Clutch Pedal Travel - Gradual Reduction - Cause?
05-13-2008, 03:34 AM
#1
Drifting
Thread Starter
Clutch Pedal Travel - Gradual Reduction - Cause?
Over the last 500 miles or so the clutch pedal had gradually dropped to the floor, so that now the clutch does not release at all.
What is the most likely cause?
Once again I have had to return to London from the Nurburgring with no clutch, although last time the Release Bearing failed completely, at least this time I could just about start the car in gear, but all gear changes still required rev matching. But by the time I got to the ferry I could no longer manouvre the car at low speed or park when I got home.
What is the chance of having my Ring time cut short twice in row with the same problem...
At least this time the GT Oil Cooler I just fitted kept the engine temps under control, never above the upper white line even with ambient temps over 27deg and the air con switched on.
Also the oil pressure was maintained by the Penrite 15W-60, never dropping below 1.5 on idle.
What is the most likely cause?
Once again I have had to return to London from the Nurburgring with no clutch, although last time the Release Bearing failed completely, at least this time I could just about start the car in gear, but all gear changes still required rev matching. But by the time I got to the ferry I could no longer manouvre the car at low speed or park when I got home.
What is the chance of having my Ring time cut short twice in row with the same problem...
At least this time the GT Oil Cooler I just fitted kept the engine temps under control, never above the upper white line even with ambient temps over 27deg and the air con switched on.
Also the oil pressure was maintained by the Penrite 15W-60, never dropping below 1.5 on idle.
05-13-2008, 08:52 AM
#3
Supercharged
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Your problem certainly sounds like a hydraulic issue . I'd put my money on either the slave or the line between the master and slave has failed and is allowing air to get into the system or is balooning so as to not develop pressure. Should be a simple fix (compared to dropping the clutch).
Your problem certainly sounds like a hydraulic issue . I'd put my money on either the slave or the line between the master and slave has failed and is allowing air to get into the system or is balooning so as to not develop pressure. Should be a simple fix (compared to dropping the clutch).
05-13-2008, 03:45 PM
#4
Drifting
Thread Starter
I've just ordered a Clutch Master rebuild kit, and I already have a new Slave which I've not yet fitted. Hopefully that will fix the problem.
Wish it hadn't failed at the Ring though...
Wish it hadn't failed at the Ring though...
05-13-2008, 04:30 PM
#6
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I had this same failure mode and it turned out to be the plastic pivot ball on the top of the release arm to pivot ball housing. It will slowly erode, and the clutch doesn't return back as far after a while.
Remove the air cleaner assembly, using a flashlight, look down the drivers side of the rear engine bay. You will see the top of the bellhousing, and a cutout with the pivot arm and ball. There should be a plastic ring around the hole in the arm, with the flange of the plastic part visible. If it looks damaged, or is missing, this is your failure. It can be reached and replaced from the top, but it requires loosening the slave rod.
Remove the air cleaner assembly, using a flashlight, look down the drivers side of the rear engine bay. You will see the top of the bellhousing, and a cutout with the pivot arm and ball. There should be a plastic ring around the hole in the arm, with the flange of the plastic part visible. If it looks damaged, or is missing, this is your failure. It can be reached and replaced from the top, but it requires loosening the slave rod.
05-13-2008, 05:13 PM
#7
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For a quick check of the master cylinder, pull the pedal up, have someone depress the pedal while you observe the master resevoir. If the fluid level rises the MC is the problem.
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05-13-2008, 05:45 PM
#8
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As Doc mentions it is probably NOT returning far enough to get a new gulp of brake fluid so over time it gets lower and lower. I had a C-4 911 that would do that adjusting the pedal made it better.
05-13-2008, 06:04 PM
#10
Drifting
Thread Starter
There is no air in the hydraulics, because any movement in the pedal does act on the release arm, it's just that now there's only a tiny degree of movement remaining.
The release arm nylon cup is new, and the fluid was flushed a few months ago.
Time to replace both master and slave and see what happens (or rather rebuild the master).
