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MG Midget and Sprite Technical - miget - sluck clutch?

Hi

I have 1973 1275 midget. just about to put it back on the road after about a year lay up.

Took a bit os starting (fuel pump contacts) and the about to move the car - foot on the clutch peddle and it went to the floor and pretty well stayed there.

Quick check over and notice the slave cylinder was leaking - few days later replaced the slave cylinder, bleed and hay, got a good clutch peddle now - but no clutch. i.e will not go into gear when engine is running.

checked that the new slave is moving the arm that comes out of the gear box casing - slave clyinder piston pushes the leaver from a gap of 2.5cm to 3cm when the clutch peddle is pressed so that looks ok?

Looks like stuck clutch plate to me - help and advice to free (if am correct)?? please

David
d scaife

Here we go again. Have a look at this recent thread:

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&mode=thread&access=&subject=97&source=T&thread=2009050615220926653
Ant Allen

Do you mean that the lever arm is moving from 2.5cms through to 3cms ( i.e. a movement of 0.5cms) This would not be enough.
Or do you mean that it is moving 2.5 / 3cms - which should be plenty to disengage the clutch.

If the latter, then I would say that the driven plate is stuck to the flywheel and needs to be shocked free, either by towing, or by putting the back up on axle stands, running it in gear and snatching it with the brakes.
Guy Weller

Agree with Guy.

If you have plenty of room, try to start the car in 1st gear with clutch down; maybe disconnect the coil if you really don't want engine to start.

Has always worked for me...

A
Anthony Cutler

"in 1st gear with clutch down" - and brakes hard on.
Guy Weller

Hmmm - I must caution against that one. I tried it and the engine fired. There's then a terrifying moment when the car is chugging you towards the bench at the end of the garage and it's dug in deep so it can't be pulled out of gear. The brakes should stop it, or in my case the key did. I don't recommend it though. Definitely remove the plugs and use the starter only if you go for this test.

My "ratchet strap test" demonstrated that I need 12 to 13mm of slave travel to disengage. Put a ratchet strap around the release arm and around the rear axle, and wind it up until the rear wheels turn freely. You need the car in gear, engine off to lock the flywheel, and something like a car ramp under one rear wheel. If you can rotate the other rear wheel then it's disengaged.

Ant
Ant Allen

I've done it that way a few times but always out on a longish drive with plenty of room. Started the car in gear then upto a low speed and hard on the brakes and clutch, always freed it eventually. In a damp garage I've had this problem occur with as little as a months inactivity IIRC.
David Billington

Hi

I meant that the lever that the slave cylinder attaches to moves 0.5cm when the clutch is pressed.

I must say i did think that, that was not a lot of movement so i tryed with a iron bar to move it further (with the slave clynder attached) but it would not move any further - I.E in the direction the piston pushes it in.

Maybe i should try it with the clynder disconnected.

in any care who do you get the slave clyinder to mush it any more?

Could the cluch plates still be stuck and would that stop the amount the cylinder can push the lever?

David
d scaife

OK - 5mm is NOT enough. Not on my car anyhow. I have about 11mm and mine's still borderline disengaging. 12 or 13mm seems enough.

Has your slave got a circlip in it to stop the piston coming out? Some have (OEM?), some haven't (aftermarket). And where abouts in the possible slave travel is the piston sitting? It could be hitting the circlip and limiting the travel - that would prevent the clutch disengaging, and if so I wouldn't expect the pedal to be at the end of its travel. If the pedal hits the floor and the piston hasn't fallen out of the slave but has only moved 5mm then I reckon you have air in it.

To prove that the mechanics work you should disconnect the slave and move the arm with a ratchet strap. A lever isn't enough force, and you risk damaging whatever you lever against. A ratchet strap is perfect for the job - just make sure you're not right next to it in case it breaks and whips back at you. Also, when you disconnect the slave pushrod, if it's the non-circlip type, be sure to retain it pushed back into the slave, otherwise it will pop out and spill fluid everywhere.

Ant
Ant Allen

The point where the slave cylinder push rod attaches to the clutch release lever needs to move about 10 to 12mm. If it isn't moving that far then either you have air in the system and it needs bleeding, or there is wear in the pivot points at the master cylinder or pedal. See the link that Ant posted earlier for lots of suggestions about what to look for.
Guy Weller

hello again

have disconnected the slave from the lever and using a racket strap as you said can get the lever to move around 1.5cm - so looks like the slave is not pushing as it should.

