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MG Midget and Sprite Technical - Stumped - clutch thrust release bearing.

Replaced the troublesome carbon bearing with a Peter May roller type a fortnight ago. All was well until today when suddenly the clutch pedal hit the floor when depressed. When pumped it worked again only to play up later in the journey.
Left it alone for a few minutes and it works fine again. Very confusing.
It was an engine only out job so the slave cylinder wasn't touched. All the symptoms seem to point to hydraulic rather than mechanical failure. Can it be a coincidence that replacing the thrust bearing has (more or less) coincided with the slave cylinder failing? Is more pressure put on the slave cylinder with the Peter May bearing? The only difference I've noted since installing the PM bearing is a very small amount of vibration which wasn't present before.
Anyone had similar issues as I don't want to replace the slave cylinder and all the associated bleeding issues unless it is the culprit!
Advice gratefully received.

Jeremy
Jeremy 3

If the slave cylinder has failed it ought to be obvious

If you were to pull back the rubber gaiter it will be full of fluid if the clutch slave is the fault.
Robert (Bob) Midget Turbo

Cheers Bob,

just checked and no fluid leaking from the slave cylinder. Any ideas what it might be before the engine comes out yet again...

Thanks,

Jeremy
Jeremy 3

If the vibration you are referring to is a shimmy when you rest your foot lightly on the pedal, that could explain the problem.

If the release ring on the pressure plate is running out of true (which happens if the spring has started to collaps on one side, for example) it produces a shimmy which is noticable through the pedal - particularly when holding your foot lightly on the pedal, at the point of contact of the release bearing. The run-out appears to slowly bat the release bearing back, resulting in extra pedal travel being needed, hence what's happenning. (This was our "Stelvio divorce" problem, when I landed myself in it by not believing my wife we now had a second car with a dodgy clutch as we climbed the east ramp ... )

I have noticed this problem is much worse when a roller bearing is fitted. I suspect the reason is that the extra weight of the bearing on the relatively large offset from the mounting lugs causes the bearing to nod forwards as the clutch arm is shuffled gradually back, so maintaining contact for longer and prolonging the effect.

The cure is the fit a new pressure plate assembly, having first confirmed there is run-out of course by using a straight edge to see if it is parallel to the flywheel face or not.

As the vibration you reffered to is very slight, it's possible it was there all along but you didn't notice it until being more critical of the clutch operation when the problem occurred - a bit like not noticing paintwork blemishes until you start polishing the car and see it in more detail as you do so.
Paul Walbran

On the other hand, if the vibration is not as I described then the rest of my post above doesn't apply.
Paul Walbran

Paul,

you must have been driving the car as you describe the symptoms exactly!
The carbon thrust bearing wasn't too badly worn but the small plate (which you remove to fit the roller bearing) on which it bears, on the cover plate, was actually loose and rattling. As it was to be removed I thought nothing of it and as the 'fingers' on the cover plate seemed fine I didn't change it - I do have a new one as well. Doh. I did change the drive plate however. They say you learn by your mistakes... I was going to Oulton Park this weekend and hoping to drive round the circuit.

Many thanks for your very helpful response and trust you are still happily married!

Jeremy


Jeremy 3

Ah yes, but the incident has been stored in the memory banks for use when it's deemed I reminding that she is always right!

Good luck!
Paul Walbran

Also, any fooling with any parts which cause the slave cylinder to move - even one time - into an area it has not seen for many moons, can be expected to cause a later slave failure. That seems not to be the case here, but it could be after you half redo the half job you just did = clutch fail #3. Hence why I always at least rebuild the slave on a clutch job; often you can just remove the seals, clean the bore, and put it back with the old seals. Secondary hydraulic failures of the master cylinder can result from the process of bleeding itself, so do not be surprised to then have clutch fail #4! Learn to bleed the bloody thing - you will have to on the road if you slack off here. Nasty cylinders forced to new positions may be part explanation of why people have so much trouble with bleeding, which I never have, except for the LHD problem with the stupid clutch hydraulic pipe. I have posted that story and cure numerous times.

FRM
FR Millmore

The modern roller bearing release on my MR2 had a light spring in the slave cylinder, in order to keep the bearing pressed lightly against the plate. The theory is that it eliminates that initial bit of play, a lightly loaded bearing can spin almost forever without wearing out, and that accelerating a bearing from rest up to engine speed creates more wear than having the bearing spinning all the time.

