gruffalo

Hi,

I've been working on replacing the timing belt for several weeks now, and I'm finally done.

To fit the flywheel lock, I removed the clutch slave. The hydraulic line was plugged with a rubber plug, and the slave cylinder left resting on my workbench.

Now, after fitting it, I have an issue bleeding it.

First I tried bleeding it using an assistant depressing the pedal, while I opened/closed the bleed nipple. Just as I normally do with the brakes.

The pedal went completely dead, and the air never stopped coming. We must have cycled the pedal 50 times, but the bubbles never stop.

Lastly I tried vacuum bleeding, but with no success.

I topped up the reservoir 3-4 times during the process, and it never went dry.

What's going on?

SeanR

Pull the slave out of the bell housing and using your hand, pump the rod in and out a dozen times or so. Re-install and test.

jcorenman

What he said ^^^

This pushes fluid (and air) from the slave up to the reservoir. Since air likes to rise in fluid, it is very difficult to get the air to flow downwards and out the bleeder-- but relatively easy to get it to float up and back to the reservoir.

Also, when fitting the flywheel lock, avoid disconnecting the slave hydraulics if possible. The hardline is trapped by the starter, if you pull the starter (and the bracket attached to the oil pan bolts) then you can remove the slave and let it dangle.
You can also pull the slave rod out of the slave, once it is unbolted and backed off an inch, by reaching in with long-nose pliers. That lets the slave move out of the way, pull the rod and then fit the lock.
And Greg Brown's cosmic clutch hose makes this trivially simple. It is an insulated flex hose that connects the slave directly to the connection at the chassis rail-- replacing the hardline under the starter as well as the short factory flex hose-- and routes around the end of the starter, not under it.

Cheers, Jim

gruffalo

I tried the exercise above. I could feel lots of air in the beginning, later it felt like I was just pushing fluid back and forth.

Full of hope I tried the pedal again. No luck. It just snaps instantly to the floor, with no resistance.

Mrmerlin

OK try this remove the slave bleeder put some PTFE sealant on the threads and screw it in.
Get a hand pump oil can and fill it with brake fluid,
put a piece of clear hose on the tip of the can hose so it will fit snug on the bleeder tip.
MAKE sure that there is room on the reservoir for more fluid to fill
pump the can till there is no air in the hose then connect to the slave bleeder,
open the bleeder nipple then pump til you have put about 1 oz of fluid into the slave close the bleeder
and check the reservoir for not being too full .
then check the clutch.
If this still doesnt work then you may have a bad MC and there are some mods that have to be done to make it work with the new replacement

G8RB8

Seal on the master is leaking.

gruffalo

Tips so far are:
1. Jerking the slave rod in/out multiple times
2. Reverse flush using brake caliper or oil pump
3. Letting air out by carefully removing master piston (Kempf method)

What bothers me is that the pedal is completely dead. The slave has mostly fluid in it now, so I should see SOME action at least?

I think I need to start debugging the MC, tips are greatly appreciated.

Kevin in Atlanta

1. You can push the slave cylinder in all the way and with a set of tiny alligator locking pliers hold it in place.
2. I used a oil pump can and pumped it in the slave bleed valve - very effective. Be sure to draw off some fluid from the reservoir.
3. Very messy and hard to get to. Also tends to destroy the carpet glue.

jcorenman

No, not "jerking". With the slave removed from the bellhousing, and connected, you want to slowly push the clutch rod into the slave, full travel until it hits the stop. Hold it there a few seconds to give the fluid a chance to move and the air to escape, and then slowly release the rod and let the spring push it back out-- slowly, so it has a chance to refill from the reservoir. If you have a helper then they will see the fluid rise in the reservoir, and hopefully some bubbles.

If you have a pressure-bleeder then hook that up to the reservoir to help push fluid towards the slave, when the rod is (slowly) released. Not a lot of pressure, 5 psi should be enough.

Yep, that will work. You can also use a pressure-bleeder (backwards) if you have one, with an adapter (smaller tubing to fit the slave bleeder instead of the reservoir cap).