Its the type with no circlip which was told is the orignal one - the piston sits about 1.5cm from the rim of the cylinder. if i stick my thumb in i can easley move the piston to the bottom of the cylinder - not sure i should be able to do this as surly am pushing against fluid - looks to me as though i could still have air in or mayble the master clylinder is also faulty ( looks pretty new though).

As i see it were the piston is, is about right and should not be able to be pressed inward easly - when you press the cluch pedel it should move it to about the edge of the cylinder rim ( about 1.5cm) - which it does and it beccomes very sold i.e you can not press it in with your thumb. Cluch pedel is very soft though - guess cos cylinder not commected to owt?

Just a note:
When i first fitted the slave i tryed to bleed it with the clyiner not attached to the gearbox so i could get to it easly ( did not know about the blanking grommet in the foot well at that stage) and of course i just poped the piston straight out - what a muppet - anyway i just put it back together spring, piston - is there any thing i could have missed, is there a set way of putting back together - am sure its right but....?

david
d scaife

If you kept it all clean then the chances are you put it back correctly. Also, if it's not leaking fluid it's probably correctly assembled.

Regarding pushing the slave piston back - with the pedal released you should be able to push it back as the master connects the pipe to the reservoir, so when you push it back you're pumping fluid up into the reservoir pot, and when you let go the spring in the slave pushes the piston out and sucks new fluid in from the reservoir. As you press the pedal the first thing that happens is the path to the reservoir is blocked off, then it pumps the fixed volume of fluid down to the slave. So with the pedal pressed you won't be able to push the slave back in. That's all normal.

15mm from the end sounds like a longer pushrod may be needed as we're after 12 or 13mm of travel and 2mm isn't a lot spare. But it will do for now. The fact that the slave is only moving by 5mm means there's either air in it, the master is faulty and not sealing off the reservoir, or the flexi is perished and ballooning. I suggest bleeding it again, with a pressure bleed kit, and with the slave tipped so that the bleed nipple is clearly at the top (it's close to horizontal when fitted and that's not good as air sits in it). If the slave is removed push the piston back as far as it will go to eliminate places for air to sit, and retain it there with some wire through the push rod clevis hole and the slave mounting brackets.

Persistence is the key to bleeding it - but seeing how mine doesn't work as I'd like it to I'll shut up now :o)

Ant
Ant Allen

Hi

Got am easi bleed and some more Dot 4 done as you said (last post Ant) and put it all back together again and..... still only moves the lever attached to the gear box about .5cm - there is no air in the system and has now had a total refresh of Dot 4.

An idea - blue tacked a nut to the arm that contects the piston to the lever on the gearbox and it now pushes the lever from .5cm to .75cm.

Moss told me that the slave they sold me was a direct replacemt not OEM but i wonder what mods made have been done over the years - the old and the new clyinder look the same from the outside but is the piston smaller or something? can not be bothered to strip out aagin just to look.

Am now goning to add 3 nuts to the end of the arm ( with a bit of srewed rod) to see if it adds further distance to the clearance needed - only a temp job but if it works it shows (i think) were my problem is????

David
d scaife

Well that puts that one to bed - extended the pushrod by putting a thred on the end and using a nut and some screwed rod - extended it by 2.5cm - but still only moves the lever attached to the gearbox by .75cm!!!

Am as sure as i can be having now bleed the system six times and used over 4pints of Do4 that there is no air in the system so... guess i will have to change the master clyinder and hope that it????

David
d scaife

David,
If you really have got all the air out of the system - and it isn't that easy to be sure - then check the pivot points for the clutch pedal. The holes wear oval and this takes up a lot of the effective movement. Changing the master cylinder is expensive, especially if it isn't where the fault lies.

Guy
Guy Weller

Hi Guy

The problem is as i see it is that the car was running fine a year ago - its only when i have come to re-comission that i have had this problem and what seamed to be a easy job ( i.e slave cylinder clearly leaking) has turned into a bit of a nightmare.

Surly if there is some ware as you say this would have caused a problem before i laid up the car?

