6 speed clutch bleeding nightmare

Hi guys we recently bought a mk5 golf 2.0 gt tdi and the gears was going in but felt notchy so we decided to do a bleed from the bleed valve on top of the gearbox as the slave cylinder is inside the gearbox.
We kept the fluid topped right up and I've tried bleeding it everyday I can with a one way bleed valve, holding pedal down undoing it then closing it and repeat, I've even tried pushing fluid up the line with a syringe and it still won't bleed properly, we get a pedal but when trying to engage gears it's like the pedals not all the way down, it's gone worse since we tried to bleed it so I'm certain there's still abit of air in the slave cylinder side of the system, anyone any ideas how to bleed this bit out?

One suggestion to try. But if your system has any leak anywhere it may never bleed out as it may be continuously pulling air back in.

This technique may sound like you've already tried it but it has one twist, the starting point.

Setup, put a hose on bleed screw to a waste container.

1. Pedal fully up.
2. Open bleed screw.
3. Slowly push the clutch pedal to the floor.
4. As soon as it hits the floor, close the bleed screw.
5. Lift the clutch pedal by hand, it must come all the way back up to start the next cycle.
6. Repeat for several cycles maybe cycling about 6 oz of fluid thru the system.

Rather than trying to build pressure, this technique flushes from the master cylinder.

Good luck.

My problem is getting worse then yours.

Collapsed pressure plate fingers. I thought I had air too.

Jason,

Is that a pre teardown comment or after teardown result? What is/was the drivability observation? Also, what car.

Gary

I am getting a pulsing through the pedal like dmf screwed but it's just had new clutch and flywheel before we bought it apparantly and it looks new looking through bell housing.
We're seriously thinking about taking the gearbox out to bleed the slave cylinder as that's where we're adamant the air is stuck

Internal slave cylinder, to remove trans you have to disconnect the line. If the line and slave cylinder connection do not have check valves in them the fluid will just flow out. Some systems do have built in check valves, not sure if yours does. Removing a trans to bleed an internal slave cylinder is not any service procedure that I have ever heard of.

OK, new clutch and flywheel, what about the slave cylinder?

Did you try the open bleed screw procedure? Bleeding these can be frustrating, I agree. Best overall advice, brake bleeding techniques may not be the best technique.

I've thought about getting a gunson bleeder that connects to a tyre valve and uses the air pressure as I've tried everything like the pumping then bleed and Also the single pump hold down open bleed and repeat etc, then I tried the syringe and back bleed forcing it up the other way but nothing, I can't help but think the air is in the slave cylinder on the other side of the bleed valve and the way the system works it's only allowing fluid coming the master cylinder side to bleed easily and not getting anything from the slave side?

Repeated pumping, ineffective. The clutch pedal is always on the floor when you open the bleed screw. The slave cyl tries to respond, miserably.

Do you have very much to loose by trying the technique I suggested? In the exact order presented, no variation.

They can be a pain in the root to bleed, some more than others. Mine was a weird one, me and a friend bled it, got enough pedal to change gears easily so left it at that because I'd just finished doing a heap of work and it was late.
Anyway the clutch seemed to bleed itself the rest, pedal got higher till eventually it was like normal after a few days lol.

I replaced a master on a ford focus and that one had me sticking a litre of fluid through the system a few times before it eventually worked.

I think the secret is to be relentless, just like with the rear brake callipers sometimes, just got to keep on trying till eventually it just works.


I vote for GCBUG00's method except I prefer to close the bleed nipple before the pedal reaches full travel. Got to go really slow though with the pedal I find.

I also had a PITA to bleed after master and slave cylinders replacement.
(I sold the car with the problem anyway)
Everyone was saying I'm sick with my imagination but I really knew that there was still air trapped and clutch not fully releasing.

Pre teardown. I have to squeeze carpet before it'll release and if I'm a faction of an inch too high from carpet, I'll bump a tooth trying to shift gears. 4 dealers bled it. All 4 confirmed the fingers are getting weak.

