Braking Issues

[Semba]

Hi all,
Went for a ride yesterday (82 911 SC), turned out to be a scary one. Came up on a light, brake pedal went to the floor, dash brake light came on, and had a weird smell all happened simultaneously. I added brake fluid and resolved the pedal to floor issue but noticed some issues.
1. After applying brakes, brakes stay on causing a difficult take off.
2. Right front and right rear rims quite hot compared to left side.
3. Pulled rims off and can't rotate rotors(except with some hammer tapping), although pads and rotors appear to be in excellent condition. Once I hit it with a hammer, they free up just fine until I apply the brake pedal again and have the same issue. Right rear seems to be better after cleaning, right front still hanging on tight.
Dash brake light stays on continually ever since it came on yesterday.

Could use your expert advice on what might be the issue(s) here so I can get it right the first time. Would rather I did not become permanently lodged into the vehicle in front of me.

Gary

[Steve@Rennsport]

Gary,

More information needed,.......

1) How many miles on the car?

2) Any recent brake work on the car of any kind?

3) Original brake hoses?


Offhand, it sounds like a failed MC but more info will help.

[James Brown]

Sounds like it's time to do a rebuild. If the pads are good, might just need a caliper cleaning and new seals. Along with new fluid and there is no leaks and the parking brake is adjusted, you should have the brakes back to snuff in one day. Check the master cylinder for leakage.

[Jesset100]

Hey Gary, No expert here as I can only tell you what I did when I bought my 82sc. I removed and replaced all the rubber hoses as well as rotors and pads. Rebuilt all four calipers and flushed all the old brake fluid and replaced with fresh brake fluid. The only thing I didn't r/r is the master cylinder as it is in good working order.
Like you said "get it right the first time".

[johnsjmc]

I expect you have one and probably more seized calipers. This usually happens with prolonged storage and old fluid(which absorbs water and encourages internal rust.) The dragging brakes will heat up until the fluid boils and the pedal falls to the floor. The smell is the overheated pads.
Rebuilding the calipers is fairly simple and inexpensive unless the pistons and/or bores are rusted and pitted.
You can rebuild them individually but I would do them in axle pairs. Flush the fluid at the same time. Examine the pads carefully for heat cracks and replace them if they are crumbling . Pad replacment is preferred anyway. If the rotors are worn undersize then they should be replaced as well.

[Flieger]

Replace the flex hoses.

[longhornchris04]

Differential temperature means 1 or more of your calipers froze up... Pedal to the floor makes me suspect the master cylinder may not be healthy.

I had a pedal to the floor problem... one of the caliper seals had blown. New fluid only temporarily solved the the problem.

I'd start the leak hunt. Rebuilding is a better option, to include rebuilding the master cylinder.

Flush the system, check for leaks, and pull and inspect the pads & rotors. If anything looks fishy, then I'd start looking into a rebuild.

Also, a pressure bleeder makes life much easier when it comes to bleeding and flushing the system.

[Semba]

Thanks for all of your input. To answer a few of everyones questions. The car has 98,000 original miles. There are no leaks of any kind from this car at all that I can detect . After I added fluid the brakes hold strong, strong pedal, etc. The car was very well maintained by original owner by Porsche dealer in Atlanta. Prior to my purchasing two years ago, the car sat for at least three years and never moved until I moved it. Original owner had left hip replaced and can't push the clutch anymore. I have not been driving as much as I would like, and won't again now until I get the brake issue resolved. I guess I am leaning toward the master cylinder but can't rule out rusty or failing calipers either. Like I said earlier, the pads and rotors appear to be in excellent condition, but most likely am dealing with very old brake fluid and it appears that everything I can see is original from manufacture except the pads of course. Thanks again for all your input and will of course graciously accept any other suggestions anyone can offer.

Gary

[Winter]

Gary, if you're going to replace the master cylinder, you might as well rebuild the calipers and replace the lines. After all, the worst part of working on brakes (IMO) is having to bleed the damn things. Once you open up the system, it's never easier to take care of everything so you only have to bleed the system once. Caliper rebuilding is easy, I know this because I was able to do it on my '75. Given the "sitting for 3 years" you'll also probably want to replace the rubber lines, a cheap and easy thing to do as well.

Good luck, the folks here helped me a ton with my rebuild, and I know that you'll get the answers you need from fellow Pelicans.

[johnsjmc]

The clue that you are dealing with sticking calipers and less likely a failed master. The wheels affected were one front and one rear on the same side. Porsche brake circuits are split front/rear not diagonally or one front and one rear. Therefore the fluid boiled in both circuits from heat generated by dragging brakes. Let it cool and the pedal returns to normal feel. Drive a distance again and it might happen again or driving it might have freed them up enough that it won,t happen as quickly.
A failed master cylinder can sink to the floor without any external leaks. The fluid bypasses the seals internally. If you sit stopped and hold pressure on the pedal this type of failure will allow the pedal to slowly sink.
I guessed this car sits for long periods of time. Stuck calipers are first suspects as they are also more exposed to road debris,heat,and moisture than the master is. In the last 35 years I,ve replaced or rebuilt hundreds of calipers and only a handful of masters.

[Flat Six]

Definitely sound like stuck calipers. Brake fluid is hygroscopic (attracts & absorbs water). In addition to reducing boiling point of BF, water in system also can cause surface rust on components such as caliper pistons, which sounds like your issue. IMHO, complete flush of BF every two years is cheap insurance.

With caliper rebuild kits available from Pelican, a relatively easy fix as long as pistons aren't so corroded they're unusable. Remember to change flex hoses, too (sounds like at least five years on the current set).

Good luck

D

[Semba]

Hi again,
Once I get the new front rortors (hopefully today) I can begin the rebuild. Have the caliper rebuild kits, have one replacement piston (cuz I broke one ) and the calipers are all nice and clean with fresh new paint. Inner hub and bearings are beautiful condition and spin perfectly, they look to have been fairly recently replaced. I can't wait to have propperly working brakes. They have not been right for a while, I just didn't realize how bad they were. I think now that because they were all dragging so bad was obviously affecting driveability.
Thanks again for all of your input.
Gary

[DanielDudley]

You want to assemble those calipers with a little silicone brake grease in the bores and around the seals. It helps to lubricate and prevent rain from penetrating into the bores.

[johnsjmc]

You should use brake fluid as the assembly lube. Silicone grease is Ok for the areas not usually bathed in the fluid. Parts like the dust seals and pad guide areas.

[Semba]

Immediately I have a question. I align the slot in the piston head at a 20 degree angle. So both pistons will mirror each other when ready to mount?

[Flieger]

Yes, the groove makes the pad angle. You want them to pinch together towards the front of the car because the friction force on the rotating wheel will tend to cause the pads to twist such that the top/rear pad edge is pushed into the rotor and wears more (wedge shaped). The groove angles the pads to counter this.

[James Brown]

If you have the ATE brake caliper rebuild kits, there is a big sheet of instructions. Read the english version-good info there.

[silverc4s]

Please replace the 4 rubber hoses (1) at each corner if they are the originals "while you are in there". They have done their time...

[Semba]

Thank You !