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MG MGB Technical - Bleeding the clutch

I am working on a 1973 MGB and I have simply replaced the clutch flexi-hose. The system was dry when I put the new hose on so I would have thought it a fairly straight-forward normal bleed operation to bleed it and get pressure on the slave and lever again. It was working OK before but the hose was brittle, original and very nastily worn.

My friend and I have been doing the standard manual bleed for about an hour and still have absolutely no pedal or pressure in the system. We get a trickle out under pressure, but not a spurt. I have even removed the bleed valve completely and still only a trickle.

What did we miss please? Something obvious I am sure.


Paul R Barrow


It is a topic very popular, check archives or my procedure:

1- A hose from bleeder to reservoir and pumping until a good flow
2- compress slave piston to its rest and hold it there( A CARPENTER CLAW WILL DO THE JOB)

3- close bleeder and try your standard procedure to bleed it and VOILA!!!
it will work fine

Jean G

P.S. I forgot to mention you must remove claw at the end
Jean Guy Catford

I'll have to go buy a carpenter claw now!

Is the hose back up to the reservior absolutely necessary? I just dump it into a catch bucket - makes great weed killer!

Thank you

Paul R Barrow

Paul. As Jean notes, press the slave cylinder's piston fully rearwards (to the rear of the cylinder, forwards in relationship to the engine). Close the bleed nipple and pump the clutch pedal a few times, then hold it in place. (An assistant makes this easier, but, you can hold the pedal down with a weight if you do not have an assistant.) Open the bleed nipple, then close the bleed nipple. Pump up again, and again, and again, repeating the procedure until you have good movement of the pushrod between the slave cylinder and the clutch fork. About 3/8" is what I measure on cars with properly working clutches.

Yes, a tube from the bleed nipple into a jar works fine. In fact, it flushes out the bad/dirty fluid into the jar and does not recirculate it back up into the system.

However, the very best method of bleeding the system is to reverse fill it from the bleed nipple up to the master cylinder, forcing air out of the complex line structure as you do so. But, this requires a tool, which used to be made by Phoenix Associates, that is not commonly available. I was given one many years ago to test and evaluate and found it the best method of doing the clutch bleeding.

Les Bengtson

Thanks guys.

I hate bleeding stuff!

Paul R Barrow

Actually, just had a scary thought. A lot of aircraft have hydraulic systems. Did they all have to be bled??? Mike
J.M. Doust

Having been a helicopter engineer for 20 odd years I can confirm that Aircraft systems usually have pumps to provide pressure constantly and so had a 'self bleed' property by design they also have a system called an accumulator which is pressurized with air to provide pressure to the system in case of pump failure
B Anderson

Remember particularly with pedal bleeding you are trying to push air down quite a large bore pipe - tantamount to pushing a pea uphill with your nose. It's even difficult with a continuous bleed system like the EeziBleed. By far the easiest method is the connect a tube between the right-hand calliper and clutch nipples (they are the same size) to reverse bleed it. Open the clutch nipple, apply very gentle pressure to the brake pedal, then open the brake nipple. When the pedal is fully down close the brake nipple, release the pedal, and repeat. Only a couple of pumps should be necessary to get visible fluid into the clutch master, then top-up.

Pushing the piston all the way back into the cylinder shouldn't be required, especially with conventional bleeding, as the exit from the cylinder to the bleed nipple is at the highest pint of the slave when it is installed. It can also be counter-productive as when you release it a spring is trying to push the piston out again, which is trying to suck fluid all the way down from the master. The seals do not like sucking fluid, they will suck air past them from the outside far more easily. This is exactly what happens when you pedal bleed and progressively work fluid through a system - except that there is fluid behind the primary seal and not air.
PaulH Solihull

Push a pea uphill with your nose? Never heard that one before, Paul. You truly are a wealth of knowledge. RAY
rjm RAY

Thank you every one. Jean's trick worked though once I had the hose connected at the bottom I cheated and filled it from the top so I didnt have to work too hard. Even so, it took a good half hour or so to get a really good pedal so great tip.

Thank you every one. My neighbor came over to help me bleed/pump etc. and his comment was "How did you manage to get this without having to pay for it?" I told him the MG community is just really good and looks after its own.

Again, thank you

Paul R Barrow

Must have had a good day when i did mine last - with an ezibleed nipple. Only took 10m minutes.
But I like Paul's method and will try that next time.
Wondering if pushing a pea uphill with your nose is harder or easier than trying to push a wet rope up a hill??
John Minchin

Wet rope won't roll all the way back down :o)

Remember the sand dune scene near the end of 'Ice Cold in Alex'?
PaulH Solihull

Ah - another film to add to my bucket list!

BTW it was made in Elstree studios - must have taken a while to truck all the sand in!

John Minchin

Never mind rebuilding Alexandra indoors ...
PaulH Solihull

This thread was discussed between 23/01/2012 and 27/01/2012

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.