Anyone that understands a clutch, if the fingers collapse and get weak, you need to go further to release.....

I have the ****tier of the scenarios. A clutch that won't release, isn't slipping, and dmf that rattles like a mofo idling...

Ordering parts next Friday.


Haha, advice question, should I replace my slave, or not open it to keep get air in it to a minimum?

jason,

OK, I'll make a prediction based on the info above.

Releases right at the floor, not slipping, all 4 confirmed the fingers are getting weak. Didn't we list not slipping already, yup.

I don't know the history, not sure which of your fleet it is but I'm not expecting collapsed fingers. This is cluing in on the "its not slipping comment" time will tell, please give us the rest of the story later. DMF can be a bit of a wild card, holding that for a reserve play.

Gary

Seatman,

There is a scenario where the master cyl can be self bleeding. Or more accurately burp out the last of the bubbles.

Two primary requirements in the design, a continous uphill path to the reservoir and it needs a piston port master cylinder. Piston port can be identified by the distance between the fluid input port to fluid discharge port. Its just a bit shorter than the system stroke. The other design, the fluid in and out are only offset by 1/2-3/4" or so, very close.

Do your best, whatever technique but its not quite bled.

The piston port has a front pressure chamber and a rear compensating chamber. Comp chamber has a large supply port, pressure chamber really small.

The piston seal at rest (pedal up) is positioned in between the two ports, just as you start to push on the pedal IF the air bubble is right spot at the small port (slight tip helps) as you just start to build pressure but before the pressure port closes voila the air bubble is squeezed out of the small port. But its only one bubble at a time. If you had a clear supply tube, you could actually see them pop out. So really short strokes CAN push a single bubble out one at a time.

These systems can also benefit from dry vacuum bleeding.

Gary

GCBUG00 said:

jason,

OK, I'll make a prediction based on the info above.

Releases right at the floor, not slipping, all 4 confirmed the fingers are getting weak. Didn't we list not slipping already, yup.

I don't know the history, not sure which of your fleet it is but I'm not expecting collapsed fingers. This is cluing in on the "its not slipping comment" time will tell, please give us the rest of the story later. DMF can be a bit of a wild card, holding that for a reserve play.

Gary

Click to expand...

So even after those details you still think my clutch is slipping, my pressure plate fingers are not collapsed, and I have air in the line?

I'm suggesting OP problem might possibly be similar to my problem.

and yes it is possible to have a clutch that will not release and it will not slip. It's called not fully releasing, which can explain notchy bumps, which is possible if the fingers lost their tension, cheap grade spring steel, from thousands of releases from the release bearing pushing into them.


But there might be a bubble in there. Happy hunting for him

Jason,

No, I'm reaffirming based on your statement that its not slipping and using that as a basis for my comments.

That heat treated diaphragm spring is the heart of the diaphragm clutch. It provides clampload, it allows the pressure plate to be pulled away for release. If it cracks, or if somehow it looses its temper it can no longer clamp the disc, slipping, no lift the whole system is SNAFU if that spring fails.

Your inspection of the clutch will be the big observation report.

I have 3 hydraulic release system vehicles, the Bug and a pair of Dodge Cummins. All have crisp hydraulic systems. As soon as the port in the MC is closed they start creating pressure immediately as they should. No appreciably delay, lag at all. But it you were to pull a slave cylinder and compress it you'll find they compress by hand indicating that the port in the MC is open, allowing the system to be at ZERO PSI when your foot is off of the pedal.

This is something about a diaphragm clutch that makes this challenging, can't hook up a VagCom and get any codes for a manual transmission clutch or release system.

Gary

Noted. Probably this weekend. It's rattling soooo bad, and goes quiet when I release the input shift...... I'm getting worried if I should continue to drive it.

hi guys we tried that technique you suggested but im certain i'd done it before and that gives me the best pedal but it still feels like its got a tad bit of air in it and still wont quite engage gears like the pedals not fully pressed down.
were thinking of trying to replace the master cylinder next before we bite the bullet and rip the gearbox out but im certain its air in the slave cylinder and it cant escape as its easier for the system to bleed from the pipe side coming from the reservoir!!

