Gearbox Rebuild

[jon burrows]

The syncro is poor dropping down into second and non-existant going into first on my MK2 overdrive gearbox. It's manageable and has been like that since I got the car three years ago, but I am looking to delve in and improve it. Ideally what I would like to do is find another gearbox to rebuild at my leisure, so that the car spends the minimum amount of time off the road. The overdrive is working fine.
Question 1 Are the boxes without overdrive identical (in terms of ratios, mountings etc) to my box fitted with overdrive, ie could I bolt my overdrive straight onto a non-overdrive box?
Question 2. Does anyone have a spare (in need of a rebuild) gathering dust?

Cheers! Jon

[Keith]

• 1 The mainshaft is different, which means you will need to strip the box to change it before you can fit an overdrive to a non overdrive box.
  
• 2 Sorry, not for a Vit
  

Keith

[Nick Jones]

To expand on Keith's post a little, the gearbox components of non-OD and OD gearboxes are the same apart from the mainshaft, so non-OD gearboxes do have considerable value as parts donors and practice pieces and tend to be easier to find and much cheaper.  You want to be a bit wary about mixing and matching individual gears between different gearboxes though - best to swap whole gear sets where possible.

Nick

[jon burrows]

Thanks guys. I had a feeling it wouldn't be that simple. Old O/D boxes don't seem to come up that often. Maybe I'll have to  have a winter lay-up instead.

[Richard B]

You can buy a S/H non-overdrive gearbox and then buy a new O/D mainshft on eBay 🤔

[Pete Lewis]

od mainshaft is tkc923

having rebuilt many of the tired units my last rebuild i took to mick papworth for a mainshaft with the 18mm spigot and a vitesse/gt6 stem gear machined to suit
makes the weak link  weedy spigot more bullet proof .  adds considerable life to these now tired boxes , wear and fatigue is playing its part  now, theres a limit to how many times you can use core to rebuild anything thats better than a compromise .....

tooth profiles changed during rhe life of these  cars , you cant  mix old with new  and i dont have any gearbox numbers to show when ??  this occured

Pete

[jon burrows]

Quoted from Richard B

You can buy a S/H non-overdrive gearbox and then buy a new O/D mainshft on eBay 🤔

That doesn't sound too bad.
Thanks for the advice Pete. Having rebuilt the engine I do fancy having a stab at the gearbox. I just hope the engine lasts long enough to benefit from it!

[Clive]

The advice I have had from our local gearbox builder is that GOOD used components are usually better than new ones available. So another gearbox may well supply many of the required parts that are worn on yours. Especially synchro rings, and possibly layshaft pin. These seem to be much better out of non-od boxes for some reason.

Agree with Pete on the mainshaft too, I expect Mr papworth can supply the required parts for the big tip conversion.

[Pete Lewis]

there were some rings made by being held in a lathe chuck which imposed some lobing

rings must be machined on a mandrill to keep them concentric

I  bought a core box from a faily local supplier to get some 'useable spares'  I  kept  in rouges gallery a mainshaft which had the tip cut off , bored to take a spigot , but it was left loose to wander about and had wrecked the stem gear  spigot bearing , it also had a mix of single rail and3 rail hubs and gears .. no wonder it was traded in  so getting second hand as a slave doesnt always gain you much except a  gear case

Pete