Looking for someone to shed light on my 1800S transmission

[jgcoutts]

I was already to do a full rebuild with bearings, seals, gaskets and synchros the countershaft is just an added bit that would have come out and gone back in regardless of its condition. Just sourcing one to install and the confusion my ID tag was causing.

Gearboxes that are ID’d as M40 with OD are likely M40 converted with the extended output shaft to take an OD, not as in my case born at Gothenburg(with birth certificate to prove it) with an OD on an M41 casting but ID’d as an M40.

There is some story here as to why and it would be great if someone with knowledge of the production line at the time could fill it in be it a mistake in punching the tag, a change after the tag was punched but before the casting drilled and taped for the fill plug or ?

[nozamaman]

Re Dereks post Nigel Ayling and I (John Smith)did rebuild a m41 using a m40 casing and the long shaft from a m41 We did it with no special tools other then pullers to remove the gears. I had about 4 X M40 boxes
at the time from which I was able to choose the best internals. If using a M40 case fill the gearbox via the gear lever hole so you dont lose any via the lower drain plug. Itworked very well.

[Underdrive]

Originally Posted by nozamaman

Re Dereks post Nigel Ayling and I (John Smith)did rebuild a m41 using a m40 casing and the long shaft from a m41 We did it with no special tools other then pullers to remove the gears. I had about 4 X M40 boxes
at the time from which I was able to choose the best internals. If using a M40 case fill the gearbox via the gear lever hole so you dont lose any via the lower drain plug. Itworked very well.

If going to the trouble of rebuilding an M40 'box to take an O/D why not drill and tap for the upper filler plug at the same time and cancel the need for any filling issues thereafter.

[nozamaman]

Good idea but I didn't have the means to tap a thread.

[Derek UK]

The filler is drilled into a boss on the casting. The thickness of the casing isn't really thick enough to drill and tap.

John. As far as I know "Olaf" is still alive and well but I haven't been in touch with John Green, who bought it from me, for a while.

[Burdekin]

I think my Amazon box is a converted M40, will check. I have a couple of M41s at the workshop so will have a gander at the tags when next over.

[Volvo_133]

I am getting through some disposable gloves with this one!
My spare od gearbox is labelled M41. I have a 4 speed unit labelled M40G with the big flywheel type output flange.
Back to the laygear. I have 3, the teeth on all 3 of them look good and intact.
They are all stamped 380172 and the teeth count on all 3 tally with your info.
Hopefully you can find one closer to home than Sheffield.
Thanks,
Chris

[jgcoutts]

P/n 380172 is encouraging, I’ve found a couple that sound promising and hope one solves my problem. Thanks

[Volvo_133]

I have had a look locally and found a used one for £140 ish. You may find a complete 4 speed box for this kind of money.
Do let us know how you resolve this.
Thanks, Chris

[Underdrive]

Originally Posted by Derek UK

The filler is drilled into a boss on the casting. The thickness of the casing isn't really thick enough to drill and tap.

John. As far as I know "Olaf" is still alive and well but I haven't been in touch with John Green, who bought it from me, for a while.

Derek, the boss in the casting is a figure eight with the upper location for the O/D filler being just as thick as the lower one. The new hole could be tapped any thread of a suitable diameter and a short bolt with copper washer fitted.