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MG Midget and Sprite Technical - 1275 Clutch Won't Disengage

My car is fixed but I'm posting in case it might help others out.

Original symptom was occasional grinding of gears during normal driving.

Replaced clutch master & slave cylinders bled carefully but couldn't get the clutch to disengage at all.

Read many forums which focussed on bleeding the system, slave cylinder pushrod length and wear of the clutch assembly. None of these seemed to be the cause of my problem.

Finally tracked it down the the new master cylinder. The actuating pushrod was about 10mm shorter resulting in 30% loss of pedal throw. (Pedal up position too low)

It was an easy fix to swap in the old master cylinder pushrod & now all is well.

Hope this is of use to someone.

Cheers,

Roger
R Sheridan

Now i have a real weird one for you.

Failure to disengage only noticed when shifting to 1 or reverse..
Replaced all mechenical components: pilot bush, flywheel, plate, cover and box.
Still the same?!

In the end it became apperant that before the swop pilot bush and primary shaft where a to tight fit.
But having replaced several things at once with the problem the same we did not notice we shifted the problem to.....
A faulty new clutch cover with one bad return spring causing enough drag to keep the primary spinning

It is never what you expect!
Onno Könemann

What is the correct length of the pushrod for the 1275 clutch.
A Anstead

It's 3 1/2 inches long end to end.

Pin centre to end is 3 1/4 inches.



Lawrence Slater

Was yours the thread that I commented on? I don't know, but I solved a similar problem with my car on the weekend.

My clutch never worked properly since a rebuild including a 5 speed Toyota Celica gearbox conversion and matching 7.5" clutch. This was despite rebuilding both master and slave, all pivot points and making an adjustable arm for the slave cylinder. I would adjust up the arm on the slave to where the release bearing was contacting the clutch permanently, and it still was only taking up right on the floor - to the point that if I installed floor mats I had no clutch!

The problem was finally solved by going to a 7/8" bore slave from an earlier 948/1098 spridget (instead of 1" bore for 1275), which was a bolt-on for the bellhousing, but required a different flexible hose. The extra travel means the clutch now operates brilliantly! I believe the actual problem probably has to do with some geometry issue in the bellhousing for the gearbox conversion, but it has been a major issue and I am very glad to have it sorted.
AndrewF

Hi
I solved my hydraulic problem by fitting a 0.7in bore master cylinder.
Just wanted to confirm that I have the correct pushrod.
Alan.
A Anstead

The next most common cause of insufficient travel after failing hydraulics is excessive play in the clevis pin at the top of the pedal. I have described it on my website at http://www.mgparts.co.nz/clutch_problems.html
(The dimension given is for the MGB, sorry can't remeber the midget one off the top of my head). When this condition is present the first 2 or 3 incehs of pedal feel extremely light - even lighter than air in the hydraulics.

One of the endearing traits of the 1275 clutch is that it is very sensitive to the amount of pedal travel - too much travel causes drag as well as too little. If the release ring on the diaphragm is pushed too far forward it ends up contacting the driven plate and pushing it on to the flywheel, causing drag. This condition can be confirmed by seeing if it engages gear more easily as you lift your foot off gradually from the flat-to-the-floor position. The problem is accentuated by linings which are too thick and can also be cause by lenghtened pushrods.
Paul Walbran

Paul, I had replaced that pin as well as the pushrod into the master, resulting in very little play at that joint. Same for the slave pushrod and pin, and rebushed the pivot for the clutch fork as well. I had little to no play in any of the joints, this was one of the first things I did. The movement at the slave was good/normal (according to Colin Dodds of Sprite Parts) but it was not nearly enough in my case. As I said, I believe in my case it must have been due to some error in the clutch geometry on my Dellows bellhousing used to match the Celica gearbox to my 1275.

I figured it was worth posting how I got around it as it may help someone else with a similar problem in future - using the earlier smaller bore slave cylinder is a bolt on swap with the appropriate flexible hose, and gives about 30% more travel.
AndrewF

As some may recall from my earlier threads, I have been battling with this problem for some time. I have a 7.5inch clutch on my new engine and despite a longer push rod and eliminating all play from the M/C and pedal (not the mention new slave and master cylinders) have never managed to find a set up that I'm happy with (its either release bearing in contact or crunching gears). The earlier slave cylinder sounds like it might just be the solution I'm looking for. Thanks for the tip!!!

Chris
Chris H (1970 Midget 1275)

Andrew

My comments were about the standard set-up, as soon as a different bellhousing goes in other potential variables are introduced - and it sounds like you found one!

