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MG MGB GT V8 Factory Originals Technical - Clutch biting point

Hello All,

I rigged up a clutch sytem with the engine out of the car (SD1 V8 5 sp) because I was concerned I may have knocked the release bearing and I wanted to make sure the new slave and master cylinders worked.

So I managed it, using the workbench and some G clamps to secure the pedal box. I filled and bled the system, and it all worked. Hey! Pushing the pedal (hard) with one hand and reaching over to spin the flange with the other.

But - I was very concerned with the amount of clutch travel before hitting the biting/disengagement point. In the car the pedal would almost be on the floor.

Thinking about it now, should I view this as a good thing since it means that as the clutch wears the biting point will move upwards?

I have renewed the drive plate, but the clutch cover plate seemed fine.

Should I also renew the release bearing?

Thanks for any advice, Liam.


Do you know that the clutch engagement point is almost on the floor or is this based on your mockup and ability to spin the trans? Sometimes mockups are not exactly real world and you won't know exactly how it will act without putting your foot on it, and getting the clutch warmed up a couple of times.

Perhaps there's still a little air in the system, or you just need a longer rod into the master cylinder, which would cause the pedal to be a bit higher at full engagement (less toe play) and allow more fluid displacement.

Wayne Pearson

Change everything you can afford to change while all is out on the bench. If the driven disk was worn out, the release bearing is suspect, as is the pressure plate.
Jim Stuart

I had a custom HTOB setup and wasn't sure about my bleeding either. Here is a great tip I used from an old thread. With a jack lift the front end up and set the wheels towards the top of a pair of ramps, but still on an incline. Make sure the car is in gear so not to roll down. Have someone SLOWLY press the clutch pedal in while you watch the position of the clutch cylinder piston. Before hand, place a make on the out position, the fully in position and the release point should be in between. I added a hard stop to the pedal (so not to overtravel the HTOB) that was a 1/4" past the release point. You will definately know when it disengages because the car quickly rolls down the ramp. Good luck with the clutch, it was a milestone for me.

Sounds like you've got it perfect. The full movement of the pedal is what you're aiming at because any less and you must increase the effort. Also the clutch is going to start to slip much earlier with the engine pushing it, (than with you). You can calculated it by measuring the diameter of the master, and how far it moves. Calculate the volume of this cylinder (pie r squared times height, (22/7)by half the diameter squared by distance moved. This volume should be a little more than the volme displaced at the slave. The distance the slave needs to move to disenguage the clutch, that is. The slave dosen't move the same distance because it should have a larger radius, that way you get a force multiplication.
I'm using a one inch slave out of a range rover with the orrigional master. One inch was what the GT used, infact they used the miget slave, which are very hard to get hold of nowdays. In theory a new thick clutch requires the maximum pedal movement. As it wears you could adjust the pin at the fork/slave, if you have a threaded pin/rod adjuster there. I have, and I don't bother!. I prefer that the clutch lets go at the same old place every time.

Hi Liam,
I'm using a SD1 bell housing with a TR7 5spd. I purchased a extension sleeve that sets the release bearing out another 1-1/4 inches and uses the TR7 slave cly. I'm using the stock B master and the feel is about the same as the B clutch. I haven't heard of anyone else on the board using this method but it works well.
It was made by a fellow in Washington state. (Mick?) He was selling conversion parts through Hemmings but I haven't heard of him in awhile.
I just happen to have it out of the car at the moment (long story) and can send you more info if you would like.

Kelly Combes

Thanks for the help everyone, that has cleared a few things up. I'm a bit calmer about it all now!

This thread was discussed between 21/04/2006 and 22/04/2006

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