rear left brake caliper, rubbing or is it the brake drum?

coupe · 12-01-2002, 07:48 AM

Hi there, I have fitted a re-built rear left brake caliper, but I still have the same fault.
Start driving, no problem...Built speed, and if I happend to use the brakes to slow down, the brake caliper seems to rub on the disc. If I bring the car to a hault, the rubbing stops as I decrease speed to 20 kms/h.

I think it is rubbing on the brake caliper, but it could also be the hand brake drum. Has anyone out there experienced the same sticky situation? Please let me know..

coupe

AFJuvat · 12-01-2002, 07:58 AM

Two possible solutions.

Brake rotor is out of round

Parking brake out of adjustment.

adjust your parking brake first - otherwise, you will either have to have the rotor turned or replaced.

AFJuvat

coupe · 12-02-2002, 09:47 AM

Hi AFJuvat. It seems to be the caliper rubbing on the rotor. The caliper seems to wonder closer to the rotor with vibration.
I was driving earlier today, and pulled the hand brake , I heard a clonk sound, I then release the hand brake, and the hand brake released and re-set itself. The rubbing whine on the rotor was still there.

My question is: If the rotor is warped, shouldn't the rubbing sound be there all the time???

From the brake master cylinder, are there any check valves or proportion adjustable valves present in the brake line system?

I have no ABS on this 951...

Thanks
coupe

AFJuvat · 12-02-2002, 10:52 AM

Hi,

There is no proportioning valve.

By what you describe (brake rubbing after you apply the brake) you are still looking at a rotor issue (it may not necessarily rub/whine all the time) or a sticky caliper.

At this point, you should probably take the brake apart and have the rotor checked.

Clunking in the parking brake - hard to tell what that is - after you have the rotor out, check all the fasteners and springs. You should also adjust your parking brake.

AFJuvat

Frank B · 12-03-2002, 12:13 PM

Sounds like a sticky Caliper. Being that it is the REAR brake, it may have something to do with the emergency brake, it may have been oput of adjustment and was applied forcefully and damaged the caliper. I did something like this to my uncle's Ford EXP. So, You may have also driven while the brake was on and warped the rotor (via heating it up) and now it's fried. Try re-tensioning the E-brake, and replace the rotor and brake pads. If that doesn't work then shoot you car, burn it and place it in an urn on your mantle.

Frank B

fnart · 12-04-2002, 04:57 AM

if you don't find anything wrong with the caliper or the disc, check the wheel bearing. noise at higher speed? low rumble low speed (easy to miss)? . does the noise change when you go around corners?? if so probably a bearing.
the good news is bearings take a real long time to totally fail.

coupe · 12-04-2002, 06:33 AM

Right! Thanks for all the advice, I have used it all, except some of Mr. Frank B advice...

Here is what I have done seince my last post.
Took the car to the shop, removed the wheel, removed the rotor. Checked the Emergency brake, no problem there. Plenty of pad left and wearing in equally.

Send both the brake rotors to the laith, for skimming. Checked the bearing, no play, no unusual sound. Checked cv joints no problem. Check rebuilt brake caliper for leaks, none found.
Checked the new brake pads, fitted a few weeks ago, all good, nothing strange.

Got the brake rotors back, fitted everything back, took it for a test drive. Same whinning sound, but not as loud. In addition to the trouble, i now have what sounds like rubing of a one brake pad on one side of the disc, when braking all the time.

I stopped the car and took a temperature reading of both rear brake rotors. The one with the faults, read 20 Celsius higher than the other...Hmmmm...strange

Next on my check list...Brake master cylinder and hoses.

Maybe there is a partial blokage on one of the brake lines/hose..

Hey AFJuvat, have you seen this before?

Thanks
coupe

Lawrence Coppari · 12-04-2002, 07:58 AM

On my '86 951, the rubbing was due to a bent hub. I thought the rotor was bent or something was wrong with the caliper. The way I determined it was to rotate the wheel with it off the ground next to a stationary object. There was about 1/32" runout on mine. I put jackstands under the car and ran the motor in 1st gear with both wheels off. Check trueness of spindle as it turns.

Frank B · 12-04-2002, 02:12 PM

Didn't wanna shoot the old girl huh?.. hmm.. try getting her drunk she won't whine as much.. .. I'm only kidding....geez..

Bleed your brakes check old fluid.. "if it's anything BUT the color that is supposed to be you may have a contaminant. Of course you want to check your Master Cylynder because if you have a blockage and you jam the brakes on.. well, they'll stay on, but if it's intermittent it very well may be something critical, i.e lines or a bent hub/axle.. I've had it happen b4 on a different car.. drag racing in a pot hole minefield.. yeah i was a knuckle head...

If the fluid is any other color than red or blue, refill them and bleed again.. that may be causing the blockage..

Frank B

coupe · 12-04-2002, 07:04 PM

Hi Frank B. I have changed the brake fluid recently.
There is new fluid in there. I;m going to get down on my knees and check the spindle.

coupe

coupe · 12-05-2002, 04:08 AM

This morning, I drove her to our workshop, and inspected the rotor, as it rotated in the brake caliper. Clearly it rubs against the brake pad in a certain place. Concluded that the rotor was warped. So took it off, placed it on a laith and dialed the outer faces and the inner hub face. The outer faces were out, so skimmed some more.

