POLL : Where does your clutch grab
Discussion
Hey Guys,
Just doing a few upgades on my tranmission and clutch this week and ran into a snag,
First, I replaced the transaxle fluid with Redline MT-90. That went off without a hitch.
Next, I decided to take advatage of the car being up on a lift and change out the clutch hydolic line (Red hose), I had just recieved my new braided SS in the mail, went on easy, maybe 20 min.
Now is when the fun started, I went to refill and bleed the clutch master cylinder with the aid of an assistant. Started out OK, had a bit of a peddle in just a few pump/bleed cycles. But it soon became apparent that I wasn't getting the full peddle back, after vac bleeding a whole bottle of fluid through the system and still no success, I started to question the integrity of the master cylinder. I looked under the dash at the clutch peddle assembly and found that the seal was leaking through the firewall. Now I'm wondering if this just happened or has this been a long time coming?
My clutch has always been very stiff and it would grab right off the floor (my car is equiped with the clutch assist spring mechanism). Could I have been experiencing the effects of the master cylinder beginning to go? I've only had the car for about a month and 500 miles. So I'm trying to get an idea of how my clutch is supposed to feel like.
BTW, it a 94' S4 with 8500 miles
Thank's, Mike
Just doing a few upgades on my tranmission and clutch this week and ran into a snag,
First, I replaced the transaxle fluid with Redline MT-90. That went off without a hitch.
Next, I decided to take advatage of the car being up on a lift and change out the clutch hydolic line (Red hose), I had just recieved my new braided SS in the mail, went on easy, maybe 20 min.
Now is when the fun started, I went to refill and bleed the clutch master cylinder with the aid of an assistant. Started out OK, had a bit of a peddle in just a few pump/bleed cycles. But it soon became apparent that I wasn't getting the full peddle back, after vac bleeding a whole bottle of fluid through the system and still no success, I started to question the integrity of the master cylinder. I looked under the dash at the clutch peddle assembly and found that the seal was leaking through the firewall. Now I'm wondering if this just happened or has this been a long time coming?
My clutch has always been very stiff and it would grab right off the floor (my car is equiped with the clutch assist spring mechanism). Could I have been experiencing the effects of the master cylinder beginning to go? I've only had the car for about a month and 500 miles. So I'm trying to get an idea of how my clutch is supposed to feel like.
BTW, it a 94' S4 with 8500 miles
Thank's, Mike
Just pulled my master cylinder out, what a P.I.T.A., looks like the seals were being eaten out by the brake fluid that we used to bleed the system. I only looked as far as it being DOT 3 and missed the fact that it was a mineral based fluid.
I guess I'd better order a rebuild kit for the slave cylinder as well ;-)
Anybody ever use Pentosin hydrolic fluid in their cars? I have a bottle left over from my last BMW that I might be able to use in the clutch hydrolic system.
I guess I'd better order a rebuild kit for the slave cylinder as well ;-)
Anybody ever use Pentosin hydrolic fluid in their cars? I have a bottle left over from my last BMW that I might be able to use in the clutch hydrolic system.
Mike,
The failure of a master cylinder is both sudden and progressive. Sudden becaquse when the seal goes, it just goes. Progressive in that the rubber seals deteriorates over time.
The addition of the SS clutch line increased the amount of force the seal had to stand up to most likely causing an already detiorating seal to finally let go. Previously, the expansion available in the old 'Red Hose" absorbed much of this force and so, lowered the amount of back force the seal had to endure.
In any case, a rebuild is in order, not very difficult, but you also need to rebuild/replace the slave or you'll just be forcing the problem downstream in no time. You'll need to use fresh fluid when you perform the work as the 'new' stuff you've used has already absorbed too much moisture to be of any further use once it's been drained a second time. Also, I am not a fan of Vac bleeding. Too many opportunities for air to draw into the system. Chuck it in favor of a power bleeder - $45 (www.thedynoshop.net/power_bleeder.htm ) and try bleeding it from the slave on up (you're forcing the air in it's most natural direction - up). Happy Motoring! Jim'85TE
The failure of a master cylinder is both sudden and progressive. Sudden becaquse when the seal goes, it just goes. Progressive in that the rubber seals deteriorates over time.
The addition of the SS clutch line increased the amount of force the seal had to stand up to most likely causing an already detiorating seal to finally let go. Previously, the expansion available in the old 'Red Hose" absorbed much of this force and so, lowered the amount of back force the seal had to endure.
In any case, a rebuild is in order, not very difficult, but you also need to rebuild/replace the slave or you'll just be forcing the problem downstream in no time. You'll need to use fresh fluid when you perform the work as the 'new' stuff you've used has already absorbed too much moisture to be of any further use once it's been drained a second time. Also, I am not a fan of Vac bleeding. Too many opportunities for air to draw into the system. Chuck it in favor of a power bleeder - $45 (www.thedynoshop.net/power_bleeder.htm ) and try bleeding it from the slave on up (you're forcing the air in it's most natural direction - up). Happy Motoring! Jim'85TE
Clutch master cylinder rebuild was a success!, I disassembled the slave cylinder to check the condition of the bore and sleeve as well as the seal, all looked like new. I removed all the old fluid by flushing the system with Pentosin 11s which is a synthetic hydaulic fluid which I ended up using instead of good old brake fluid. I had my doubts about using the brake fluid that I had started with since the seals in the master cylinder were half turned to mush.
I may have found a reason why I had so much trouble bleeding the system. It has to do with the clutch assist spring that "was" on my car.
When bleeding the system, holding the peddle to the floor and cracking the bleed screw open releases all of the pressure in the system leaving only the small spring in the master cylinder to return the peddle to the top position while drawing a portion on fluid from the resevour. In my case the assist spring holds the peddle to the floor, it requires you to put a toe under the peddle and help it up, which after a certain travel, the peddle springs back to the top position with some force.
This is where the problem is. When the peddle pops back at that speed, the small pin hole from the resevour that feeds the bore of the master cylinder can not keep up with the volume that the piston is displacing, causing air to be sucked in passed the bore seal.
Once I removed the assist spring and began the bleeding process again, this time letting the spring in the master cylinder return the peddle to the top position (at its own pace), I had a solid peddle in about 5 cycles.
Hope this little bit of info helps someone out there!
Cheers, Mike
I may have found a reason why I had so much trouble bleeding the system. It has to do with the clutch assist spring that "was" on my car.
When bleeding the system, holding the peddle to the floor and cracking the bleed screw open releases all of the pressure in the system leaving only the small spring in the master cylinder to return the peddle to the top position while drawing a portion on fluid from the resevour. In my case the assist spring holds the peddle to the floor, it requires you to put a toe under the peddle and help it up, which after a certain travel, the peddle springs back to the top position with some force.
This is where the problem is. When the peddle pops back at that speed, the small pin hole from the resevour that feeds the bore of the master cylinder can not keep up with the volume that the piston is displacing, causing air to be sucked in passed the bore seal.
Once I removed the assist spring and began the bleeding process again, this time letting the spring in the master cylinder return the peddle to the top position (at its own pace), I had a solid peddle in about 5 cycles.
Hope this little bit of info helps someone out there!
Cheers, Mike
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