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MG Midget and Sprite Technical - Clutch issues
|Trying to track down an issue with my gearbox that makes grinding noise at times when changing form second to third, and even worse from forth to third. Sometimes it is difficult to engage gears at stop. After pressing clutch several times, it slips into second, then back to first no issue, though this is inconsistant. I have changed the fluid to MTL and confirmed that this is full.|
The car is a 73 1275, very low mileage and clutch had been replaced prior to me owning.
Extension when clutch is engaged at slave is 3/8"
Do I look at bleeding the clutch, rebuild master and slave or is it more likely to be gearbox teardown time.
Any other tests that I can further pinpoint this issue.
|as there's no one else around|
I'm no expert, in anything, no no no
unless the gearbox is particularly noisy when the car is on the move and especialy around third gear then it sounds to me like a clutch issue (pumping)
things to consider:
it may need bleeding, they are a pain and there are techniques to it
did you change the fluid before or after the problem started
very low mileage, sitting around for long periods does the car no favours
clutch replaced before your ownership but how long ago and how many miles since
I'm told it's more sucess to replace with new that to rebuild - others might disagree tho'
you could pull back dust cover to look
is this MTL more for high performance/speed/heat use (I don't know)
and my favourite - when was the gearbox oil last changed (or level checked)
sorry all questions no answer but more info may be needed by those that can help
|Ok some more info. I replaced the transmission oil to make sure that was not the cause. It has always done it. I change from forth to 2nd and 2nd to third is very gingerly and it is fine. MTL is a recommended fluid in the USA for the midget gearbox.|
Clutch was new after it seized from sitting still. Car has only done 19000 miles. Is the 3/8" movement on the slave cylinder the normal. Also looks like master and slave are original.
|er, I was hoping someone else would help you as I'm not really too good|
right, assuming you installed the new clutch, how long ago in time?
not sure about 3/8" but I think I've seen that figure (think)
the problem was there before you changed oil,
can you remember what the old oil looked like, watery?
had some metal bits in it?
we use the same oil as you put in the engine in a 1275 g/box (20w/50 here)
original master and slave so they could be stiff, need to look whilst someone else presses pedal and behind dust boots
have you tested for slipping clutch?
|you may already know this but just in case - http://www.ehow.co.uk/video_4754387_diagnose-slipping-clutch-car.html|
cause could also be contaminated clutch, but it's not catching
PS - I originally thought you meant mtl clutch fluid, its very late over here and I'm an idiot
|Allan, as Nigel says I also am not an expert but can suggest some things that may help:|
The symptoms sound like the clutch is not disengaging fully to me - dragging on the flywheel maybe - and on occasion giving a crunch and may also explain why you can't always get first from standstill.
Could be the slave is not always giving you full travel ( air or just leaky hydraulics ?)
Or could be the clutch level or bearing are not getting full travel when you press the pedal....
I am not familiar with the midget clutch assy - level wise - but think its possible there maybe wear somewhere in the pivots or where the slave pushrod meets to lever arm.. Aletrnatively the arm to bearing.
looking at the Hayne manual - looks as though its not possible to see without pulling off the bellhousing... oops...
First bet I would say is to make sure hydraulics work and that pivot you can see at the end of the slave cylinder is not worn...
|"Clutch was new after it seized from sitting still"|
can you elaborate on this please, are you saying you've had a whole new clutch fitted because the old one stuck to the flywheel? If so, who did the work? You, or a workshop?
From the previous owner, he had the clutch replaced due to it being seized. It was done at a workshop.
When I got the car, the other issues that I addressed were replacement of Brake master and one slave cylinder. Not driving the car can be quite hard on the car as in excess.
|"Also looks like master and slave are original."|
" replacement of Brake master and one slave cylinder"
"Not driving the car can be quite hard on the car "
38 years old and you have replaced half the hydraulics, but not in the clutch system.
The symptoms are of failure of the hydraulically actuated clutch to release cleanly and consistently.
Might be a clue or three!
If you are lucky, it is crud built up where the seals in the cylinders rest. If not, there will be big pits there.
3/8" movement is minimal but usually works on a worn-in clutch; for a newish one, not enough.
|I had this problem in spades on my '66 Mk11. Turned out the clutch release bearing was worn away and the release fork was bent. Try extending the reach of the slave cylinder push-rod by inserting a nut between the end of the rod and the piston in the cylinder. If gear changes are smooth, then this points to a worn release bearing - in which case its an engine out job - sorry !|
|M J Chapman|
I was thinking somebody would know if 3/8 was good or bad before I moved forward. I am leaning towards just buying new, rather than doing a rebuild, though I could be persuaded. Any comments on when not to do a rebuild. Also, on the new ones, are VB and Moss the same and should I go with generic or the Lockheed.
|sorry as normal I didn't make myself clear before, I'm told it's more sucessfull to replace master and slave with new that to rebuild/reseal them - others might disagree tho'|
If bores are perfect after cleaning, rebuild. If there are pits, replace. When they sit, moisture in the system lies on the bottom of the bore, often right where the seals are, and eats the bottom of the bore.