Checked the hub, using a vernier gauge. Placed one end against one of the e-brake pad and adjusted it to the side of the hub., turned the hub and conformed that the spindle is not bent. Double checked it in another location. Great! No problems here.

Re-fitted the rotor, brake caliper. Turned the hub...F**k still warped!!!
The two tiny screws that hold the rotor in place, are not placed in the centre of the rotor, bad design.

Conclusion, the rotor is warped, to thin to even bother trying to re-machine. Time for a new one.

Maybe I'll just swap with the other on the right hand side. Just for fun...

Frank B · 12-05-2002, 08:49 AM

O.K. Now what would be a good idea is to replace Both rotors at the same time, money pending. Try to use the drilled rotors, they stay cooler.. well, cool off quicker, and they are a good investment.

What color was the fluid when you drained it?.. refill with FORD heavy duty Brake fluid, it's amazing and it's blue. Also, check the hose coming out of your Brake/clutch reservoire for deterioration/damage they rot right at the connection of the reservoire, have it replaced or do it your self if you like smashing your fingers. (I have gigantic hands and cannot handle some of the maintenance). And make sure that your e-brake is adjusted properly your prob sounds like some one drove with the parking brake on at some point and didn't notice it, I've done it B4 and yep.. I burned up a pad and a rotor and fried a caliper.

Good luck coupster
Frank B

coupe · 12-05-2002, 09:05 AM

Hello there Frank.
The brake fluid was replaced by my independent Porsche especialist mechanic(ipsm). At their workshop, the chap that did it, told me that there was a funny smell and that it had a funky colour. He also told me that he had a hell of a time bleading and flushing the system. He suggested I get a new master cylinder.

I think that, I will get the rotors after all, I can't stop now...
let me see.. I have done since September; CONTROL ARMS, TIE-RODS,ALL BUSHES ON SWAY BARS,ENGINE MOUNTS,STEERING RACK,ALL FILTERS,break pads, complete clutch, cured all oil leaks on engine.new speedometer....the list goes on..

But I love that old girl...Will not let her die...

coupe

coupe · 12-08-2002, 06:18 AM

Hi there.. I'm back again with the same fault, even after replacing both rotors with OEM ones.

Even with the new rotor in, I can see the rotor drift towards the break pad as I turn it by hand. It seems like the new rotor is warped, but I know that it isnt so.

I have checked the hub, with the rotor off, it seems in good shape. These checks were performed with all the parts cold.

Could it be the bearing??? Do any of you know what the SKF bearing part number is, along with the dust seal??

If it happens to be the hub or the spindle, are these parts easy to get? Are they affordable?

Sorry for sounding so deperate, but with all honesty... I REALLY AM......

Help....

Coupe

Lawrence Coppari · 12-08-2002, 11:43 AM

To check the hub you should run the motor with the back end raised in 1st gear. That way it turns slowly. Don't measure. Place an object on the garage floor and place the end of it right next to the tip of the threaded portion. Put a flashlight behind it and watch to see if gap changes.

If the bearing has slop in it, the hub will not turn true. Something is out of whack. It's the rotor, bearing, or hub. Is there rust or crud build up where the rotor is held against the hub. There is another possibility. You could put the rotor on the other side and see if it acts as badly.

coupe · 12-09-2002, 06:55 AM

Hi Lawrence. I seriou;y think that it is the bearing. I hear it whine almost everytime know as a cruise.

Do you know the rear bearing SKF number? That would same me some cash. I believe that i will change the trailer arm rubber bushes, lock lut on the hub too while I'm at it.
Thanks

Coupe

Lawrence Coppari · 12-09-2002, 08:00 AM

Coupe,
I have the old bearing in my junk pile. Is the SKF number stamped on it? I could check tonight. The new one was purchased from Pelican. I did the heating/freezing thing to install the new one. As I recall, the new bearing was made in Spain. My car is a 1986 turbo.

The Porsche manual says to change the nut - the 32 mm one.

coupe · 12-09-2002, 09:03 AM

Hi Lawrence,
my 951 is a 1986 model too.

Bearings are bearings and they are made by bearing manufacturers, not car makers, and this is the reason that I would rather buy it from a bearing maker like SKF. I know that the front and rear bearings for our 951 are made by SKF. If you could be so kind and look at the number stamped on the side of the bearings including the letters, or the data on the old SKF bearing packet.
Regarding the self-locking 32mm nut, did you also buy new ones? If so, from where can I get a set? Did you have to replace any other bits around the bearing such as grease seals or spring-clips?

I also took a look at the rubbers on the trailing arms, and I plan to get these changed too. The ones on my car are gone... Have you done this work already? I think that pelican sell these parts for our cars too. I shall have to get in touch with their sales department.

Thanking you in advance
Coupe

Lawrence Coppari · 12-09-2002, 09:17 AM

Hi Coupe,
The bearing is a sealed unit so there are no seals per se (other than on the bearing itself). The bearing is a substantial thing. It is not like the situation at the front wheels.

I bought the nut from the Porsche dealer. It cost about $12. You need 368 ft-lbs torque to put it on properly. The book says 500 newton-meters.

My rubber bushings at the rear were ok so I have not had to replace them.

I'll check for any numbering on the old bearings and post it tonight.

Lawrence Coppari · 12-09-2002, 12:23 PM

SKF number: 305988