MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

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 MGB Technical - Clutch Pedal Vibration / Noise

Just finished re-build and new clutch, but not release bearing. Car drives perfectly for 20 miles, then noise when clutch pressed. Clutch bite very low. Pedal vibrates under foot when pressed. Any clues?? Please tell me I don't ahve to strip the engine out again ! :( Thanks, Andrew
Andrew Walton

You have to strip the engine out again. Why on earth would you replace the clutch and not the release bearing??? The symptoms are exactly those of a release bearing having either worn through or collapsed. The only way to find out is to take out again.
Mike Howlett

Couldn't agree more. It was absolutely mad not to replace the release bearing as all the typical release bearing problems are now showing up. Sorry but you will have to pull it all out again. At least you will know for next time.
Iain MacKintosh

Thanks for breaking it so gently chaps ! I didn't replace it, because it looked fine and have never had problems before although it is only my second full re-build so not much experience of this component. I replaced the clutch as it is always sensible to do so - where would you stop? The car sailed through it's MOT so I'm happy about that and will soon get this sorted. I'll have a look throught he rubber boot to see what I can see - any damage etc. Thanks
Andrew Walton

I wouldn't even leave a roller bearing release bearing in there if I had the engine out, never mind a carbon one, regardless of its apparent condition. Neither would I use a roller bearing again in the roadster, but that's another story.

As to the low biting point, that doesn't really point to a release bearing problem. The MGB hydraulic clutch automatically takes account of any mechanical wear *anywhere* in the mechanical linkage from the slave piston right through to the friction plate and flywheel. As wear takes place the piston simply moves further and further out. If the release bearing or release arm breaks then the piston moves so far out under repeated pedal operations that it and the fluid comes out of the end of the cylinder.

Mechanical wear at the pedal end of the hydraulics is a different matter, and *does* cause a low biting point, as does air in the hydraulics.

When very very worn the release bearing can rub on the cover plate, and that will cause noise and vibration. There is a known problem with some types of carbon bearing where the carbon ring is pinned into the casting instead of being bonded. The roll pin for this is very obviously on the side of the casting. On this type you can get sudden and total breakup of the carbon ring, see http://www.mgb-stuff.org.uk/wn_clutchframe.htm and click on 'Release Bearing'.

The beggar with clutches is that it's a big job to look at the stuff inside the bell housing, and if you don't find anything obviously wrong, or do but miss something else wrong as well, you don't know about it until it is back together again!

Paul Hunt

Thanks for advice. I observed what was happening and the clutch yoke was viabrating. So as a chance, I bled the clutch and got a shot of air out. All works perfectly and quietly now ! I guess the clutch was not fully releasing and maybe 'bouncing' causing the noise?? Glad I didin't knee jerk and rip it all apart. Logic and observation always seems to save time and energy. But a tip for anyone with a newly assembled clutch, air may 'settle' in as it was air free when fitted. Will keep eye on it and let you know. Andrew
Andrew Walton

Oh wow, weren't you lucky. That is a most unusual situation and am very glad it didn't all go pear shaped. Keep us informed on progress and I hope that the fix keeps going.
Iain MacKintosh

There is a spring in the slave cylinder which tends to push the piston out to take up any slack in the mechanical linkages to the cover plate. That means there is the resistance to the fluid flowing up and down the pipe to damp movement of the release arm. With air in the slave I can see there is more likelyhood of it moving back and fore quickly i.e. rattling, like air in hydraulic suspension dampers. Well spotted, and definitely one to (try and) remember!
Paul Hunt

This thread was discussed between 28/09/2009 and 29/09/2009

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now