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MG Midget and Sprite Technical - 1275 Clutch pushrod length

Cannot find this recent thread I think there was one?

Having problems that on a new build 1275 engine to 5 speed type 9 conversion . New cylinders and fully bled system but I cannot totally disengage clutch. When viewed from underneath clutch pushrod is pushing fork but when static I can push pushrod back into cylinder quite a way so could this be the problem that pushrod too short? As pushrod is not adjustable would a longer pushrod help? Could the cylinder be running out of travel? What were the pushrod measurements on the other thread that I cannot find?

Thanks Roy
R Mcknight

Roy, if you are using the standard 1275 slave cylinder, it should not fully retract. As a self adjusting cylinder, in the disengaged position is should be somwhere around 1/2 - 1/3 of the way down the bore. As the clutch plate wears, the disengaged point will shift automatically to where the release bearing comes to rest.

If the piston is being pushed out of the bore with the pedal depressed, then the pushrod is too short, otherwise it is fine. Lengthening it will have the effect of only pushing it further into the bore, both in disengaged and full pedal situations and won't achieve any more stroke. Lengthening it too far will cause it to bottom out and p-re-load the release bearing, causing premature failure.

The stroke from the standard slave cylinder is about 8-10mm. It is likely that with a different clutch/gearbox combination the stroke requirements will be different from the original. This can be varied only by changing the area ratio between master and slave cylinder, though it may be possible to gain a bit more pedal stroke which would help. The simplest way to change the area ratio is to fit the 1098 slave cylinder (7/8" v 1") which will give 30% more stroke at the slave. Further gain canbe made by increasing the master cylinder bore from the standard 0.7" to 3/4 or more.

To establish which combination to use, manually push the clutch arm to disengage the clutch, with a helper applying torque manually to the crank pulley nut while the car is in gear so you can determine the release point.
Paul Walbran

With the type 9 conversion it can sometimes be necessary to need to use a longer than standard pushrod to bring the release bearing as close to the flywheel as the regular 4 speed gearbox design required. The situation should be helped by the use of a roller release bearing but some have been made using a shorter carrier section which increases the distance of engagement in comparasion with standard.

A longer pushrod may help but ultimately its worth spending the money on a Burton co-ax conversion or making your own.
Daniel Stapleton

Roy
Daniel is correct with regard to some t9 conversions. To quickly prove / disprove put a shim twixt pushrod and piston.
Alan
Alan Anstead

The problem does not arise if you make your own Bellhousing from the original gearbox that suits your engine. This is for a 1275 / t9 using a ribcase gearbox.
My Frogeye uses a 948 / T9 using a smooth case version.
Alan


Alan Anstead

even with std. 1275 new bits of varying tolerances I've had issues with getting the pushrod the right length. Ended up making an adjustable one last time round.
Dean Smith ('73 RWA)

Thanks for the info guys.
Have the feeling that if hydraulics were connected to a standard 1275 clutch it would work ok, problem seems that with the hybrid box and clutch set up. Found in my notes that there are 2 lengths of pushrod for 1275, 3 1/4 end to centre of hole and a 2 11/16 style. Maybe the later repro part is smaller so will pull it out and have a look, and then try a nut to shim it out to test.
Too late to change to concentric release now as don't want too pull engine and box out so maybe a job for the future.
With the 1275 5 speed conversion you remove the release pad on the diaphragm fingers so the release bearing works on the fingers, when used with a concentric release bearing is that the same ?
Also use of an earlier clutch slave GSY110 would give more throw but would that not make the clutch heavier?

Cheers Roy
R Mcknight

Roy

Where did you get those pushrod lengths?
Dave O'Neill 2

Hi Dave. Link to this thread that I was looking for. Even more confused as to what length pushrod works best on a 1275 with a type 9 box and roller release bearing.

http://www.mg-cars.info/mg-midget-sprite-technical-bbs/clutch-slave-pushrod-1275-201408041919436235.htm
R Mcknight

That's a neat bellhousing Alan. Who did that? How much did it cost?
Lawrence Slater

Lawrence
It cost £20 for the aluminium plate and as I can't TIG weld the welding cost £30. A bell housing for £50 as opposed to almost £200.
Alan
Alan Anstead

Superb. I can sense a number of people contacting you as I write.

"Hi Alan, would you make one for me too? How much would you charge? "

:).
Lawrence Slater

There was only one pushrod listed for the 1275. The shorter pushrod quoted in Roy's post above is for A series pre-1275, also does MGA & MGB.
The thread Roy links to is interesting, as the photos show what happens if the clutch arm is pushed too far! That's when they can end up apparently needing a longer pushrod in an otherwise standard installation.
Paul Walbran

'Hi Alan, would you make one for me too? How much would you charge?"
No chance!
But Masc members may be able to read how it was done with basic workshop tools in a future edition of Mascot. An article has been submitted to Editor for consideration along with many pictures.
Alan
Alan Anstead

Found this interesting link about clutch forks and cylinders.

http://gerardsgarage.com/Garage/Tech/TO_Bearings/tobearings.htm
R Mcknight

This thread was discussed between 27/12/2014 and 03/01/2015

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.