Brake squeak when running hard

gremlin · 09-11-2016, 04:07 PM

I was out at a local drivers education even last week and as I started to push my car harder through the back section I started to hear a squeal when I applied the brakes, it sounded like a tire locking up on an airplane on landing, and there were definitely no lock up's occurring. it wouldn't start happening until I was several laps into the session and would stop if I backed off the pace a bit.

IN all cases I was turning through a left hand corner when it occurred, and once I heard it just coming off the track, I was unable to replicate it on the way home. I also tried to press harder on the pedal when it happened and that seemed to make it stop but I've not heard it in 20+ years of tracking the car and I had not heard it last month at the previous track day (different track though).

Wheel bearings were new in the past year, so were the brake pads, it's a 1971 911 T with a bigger motor, but I have 964 brakes front and rear, and hats that are sized to match (diameter of a '89 Carrera but thickness of 964 hat). The front hats are looking a touch worn (slots are getting harder to see in them), so I don't know if that has anything to do with it.

Anyone see anything like this before?

thank you!

cashman · 09-11-2016, 04:36 PM

"Wheel bearings are new".........Make sure the fronts aren't too loose. Since it's happening on the turns I would start there.

gremlin · 09-12-2016, 06:45 AM

Quote:

Originally Posted by cashman

"Wheel bearings are new".........Make sure the fronts aren't too loose. Since it's happening on the turns I would start there.

Cool, guidance on this? I've done the tighten until you can't move the washer and back it off until you can thing twice, and still have a slight play I get when I'm rocking the wheel itself. but I have to get on the wheel on the lift and reef on it, can't do it on the ground.

faverymi · 09-12-2016, 07:51 AM

Check your tires walls and shoulders.

I bet it's just rubbing.

Roll fenders . Realign.

gremlin · 09-12-2016, 09:18 AM

good thought but unlikely. Alignment just finished nothing is touching, also doesn't jibe with it happening when the brakes are hot, it wasn't in the fastest corners...

cashman · 09-12-2016, 10:16 AM

Quote:

Originally Posted by gremlin

Cool, guidance on this? I've done the tighten until you can't move the washer and back it off until you can thing twice, and still have a slight play I get when I'm rocking the wheel itself. but I have to get on the wheel on the lift and reef on it, can't do it on the ground.

My advice..... remove the grease cap. Loosen the clamp bolt. Spin the wheel hard, as the wheel is rotating, tighten the clamp bolt only finger tight and your done. Don't tighten it so much that it stops rotating. My guess is when you are backing off you are backing off too far. Go for a test drive and see if it solves the problem. If it does, your bearing was too loose. If it doesn't....move onto plan B.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by gremlin

I've done the tighten until you can't move the washer and back it off until you can thing twice, and still have a slight play I get when I'm rocking the wheel itself.

I am talking way out of school here.

When I tighten wheel bearings, I would never allow it to be loose enough to spin the washer. Call me an idiot (and that's ok if I am - I learn something every day here) but I tighten until I feel the tire/wheel slow down with a hand spin and then back off enough to JUST spin freely.

I have no reference point other than how I have done it on everyday cars and I have never done it on a track car with hats.

gremlin · 09-12-2016, 11:32 AM

Looking here Porsche 911 Front Wheel Bearing Replacement | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article the directions to replace the wheel bearings say:

You'll now need to adjust the wheel bearing. While rotating the disc and bearing hub tighten the locking nut in small increments until the thrust washer (yellow arrow) can barely be moved back and forth with the light push of the tip of a screwdriver. Then tighten the 6mm bolt on the end of the nut to spec.

this is what I did to tighten the bearings. Per my original post the noise only occurs when the brakes have heat in them, I had to do three or four laps getting it up to speed and then be driving it hard, as soon as I backed off the pace for a lap it would go away the lap after the back off, and return when I Got back on it, so I Can't possibly "take it for a test drive" unfortunately it'll require a track day.

cashman · 09-12-2016, 11:45 AM

I used to follow that procedure. However, doing the finger tight version has been better for me on track. I used to get more brake pad knock back with the "move the washer method".

gremlin · 09-13-2016, 07:01 AM

What do you mean by brake pad knock back? Is this a clunk when applying the brakes (I hear something when I'm backing up sometimes) or is the disc shimmying and pushing the pistons back in resulting in a longer initial pedal throw? I'm not having anything like that.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by gremlin

this is what I did to tighten the bearings.

Got it. Thanks.

cashman · 09-13-2016, 07:54 AM

Quote:

Originally Posted by gremlin

What do you mean by brake pad knock back? Is this a clunk when applying the brakes (I hear something when I'm backing up sometimes) or is the disc shimmying and pushing the pistons back in resulting in a longer initial pedal throw? I'm not having anything like that.

Correct, the pads being pushed back in, but I've also had squeal. You mentioned the issue is with the brakes (noise) and during turns. I'm not a mechanic but more of a common sense guy. I can't think of any other movement that would be happening causing a brake noise during a loaded turn. Any suspension movement would move the rotor, hub, and caliper as a unit. Any ball joint or bushing issue would move the rotor, hub and caliper as a unit. You mentioned you just put in a new bearing and never had this issue before. A loose bearing would allow a little play in the hub/rotor to potentially start rubbing differently on the caliper/brakes. That's why I would start there. Since you are having no problems now (not on track), I would leave the bearing as-is and tighten it as above before your first track session. If your unhappy with the result, adjust the bearing back after the first session (It's not that complicated of a job especially since you recently removed the dust cap). Only other area I can think of movement would be a worn spindle. Good luck