Breaks too tight? Help!!!

I have a 81 911SC that I had new front/rear disks installed on, along with a rebuild on all the calipers, new SS braid lines, new pads, and new ATE Blue fluid. I have started to notice a sound coming from the left front that is a kind of slight grinding noise. The sound is in tone with the speed of the car (slower you go, the slower the sound) about once every rotation of the tire. I removed the front wheels, and found no apparent cause of the noise. I tried to rotate the wheels and it felt faily stiff to me. I am just not sure if it should be stiff to turn, or should the wheels spin freely with out the breaks applied? Also, when I removed the pads to inspect them I had a very difficult time getting them back in. I have read in Bruce Andersons book that this may be caused by blistering break lines that do not allow the pistons in the calipers to fully retract when the break pedel is released. Which lines would these be? The lines from the calipers to the solid lines are new, so I can't imagine it being these. Also, what is the line that runs from the top of the resivour, and where does it go? This line is old and is showing signs that it needs to be replace. Thanks in advance, Paul

Here's a tip that was developed over several months of mystery, just in case this is your situation. I had a wheel-rhythm chirping, clicking type noise I thought was associated with brakes. Not so, it turned out.

Raise the rear of your car and support it securely on jackstands (can you tell I've read shop manuals before) Start the car, release the handbrake, put it in gear and let out the clutch. Does this make the noise happen? (I know the noise comes from the front, but humor me). If the noise happens, remove the speedometer and notice that the device making the noise is the square OXS counter that runs the OXS warning light. This can be safely silenced. but e-mail me first. Hope this is your noise.

Also, FWIW, brakes do drag just a little, or at least you can hear them slightly when you turn them off the ground. But they should not create any real resistance. You're right, with new soft lines ther shoudl be no pinching problem. the only other idea I have is if the pedal has been adjusted, sometimes the adjustment is too tight, and won't allow fluid to move between the master cylinder and the reservoir. This is necessary to release pressure in the system back tot he reservoir. AS brakes heat up, of thsi system is "closed," pressure will build. I replaced a clutch in a 4WD vehicle (not easy) because its hydraulic system was adjusted too tight this way. Guess what idiot adjusted it too tight? Right!

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'83 SC



[This message has been edited by Superman (edited 12-29-2000).]

Super,

I tried you tip, and it was not the source of the noise. I am stumped! Another questionfor you. I have replaced the oil temp and pressure senders on my car. Now the pressure starts at 140# then will only drop to 60 or so, at all rpms, when the car is extreamly hot. Is this right? I thought that it should read about 10# for every 1000 rpm. Second, the temp reads around 170 at all times under load, but will bounce to 230 - 250 when at idle (after it is warmed up). Is this normal? Some fellow Autocrossers say that their temp will creap up at idle, not bounce. Thanks for your help, Paul

Neither sounds normal to me. One thing about the blood pressure gauge system that has been memorable for me, is that an open connection between the sender and the gauge will PEG the gauge. This tells me that whenever readings are too high to be trusted, a dirty or poor connection will be a likely cause.

My gauge goes nowhere near 140#. It is expressed in "bar," with the highest being 5 bar, which would be about 75 psi. I suspect the pressure relief system would release pressure before 140#, but Warren is probably more familiar with these values. I do have the spec book at home however, and you're more thn welcome to email me there.

Temp gauge behavior also sounds goofy. Mine has two lines, and temp pretty much stays below the first line, but then I live in a place with cool, moist air all the time.

With these problems, my best advice is to have a look at your system's voltage. If you system voltage is too low (under 13.5 volts with no devices on) or if it's not holding steady, many electrical gremlins will occur. The other thing is to freshen electrical connections, starting at the battery.

Sorry I can't be more help now, but again, e-mail me if you think I can help some other way.

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'83 SC

Maybe the wheel bearings are to tight.

I just had to rebuild one of my "recently" rebuilt "s" calipers. One of them was sticking do I pulled them apart to see if I could find anything wrong. The outer boot on one of the pistons was gouged. The boots were looking really new, so it looked like whoever did the rebuild gouged the seal with a screwdriver during rebuilding. This allowed a lot of crap into the piston. Thus the sticking.
To put a long story short, I rebuilt them and they seem to be working fine. While I picked up the kit, my mechanic said that if you don't line up the notches on the piston correctly(like the kit paperwork shows) you'll get brake chatter.
This might not be the case, but it would be easy to pull the caliper and look to see if they were lined up. Just an eyeball would be good enough, I think.
Ed '70 911t w/930/10

Your brake problem sounds like one of the pistons is getting stuck in the bore-either due to corrosion or pitting of the piston or caliper bore, or due to a botched rebuild (most likely a torn or pinched seal.) Remove the pads from the caliper, bolt it back on, and spin the wheel-if it spins freely and quietly with no pads in the caliper, then it's not the bearings. If you're having problems pushing the piston back far enough to get the pads back in and the caliper mounted back over the rotor, then that reinforces my thinking it's a stuck piston problem. Either rebuild it carefully, or replace it-brakes aren't anything to take chances with. The guage problem-if it's an electric guage-sounds like a classic bad ground connection problem. Check the transaxle-to-chassis ground strap and the battery-to-chassis ground cable for corrosion or loose connections first, then move on to the engine compartment wiring harness if those aren't the cause.

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Clay Mcguill www.geocities.com/the912guy

I agree with the others above about the brake drag. I have another thing to add about the high gauge readings. They must have a good connection between the sender and the engine. I.E. if you used silicone on the threads it can't make proper contact. Or corrosion or any other foreign material between the sender and engine. To test, simply touch a wire between the sender body and the block and watch the gauge for fluctuations.( engine running of course). You may need to remove them and clean both sets of threads. The trans and battery ground straps mentioned above are also critical but since it's only since you replaced the senders, I thought I'd mention this. Good luck.

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Tyson Schmidt
72 911 Cabriolet

This site's just cooking with great information. Pelican's created a monster.

I'm going to rebuild my calipers. Are there any special instructions about honing? Can you just use one of those tripod things in your drill?

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'83 SC

Yeah, just don't get too crazy with it. I rebuilt mine without the honing process and they came out perfect. Don't lubricte the seals with anything but brake fluid or you'll have over-retracting caliper pistons and the resulting very low and unpredictable pedal height. (very scary personal experience)

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Tyson Schmidt
72 911 Cabriolet

As the previous post stated, it sounds like the wheel bearings are too tight and possibly not packed with grease correctly? The bearings on the front have to be repacked and tightened after rotor replacement on the fronts. If you feel up to it, pull your front grease cap off and loosen the bearing nut slightly.

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8 9 9 1 1, The last of the line.