MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - MGA clutch

Hi everyone. I've a problem with my clutch changing and scrunching gears when I change gear. The history is that I changed the clutch a little while ago and I realised too late that I never greased the splines on the first motion shaft where the friction plate slides up and down. I have a suspicion that the friction plate is responding only slowly when the clutch pedal is pushed and I have to wait for the gearbox revs to die down before I can get a smooth gear change. Can this be a logical explanation for the symptom and if so can I somehow grease the splines insitu?
With thanks
John
J H Cole

John. The answer is no. When installing a new clutch plate (driven plate is the Brit term for it), the first motion shaft should be cleaned, the clutch plate assembled to it and determined to move freely, then removed and the clutch and pressure plate installed onto the fly wheel. Use of grease, or other wet lubicants, is always a very poor idea. As the first motion shaft rotates, it can allow grease, oil, or other liquid/semi-liquid lubricants to fly outwards and contaminate both the clutch plate and the fly wheel. That, would cause contamination of the mechanism resulting in a slipping clutch. It is a very bad idea to lubricate the first motion shaft or the center opening of the clutch plate.

As soon as the pressure plate is forced out of engagement with the clutch plate, there is no longer any driving force being applied to the first motion shaft because the clutch plate is no longer being forced into engagement with the fly wheel. Thus, the symptoms you describe sound like the clutch hydraulic system has a problem, not the mechanical portion of the clutch. Check for movement of the pushrod for the slave cylinder. My measurements show that at least 3/8" of movement is necessary for the clutch system to operate correctly. (Some others, such as Paul Hunt, a very compentent experimenter, believe that 1/2" of movement is necessary and desirable.But, I was not there when he took his measurements, only when I took mine.) If there is insufficient movement of the slave cylinder push rod, the throw out bearing will not be moved sufficiently to allow the clutch plate to fully disengage from the fly wheel resulting crunching or grinding of gears when shifting. Which sounds very much like the problem you describe.

Short push rod travel can be caused by bad seals in the clutch master cylinder or slave cylinder, or both. They do need to be replaced at some interval. In additon, wear on the push rods for the clutch pedal and the slave cylinder can wear over time (it is of benefit to lubricate them with a light grease), causing the slave push rod not to be able to move properly. The clevis pins associated with the clutch pedal to master cylinder push rod and the slave cylinder push rod to throw out bearing fork can wear drastically and cause problems. Finally, the throw out bearing fork's hole where the clevis pin holding it and the slave cylinder push rod together can wear into an oval. One, or a combination of several, of these problems should be the root cause of your problem.

Les
Les Bengtson

I'm wondering if there might be a possibility that maybe you might have the wrong oil in the gearbox.
If it happens to have thicker gearoil in there instead of the spec. engine oil it'll behave like that---
William Revit

Hi John, you could also bleed your clutch slave cylinder, if you have any air in the hydraulics then you will not get enough travel to fully activate the pressure plate and this will also cause grating of the gears.
I Hazeldine

This thread was discussed between 21/03/2025 and 24/03/2025

MG MGA index

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