These can be very difficult to bleed. I came across a procedure that is super simple and has worked every time for me thus far.

First thing to note is the basic design of the 02M/02Q slave cylinder makes slave bleeding very hard. When changing the slave I always pre-bleed it by manually cycling it on the bench and making sure it is full of fluid and inlet capped before assembly.

To bleed the clutch system:

1. Check brake/clutch reservoir fluid level, make sure it is toward the "max" mark.
2. Connect a good fitting hose from the driver front brake caliper bleeder port to the clutch line bleeder port.
3. Open both bleeder ports.
4. Gently and slowly pump the brakes. I can usually hear the air bubbles being pushed from the clutch master cylinder as I'm doing this.
5. After cycling until no more air is heard, close both bleeder ports and re-check reservoir fluid level.
6. Finish by briefly vacuum bleeding the clutch to get any small air bubble that may have formed between pumping the brake and closing the bleed port.
7. Do final check of fluid level.

This method reverse pressure-bleeds the clutch in a closed loop fashion and wastes minimal fluid while doing an excellent job of bleeding the master cylinder. So far, worked every time.

What is the wizardry process you are describing?

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A5INKY said:

These can be very difficult to bleed. I came across a procedure that is super simple and has worked every time for me thus far.

First thing to note is the basic design of the 02M/02Q slave cylinder makes slave bleeding very hard. When changing the slave I always pre-bleed it by manually cycling it on the bench and making sure it is full of fluid and inlet capped before assembly.

To bleed the clutch system:

1. Check brake/clutch reservoir fluid level, make sure it is toward the "max" mark.
2. Connect a good fitting hose from the driver front brake caliper bleeder port to the clutch line bleeder port.
3. Open both bleeder ports.
4. Gently and slowly pump the brakes. I can usually hear the air bubbles being pushed from the clutch master cylinder as I'm doing this.
5. After cycling until no more air is heard, close both bleeder ports and re-check reservoir fluid level.
6. Finish by briefly vacuum bleeding the clutch to get any small air bubble that may have formed between pumping the brake and closing the bleed port.
7. Do final check of fluid level.

This method reverse pressure-bleeds the clutch in a closed loop fashion and wastes minimal fluid while doing an excellent job of bleeding the master cylinder. So far, worked every time.

Click to expand...

ive never heard of that before but i'll give it a go i can see how it could force fluid into the slave cylinder to bleed that side possibly but do you need to close the bleed valve between pumps?

glenandem said:

ive never heard of that before but i'll give it a go i can see how it could force fluid into the slave cylinder to bleed that side possibly but do you need to close the bleed valve between pumps?

Click to expand...

No need to close the bleed ports between brake pedal pumps. That is part of the beauty of this method. Since the brakes and clutch use a common reservoir on our cars, this is basically a closed loop method and there is no where for air to come in from. You are basically using the brake system as a reverse pressure bleed pump for the clutch system. True, you will force the volume of your connector hose worth of air back through the clutch system, but it will end up in the reservoir where it vents out and does not reenter the brake system. Theoretically, you could pump the brake pedal endlessly, but there is no need because it will force bleed the clutch in short order.

Just remember to pump nice and slow, don't want to blow the connector hose off the bleed ports, or damage the clutch master cylinder seals.

A5INKY,

Looks like a reverse fluid injection technique utilizing the brake master cylinder. I've never tried it. The only comment is your technique is using two methods, DIY RFI and vacuum bleeding. But if you get the results, enjoy.

I think the big take away should be how challenging getting the air bubble out of these systems.

