Bleeding clutch!!!

[Graham Lyons]

Anyone got any wrinkles on bleeding the Mk 2 clutch? I can't seem to get rid of that last bubble. Somneone told me not to use Red Dot fluid because its viscosity is too low to flush out the bubbles. Sounds reasonable to me.

 

[Michael J.]

Try bleeding it both ways. From the bottom, use a Mitey-vac to pump fluid from the slave cylinder bleed screw back up into the master.

 

[Graham Lyons]

OK, wondered if that were possible. Seems like a logical way to do it anyway since bubbles travel up!

 

[piman]

Hello Graham,
I have seen quite a few post here about problems bleeding clutches and I don't understand why.
I have bled clutches in the past by merely opening the bleed screw and letting gravity do the work (a bit slow though).
These days I use a pressure bleeder, but if you are using an assistant have him\her pump the pedal, (bleed screw closed) until there is a 'pedal'. Hold firm on the pedal while you open the screw, tighten then have the assistant raise the pedal and repeat until there is no air coming out of the bleed nipple. Just ensure that you don't allow the reservoir to get too low during this.
If this does not work and you can't get a firm pedal there is probably a master cylinder fault.
Also ensure the small flexible hose at the rear of the head is in good condition.
Viscosity of the fluid is, I think, irrelevant.

Alec

 

[aeronca65t]

...and on some cars, it's useful to "bleed" the top of the line as well. This can be achieved by having an assistant pump up the pedal and hold it down firmly while you loosen the line going into the master cylinder. It makes a mess of course, but it may get some of those stubborn upper bubbles out (wipe up quickly or the paint will be spoiled)

[ 04-13-2004: Message edited by: aeronca65t ]</p>

 

[Graham Lyons]

I have bled clutches before too, Alec, and I have had friends try to help me with this one, starting out just as confident as you (and me when I began). I still have a soft pedal on the first stroke.
I'll have a go at aeronca's method next.
Thank you both for your help.
Graham

 

[piman]

Hello Graham,
sorry if I was trying to teach you to suck eggs, but it is not always apparent what experience the person asking the question has.
What were the circumstances leading to this soft pedal?.
I have just had a quick look at my MK 2 Service manual, which states "on no account allow the master cylinder reservoir level to drop below half while bleeding the clutch" (Just in case)

regards,

Alec

 

[Graham Lyons]

That's OK, Alec. I was also less offended than it may have sounded.
It just happened one day in the middle of a drive. Perhaps the level may have dropped a bit low and let air into the system although I only needed about 20mls to top it up.
Even though they looked alright, I have replaced the rubbers in both master and slave cylinders (both resleeved less than 2 years ago and bores look perfect).
I remember the mechanic that did the work two years ago said he had a lot of trouble bleeding the system. I've moved towns since but I'll give him a ring and see how he finally did it.
And yes, you do need to top up the reservoir a lot. It's not large and runs out very quickly. My last attempt involved three people. One on the pedal one at the bleed valve and another topping up.
Graham

 

[Graham Lyons]

Problem solved! The mechanic used a pressure pump.
I also learned that someone had fitted a spring on the slave cylinder à la really early Mark 2's which made the pedal marginally softer. It wasn't the problem, but it's typical of what you find on a 40+ year old car that has been visited, many and oft, by cowboys. It was scary what I found had been done in the way of brake hoses when it came to me.
Thanks all for your advice. I know a lot more (fact and fiction) about brake fluid now than when I started.
Graham

 

[piman]

Hello Graham,
with that later clutch there is a specific free play setting of 0.75" at the slave cylinder. If you remove the clevis pin, then push the piston as far back as you can into the slave cylinder, then push the actuating arm until it touches the release bearing, there should be that gap between the two 'eyes'. By the way throw the spring away.

I also wonder if now it will bleed using manual methods?

Alec.

 

[Graham Lyons]

A good point, Alec. The slave piston return would be faster without the spring so you never know. I'm not about to let air into the system to try it, however. The spring has been thrown.

I did check that rod adjustment and it was out by about 0.5".

Graham