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MG Midget and Sprite Technical - Difficult first gear engagement.

Please can anyone suggest reasons why I am experiencing a gear grinding problem when driving my late 67 MK3 Gan 4 midget.

Currently I can't change from second to first without the gears grinding when the engine reaches normal running temperature, around 160F.

There's no problem when the car moves off from cold, the gear change is quite smooth & grind free but as it gets warmer the grinding begins.

Regards
J Bond

I am sure that the others will ask you which oil you are using, so I will do it first, so they can then concentrate on helping you :D
CH Hamon

I'm unclear what you are doing. Are you changing from 2nd to 1st whilst the car is moving? If so it's bound to grind as 1st is not synchromesh.
Bill Bretherton

That's my thought too Bill. If you've never driven an old design car before, you would assume that you can just push it into first gear while moving as you can on most cars since about 1970. Not so on any Spridget except the 1500 rubber bumper model.
Mike Howlett

John,
I think more info and clarification might be required.

Oil 'thins' as it gets warmer.

Have you checked the gearbox oil level, when was the oil last changed?

Are the clutch and its hydraulics in good order - fluid, hoses, cylinders, arm, bearing, clutch itself.

Is the engine running smoothly?

Has the car been sitting round for a while and isn't used a lot/regularly/frequently on reasonable length journeys?
Nigel Atkins

From the vehicle profile the car was sold in 1978 then repurchased in 1997 so I guess J is familiar with the lack of synchromesh on 1st gear :)

Simon
S Holt

Thanks


I have 20/50 oil in engine and gearbox, probably used for about 300 miles.

If I set off with a cold engine & after 1/2 mile or so I stop at traffic lights & change from 2nd to 1st the gears don't grind.

If I drive a longer distance up to when the engine reaches a normal running temperature of 160F & stop again & change from 2nd to 1st the gears will grind.
J Bond

Try the same routine, but double declutch (do you understand how to do that?) before going into 1st. Report back.
anamnesis

from your description, heat is affecting clutch throw-out in some way. Is the biting point close to the floor when warm?
David Smith

typical symptom of oil on the clutch plate--is there oil leaking from the bottom of the bellhousing
William Revit

Is the clutch fluid level correct?
Is the clutch fluid less than two years old?
Old clutch fluid can give the symptoms you have.

Simon
S Holt

Working through the fault suggestions as follows:

1. When I double declutch the gear change is slightly better but it doesn't stop the grinding completely.

2.Biting point is the same, cold or warm engine.

3.I have had an oil leak under the car for many years, don't think it's from the gearbox because when I change the oil it is always just below the filler plug.
From time to time I need to top the engine oil up though.

4.The clutch components externally appear to be in good condition, master cylinder stays full, no visible leaks, changed the fluid about two years ago.
The clutch was replaced about 20 year ago but it has only been used for about 3000 miles.

The whole problem does appear to be heat related though, causing the gear grinding to become worse as the engine unit heats up.

Weather not to good in Lancashire today, raining again, need to wait for some sunshine before I can get the car out and have look under the body, I will take a photo of the area where the oil leakage is occurring, may help to diagnose the cause of the gear grinding.

J Bond

If you can get under the car you could perhaps remove the rubber blanking plug/grommet and have look inside and take a flash photo and also perhaps get something inside to take a sample of any fluid in there. Sometimes just the colour, consistency, feel or smell can give you a clue as to what it is so where it comes from.

Also IIRC(?) you might get an angle to see the clutch arm yoke and release bearing, might need a mirror, or I might be on fantasy island with this.

Bit of a tangent, fyi thing, but if using engine oil in the gearbox, the MGB WSM has to change the oil every 24k-miles or 24 months whichever is the sooner (soonest?). At an *average* of 150 miles a year 300 is 2 years. :)

I very much doubt the age of the oil is the cause here but wonder how much condensation contamination might take place unless the garage or storage facility is a strictly controlled heat and humidity environment. I know the climate on the hardstanding where my Midget sits is (seems?) damper that it was years and decades back, whether that's because of climate change, EU/Brexit, Scottish or Cornish independence I don't know.

Nigel Atkins

I think it's clear then that you have clutch drag, if even double declutching doesn't stop the gears spinning; which is what's happening as you have no synchro on 1st.

I wonder if the clutch centre plate is binding on the input shaft when it gets hot, and not easing back from the flywheel, hence keeping the shaft spinning. Normally you can drop into neutral, back into 2nd momentarily to stop the spinning, and then into 1st.

Fit a type9 ? 😉

anamnesis

Agree with the clutch dragging somewhere. Clearly it is not disengaging fully to engage. Could be an oily clutch plate for sure, could be clutch pedal travel is insufficient, could be air in clutch hydraulic fluid, could be leaky master/slave....
Oggers

Radical and unpopular idea for a show car but I'd be driving it around a lot and using the clutch a lot, into 1st when required, to see if anything gets better or worse. Lack of use often hinders following use, I was quite surprised how much rust was on the handbrake rods on mine from lack of regular use and the handbrake isn't an item that gets that much exercise when out on drives.
Nigel Atkins

Can you engage first or reverse from stationary cleanly (after giving everything in the gearbox time to stop spinning)? That would be my way of checking for a dragging clutch.

This may sound ridiculous, but have you got carpet in the driver's footwell? When I first got it, getting my Sprite into gear from cold was no problem but when it was hot it used to be difficult to the point of impossibility at times. Removing the thick sound deadening carpet gave the clutch pedal at least another 1/8" travel, possibly more, and the problem went away.

I never delved any further to find what the cause was as I have been happy to run sans carpet to save weight on the track - every little helps!