I wonder if such a system would be appropriate in a retrofitted spridget? Didn't the 1500s have a light spring holding the bearing against the clutch?
Growler

Just so, Growler. People always talk about "keeping the bearing from spinning" which is ludicrous given the water pump and alternator bearings always spinning under far greater load.
Don't think there is a pressure/antirattle spring in the Spitfire/1500 slave, but there certainly is no pull=off spring. Frightening to not remember, since I have probably changed 1000 Spitfire clutches!

FRM
FR Millmore

Had booked tickets for Oulton Park last Sunday and was blowed if I wasn't going as there was also the opportunity to drive the track.
So with the breakdown recovery on speed dial we set off.
Outward journey relatively stress free with only a couple of times when the clutch pedal hit the floor, nothing unmanageable but return was more interesting.
Most of the time used only second and top as gear changing became more of a lottery. Interestingly after setting off in second and revving to about 3000+ the change to top worked easily every time with a good pedal. Centrifugal force at work maybe?
Now the fun begins with the engine coming out again...

Jeremy
Jeremy 3

Whether or not caused by "clutch stresses" I wonder if what you described isn't more likely the effect of a failing master cylinder

I had that happen a time or two, too after I put the type 9 and the Peter May roller bearing into my car

I found that fluid was circulating within the master cylinder, past the seal's 'non return' shape, causing the pedal to dive to the floor. There was no sign of leaking fluid 'cos it stayed in the master cylinder.

I suspected (at the time) that having the diaphragm fingers running off line may have caused it, especially as I ended up breaking several clutch cover plates in service. The diaphragm spring plate simply cracked because of the eccentric wear patterns induced. I think the master cylinder seals wore so that they couldn't cope with a change in the resting position.


I got home several times when that happened by frantic, undignified pedal slamming.

At the time I was running a combined dual master cylinder, which was a bugger to have to replace. Now I am using separate cylinders so future repairs will be easier and because I now run a concentric slave there is no off-centre running any more.


I read that the roller release bearings within concentric clutches should run lightly engaged at all times, thus preventing slow clutch take up

My roller release bearing has a light spring within its rubber bellows to do this for me.

It was the "Pedal Tramping"© which made me decide to fit a concentric slave cylinder
Bill1

Bill,

thanks for your ideas. Just been out to check it and of course it's working perfectly...
I'll contact Peter May to see how to add a spring to ensure the bearing stays in contact all the time.
Excuse my ignorance but what is a concentric slave cylinder and how is it made or can you buy one ready made?
Like you there was much "Pedal Tramping"© on the way home from Oulton Park!

Jeremy
Jeremy 3

This is a concentric slave cylinder, (this one lives in The Netherlands with a notable member of this "parish") it needs to be adapated from that on a different car to work.

Instead of a slave cylinder bolted on the outside of tyhe bellhousing and operating the clutch bearing via a pivot this makes the slave work directly inside the bellhousing by pushing the bearing onto the diaphragm fingers.

The slave cylinders often used are Ford or Saab units which have the bearing mounted on the front

My own uses a Saab version, Guy and Arie and others use Ford ones.

It sits on an adapter supplied by Burton Engineering and cures "tramping" immediately. It doesn't cure faulty master cylinders, sadly.

There MAY even be a book with some of this stuff in it, but if you like I have quite a bit of info here that you can have if you decide to go down this route.


Bill1

Bill,

be very grateful for any info you have as the car has been blighted with clutch problems since being restored and I'd very much like to sort it out once and for all. At the moment I'd rather be using it then working on it!
I take it the book is Daniel's book?
My email address is jeremytickle at ymail dot com
Thanks again,
Jeremy
Jeremy 3

I think Peter May sells an adaptor that allows fitment of concentric slaves to A series gearboxes

I only have info for the use of these with type 9 Ford boxes

Is that what you need?
Bill1

He does indeed but they're not cheap...
Forgot you were running a 5 speed box as mine is the original 4 speed but thanks for your help and advice.
It makes sense to start with the master cylinder and see where it goes!
Jeremy 3

This thread was discussed between 11/07/2012 and 22/07/2012

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