Bleeding the clutch

Technical MGB discussion
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Joined: Tue Jun 05, 2018 8:26 am
Forename: Andy
Surname: Hillman

Bleeding the clutch

Post by Andyh » Thu Jan 23, 2020 6:02 pm

What is the most effective method of bleeding the clutch system? After bleeding in the normal way, we still seem to have air in the system somehow... which manifests in having no clutch once the system warms up...although, when the car is cold, the clutch does operate.
Any thoughts?

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Paul Scott
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Re: Bleeding the clutch

Post by Paul Scott » Thu Jan 23, 2020 6:53 pm

Hi Andy,
When I renewed the master, slave copper & rubber hose I clamped the pushrod on the slave fully home. Then with my trusted helper (the wife) bled the system as normal.

When pushing the rod back into the cylinder I opened the bleed valve to ensure no air was trapped in the slave.

All good & no issues.

This may help, I'm sure there will be more ideas coming through shortly.

1975 MGB Roadster
Webguru for MGB Register

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Peter Cresswell
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Re: Bleeding the clutch

Post by Peter Cresswell » Thu Jan 23, 2020 7:05 pm

I just use one of one man brake bleeding kits and it always works fine.
Couple of points though
1.Keep an eye on the fluid level in the master cylinder. The slave cylinder is quite large diameter and the master cylinder is equally small so it empties quickly.
2.don't stop pumping the pedal when the bubbles stop appearing in the tube. There is often some more behind the first blob of fluid that comes through.
3. Best method though is to get someone to help by pushing the pedal down when you have opened the bleed ripple, then close it before telling them to let the pedal up. It is the down/up routine!
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965

Vic Butler
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Re: Bleeding the clutch

Post by Vic Butler » Fri Jan 24, 2020 11:42 am

Pressure or vacuum bleeding. Hydraulic clutches are notoriously difficult to bleed.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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Tom Brearley
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Re: Bleeding the clutch

Post by Tom Brearley » Thu Jan 30, 2020 9:59 pm

I found holding the pedal down overnight beneficial. The theory seems to be that air migrates to the high point and releasing it in the morning sucks that air into the master. The pedal got firm after 3 nights.

There's a nice Moss video on Youtube demonstrating the efficacy of pushing the slave piston fully home here

I also tried hanging the slave vertically, but you need to remember not to press the pedal. Otherwise, the piston pops out and deposits the seals and fluid on your garage floor. You then need to buy a new seal kit. Don't ask me how I know that.

1973 MGB GT
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Re: Bleeding the clutch

Post by TomMGBGT » Tue Jan 19, 2021 7:31 pm

Hi Andy
I have the same problem with my clutch on the BGT, did you manage to resolve yours and if so how

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Charles Farran
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Re: Bleeding the clutch

Post by Charles Farran » Tue Jan 19, 2021 8:18 pm

Not sure if you have also installed a new slave cylinder - if so , many of us found that to minimise packing the bleed screw comes in the wrong aperture so that the whole thing fits in a box.I realised this when i had it on the car & tried to bleed the system....
1980 Roadster

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Re: Bleeding the clutch

Post by Bumpa » Wed Jan 20, 2021 9:18 am

A technique I have used on several cars is to bleed it from the bottom up, the way the air naturally wants to go. I start with the system empty and connect my full Eezibleed bottle to the slave bleed nipple. Then by applying a very low pressure from the spare tyre (around 10 psi) you can watch the fluid slowly enter the bleed nipple, and then a minute later it appears in the master cylinder. Once the master is half full I shut off the bleed nipple and voila, the clutch works.

Don't forget to blow up the tyre once you have finished!
1969 MGB GTV8 3.9 Conversion, 1977 Triumph Dolomite 1850HL, 1971 MGB roadster undergoing restoration.

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