What interested me most in the 1275 clutch saga over the years was finding that too much travel would pick up the driven plate and push it onto the flyweel. Worked it out with the assembled clutch and flywheel on a drill press table, using the chuck to do the job of the release bearing and watching/measuring what was happening - very instructive. Haven't run across it with any other clutch combo.
Paul Walbran

Whilst on the subject of clutches. Can anyone tell me the length of a 948 Frogeye clutch slave cylinder pushrod. I seem to have several of different lengths in my spares bin.
Alan
A Anstead

Chris, I think yours was the thread I had posted in previously about my car and this problem. I went searching for it to give you the answer I had found, but didn't find it. Hope it works as well for you as for me! You do need a different flexible hose to suit.
AndrewF

Andrew

Thanks for thinking of me - even if you couldn't find the thread! I've ordered an early slave cylinder and pipe. I presume that the non-slave end of the pipe simply attached to the copper clutch pipe using the old compression joint thingy.

Chris
Chris H (1970 Midget 1275)

Andrew

My early type slave cylinder arrived today together with a length of copper pipe with fittings each end. I was expecting a flexible pipe as is fitted to the later type. What I have looks like it goes all the way from slave cylinder to master cylinder with no flexible bit. Is that correct? Can anyone with an early Midget/slave cylinder confirm that?

Puzzled

Chris
Chris H (1970 Midget 1275)

Hi,Chris,I have the same motor & box as you from the same specialist in my Frog with original dual MCand small slave,works fine,but heavy pedal.Rigid pipe is correct and must have a coil for flexibility;normally about 1 foot before slave.
Cheers, Alistair
A.G Peters

Alistair

I think you have highlighted a problem I have. You have the original dual M/C and that has a smaller thread on the compression joint of the outlet pipe. The 1275 M/C has a larger connection. So, AndrewF, what M/C do you have and if it is a 1275 one how did you deal with this issue? You said it was a 'bolt on' solution but it is not really is it?

Chris
Chris H (1970 Midget 1275)

Chris, I did say "bolt on swap with the appropriate flexible hose", I meant that it bolts up to the bellhousing, uses same pushrod etc, I'm sorry I wasn't more clear. I also didn't realise the hose on the earlier models was solid. I was supplied the hose and slave by Colin at Sprite Parts, he tells me my hose was from a mini that uses the same slave, but it had to have the connection at the hard line end modified as it was incorrect (it had a smaller internal thread for the hard line than was required). Over here it is easy to have the flexible brake/clutch lines made up if you can supply the correct information, I would expect it to be the same there? Another option could be an adaptor between your original flexible line and the slave cylinder. I can probably find out more if you want. Sorry again for the confusion.

Andrew.
AndrewF

Anfrew

No criticism was meant. I think you were clear enough - I just didn't read your thread carefully enough and I was disappointed to be unable to make the modification immediately (I've no patience!!). I think the answer is to have a flexible hose made up with the right fittings at either end and that should be possible.
Chris H (1970 Midget 1275)

Sorry to reactivate this thread but this may be of interest to someone. As you will see I have been battling to get my 7.5 inch clutch to disengage and thought I'd tried everything without success. I'm pleased to report that I seem to have fixed it, thanks to the information in this thread. Here what I did.

First, purchased an early type clutch slave cylinder (with smaller bore) - part No. GSY110 (as suggested here). Second purchased an uprated clutch hose for a 1275 (part no.TT3041). Important note - the hose is for a 1275 and the slave is for a 948/1098cc clutch. The hose will NOT fit the slave cylinder as supplied but it is a different arrangement to the standard rubber clutch hose. At the slave cylinder end the uprated (Goodrich) hose connect to a two-way adapter (one end screws into the 1275 slave and the other end into the hose. I then went to Pitek (a hydraulics company - lots of branches and an web site) and they ordered me a similar adapter with the hose size coupling on one end and the (smaller) slave cylinder coupling on the other. I don't recall the sizes but if you take your hose and early slave to a Pitek branch they will tell you what size/thread is required. I got my adapter/coupling the next day.

Having now fitted the new hose and slave cylinder I seem to have a fully operational clutch again. Time will tell but so far it seems good.

The downside of this is you have to dismantle the clutch hydraulics and bleed the system but I never seem to have any trouble with that using my cheap Halfords non-return valve on the end of a tube. The upside is that it seems to work and, if you wished, you could simply use the original adapter/coupling and refit the original 1275 slave to the uprated hose (but why would you).

Of course, fitting a different slave cylinder and a braided hose means I've changed two things at once so cannot be certain if the result follows from the slave or the braided hose (or both). I guess that the braided hose might, just, on its own give a little more movement at the pushrod with the original slave but I CBA to go through the process of repacement and bleeding twice.

I hope this is of interest to anyone with similar clutch troubles to mine.

Cheers

Chris
Chris H (1970 Midget 1275)

Good to hear Chris! I hope it didn't take too long/too much effort to sort the flexible hose out, and I'm glad to hear you got the problem sorted.

Cheers,

Andrew.
AndrewF

This thread was discussed between 19/08/2011 and 27/09/2011

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