mgb/rv8 clutch master/slave cylinder problem

JT45 · Post by **JT45** » Tue Mar 27, 2012 8:03 pm

Hi all,
I am looking for some advice as to which clutch master/slave combination
would best suit my mgb/rv8,ie mgb roadster with rv8 engine/gear box.
The existing master is leaking and badly corroded so needs changing.
At the present time the pedal is extremely heavy,can changing cylinders
affect this.ideally i would like it lighter.
any suggestions

thanks
jt45

Ian Anderson · Post by **Ian Anderson** » Tue Mar 27, 2012 8:49 pm

Yes changing cylinder size will greatly affect pedal pressure.

Say you leave the slave as it is / replace like for like, if you decrease the size of your master you will get a lighter clutch pedal, but the down side is the resultant movement at the slave is reduced.

So you may get a lighter pedal but you could end up withba clutch that does not disengage properly.

Ian

Denis247 · Post by **Denis247** » Tue Mar 27, 2012 9:42 pm

I gather, like me, you don't have a lot of pedal travel. So you have to pump enough fluid to fully operate the slave with little pedal travel = heavy pedal.

You can't mis-match the master/slave cylinder combo otherwise you'll get the wrong travel at the slave = incorrect clutch operation.

It may be possible to alter the position of the master operating rod where it connects to the pedal, resulting in a little more travel = lighter.

Unfortunately I wasn't able to do this on my Lotus, but looking on the bright side, it does give your left leg a good work out, and it stops the missus wanting to drive !

richardpope50 · Post by **richardpope50** » Wed Mar 28, 2012 9:39 am

It's easy to work out how the change in cylinder sizes will affect things as it is only a volume calculation. Measure the volume of the slave (pie (3.142) x radius squared) then see how much master cylinder fluid (= travel) is needed to move the slave. If pedal travel is more than before then it will be easier by that ratio.

Obviously you need to ensure that there is enough travel as per above posts.

When I fitted my Girling M/c I discovered that whilst the clutch was light it did not disengage. I therefore had to find a M/c with a larger capacity and Girling did not have one large enough. I found a Wilwood M/c available from Rally Design and it solved the problem - not too bad a price compared with some others and they have a good range of sizes.

richardpope50 · Post by **richardpope50** » Wed Mar 28, 2012 9:42 am

I should have added that as Wilwood is American, the pipe connection sizes are different but there is a cheaper way around this than buying an adapter for some £80. You can re-tap the input connection.

Ian Anderson · Post by **Ian Anderson** » Wed Mar 28, 2012 11:53 am

Also make sure that the pivot points both on the pedal pivot to pedal box and clevis pin to pedal are not sticking - either of those could increase pedal force required

also check the same on the clutch slave release arm

Ian

JT45 · Post by **JT45** » Fri Mar 30, 2012 5:06 pm

Hi all
thanks for all the advice, i will have to build up my left leg muscles a bit more.
can any one advise me part no ect for master/slave cylinders?
regards
JT

richardpope50 · Post by **richardpope50** » Sat Mar 31, 2012 8:50 am

All the original MG parts are widely available and I would expect the MG RV8 ones to be too which may be your answer. Also all Girling ones are widely available via aftermarket web sites with integral / remote reservoir options. Measure your current bore and use that as a part / requirement reference or Google 'girling RV8 clutch master cylinders' for loads of references.