Hot clutch issues

[Jimmy P]

My mechanical friends....What causes these symtoms:

I have an Audi 016 transaxle but I don't think this has anything to do with the trans. I believe this is strictly clutch related.

Clutch has less then 4 K on it with NO drop clutch starts. (read: Its been treated with respect)

Clutch works seamlessly and smoothly when clutch is cold. Pedal has good feel at both top (slight bit of play at top) and bottom bite is as it should be. Grabs well and engages smartly.

Once warm, pedal gets sloppier at top and there is much less to no resistance throughout movement and bite at bottom is much quicker to engage then when cold. After more time pedal loses feel and will almost go to floor without resistance.

With pedal on the floor gears can still be selected but it takes time and patience.

Your thoughts...my research shows these possibilities: Slave cylinder (would love it to be this as its easy to get to and relatively cheap) master cylinder (would hate it to be this as its buried and would require me finding a 12" tall mechanic with arms like an ape.)

 

[Dave P]

Could be the fluid is boiling if the cylinder is getting hot from the headers. I often thought about that issue. as I have been working on assembling mine. A good fluid like AP600 or better may help.

 

[Randy V]

Sounds like the fluid is boiling as Dave pointed out... Bleed them really good and if you can insulate the line or move it away from heat sources, you should be golden!

 

[Randy V]

Additionally - once brake fluid has boiled, its resistance to boiling is decreased dramatically... It will seem fine when cool, but its hot properties will be entirely different..

 

[Phil]

Jimmy:
I would second Dave and Randy's advice, It sounds like your line may have moved closer to an exhaust component, and I would bet the fluid absorbed some moisture thru a faulty seal at either end, but most likely near the slave.
Good luck, let us know how you fare with that problem.
Cheers
Phil

 

[Jimmy P]

Many thanks Gents. Looks like the consensus is boiling fluid which makes sense given the location of the slave to the headers. I will check the entire system for proximity to heat, replace fluid with the best I can get, check slave cylinder and see if I can design a heat shield for it. I will let you know my results.

Wow, I love this for place.

 

[Pat]

Jim, actually changing the master isn't that bad. It would be useful to insure the master is full and have a look at the fluid. That will also insure you don't have a seep someplace. If the fluid has gotten dark or clouded you probably need a change and you'll need to get to the master to put the fresh fluid in anyway. One thought, you may want to be sure the A/C condensation drip exits the car and doesn't leak on top of your master cylinder. Brake fluid absorbs water like crazy and once it's contaminated you'll need to replace the fluid.

 

[Cliff Beer]

Hi Jimmy,

I probably have the same situation in my car given the proximity of our chassis #'s. When I bought the car, one of the first things I did was to have the headers coated. I can't quite recall the product (jet hot???) but it did lessen the surface temps of the headers by a good 40 degrees or so. I believe the temps were around 260-280 or so before (using my basic IR temp reader) and they're around 220-240 now. Might help with that boiling fluid....

Good luck!

 

[Jimmy P]

Veek (Pat) and Cliff, as always my sincere thanks for your suggestions. I hope to get to the job this weekend but we all know how plans can go. I'll keep you updated as to progress. BTW Cliff my headers are coated so.....will replace fluid and check proximity of line.

 

[Scott]

The fluid is probably old and saturated with water, which alters it's boiling temperature significantly.

 

[Jon Metrick]

Its worth giving this a try to remove the clutch out of the equation. Try running the car with it in neutral all the way to operating temp. With it in neutral the clutch should be staying cold as your not engaging/disengaging the clutch as if you were driving. This way you can completely remove the clutch out of the equation as its staying cold. See if once the engine is warm if the condition your describing happens. If it does, then yea like others have said it sounds like the fluid in the slave is boiling due to the heat of the engine. I hope you understand what I am saying as I don't know how else to explain it. Keep in mind the brake fluid in the slave is hygroscopic (absorbs water). Once water has been absorbed into the fluid it lowers the boiling point. So make sure those caps are sealed on the slave cylinder. I hope this helps.

 

[Jimmy P]

Gentlemen, for all those who responded I thank you. The issue has been fixed. All of you were right on the button and I took your advise on all counts. I replaced the fluid with AP 600, and with the help of a friend bled the entire system, I checked the line for proximity to the headers and was concerned about the slave sitting below the header so I designed a very simple heat shield. I looked for any potential issues with **water and insured the cap to the master reservoir was tight with a good seal. I took the car on a test run and even with the air temperture hovering close to 90 the clutch worked as it should. I'm a very happy boy!

One of the best tools I have in my sparce tool box is this forum. Bloody fantastic.

**one area of concern might be the location of the fluid reservoir in my CAV and what happens to excess water when I wash the car. Hmmm?

 

[Randy V]

Glad to hear it's all worked out!

:thumbsup:

 

[Dave P]

Great to hear you have the problem fixed. The heat shield is a good call. I will be installing one on mine with a 4 mm layer of Teknofibra applied to it.

 

[Pat]

Great news Jim. You can go to most speed shops and find some good reflective heat insulation for the slave. I also found that the exhaust was blistering the paint where it exits the car. So I insulated there as well.

 

[Jimmy P]

Good call Pat...will take a look there also. Vrooom Vrooom! BTW are you attending the upcoming Lake Mirror Event in Lakeland?