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MG MGB GT V8 Factory Originals Technical - Slave cyl question: Tr8 'box

I replaced the clutch s/c in front of my TR8 gearbox and maybe it was like this before but I don't remember it: the clutch feels like a competition clutch in a old hot rod -- it snaps from totally off to totally on in a fraction of the pedal throw. Leaving red lights requires considerably more precise footwork than it does in, say, a Toyota. Is there a way to mellow it out, so that the clutch's takeup is a bit more gradual? I mean, I just don't see one single thing to adjust on there. Also the pedal pressure is one hell of a lot stiffer than it is in, say, a stock MGB.

Is the answer by chance to use a slave cyl with a narrower bore? If so, would the SD1 slave cyl be narrower than the TR8 version?
Bill Withum

This may not be the fault of the slave - if you want some help you need to tell us a bit more; like what car - which components - where's it been recently.


Sure Roger, thanks: it's a Rover 5-speed sourced from a TR8 on the back of a 3.9V8. You're going to want to know exactly what clutch is in there and I can't say other than that I think it's a stock TR8 unit. The m/c is just your plain vanilla '74 MGB issue.

It doesn't leak but it's really an awful feeling clutch pedal -- push it down a couple of inches, then there's kind of a point where it binds a little and that seems to demarcate the point where the tranny is fully decoupled ... you can still push the pedal down about an inch more, should that strike your fancy, but it is really stiff and there's nothing more to be accomplished.

Now I do seem to vaguely recall that the SD1 s/c does indeed have a narrower bore than the TR8 and it so it seems to me I may have inadvertently replaced the SD1 unit with a TR8 unit. With a narrower bore, it seems to me the pressure would be less, the throw longer and the takeup more gradual. Or did I get that exactly backward? Any ideas?
Bill Withum

I am no expert but I have been down this road when I replaced the MG box in my factory V8 with the TR8 LT77S - I believe your basic problem is the m/c designed for the lighter 1800 clutch -

You don't say which bellhousing you are using but my guess is the s/c travel (& diameter) is matched to the bellhousing and if the slaves are same then there is not a lot difference in bellhousings either.

(I do know that clutch plates etc are pretty well interchangeable although competition plates are hard work and would are not suitable for evryday use.)

Yes - smaller diameter will give loner travel but
in principle I believe you should be looking to change the master cylinder in order to deal with the heavier V8 clutch. Your countrymen will have ideas about a US equivalent but my advice would be to use either the
GMC1011 from the GTV8 which will cost you 42 plus shipping from the club or GMC 1014 from the TR8 which will cost you 61.75 plus shipping from Rimmers. At the same time, I would buy the refurbishment kit which would guarantee you never look at the beastly thing again.

Your description of the clutch action still worries me because the symptoms ressemble the action found when the flywheel and clutch plate become contaminated with oil or otherwise get very highly polished. Only you know if that is possible - but it doesn't change the advice to look for a new M/C 'though.

Now the crucial old lags advice about the TR8 arrangement is that the travel on the slave/ the length of the lever was too short to move the clutch the distance required (design fault entirely consistent with TRs) and your friendly mechanic would extend the length with a small socket (needs 1.5 cm).

Hope this gives you some ideas.


Years ago, with my first V-8 I had a REAL HARD clutch to try to push & I left it that way were the old lady WOULD NOT drive it!!!!! After she left I changed to a slave cyl. that has a larger bore & this made a much sofer clutch to push. I use this slave cyl. on ALL of my conv. & I have no complaints. I also use the Rover & TR.-8 clutch kit & all works well.
Glenn Towery

I used s/c from Glenn. I works fine. Not to stiff at all. I had a bear of a time bleeding the first time, but after that no problems.

Glenn - is that a readily available slave with a metric thread or does it fit the MG's flexible hose?

I suply all the fitting to plum in with a new hose, that you loc tight to stop a leak, have done it this way for 20 years & have NEVER had a leak
Glenn Towery

What is the cost of this s/c from Glenn? What car is it off (I assume an SD1??)

This thread was discussed between 08/08/2002 and 19/08/2002

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