This is tricky. Tom M likes this method and I have seen it work, and work well-- air likes to get stuck in the upper reaches of the MC. But reverse-bleeding (externally or by pushing the slave-rod) will also flush the air.
Tom's method is not to remove the master piston, which will certainly barf fluid everywhere, but rather to remove the circlip and then ease the piston out just far enough so that it burps air and a drop or two of fluid, then push it back in.

It does not take a lot of air to make a dead pedal. But yes, you should start to see some clutch action. I think your master or slave is probably still mostly full of air.

Here's another potential issue: The last couple of new MC's that I have seen were mis-machined-- one from 928 Int'l and one from Porsche. There are two small bleed holes, visible with the fill-adapter removed (the fitting for the dreaded blue hose). The larger one towards the pedal bleeds the space between the seals, and the second smaller one fills and bleeds the main hydraulic circuit. This is the hole that refills the MC as needed, and through which any air needs to pass through, back to the reservoir when reverse-bleeding or pushing the slave-rod. This bleed hole is close to the rubber piston-seal and gets cut off as soon as the pedal starts getting pushed.

The problem I encountered was that the smaller main bleed-hole was already getting occluded by the rubber piston seal with the pedal at rest (and properly adjusted). So there was no fluid path from reservoir to MC, and no place for air to escape (or excess fluid, as things warmed up). With the MC removed you could see the rubber piston through the small bleed hole.

Removing the circlip and grinding about 0.010-0.015" off the washer fixed it. I don't know how common this is, but it gave me fits until I found it. And yes, getting the MC out of there is a bitch. If you remove the hardline from the MC first, it will come out without loosening the brake booster or cutting up the fender.

Hopefully this last issue is not the problem. You should be able to get it properly bled by pushing the slave rod. You will need to get the slave out of the bellhousing without disconnecting the hydraulics however, see my comments above.

Good luck! Jim

the flyin' scotsman

I drove the GTS back from Witchita to home last summer using the 'Tom' method.........3000kms.

I got back but it wasn't until I reverse bled then did the trick with the slave cylinder pushrod was all the air expelled.

Dutch 928 fan

+1 on the reverse flush using the brake caliper (attach line from brake caliper nipple to clutch slave, open both, pump brake pedal many times).
Advantages: no mess, no need to top up fluid, just pump it around and around by yourself without a helper.
Worked perfectly after I replaced my leaking slave cylinder.

gruffalo

Thanks guys, I really appreciate all your help and enthusiasm!

My car does not sit level at the moment... I've got the front rised since I've been doing the TB. Could this be making matters worse?

BTW my car started right up today, after sitting for 6 months, and me doing the TB for the first time

cpayne

Would this work as another solution?

gruffalo

Guys, still no luck on this subject

Today I first hooked up a hose from a brake caliper to the clutch slave. I had my son sit in the car and cycle the brake pedal. He did 10 calm full strokes, while I watched to make sure no more air was being pumped in. I closed the bleed nipple on the slave, and tried the clutch. We got some action. Maybe half of the pedal range was "active".

Encouraged by the improvement I decided to try pushing the slave rod in /out multiple times. I removed the slave and did 20 cycles, full stroke length, end to end.

We tried the clutch. Now it was worse! Maybe 25% of the pedal range (inner) moved the slave.

Then I rigged the oil pump I just got, and started pumping into the slave. I had my son watch the reservoir. I pumped it from the min mark and all the way up until it was way past the full mark. Tried the clutch. No change. I had a clear tube from the oil pump, and no air bubbles got in there.

I have to add that I can see no leaks in the system, and the clutch has been working perfectly since I got the car, more than two years ago.

At least I got to some quality time with my son...

Ideas, please! I wanna drive! I wanna test out my new x-pipe!

Mrmerlin

at this point I would suggest to replace
the MC
and the slave
and if the flex line is original replace it as well
and get a new Blue hose.

once you have all new parts your clutch should work for many years without any need to go through this again

NOTE if you get a new MC, then the pistons should be swapped as well as the shorter spring from the old MC
you will take the new MC apart,
and remove the rubber seal ,
and install the new seal on the old piston,
then install the old piston and old spring unless its damaged,
in that case cut down the new spring to prevent coil bind,
then install these parts into your new MC .