Bleeding the clutch: Am I doing it wrong or is my clutch slave cylinder bad? - Alfa Romeo Bulletin Board & Forums
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post #1 of 37 (permalink) Old 02-22-2016, 11:43 AM Thread Starter
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Bleeding the clutch: Am I doing it wrong or is my clutch slave cylinder bad?

I purchased a partially restored S2 spider. I am trying (unsuccessfully) to bleed the clutch. I'm pretty sure I am doing it correctly but just to check:

- Attach hose to bleed valve nipple. Submerge other end in cup of brake fluid.
- Fill fluid reservoir up to "max" line.
- have friend sit in driver's seat
- open bleed valve
- have friend pump clutch pedal
- ensure reservoir remains filled above "min" line
- when no air bubbles emerge in cup of brake fluid have friend hold clutch pedal to the floor
- close bleed valve


That was my method. Pumped the clutch pedal for a good ten minutes. I could not get it to work. If I repeat the above, sometimes some air would still emerge from the hose under the car. Am I doing something wrong or should I start to consider the possibility something has broken?
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post #2 of 37 (permalink) Old 02-22-2016, 11:52 AM
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Did you pay attention to how the bleed nipple on the slave was oriented? Mine wants to sit naturally with the nipple at the bottom of the slave cylinder, but you won't get any air out with it sitting like that. When I do mine, I rotate it and hold it by hand so that the nipple is at or near the high spot.

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post #3 of 37 (permalink) Old 02-22-2016, 11:59 AM
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It is often difficult to bleed a clutch system - you are trying to push air down - the opposite of what it wants to do.

I prefer to reverse bleed. Get a large syringe (or a clean pump type oil can) and attach it to the bleed screw with a short length of tubing. Open the bleed screw and push fluid up to the reservoir (make sure if does not overflow as brake fluid is also a good paint remover). This way you are push air up - the way it goes naturally.

Also, make sure the bleed screw is uppermost on the slave cylinder. The slave cylinder can rotate in its mount on the bellhousing.

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post #4 of 37 (permalink) Old 02-22-2016, 12:38 PM
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I guess my first question would be, why are you bleeding the clutch hydraulic system?

Did you replace the slave or master cylinder?

If you replaced the master, did you bench bleed it first? Bench bleeding a new master is pretty much a "must do".

I second the comment by GV27 (make sure the bleed nipple on the slave is at 12:00) since air rises.

When bleeding, I open the bleed screw, have wife (or friend) push clutch pedal to floor and hold it there, then I tighten the bleed screw before allowing helper to release clutch pedal. Repeat this step several times.

It sometimes helps to depress the slave piston pin all the way into the slave body while the bleed screw is open, because air can get trapped at the far (cylinder) end of the slave, and since the feed and bleed are both at the opposite end, cycling fluid with only the clutch pedal doesn't always clear the air out of the entire slave chamber.

Another tip: if you loosen the bleed screw too far, air can get sucked in from around the bleed screw threads, so try to only open it 1/4 to 1/2 turn when bleeding. Maybe even put some teflon tape or putty type sealant on the bleed screw threads.

Finally, one last possibility: If, during your clutch work, you had to release or separate the connection between the hard line and the rubber hose, make sure that connection is real tight again. One way to check it is to leave the bleed screw closed, and have your helper push hard on the clutch pedal while you watch that threaded connection. If you see the slightest drop of fluid sneaking out of that joint while the line is pressurized, air will continue to sneak in there while you are bleeding (ask me how I discovered this).

Good luck,

Edward
'88 Quad - "Claudia"

Last edited by Norseman50; 02-22-2016 at 12:41 PM.
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post #5 of 37 (permalink) Old 02-22-2016, 12:40 PM
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Jarred,
Using your method, make sure that the nipple is at 12 o'clock as Eric suggested but also make an inverted U with the tube as it leaves the nipple. That way you have a column of fluid above the nipple and if anything is sucked back you know it is liquid and not air. Also, you can get a bubble of air trapped where the hydraulic tube meets the master cylinder. Have a friend put a little pressure on the clutch pedal and crack the fitting - have a rag around it to contain the brake fluid that escapes. This will vent the air bubble.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #6 of 37 (permalink) Old 02-24-2016, 10:40 AM Thread Starter
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All,

I did not know it was easy to rotate the slave cylinder. I never tried. Tonight I'll jack the car up again and try to rotate it. If it's not stuck (rust might be working against me on this one) I'll have someone help me repeat the bleed process.

