry, but I'm still stuck on the wheel bearing theory... In fact, I just had a thought -- and that can be dangerous... I think the inner race of your inner wheel bearings (the larger one) might be the wrong size for the spindle (or perhaps the spindle is worn and there's play). Between a propper fitting outter bearing, and the seal at the rear, the wheel would "feel" right when you try to shake it by hand -- but under extreme loading, the hub would move a little bit -- until the inner race of that inner bearing contacted the spindle shaft (let's say it's 1mm oversized). This movement -- this pivoting on the outter bearing -- would cause the brake rotor to move relative to the calipe, and push those pads back in.

Do you own a dial, digital or vernier caliper? If not, I'm sure your mechanic does. If it was my car, I'd take that hub off and measure the ID of that inner bearing and the OD of that spindle shaft. If the size difference is more than 0.002" (about 0.05mm), that's your problem.

Good luck, keep me updated!

Van

p.s. I'll have to see if I can logon with my blackberry!

jeeper31

This gives me new hope as this is the only other solution that seems viable. Whether or not I get around to doing it or I point my mechanic in that direction remains to be seen though.

Although it now comes to mind that i think the problem occurs on both sides. (Monkey wrench)

jeeper31

Looked up spindle last night in the PET and it seems that it is part of the steering knuckle WHICH is about $1000 from paragon. Hope this is not the problem.

The thing that has me confused is that the problem does not appear to be localized to one side. it seems to happen when either wheel is off the ground but does not happen when BOTH wheels are off the ground.

Van

Makes perfect sense to me -- BOTH inner wheelbearings (inner races) are the wrong size... When both wheels are in the air, there is no sideways force applied to the wheel, so the rotor stays right in position.

But, when one, or both wheels are on the ground, the force of turning them, in conjunction with a bearing that's the wrong size, causes that rotor to move relative to the caliper.

*Oh no, I just had another thought... Is there a chance that you put the inner wheel bearing into the hub upside down? That could also cause this symptom -- it would all go together nicely, but once put back on the spindle, it would really only be supported by the outside bearing...

jeeper31

Hmmm. It does make sense what you say although I when I had difficulty getting the races into the hub my mechanic said maybe I got the wrong bearings. I brought them to him and he verified they were the right ones and he pressnd them into the hub for me. If i recall correctly the bearing only fit into the races one way correctly so I am 99 percent sure that I put them in correctly. the mechanic also told me the bearings were spot on. I don't know if he actually looked or was talking about how I adjusted them.

Van

I bet he meant your tightening adjustment was spot on. Next, I think we have to measure everything with a caliper.

jeeper31

Dont' know fi this helps BUT upon th first press it seems that the pedal might be a bit spongier than usual. When I depress the brake pedal again itis solid.

Oddjob

Couple things to add to the discussion:

There is a lot more brake pedal travel required on Turbo S cars than n/a cars (same master cylinder but much larger caliper piston/cylinder volume), so the Turbo S pedal will feel spongy or soft compared to the 944S. I always much preferred the brake pedal feel of my S compared to the Turbo S. If you can access to another Turbo S, try to get an opportunity to drive it to compare the brake pedal feel to yours.

I would think any wheel bearing problem significant enough to allow the hub/rotor to wobble would give some other obvious symptoms - like grinding noises when turning or even vibration in the steering wheel at speed.

Different pad compounds will affect pedal effort/feel.

Brake bleeding. Can never be ruled out as a potential cause of brake problems. Cars with the ABS system are even more prone to bleeding problems, because of the much more complicated line routing through the hydraulic unit. If the car exibits any symptoms of brake lockup, instead of or initially before the ABS kicks in, its very likely air in the lines.

Master cylinder seals. If the seals in the master cylinder are worn, the brake system can slowly depressurize past the MC piston seals, back into the reservoir. This would cause a soft pedal when initially engaged, but pressure could be built up by the second push (if the seal are not completely shot, you can pump up pressure faster than it leaks past the seals).

Sorry, I did not read through this entire thread thoroughly; did you mention the mileage on the car, the type/brand/age of pads, fluid and when last changed?