Here is something that caught my eye, never tried one but interesting. http://www.speedbleeder.com/size.htm

GCBUG00 said:

A5INKY,

Looks like a reverse fluid injection technique utilizing the brake master cylinder. I've never tried it. The only comment is your technique is using two methods, DIY RFI and vacuum bleeding. But if you get the results, enjoy.

I think the big take away should be how challenging getting the air bubble out of these systems.

Here is something that caught my eye, never tried one but interesting. http://www.speedbleeder.com/size.htm

Click to expand...

Yep. Honestly, I don't think the vacuum bleed at the end is doing anything but giving me peace of mind. What you refer to as "RFI" is what does the job. I think this is the case because the clutch master is really hard to bleed by conventional methods. I've had them fail to bleed with a vacuum bleeder and even the old style pump and crack open the bleed port method you recommended. This "RFI" technique does the trick every time though. I do quite a few auto to manual trans swaps and have to bleed out "dry" clutch hydraulic systems. Once I figured this out, 10 minutes tops and DONE.

A5INKJY,

Its a really long story, but I see these as plumbing problems. An air bubble is hiding somewhere, how can I get it out? They can be diabolically tough as you are trying to beat a trapped air bubble. Sometimes going up and out is easier than down and out.

And IMHO there is no one surefire works every time on any and every model procedure. We all have a collection of hammers, each serves its purpose. Same with bleeding techniques.

RFI has been the name of Reverse Fluid Injection tools made by Phoenix http://www.brakebleeder.com/solutions/bleeding-brakes/which-tool-to-buy/

Gary

well i was certain i'd bled it properly so we bit the bullet and ripped the box out and found a goosed release bearing, some idiot has replaced the clutch but not replaced the release bearing!!

Bummer but at least now I suppose it'll work

A5INKY said:

These can be very difficult to bleed. I came across a procedure that is super simple and has worked every time for me thus far.

First thing to note is the basic design of the 02M/02Q slave cylinder makes slave bleeding very hard. When changing the slave I always pre-bleed it by manually cycling it on the bench and making sure it is full of fluid and inlet capped before assembly.

To bleed the clutch system:

1. Check brake/clutch reservoir fluid level, make sure it is toward the "max" mark.
2. Connect a good fitting hose from the driver front brake caliper bleeder port to the clutch line bleeder port.
3. Open both bleeder ports.
4. Gently and slowly pump the brakes. I can usually hear the air bubbles being pushed from the clutch master cylinder as I'm doing this.
5. After cycling until no more air is heard, close both bleeder ports and re-check reservoir fluid level.
6. Finish by briefly vacuum bleeding the clutch to get any small air bubble that may have formed between pumping the brake and closing the bleed port.
7. Do final check of fluid level.

This method reverse pressure-bleeds the clutch in a closed loop fashion and wastes minimal fluid while doing an excellent job of bleeding the master cylinder. So far, worked every time.

Click to expand...

That has to be verging on genius!

Where's a like button when you need one lol

GCBUG00 said:

OK, new clutch and flywheel, what about the slave cylinder?

Click to expand...

Always an assumption that an internal slave cylinder and bearing gets replaced, assume, right.

Glad you found it, sorry for you it was on the inside.

Got it bled OK? What technique worked for you?

GCBUG00 said:

Got it bled OK? What technique worked for you?

Click to expand...

x2. Please share.

cheers guys, one even better it had a few driveshaft bolts missing, some gearbox bolts loose and 2 of the bolts holding the pressure plate on missing, i reckon the splines not being even and two sticking out have wrecked the release bearing!
flywheel feels abit wobbly too so ive told him start again and replace the lot!

OK, glad you're finding lots of things to fix and improve the situation.

The 2 missing pressure plate bolts will allow the diaphragm spring tips to be uneven, higher than the others. So the high tips were creating the starting point for the release bearing and the available release stroke from this false starting point didn't allow the clutch to fully release. Plus any possible damage.

Missing bolts, IMHO a real sign of an unprofessional repair.

BTW splines are the gear like teeth on the trans input shaft and the matching splines in the clutch disc hub.