I have not replaced the master or slave cylinder, when I got the car I found there was no hydraulic fluid in the clutch line. I haven't owned the car for long enough to need to replace worn parts. Just trying to get it in a condition where its drivable for now.

Ed, are you suggesting I remove the fitting where the tube meets the master cylinder and screw it back in to let the air out?

I'll report back after I get the chance to try your suggestions. Might be a few days.

Thanks.
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post #7 of 37 (permalink) Old 02-24-2016, 11:02 AM
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Ed, are you suggesting I remove the fitting where the tube meets the master cylinder and screw it back in to let the air out?
No, just loosen the nut half a turn then tighten it when some fluid escapes.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #8 of 37 (permalink) Old 02-24-2016, 01:42 PM
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If you loosen the output port screw on the MC to bleed it a bit there, just make sure you have an old towel or plenty of rags wrapped around it and covering the engine compartment in that area. Brake fluid is murder on painted surfaces.
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post #9 of 37 (permalink) Old 02-24-2016, 02:18 PM
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When you say 'pump the clutch pedal', what do you mean? Up and down?

With the clutch pedal up, open the bleeder. Push the pedal down, then close the bleeder before letting the pedal back up. Pedal up, open bleeder, pedal down, close bleeder. That way doesn't let any air get sucked in from below.

As others mentioned, make sure that the bleeder is up high on the slave. Rotate the slave if you have to.

Bleeding at the master can help too, if you can't get a a good pedal feel.

bs
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post #10 of 37 (permalink) Old 02-24-2016, 02:50 PM
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when I got the car I found there was no hydraulic fluid in the clutch line.

well if parts are original - or at least old - and there is no fluid in the system, barring an alternate explanation, I would assume the slave has a leak and is in need of replacement. I guess once you bleed & fill it you will find out. just be advised that if these hydraulic parts sit dry for a long time, the seals go away pretty quickly.
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post #11 of 37 (permalink) Old 02-24-2016, 03:15 PM
You probably need to determine root cause. I would close the bleed screw and start pumping the pedal. If the pedal starts to firm up and the slave starts to move after a few pumps then there is air in the system. If there is no change in resistance regardless of how many cycles then you likely have a bad master cylinder and the piston is moving thru fluid and not pushing against it. If the pedal is hard but no movement of the slave then the slave is likely frozen. Knowing what's wrong will point you to a solution.

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post #12 of 37 (permalink) Old 02-24-2016, 03:22 PM
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And if your MC seals are shot and not pushing fluid to the slave, it's probably just letting the fluid past the seals out the back. It wouldn't hurt to check under the MC for signs of fluid.

Last edited by Norseman50; 02-24-2016 at 09:46 PM. Reason: Erroneously referred to brake MC when topic was only about clutch MC. Sorry, please ignore.
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post #13 of 37 (permalink) Old 02-24-2016, 03:56 PM
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Hydraulics

In my experience finding a dry hydraulic clutch is a pretty good indication that soon you will be purchasing a new master and slave cylider and flex hose.
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post #14 of 37 (permalink) Old 02-24-2016, 07:34 PM
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And if your MC seals are shot and not pushing fluid to the slave, it's probably just letting the fluid past the seals towards (or into) the servo/booster unit.
It wouldn't hurt to check the face of the booster under the MC for signs of fluid, or remove the MC from the servo altogether and peer inside just to make sure, but it usually won't go inside the booster unless the engine is running and the vacuum is sucking it in.
Umm, we're talking clutch not brakes...
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post #15 of 37 (permalink) Old 02-24-2016, 07:40 PM
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In my experience finding a dry hydraulic clutch is a pretty good indication that soon you will be purchasing a new master and slave cylider and flex hose.
Yep. Might as well just replace them now and save yourself doing the job multiple times.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
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