95% on new cylinders!
|I am just going to go ahead and get the new ones ordered, then replace them. Minimize any down time and then I know I will have plenty of years of trouble free hydraulic issues.|
FRM did you go to Carlisle?
|No I am at the other end of PA, so I went to the All Star Sprint races at Mercer, beats Rapture anytime!|
|I have replaced Master and hydraulic line to slave. Using eezibleed to bleed system, I have one inch travel on the master and only 3/8 on the slave. My next thing is to put a nut between the slave piston and rod to see if the extra length will help. I did not replace the slave as it appeared to be in very good condition with no pitting. I did rebuild the slave.|
Is there a reason it is happening only in third gear. If I go from 2nd to 4th gear, or from 4th to 2nd, I do not have an issue.
You still have air in the system. The ratio of motion between master and slave is in proportion to the square of the bore size. I believe that the master is 3/4" and the slave is 1", but you might measure to be certain. If I'm correct, then the slave would move .562" for 1 inch master piston travel. The only possible loss of motion is in compressing an air bubble or expanding the hose. Putting spacers in or altering the pushrod length will not fix this and might cause other serious problems (destroyed pressure plate)
Put your hand on the clutch pedal and push down slowly one time. I think you will find a noticeable "step" in pressure about half way down - that's when you have compressed the bubble and are finally starting to activate the pressure plate.
These cars are notorious for having an air bubble trapped in the horizontal section of pipe above and behind the battery - a really stupid design that I change by rerouting the pipe to avoid the long high section. The bubble just moves to and fro while the fluid runs underneath it.
I have never used an Ezibleed or similar. The trick is to move enough fluid fast enough to expel the bubble. It helps to have an assistant. Two methods, 1) is easier, 2) is more effective:
1)Air out the slave. Jack up the RH side so the bubble moves to the right end of the high section of the pipe. Open the bleed screw and push the slave piston in until it bottoms, close bleeder, hold the piston in against the spring. Have assistant quickly depress the pedal and hold it. Repeat the bleed step - if you are lucky you will get a big bubble out. Repeat a couple of times. If no success, go to:
2)Air out the master. The car needs to be up so you can get to the slave, but the LH side should be higher so the bubble is on the left, close to the master. The advantage here is that the bubble doesn't have to move as far in an unnatural direction (down) before it escapes out the master, and the slave displaces more fluid than the master. Assuming your slave has a circlip to keep the piston from falling out, Remove the slave pushrod. Have assistant depress the pedal by hand until the slave piston is against the circlip, release pedal. Now, push the slave piston quickly to the back of the cylinder. This should push the bubble backwards into the master. See how it feels. With the slave piston against the circlip, the pedal should be absolutely solid. Then if there is still any movement, bleed the slave by pushing the piston in while opening the bleeder. Repeat all this if necessary, but I rarely have to do so. Refit the pushrod.
Problem re 3rd gear means that 3rd synchro is probably weaker than the others, but no synchro will be happy for long trying to overcome a dragging clutch.
Thanks for the further info.
I worked through method 1 as listed above.
After completing this I have 7/8 movement at the master cylinder and 9/16 at the slave.
I did check the clutch and get a good feel all of the way down, but still have the noise in third gear.
After all this, does it point to the gearbox.
So I take it that you can now get into gear at a stop no problem?
Probably gearbox, third synchro is toast. Usually it is second that goes first, but it varies by driver and prevailing traffic conditions. It gets worn out by poor driver skills, and if that is the case, a dragging clutch is multiplicative by a large factor. Hanging up throttle linkage doesn't help either, if it has ever had that problem. A really bad driver can take the synchros out in a few thousand miles of city driving. Quite possible that most of the damage was before you got the car.
It is possible to learn to drive it without fixing the synchro (or without the clutch releasing at all) , but if it is really bad then v. difficult.
I guess I will continue to keep driving it with controlled changes into third gear and minimize changes from forth to third, but change from forth to second.
I have no reason to take the motor and gearbox out at the moment, but when I do, I will get this fixed.
|Have you checked for wear in theholes at the end of the pedal arm where it meets the master cylinder and play in the pivots of the clutch arm, this can take up a lot of the available motion. An easy fix with the pedal arm less so with the clutch arm!|
You need somebody to teach you how to "double clutch" to successfully up or down shift into 3rd (or any gear). Then you can forget about it, and not wear out the pieces if you do fix it. I've driven many cars many thousands of miles with bad synchros, sometimes with the broken parts lying in the bottom of the case.
Yes you are correct. Just one of those skills that I never mastered.
Maybe its a good time, especially when changing from forth to third.
This thread was discussed between 19/05/2011 and 07/06/2011
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