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MG TD TF 1500 - Gearbox rebuild - checking for wear

Hi, I have obtained a second hand gearbox from a TF to replace the one in my 53 TD. I have stripped the new box to check it over and have found the following issues:
1. A slight chip to one of the teeth on the layshaft (see photo). Does anyone know if this is likely to cause a problem? I have a layshaft from my original gearbox which I could use, but I wonder if it would be better not to mix and match too much, on the basis that the gears will have 'got used' to each other over the years.
2. There is about 1mm (40 thou) of free play between the selector fork and the 3/4 gear sliding hub. The other photo shows me measuring this with a feeler gauge. The slack appears to be primarily due to wear in the groove in the sliding hub rather than in the fork. Does anyone know if this degree of wear could give rise to trouble selecting the gears? If it just results in a bit of slack in the movement of the gear lever I could live with that. Unfortunately I have not run the car with this gearbox, so I don't know what it was like before.
Any advice gratefully received!
Pete





P Willows

Hello Pete, I would not give the chipped tooth a second thought. I cannot comment regarding the space you measured between the fork and the slider. Is there a number in the shop manual?
Regards, Tom
tm peterson

Thanks for that Tom. I'm not aware of any prescribed degree of tolerance for the fork and slider, but the other one is a noticeably closer fit.
P Willows

Top and third get the most stick so that is where the main wear appears. First is surplus to requirements and you are only in second for a minute or so.
I would check if the 3/4 fork in your present box is worn less than the replacement and use that in the replacement if so. I have seen boxes far more worn than that but still working perfectly.
Ray TF 2884
Ray Lee

Thanks Ray. I'll have a look at the fork but I think most of the wear is in the groove in the hub. Still, worth checking. I'm encouraged from what you say about your experience with other boxes though. My gut feeling is that it will probably be ok but I've never taken a gearbox apart before so a bit out of my comfort zone!
P Willows

they are tough old box, my first gear makes a horrible noise but has done it for the 48 years I have owned it.
it still changes sweetly so I will put up with it.
Changing the selector fork is an easy job you are not touching the gear train. you just have to watch the detent ball bearings and springs do not fall into the box.
Ray
Ray Lee

A few comments in the archives show 10-12 thousands clearance correct.40 seems excessive. I agree about chip- forget it. George
George Butz III

Pete, Good chance the needle bearings are rubbish if you have not taken a peek at them yet. Either wear or corrosion. How are your synchros? I cannot really tell from your pic, but unless the slider has a significant groove worn in the faces where the forks contact, I believe the wear is in the forks.
Regards, Tom
tm peterson

Thanks all for the comments. The needle rollers and synchros look ok. The synchros have clearly defined marks on them, which hopefully is an indication that they are not too worn?
P Willows

Pete, I cannot comment on your statement of “clearly defined marks” without more info. Are the marks clearly machined grooves horizontal to the length dimension? If so, then I would say your synchros are OK. The synchros are pretty beefy.. something in the neighborhood of .125”

Regards, Tom
tm peterson

Just came across this thread--
First off that chip, it's not a minor chip ,i reckon you'll hear that going clonk clonk clonk if that's the drive side, which it looks as though it is--which gear on the cluster is it front/rear and is there any damage to the gear that runs on it-
Secondly that 3/4 slider needs replacing, it 'could' interfere with 4th gear getting fully engaged and cause wear resulting in it jumping out of 4th gear, which may have been happening as wear like that is usually from driving with a hand on the gearlever all the time pushing against that slider
Thirdly syncro rings are easy to check for wear, simply put the ring on the gear that it's going to be used on then push it onto the cone with your fingers, then measure the gap between the syncro and the gear---new is just over .090" usually .093"-.095"----then .060" is fairly worn and not worth reusing .050" and less is definitely stuffed and won't work properly

willy
William Revit

Tom - yes the marks on the synchros are little machined grooves running around the synchro and cutting across the much deeper grooves. I have tried to pick them up on the attached photos although they do not show up very clearly.

Willy - I measured the gap as you suggested - the gap for 3rd and 4th was about 50 thou, the gap for 2nd was about 90.

Regarding the chipped tooth, it is on the largest gear at the front. The gear it meshes with looks ok. I've not worked out if the chip is on the drive side or not.

Pete





P Willows

Peter
If that's the front gear on the shaft ,then the chip--s are on the non drive (overrun) side so if you use that cluster they shouldn't make a noise on drive but maybe on the overrun, but, i'd be tempted to get in there with a small grinding wheel and just take off the sharp edge around where it's chipped out to prevent any load that might break the edge of the chip further and doing this will also eliminate any noise from there on the overrun-----Of course the best option is another undamaged cluster but it should be ok
Sounds like 3-4 syncro rings need replacing---as you say they look ok in the pic but must be worn
willy
William Revit

Peter
If that's the front gear on the shaft ,then the chip--s are on the non drive (overrun) side so if you use that cluster they shouldn't make a noise on drive but maybe on the overrun, but, i'd be tempted to get in there with a small grinding wheel and just take off the sharp edge around where it's chipped out to prevent any load that might break the edge of the chip further and doing this will also eliminate any noise from there on the overrun---and while you're in there just tidy them next 2 up as well--Of course the best option is another undamaged cluster but it should be ok
Sounds like 3-4 syncro rings need replacing---as you say visually they look ok in the pic but must be worn, you could take the punt and reuse them but it's a lot of work to pull it out again for the sake of a couple of rings
willy
William Revit

Thanks Willy. Regarding wear in the forks and slider, I'm thinking I might build up the box with the original components, bolt on the remote and leave the lid off so that I can see how it operates before I put it back in the car. Hopefully it will be clear if the gears are fully engaging or not.
P Willows

This thread was discussed between 12/02/2023 and 20/02/2023

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