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Clutch hydraulics driving me nuts

 
Old 01-07-2012, 06:17 PM
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DougM
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Default Clutch hydraulics driving me nuts

I have read just about every thread on bleeding, adjusting etc.....
I have a new master, new slave, new blue hose. I have gravity bled, pressure bled, vacuum bled, opened the master from the foot well, tried to force air out by manually pushing in the slave rod. Anytime I do any of these the clutch works like a charm until I go for a drive and then park it. After sitting, the clutch becomes weak and I get a dragging clutch, until it warms up again. I have adjusted the tabs on the pressure plate and adjusted the master pushrod. The fact that it works when warm, and also right after I do anything with the hydraulics leads me to believe it is strictly a hydraulic issue.
The only thing that seemed a little different from threads I read is burping it at the master cyl. When I pulled the circlip, the piston popped up as if it is under pressure. Is there a spring under it? To get it back together, I have to hold it in with the pushrod while installing the circlip. I also noted that there is a metal washer under the circlip. I found some posts referring to a fix by removing the washer. I have not tried that yet.
Any suggestions?
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Old 01-07-2012, 07:15 PM
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I bet you are going to find a leak at either your new master or slave cylinder.
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Old 01-07-2012, 07:37 PM
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Is the new master cylinder the correct one? Search the forums for info regarding master cylinder internal differences. I had a similar problem; intermittent dragging, bleeding cleared it up, then started dragging again. Turned out the master cylinder piston was too long and didn't travel far enough to fully disengage the clutch consistently. The fix for that was to cut 4mm off the end of the piston's rod. Hopefully someone else will chime in, I know there are photos and more info regarding this fix.
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Old 01-07-2012, 08:47 PM
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After some more reading......
I think it may require more bleeding at the master. When I pulled the circlip, I didn't realize that the piston would pop out so I probably let air back in. I went out and removed the clip with the rod still attached and then was able to slowly let the piston out using the rod. After a little bit of fluid cam out, I pushed it back in and put it back together. Started the car and no grind. Will need to take the car for a drive tomorrow and then park it to see if it continues. May just need a few bleed procedures.
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Old 01-07-2012, 08:59 PM
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Best bleed method I found was to connect the front wheel brake bleeder screw to the clutch slave bleeder screw with some tubing and crack them both open,
and use your brake pedal to force the fluid into the slave and up and out of the reservoir this works great and no need to keep refilling with brake fluid since it in a closed loop.
I would flush my brake lines first to use this method.
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Old 01-07-2012, 09:09 PM
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Paul's trick reverse bleed technique should work unless the brake bleeder sucks in air around the loose bleeder when you release the brake pedal. A two-person method with someone closing the brake bleeder between pumps would remove that issue.

I was frustrated by trying to bleed the clutch system until I tried a reverse bleeder tool (purchased from Phoenix Systems). Worked like a charm using it at the slave bleeder and has worked easily every time since, but the tool is rather expensive unless you plan to do this regularly.
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Old 01-08-2012, 02:07 PM
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Kevin in Atlanta
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After replacing the clutch slave I tried everything - nothing worked until I attached a clear tube to the slave and a new oil sprayer with a charge of fresh brake fluid - pushes the brake fluid up the the master along with the bubbles. I sold my motive pressure bleeder! Need a second set of eyes watching the reservior. It was the easiest bleeding job ever!
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Old 01-10-2012, 07:53 PM
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DougM
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I went ahead and pressure bled it from the slave up so there would be no air in the system. Like before, It works great the first time out. Then after sitting and cooling off, I get drag again.
Maybe a leak, but I cannot find any? When under pressure, I don't hear any leaks?
I looked some more and finally found this thread about newer master pistons being a little longer and needing to be cut down a few mm.
https://rennlist.com/forums/928-foru...e-old-one.html
Just to confirm, would this be the case with a new master on a '84 car? When I replaced it, I did not keep the old one so I don't actually know if the internals are different.
What gets me is that just after bleeding it in any way, it works fine when cold and continues to as it heats up. Once it cools again, then it drags when cold(grinds into reverse). Once warm, it will work again.
Could these be the symptoms of the piston being too long as the other thread discusses?
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Old 01-10-2012, 10:04 PM
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The new master cylinders need to be modified to work with DD clutches, but have you pulled the boots to look for leaks?
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Old 01-10-2012, 10:45 PM
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Yes, I have pulled the boot. Actually, I currently have it slid up the pushrod because I was trying to bleed it a few times to rid of trapped air. I will drain the system tomorrow and pull the internals. From the pics in the above thread, I guess I will need to shave a few mm off if I have the same internals. I was just confused from reading it if it meant it was a mod for early cars or all DD clutches.
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Old 01-10-2012, 10:58 PM
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Originally Posted by DougM View Post
Yes, I have pulled the boot. Actually, I currently have it slid up the pushrod because I was trying to bleed it a few times to rid of trapped air. I will drain the system tomorrow and pull the internals. From the pics in the above thread, I guess I will need to shave a few mm off if I have the same internals. I was just confused from reading it if it meant it was a mod for early cars or all DD clutches.
All cars with DD clutches.
And just looking at the slave end means you have only looked at one end of it, look at the master also.
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Old 01-10-2012, 11:42 PM
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Don't know if this would help, but its interesting. I think this is enzo in another post I couldn't put by mouse on.

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Old 01-15-2012, 01:02 PM
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On the DD clutch setup, how much of the piston stop needs to be cut down? In the link above, there are all sorts of lengths described, but some are for different car models. I started with 4mm but it doesn't appear to be enough yet. But I do not want to take too much off. Also, I do not have the original spring so I have the use the new longer spring. Should some of that be cut off or does it get short enough when compressed?
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Old 01-15-2012, 01:32 PM
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Hi Doug cutting the tip off the MC is going to involve 2 parts,
one getting the piston cut down,
then also cutting down the spring length.

For the piston you need to measure the depressed depth of the piston do this after removing the new rubber seal what has to happen is the piston only goes far enough into the MC bore so the rear seal wont go past the feed port or it will leak when pushed full bore.
The amount of tip removal will be in the neighborhood of 4 to 5 MM.

Once this is done the next part is to compress the spring to simulate full compression,
what you dont want to happen is for the spring to compress on itself and go to coil bind,
over time this will cause the spring to shatter and thus cut the seals of the MC and the slave.
This may entail removing about 2 coils of the spring, careful measuring is needed for all of these parts.

Once this is done you need to make sure the rest of the poarts your using are new.
If you have not already done get a new flex line for the MC to Slave and a new Blue hose for the MC feed..

Also remove the clevis pin and clevis at the pedal on the pushrod,
make sure these parts have no play if they do have play replace them.

Based on your description of whats happening you have a few issues one is a MC thats not going to full stoke and the other is a weak fluid line thats not holding -pressure when it gets hot.
Also make sure you have the heat shield installed on the left manifold header connection this will protect the flex line from heat.

Following these instructions to the letter should have you back on the road with no more issues
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Old 01-15-2012, 02:08 PM
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IIRC the end needs to be cut 4.65 MM
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