05-13-2008, 11:58 PM
#11
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The clutch hydraulic circuit "runs out of fluid" a long time before the Brake hydraulic circuit does due to the inlet in the reservoir to feed the clutch MC being higher than the brake system inlets. This is for safety reasons - a slow fluid leak in the clutch circuit will not lead to brake failure.
If you have a leak in the clutch system and the fluid is not topped up you will experience precisely the symptoms you describe, but the fluid reservoir will not appear dramatically low. BTDT on the way to the 'ring.
If you have a leak in the clutch system and the fluid is not topped up you will experience precisely the symptoms you describe, but the fluid reservoir will not appear dramatically low. BTDT on the way to the 'ring.
05-14-2008, 03:31 AM
#12
Drifting
Thread Starter
First thing I checked was the brake fluid resevoir, which is in fact overfull because I just replaced the discs and pads, and was too lazy to drain the excess fluid.
05-14-2008, 10:14 AM
#13
Team Owner
do a search for this post another way to save time on bleeding the clutch hydraulics----------------------------------------------------------------------------
In the past week I've submitted an NIH grant, revised a manuscript, and graded a bunch of midterms from my graduate students' immunology course. Here's my edit of what Stan said: (I only did this 'cause I will need these instructions soon and I really appreicate you writing it out, Stan! )
I am working on a 86.5 and part of the job was to replace the clutch master and slave and blue hose.
Given that its usually pretty hard to get out all of the air from the system easily, and not use a whole lot of blue fluid to boot, I removed the whole system from the car:
1. Disconnect the battery, cut the blue hose from just under the reservoir and catch the fluid that comes out.
2. Remove the 2 bolts that hold in the master cylinder.
3. Remove the pushrod from the clutch pedal and also the rubber boot from the master(This is important as keeping the bellows on will make removal difficult).
4. From under the car remove the line holding connection at the swaybar mount , the heat shield at the left exhaust header and remove the 2 bolts on the oilpan that secure the line.
5. Remove the slave-to-bellhousing bolts, remove the starter. The pushrod for the slave should be able to be pulled out of the slave
6. The whole clutch hydraulic system can now be removed from the car.It may take a bit of maneuvering and the top hard line may need a slight bit of bending, not much to get it out.
7. On the work bench refit the new master and slave to the old lines. Pay attention to the orientation of the hoses to the respective cylinders.
8. After this, open the bleeder on the slave and put the master in a vice. Hold the slave so it’s higher than the master. Using an oil pump type can filled with fresh brake fluid, begin filling the master thru the new blue hose till the fluid comes out of the bleeder.
9. Try to move the lines around so as to make sure that any air pockets are moved to the slave. All of the air should purge from the system.
10. Secure the bleeder, and plug the blue line with a clean bolt. Remove the rubber bellows from the new master cylinder and add some tape to the exposed end so dirt doesn’t get into the end when refitting,
11. Refit the whole system into the car starting with the Master. Once the bolts are installed, the blue line should be connected and the reservoir refilled.
12. Secure the swaybar mount, followed by the starter, then the slave to bellhousing.
13. Refit the master pushrod and bellows, adjust so it is not pressing on the master leave about 1 to 2 mm of play .
14. Bleed the clutch with your favorite power bleeder or helper, you should find that the clutch will be high and hard with little or no air , so you will use about 1 oz to bleed it. Don’t hold the bleeder open for more than about 3 seconds as the reservoir may drain, since it’s a smaller reservoir.
15. Reconnect the battery, Done, and no wasted fluid and no skinned knuckles from trying to remove the fittings on the cylinders.
16. As a side note now is a great time to clean out the reservoir. To do this I pulled out the reservoir, drained out the old fluid and sprayed brake cleaner into the res. After doing this I took Simple Green and sprayed this followed by a hot water flush of the reservoir. Then I took isopropyl alcohol and sloshed it a few times, followed by a blow dry with compressed air. Now the reservoir looks like new and all of the old dirt is removed from inside.
If this were for credit, I'd give Stan an A+.