The master cylinder does apear to have lots of rubbish in the bottom and the seal on the old slave cylinder was gone completely - no were to be seen ( in bits in the bottom of the master?) - just seams - new master - slave - and flexi hose - what else can it be?

Cheers David
d scaife

David,
Yes you are probably right. I had missed the point that it had been working fine previously.
I suggested checking for wear in the pivot points first only because it is very simple to check and cheap to repair. Master cylinders are quite expensive to replace. But if there is visible muck in there it could well be that you are right and the seals have deteriorated whilst it has been standing. Maybe a replacement seal kit would fix it.

Guy
Guy Weller

I'm slightly confused by what you said about the slave travel. It was moving by 0.5cm, so you extended the pushrod, and now it moves by 0.75cm? That cannot be. Extending the rod commences travel further back in the slave but does not give extra travel. It's hard to mearure this accurately so maybe that's what changed.

If the master is old then cleaning it out and fitting new seals is a good idea. Inspect the clevis pin whilst you're doing it. Personally I'd take the master apart, inspect the bore, and if it's ok just fit new seals.

Pumping fluid though doesn't necessarily mean al the air is out. I've learnt this one myself in the last few weeks. Tip it, shake it, if possible drive it, bleed it again, and a bubble will emerge.

The final option (the one I'm taking with mine) is to get more travel on the pedal. Mine hits the floor (it used to hit the accelerator arm till I cut some off it). Taking a bit of metal off the back of the clutch pedal will definitely give more travel.

Ant
Ant Allen

Oh the wearisome clutch problems.
I have similar problems. Only got the car in september and the clutch disengagement wasn't the best when I got it, but it drove. Having read up on it before buying had hoped it would be as simple as removing play in the pushrod eyes. Checked them and they are all fine, but found the slave was leaking and on striping it the seal was perished and the bore was corroded. So, new slave and flexible pipe, bled three or four times and cannot get it into gear with the engine running. The slave pushrod does move when pedal is pressed, and although I didn't measure it at the time, it seemed to be moving enough (13 or so mm). So tried the ratchet strap trick and still not able to engage gears. Could this be a stuck clutch then? Starting the engine in gear with the wheels off the ground and drive is transmitted. I'm about to move house to a house with no garage, but have managed to get a loan of one until my new one is built, but it is tiny. Not looking forward to trying a clutch change in it.
So will jamming on the brakes with the car in gear and the wheels off the deck free it if that is the problem?
B Slater

Just back in from the garage having tried the above. Still no success. With the car started in gear, clutch pedal down, i can use the brake and the wheels stop turning (or at least the one I can see) while the engine keeps running, but still not able to change gear. I'm now confused.

Any ideas guys.
B Slater

Hi,

Has anyone solved these problems yet? I now have the same thing happening to mine and I am a little bit lost. Garage reckoned on a new clutch - I disagree as It drove there under its own power (seems to be tha if the slave is replaced, the gears wont shift - which is sh*te!!!)

Thanks!!

Ben
B Cavagan

Treat it logically to eliminate problems.
First check for worn pivots etc, particularly at the pedal. If wear is within acceptable limits that is a good start. As it was working OK, wear doesn't really seem to be a plausible explanation.

You also know that the clutch was working OK so it cannot be a problem with wrong clutch components. But it could be that something broke / disintegrated (maybe the release bearing?)

This then leaves either that you still have air in the system, or that the master cylinder is not operating right (deteriorated piston seals is a distinct possibility)

If the slave cylinder had started to leak through the seals then it would not be surprising if the seals in the master also leaked - they will be of much the same age. If you are sure that it is bled properly, then master cylinder seals seems like the next most likely fault, and certainly worth checking before going to the trouble and cost of removing the engine to check on the (previously OK) clutch.

Guy
Guy Weller

Has anyone actually measured one of the replacement slave cylinders? I'm wondering if the manufacturer's gone metric & approximated, so the bore is a bit larger & the stroke is a bit shorter??
David (davidDOTsmithAT stonesDOTcom)

Back to my suggestion,on another thread, that if the dimple in the slave piston is deeper you may need a longer pushrod.
Alan Anstead

Thanks Guys,

The garage were under the impression that the car was towed there, and not driven (I had the RAC man drive it to the garage but I moved it into the workbay myself and the clutch was fine, so unless it has developed a problem at the garage then I doubt this is causing the problem!!

