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MG MGB Technical - Clutch Hydraulics Diagnosis

Is there a simple diagnosis to determine if the clutch slave or the master cylinder is faulty.
The system is NOT leaking fluid, just pressure drop while the pedal is down.
JR Ross

If the system is not leaking fluid, then it's a good bet that you have a master cylinder that is bypassing the fluid internally. They can be rebuilt if the bore is fairly clean. RAY
rjm RAY

Agree. If no leaks but the clutch gradually re-engages while the pedal is still down, then the pressure seal in the master is leaking back.
PaulH Solihull

I've replaced the Clutch master cylinders internal seals. The pedal is easy (too easy) to depress and fluid does not come out of the rear flange. I have a feeling that one or more of the seals are the wrong way round. Does anyone have a sketch or drawing of how the internals with seals and spring should look ?.
P Liles

The factory workshop manual, Haynes manual, and the Moss Motors catalog all have an illustration of the clutch master cylinder and how it goes together. None are drawn in quite the detail one would like, but can be used. One of the rebuild kits I used had a better illustration enclosed. Which master cylinder do you have? There were two of them and Moss lists the rebuild kit for the earlier version as no longer available and sells a kit to convert the earlier model to the later conformation.

Could it be you have the wrong kit?

Les
Les Bengtson

Les
I'mpretty sure I have the correct kit, just dont have a diagram. I have a 77 BGT and a master cylinder without the grooves. MG Hive in the UK supplied 2 kits since when I ordered I didn't know one from the other.
P Liles

I have gone through my spare parts and do not have a spare clutch master cylinder to take apart. I did find, however, a clutch master cylinder rebuild kit (Delphi LK10960) which has an illustration included. The spring goes at the outlet end of the cylinder, followed by a "retainer-spring" (item 18 on the factory illustration). Then, the diagram with the rebuild kit shows a rubber seal having a lip with the lip facing forwards, towards the spring and spring retainer. Then, a flat washer (washer-piston, item 16) is between the cup seal and the piston. There is a seal towards the pushrod which is sown with the open end of the V towards the spring end. (From memory, this seal fits onto the pushrod, but the illustration does not show that.

This is, I am afraid, all of the help I am able to provide. Mayhap someone has a spare master cylinder which they could take apart and photograph?

Les
Les Bengtson

Both seals should face in the same direction, i.e. towards the outlet from the master. The seals are different, but it should be much more difficult to get the the wrong way round that the right. I'm attaching the drawing from the Leyland Workshop Manual but it's not very detailed as to the seals themselves - items 14 and 17. There should be a thin washer (16) between the main seal (17) and the piston (15) to prevent the seal blocking the feed holes in the face of the piston.

Make sure the piston is coming back far enough for the main pressure seal to clear the bypass hole in the cylinder or fluid will not be able to get from the reservoir into the cylinder.

PaulH Solihull

This thread was discussed between 03/07/2011 and 01/04/2012

MG MGB Technical index

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