Gear alignment T25/T3

[Aidan]

The selector shaft only touches the nylon bush and seal at the selector ball end and only the cage should touch the fixed pin, which allows it to slide side to side but prevents the cage rotating and the big pressed metal cup touches the case, but again should be able to slide in the bore - can you push the cup into the case, take the top hat out and you might see the cup is free to slide on the shaft between the inner stop circlip and the circlip that the top hat sits on - but it doesn't look damaged so should slide

https://www.youtube.com/shorts/6gJ_NO5BL0g apologies the embed YT video didn't work for me, it never does

you can put a bit of oil or grease in the nylon bush and seal and in the case to lubricate the parts, you can polish the shaft (say with a green washing up scotch pad or fine emery) where it passes through the bush and seal if it is very rusty

I suspect the 3rd 4th fork is the issue, it may appear to be in neutral but may be very slightly out and is putting pressure on the cage at the point I am pointing at in this pic


When fully in the hammer (to the right of my finger tip) is in the middle of the cut out in the 3rd 4th fork and can move the selector fork when the shaft is rotated and the cage slides through the selector fork when the shaft is pushed in to the other 2 planes so the hammer either interacts with the relay lever or the reverse selector fork to engage those gears

I suspect that if you try and engage 3rd or 4th gears by moving their selector fork that you may not be able to engage either gear as easily as you can 1st and 2nd, or if you do that you can not get back into neutral
If this is the case then I would diagnose a broken 3rd4th synchroniser hub that has cammed and is preventing the slider part of the synchroniser moving easily and preventing the fork being relaxed in neutral and thus rubbing on the cage of the selector shaft preventing free movement

[Vodim]

Thank you! Will have a look at this tonight. For the videos you can go in to Youtube and search for MrBengtBanan and you will see my account with the videos. I only have the 4 videos uploaded there.

[Vodim]

Ok, so the "cup" moves freely in the case. Good idea removing the hat, that made it clear that the cup was not the problem. I also tried moving the fork for gear 3 and 4 (at least I think that was the fork I tried) and I can move it backwards, into gear 3 and back to neutral. Two pictures of that below so you can confirm that I'm on the right fork. Moving it into 3rd is quite easy, it doesn't even feel like it goes into a gear, it just goes back with a heavy clunk. Perhaps it does not go fully in but then again it is moving quite a bit as you can see. I can push it back into neutral but not forward by hand. Difficult to get any power in there though as it is so tight.

If this confirms the 3/4 gear hub problem you mention, what can I do? Do I need to take the entire gearbox out or perhaps just the front part of it? I am in no hurry and am enjoying to learn as much as possible about the car so I don't mind a bigger job. Then again, if there is a quick fix (which I'm sure there isn't ) that would make it run ok, I would go for that atm 

[Aidan]

that's the reverse selctor fork that you have moved, hence it only moves in one direction



3rd 4th fork is the one marked green

reverse fork is marked red

the hammer operates the relay lever at the top

[Vodim]

Thank you! I was finally able to get back to my little project tonight. Tried the 3rd 4th fork and it went back and forth fine. I also drained the oil and there were some filings on the magnetic stick. I hope it is possible to view the three films I attach. I'll try to attach them as embedded and as ordinary links. Sorry for the excessive filming but it seems like the best way to show how it looks.

https://youtube.com/shorts/2Ghwts7e-cA?feature=share
https://youtube.com/shorts/aPbqVcJjSqA?feature=share


https://www.youtube.com/watch?v=IGaufjy0r34
https://www.youtube.com/shorts/2Ghwts7e-cA
https://www.youtube.com/shorts/aPbqVcJjSqA

[Aidan]

Okay so all gears select, all looks normal
the drain plug magnet looks pretty average, depending on the mileage and use since last, if any, oil change
Build up of fines isn't terrible, a bit heavier than one would like to see, but it depends; there's a slight fine sludge build up on the stem, if that was a heavier build up on the stem then I'd say worn/wearing big bearings, but there's no smoking gun, no piece of selector fork bearing shell or bits of synchroniser springs or keys or anything big

Line up the forks and put the selector fork back in, it isn't at all clear as to why is doesn't freely slide to and front in neutral

See what you have cold and with everything lined up, and if it goes back in all the way, then reassemble and pop cover back on

Fesh oil won't hurt so you might want to buy some in case you find it is okay and you want to try driving it again to see if it is different when hot

The full procedure for working on the box is in the Bentley manual so you can take a look at it and decide if you fancy having a go if it comes to it

[Vodim]

Thanks for all the advice Aidan! Would have been lost without it.

It doesn't feel great to put it back together again when I have to tap in a shaft that should slide freely.. I was thinking about a couple of things:

1. When going through the forks/arms through the opening where the lid usually is, the only gear I cannot get in now is second (relay lever forward). Does that say anyhting?

2. When I put the gears in, like 3 and four for example, they go in with a click. When I put the back in the middle, or neutral, they don't go into a fixed spot in the same way. I can move them back and forth quite a few millimeters within the neutral position if you get what I mean. That is what makes it difficult to align them. Are there any detent springs or similar that are supposed to keep them in place when in neutral? If so, that would be a good place to look I suppose. I don't find anything about this in the Bentley manual though.

3. Also, in the picture attached from the B manual it says "requiring disassembly of transmission". Does this mean having to take the entire box off? Or can I take off the gear carrier part in the pic while on the car? I'm thinking this will allow me to see the shift forks better.

[Aidan]

it's a gearbox out and full disassembly job to examine the synchronisers, forks and selector fork bearings and the relay lever - the lever and the fork bearings go into the case at the beginning of the assembly and the forks and assembled shaft assemblies are then fitted into the gear carrier and the gear carrier fitted into the main case

the neutral position of each selector fork should have some float, in use the forks will find an unloaded position and the synchrorings will be free to spin with the shaft, and the change gears will be free to spin at different speeds relative to the shafts and each other when not engaged - with the clutch released all gears spin, in neutral or in gear, in this last case the selected one is locked to the shaft

do not try and pull the gear carrier off the mainshaft that is just wrong and you are putting forces on the gears using the overlaps to provide some stop surface

can you see from contact marks on the cage of the selector shaft what is rubbing on it ?

in neutral with someone pressing the clutch can you rotate the top shaft ?