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MG Midget and Sprite Technical - Three questions about gear selection issues...

Hi - Multiple questions I am afraid!

I have pulled the engine and gearbox from my Frog (all standard) for two reasons. The amount of oil I have leaking and, the biggest issue, not being able to select gears without crunching them.

The symptoms have been the inability to select any gear, including reverse, while stationary without a huge graunch, as if I have not pushed the clutch down. Working through logically my thinking is hydraulics, or clutch or gearbox. I think it is clutch but want to discount other issues before getting everything back on the car.

The first thought I had was hydraulics, but there were no symptoms when I put the car away. No leaks to see and but trying it this week sometimes I have drive, with the clutch down (as if the slave or master cylinder are letting the fluid through) and others I don’t.

Q – With the master cylinder cap off should the fluid level rise when the clutch is depressed? Is this a symptom of fluid passing passed the seals in the MC?

So the clutch; nothing broken or out of line. The release bearing looks very worn (about 2mm left).

Q - If the release bearing is worn that will presumably mean the clutch is not fully disengaging as the pressure plate is not being lifted off the clutch plate. Therefore the input shaft will still be tuning the gearbox. Correct?

And finally the gearbox. Off the car this seems fine. Removing the side plate to see the gears everything looks fine. Nothing loose, no missing teeth r any obvious wear on any of the gears or bit you can see. Turning the input shaft by hand with the gearbox in gear, turns the output shaft and using fingers I am not able to hold it still (which you would expect). When the gearbox is in neutral there is some movement on the output shaft, but if you hold it you are able to keep it still.

Q – Is this normal? I presume there is some ‘force’ transferred to the output shaft in the same way that a rear wheel might turn slightly when the engine is running and the rear of the car is jacked up.

My current thinking is that the most likely issues are the clutch components. If I replace everything and reassemble the car, changing the slave cylinder while I am at it, things should be ok. But if there are any issues with the gearbox I will have to pull everything again which I want to avoid.

What do you think?

Mark
Mark '59 Frog

1st and reverse are crash gears. No synchro.

2, 3, and 4, are synchro assisted gears. You could have both issues. Poor clutch disengagement, AND worn synchros on 2, 3, and 4.
Lawrence Slater

Just trying to eliminate the hydraulics.

Did you check the clutch arm was giving full movement when the pedal was depressed when still in the car?

If you had done that you may have seen either 1) full proper movement or2) the clutch arm not moving far or 3) even while the pedal was fully depressed and held down the clutch arm slowly lifting off.

Either of these would point to clutch hydraulics rather than the clutch itself or gearbox.

1) No problems look at other factors
2) Air or water (hydroscopic) in the system or slave leaks
3) Usualy internal seal leaks in the master from one side of the piston seal to the other and back when unpressurised (in a modern replacement cylinder there may be fluid on both sides of the piston)
Dave Squire (1500)

Thrust bearing sounds badly worn so may be the major culprit or playing a very significant role; however my experience/gut instinct is with the hydraulics.

Will you post solution when you find it? Good Luck!

Jeremy
Jeremy 3

I would disagree about the thrust bearing.

You can have a lot of wear on the bearing and have no ill-effects with regarding to disengagement.

Also, the hydraulic clutch is self-adjusting, so takes up wear - within reason.

Another point to note is that is is very difficult - nigh-on impossible - to see the first speed gear and its corresponding cog on the laygear, with the 1st/2nd selector fork still in situ.
Dave O'Neill2

I agree with Dave, a worn carbon thrust bearing will give no symptoms until it is all gone and the metal support touches the clutch. Then you will hear it. The hydraulics automatically take up the wear and the clutch will disengage normally even when the carbon is very thin.

Fluid should not rise in the master cylinder when the clutch pedal is depressed. Think about it. You are pushing fluid down the pipe to force the slave piston out. If the level rises the flow is going backwards. The fluid level should not alter when you push the pedal. The reservoir should only be open to the circuit when the system is unpressurised with the pedal fully up.

If you can't select any gear at standstill without a graunch the clutch is not disengaging and I would be 99% sure it will be the hydraulics that are faulty. The straight cut first and reverse gears might cause mild crunching problems, but if it graunches when you try to engage 2nd, 3rd or 4th at standstill, the clutch is definitely the problem.
Mike Howlett

Thanks Chaps

My gut instinct is hydraulics, but you know how you can convince yourself of anything when you get a car to bits. I was hoping something would be obviously broken.

I am hoping the gearbox is ok. The fact that selection in all gears is bad makes me think it is not the gearbox and as it has got gradually worse, particularly over a 1k trip to France in September it seems more likely to be wear or leaking hydraulics than gearbox. Plus everything I could see looked in good condition with no real wear. A gearbox would probably go big style or be a problem for a lot longer if it was wear.

I did play around with the clutch before pulling the car apart, adjusting the movement of the push rods to see if that made a difference and it didn't. Didn't think to look at the actual clutch fork - seems obvious now!

I have ordered new everything on the hydraulics and clutch side so hopefully it will be fixed even if I am not sure by what!

Thanks again

Mark
Mark '59 Frog

Good luck Mark, be good if you can post a couple of pictures of the offending parts once you've got it sorted.
I've had real problems with thrust bearings - mainly because of poor quality and have replaced with a Peter May roller bearing and still having issues with clutch and subsequent gear selection, so a bleeding weekend beckons!

Jeremy
Jeremy 3

I agree it sounds like hydraulics I have just replaced the M/C (nos lockheed item) on my frog as I noticed a slight weep from the clutch pushrod. On stripping it the bores were worn, Hence the new cylinder. Although the gears did not crunch the clutch is now much smoother. Interestingly when I press the pedal there is a slight rise in fluid level momentarily.

The only other area to check is the pushrod on the slave cylinder. I have found that a worn rod and clevis pin can limit movement.

Bob Beaumont

Interestingly, you are more likely to lose movement from wear in the pedal/clevis pin/pushrod than wear in the slave cylinder pushrod and pin, which 'should' be taken up by the self-adjusting nature of the set-up.
Dave O'Neill2

Hi

Just to say replacing everything seems to have done the trick! New clutch, new slave and new M/C.

The MC was shot and seemed to be letting fluid pass on both circuits(worrying on my brakes). The slave cylinder rod had an oval hole in it and the clevis pin was worn. The clutch looked fine but was just very worn.

Everything is now back in and running and not a graunch or even a click in any gear. Just need some sunshine for a long run now.

Thanks as always for the advice and reassurance.

Pic of the car this week almost ready to get on the road. I had forgotten how much time an engine out can take when you have to work as well.

Mark


Mark '59 Frog

...and the engine after some TLC and a clean ready to go back in.

M


Mark '59 Frog

This thread was discussed between 07/04/2013 and 18/05/2013

MG Midget and Sprite Technical index

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