In the past week I've submitted an NIH grant, revised a manuscript, and graded a bunch of midterms from my graduate students' immunology course. Here's my edit of what Stan said: (I only did this 'cause I will need these instructions soon and I really appreicate you writing it out, Stan! )
I am working on a 86.5 and part of the job was to replace the clutch master and slave and blue hose.
Given that its usually pretty hard to get out all of the air from the system easily, and not use a whole lot of blue fluid to boot, I removed the whole system from the car:
1. Disconnect the battery, cut the blue hose from just under the reservoir and catch the fluid that comes out.
2. Remove the 2 bolts that hold in the master cylinder.
3. Remove the pushrod from the clutch pedal and also the rubber boot from the master(This is important as keeping the bellows on will make removal difficult).
4. From under the car remove the line holding connection at the swaybar mount , the heat shield at the left exhaust header and remove the 2 bolts on the oilpan that secure the line.
5. Remove the slave-to-bellhousing bolts, remove the starter. The pushrod for the slave should be able to be pulled out of the slave
6. The whole clutch hydraulic system can now be removed from the car.It may take a bit of maneuvering and the top hard line may need a slight bit of bending, not much to get it out.
7. On the work bench refit the new master and slave to the old lines. Pay attention to the orientation of the hoses to the respective cylinders.
8. After this, open the bleeder on the slave and put the master in a vice. Hold the slave so it’s higher than the master. Using an oil pump type can filled with fresh brake fluid, begin filling the master thru the new blue hose till the fluid comes out of the bleeder.
9. Try to move the lines around so as to make sure that any air pockets are moved to the slave. All of the air should purge from the system.
10. Secure the bleeder, and plug the blue line with a clean bolt. Remove the rubber bellows from the new master cylinder and add some tape to the exposed end so dirt doesn’t get into the end when refitting,
11. Refit the whole system into the car starting with the Master. Once the bolts are installed, the blue line should be connected and the reservoir refilled.
12. Secure the swaybar mount, followed by the starter, then the slave to bellhousing.
13. Refit the master pushrod and bellows, adjust so it is not pressing on the master leave about 1 to 2 mm of play .
14. Bleed the clutch with your favorite power bleeder or helper, you should find that the clutch will be high and hard with little or no air , so you will use about 1 oz to bleed it. Don’t hold the bleeder open for more than about 3 seconds as the reservoir may drain, since it’s a smaller reservoir.
15. Reconnect the battery, Done, and no wasted fluid and no skinned knuckles from trying to remove the fittings on the cylinders.
16. As a side note now is a great time to clean out the reservoir. To do this I pulled out the reservoir, drained out the old fluid and sprayed brake cleaner into the res. After doing this I took Simple Green and sprayed this followed by a hot water flush of the reservoir. Then I took isopropyl alcohol and sloshed it a few times, followed by a blow dry with compressed air. Now the reservoir looks like new and all of the old dirt is removed from inside.
If this were for credit, I'd give Stan an A+.
05-14-2008, 02:29 PM
#15
Sounds like the master return spring is dead. FWIW my clutch was only "right" after replacing the ball cup, blue hose, master and slave and the flex line, and then multiple bleeds. With the master fully returned, you're only supposed to have a small amount of free play before the rod contacts the piston, basically one turn's worth of the rod end. If that's what you mean by "away" then you're ok. But if it's leaving the piston well inside the master then something is catching in there.
Replacing the guts of the master is easy to do in the car, but if it were me (and it was!) I'd replace the whole thing, especially on a car that sees the track. And if it's catching inside then the body of the master is probably toast too. Stan's procedure is spot-on and I'd do it his way next time. Master cylinders are very inexpensive, relatively speaking.
Replacing the guts of the master is easy to do in the car, but if it were me (and it was!) I'd replace the whole thing, especially on a car that sees the track. And if it's catching inside then the body of the master is probably toast too. Stan's procedure is spot-on and I'd do it his way next time. Master cylinders are very inexpensive, relatively speaking.