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There was no change to 4th. gear with CP-1000 kit. Is your "old number" 57-4787(8) ?

Looks like David just saved this bozo from an expensive mistake! David, you’re box appears to have cp1000 installed correctly. Cp 1000 didn’t call for the lay shaft to be replaced. Layshaft 57-4900 was introduced to solve another problem, that of the 5th gear drifting into 4th and effectively causing the box to be in two gears at once with ugly results. That circlip groove was to stop that. I’m wondering if I can cut that groove in my layshaft or if I should just buy 57-4900.

Markie -

The groove for the 5th.gear "circlip" (actually more like a snap ring) was not in the layshaft, but internally in the 5th. gear pinion ........
Visualise a piston circlip, and the way it retains the gudgeon/wrist pin. This new pinion was also wider than the earlier one.

No, the number on my LS 4th gear is 57-4384. With the shaft broken I can't remove the 4th gear to look at the number on the 5th, but I assume it to be 57-4383.
Looking at the inside of the case, it appears that the original first-gear dog met a bad end.

That's the last version of the improved layshaft. I believe it came out in 1979.There's also a version with a snap ring and groove between 4th and 5th gears that came out in 1976 or 77, although I may have the chronology backwards. Anyway, there are 2 versions of the improved layshaft.

Eric.

eric, sell him a whole new gearbox like you did for me. that one is working fine after i fitted a single gasket between th ecases and inner cover. easiest way to make sure it all works together.

I could but the last good used one I saw on eBay went for $800.00!


If you have the bigger 1st gear and dog, you have the later selector fork. The early selector fork will not fit the newer 1st gear.

Eric

Proper gaskets are NOT optional on Triumph gearboxes. The spacing is important, kinda like the end float on an A65 lay shaft.

The 4th and 5th layshaft gear part numbers changed around 76/77, however, according to Service Bulletin 439 the 57-4600 57-4900 layshaft assembly was introduced from EH33674 (T140V/TR7RV) so mid-'73 model year which the '74 parts book appears to confirm. The 57-4900 layshaft assembly part number apparently continuing to the end of production.

The bare layshaft is 57-4901
http://www.klempfsbritishparts.com/LAYSHAFT--BARE--5-SPEED-0

my original april 72 gearbox didnt use any. the later assembly has a slightly longer working length and binds the layshaft without one.

Wow! Just when I thought I had a handle on it.

I updated a 1972 T120RV five-speed gearbox to the later specifications using parts sourced from Coventry Spares, including the layshaft. The conversion went pretty well until indexing it with the leaf spring. I must have had that transmission in and out of the gearbox a dozen times. I finally used some monofilament fishing line fed up through the drain plug and looped around the leaf spring to pull down the spring in attempt to keep the camplate from moving at the last moment when pushing the cover into place. One of those jobs I would not look forward to doing again.

i used to assemble the box in a fifth? gear and let the spring roll the camplate as it went in.

but it was always fussy.

i put in a plunger and indexin g is easy but zhifting is the same

I was surprised to see that the gaskets are not listed in the parts catalog. They are there in the catalog for the same year Trident. I've never seen a unit Triumph gearbox without gaskets, but I have seen posts where people ended up with rough shifting because they tried to use goo instead of proper gaskets.

i didnt use any on two 1970 T120 cases ive had in my race bike. i have some 67 cases im assembling now, so we ll see. i was always under the impression that the gaskets were a T140 thing

i think the right side layshaft thrust washer presses the first gear locking dog against the inboard circlip when there is insufficient end float. i dont know exactly which dimension was changed.

Maybe just a later five-speed thing?
In any case, I found the lay shaft and the other parts I need at MAP. Kind of a shame that I must disassemble the primary to fit the new lay shaft bearing, but it must be done.
The only bodge I've noticed is that the shock drive has the wrong screws in the cover.