Colin
C Mee

The puzzle, or clue, depending on how you look at this, is why it works ok when cold, but not once it is warmed up.

Following Simon's idea, if you have water contamination in the clutch fluid the clutch would still operate when cold as the water is uncompressible, at leat at clutch system pressures. But if it then warms up to the point of the water vapourising (heated up as the system is repeatedly subject to pressure as you drive the first few miles)the water vapour would be compressible and the clutch would not therefore disengage as well. Does that sound like a plausible explanation?

As an aside, I find that 55 years after learning to drive in cars with A series boxes and minis, when at a standstill I still select second before then selecting 1st, doing this in any manual change car I drive, irrespective of make or synchro gearboxes..
GuyW

Could it be a failing spigot bush ?
Heat and lack of lube causing it to drag the input shaft around when it heats up.

I have only used / installed the brass/bronze types but I understand some of the later 1275's had a roller bearing.

Worth checking the hydraulics first before pulling the engine.
richard b

I 2nd the potential for a dodgy spigot. Meant to include that earlier.
anamnesis

Guy,
Water contamination was my thought, although I would be surprised if it was that bad after being changed about two years ago.
I had the same symptoms a good few years back when driving through central London on a very warm summers day. Once back home in North Devon, I flushed/replaced the clutch fluid and all was good. Must admit the old fluid was probably nearer 4 or 5 years old!
Simon
S Holt

I actually think Richard's suggestion is more convincing. This, "only when hot" clue seems to rule out most other suggestions.
GuyW

Hi all.

I have made a start today to try & resolve the crunching first gear engagement issue, decided to start with draining the clutch fluid, replacing the master & slave cylinders, fill the system with Dot 4 fluid & bleed.
However I have found two problems whilst trying to remove of the existing slave cylinder, I have managed to remove the lower bolt but I'm struggling to get a spanner on the top bolt, is there an easy way of do this?

Also the pin joining the slave cylinder pushrod to the clutch release arm appears to have rust fused and I am unable to remove it, I've tried spraying the area with releasing fluid & the tapping the end of the pin with a hammer and nail punch but it will not knock out of the connection, any ideas on how I can resolve this issue.

John
J Bond

John,
If the clevis pin is really seized that could be a large part of your clutch issues.

I assume you have already removed the split pin ?

I would first try getting a Mole type wrench on the end and try rotating it to release it.

You don’t want to knock it about as it may bend the arm.
You could try a bit of heat if that doesn’t work but you may burn the rubber gaiter.

With the top bolt it is difficult to access but to make reassembly easier cut out the top so it slides in and only needs tightening - see the archives as Alan A has posted pics of this mod.

R.



richard b

As someone mentioned Slave cylinders, has anyone heard that although they are bored 1" (25.4mm) they are actually fitted with 25mm rubbers? That could explain why my 3 year old slave is now leaking.
It begs the question if they can only get 25mm rubbers why don't they bore them out to 25mm?
Or is it a case of 25mm is close enough and the customer won't know?
Rob
MG Moneypit

If it's rust I've never had a failure by using a god penetrating/releasing fluid (which ordinary WD40 isn't) and time and patience, although many find patience very difficult to find and at low stock or out of stock.

Thoroughly soak with something like PlusGas or GT85 leave to soak in at least overnight, longer if possibly then try to break the rust seal by doing as Richard has put. If that doesn't work then repeat, soak leave as long as possible.

Let the chemicals do the hard work and you 'just' have to have time and patience (impossible for some, get the torch out).
Nigel Atkins

Removed the old clutch slave cylinder today but the push rod is still attached through the clutch lever arm, still can't knock the pin through the end of the clutch arm, soaked the parts with GT85 releasing fluid and now leaving alone for a few days.
If the releasing fluid fails to free up the pin to knock out, not sure what to do next for the best.

John
J Bond

So what is moving / seized ?

Does the piston rod move ? and if so does it take the clevis pin with it when it rotates ?

You can try a Mole wrench across the ends of the clevis pin and rotate the p/r etc.

If the piston rod is seized to the pin and rotating/ heat won't move it then I'd cut the piston rod out carefully avoiding the clutch arm - hacksaw/thin disc grinder / Dremel with reinforced cut off wheel etc.

Don't forget the Alan A slotting mod for the top bolt re-assembly.
richard b

The old piston rod rotates on the clevis pin, tried to rotate the clevis pin with mole grips but it won't rotate, totally seized.

If I cut out the middle part of the clevis pin I will have to remove the two parts of the clevis pin that remain in the clutch arm which would still be seized.


John
J Bond

John,
leave the GT85 to soak in and have a go at getting the pin moving whenever you feel like it tomorrow, if it doesn't move or doesn't move enough then in GT85 and leave again until whenever you feel like trying on Monday. I can only think of once when I have to try three times over three days and that was for something underground.
Nigel Atkins

John

Could you not just pull the slave away from the piston rod, then leave the rod in situ attached to the release arm i.e. re-use it?
Bill Bretherton

Bill
If the pin does not rotate won't the friction increase as the motion is on an arc ? and hence make the clutch a bit more stiff to operate ?


R.
richard b

Richard

I understood John to mean the rod rotates on the pin. Is that not ok?
Bill Bretherton

The clue, if it was accurate, must surely be that the gear only grinds when it's hot. So heat- related change to the clutch (driven plate??) Or gears dragging once warmed up ( dry spigot bearing, or maybe an oil issue?)
GuyW

This thread was discussed between 24/06/2021 and 18/07/2021

MG Midget and Sprite Technical index

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