The garage see my point so are going to check the slave again and check the bleeding is done properly!!

Lastly, the master I have has the metal reservoir, not the plastic as seems to be the norm in new units. Is this a particularly old unit (possible original) that could be giving up and needs replacing??

Thanks!!

Ben
B Cavagan

Ben,
Possibly the original master cylinder, but nothing necessarily wrong with that! But the seals inside are rubber which does eventually degrade and start to leak. It is pretty straightforward to replace the seals so long as the inside of the bore hasn't become corroded or badly scratched. One clue is to look inside the master to see if there is debris in there - particularly bits of black rubber particles in the fluid which may indicate a need for replacement seals.

Guy
Guy Weller

Thanks guy, I lost all (every drop) of fluid when the slave went, wasn't really a leak as a total evacuation!! No way i could see it there was any debris in there.

On the up side though it is now fixed!!!!!!!!

It would appear as David and Alan are right, the dimple in the new slave was deeper so there was insufficient movement to disengage the clutch!!!

If you replace a slave, check this!!!

BC
B Cavagan

It now begs the question. What is the depth of that dimple on an original clutch slave cylinder piston? If the original depth can be found the correct length for a replacement pushrod can be calculated not guessed
Alan Anstead

Too deep a dimple or too short a pushrod (or a combination of both) would move the operating range of the slave piston nearer to the end of the slave bore. Ultimately I guess that the piston would move far enough that the seal reached the end of the machined bore and suddenly discharge its fluid. Particularly if there is no circlip fitted to stop it.

Apparently, the clutch release fork can also bend and whilst this in itself doesn't reduce the amount of movement at the clutch, it would have the same effect as a short pushrod in moving the operating range of the slave piston nearer to the end of the bore.
Guy Weller

agreed Guy - I've seen racers who use the original release mechanism weld a stiffener along the back of the release arm to prevent bending when using heavy-duty race clutches like the Peter May or the Caterham ones.
David (davidDOTsmithAT stonesDOTcom)

Thats true Alan, I dont have the old slave, but I (like the garage) assumed that the dimples would all be the same depth, given that it has a rather large effect on the operation.

I am of the opinion that they should produce a matched cylinder and puchrod set, rather than allowing the owner to re fabricate parts to overcome their misgivings!

I didnt like the idea of an extended pushrod until I saw the 2 slaves side by side, then it was the only way to sort the problem. The part fitted was from Moss, so watch out!!

Ben
B Cavagan

You can get longer pushrods - The mini uses a 3 9/16ths rod whereas midget / sprite standard is 3". I put the part number in a recent thread on here.

Ant
Ant Allen

I recall you saying, but what they dont say when you buy the new slave is that this part would also be required to make it fit, plus using a mini part relies on the person fitting the slave knowing what the problem is.

Ben
B Cavagan

Although mine's a 1098,I bleed the clutch single handed by taping a length of pvc tubing from the bleed nipple up to the dash (see Pic). This allows synchronised opening of the bleed nipple and pressing of the pedal in the time-honoured way, with the tubing acting as the "jam-jar".You can see any bubbles in the tube and when its full, just release it from the nipple and let it drain into the ever-present drip tray underneath.
Oh and before you ask - no, I dont have pink carpets in my Midget - its an old bath towel !!


M J Chapman

Is the hole in the tunnel/footbox unique to the 1098 and 1275 era cars? I am sure my 1500 doesnt have one of those - that would be why trying to bleed single handed is an absolute pain!!!

I think you have just started a new trend - pink interiors for classics!!!
B Cavagan

The hole is to the far / bottom / left hand side of a right hand drive footwell covered by a large rectangular removeable rubber grommet. It started out on Frogeye but may have been discontinued on later cars.

But why struggle in the confines of the footwell when a remote bleed can be fitted in the engine bay.
Run a flexible / fixed brake line from your bleed nipple aperture to a union with bleed nipple on a bracket attached to the back of the engine.

Continuing on about dimple depth in slave cylinders affecting push rod length. I have examined seven old slave cylinders and dimple depth varies up to 0.020 (twenty thou) inch
Alan Anstead

This thread was discussed between 02/06/2009 and 19/06/2009

MG Midget and Sprite Technical index

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