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Originally Posted by DavidP
LS 1st, 2nd, and 3rd are later parts, but 4th is the old number.

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


1978 T140E
1979 TR7V
1960 Royal Enfield Bullet 350
1973-81 (6x) Bultacos
Waste not, want not.........Thrift is a virtue.
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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 #830060 11/16/20 11:40 pm
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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.[Linked Image from feked.com]

Last edited by Lorenzo; 11/16/20 11:53 pm. Reason: add picture

1978 T140E
1979 TR7V
1960 Royal Enfield Bullet 350
1973-81 (6x) Bultacos
Waste not, want not.........Thrift is a virtue.
Lorenzo #830066 11/17/20 12:40 am
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Originally Posted by Lorenzo
Originally Posted by DavidP
LS 1st, 2nd, and 3rd are later parts, but 4th is the old number.

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

GBbooboo.jpg

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71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Lorenzo #830068 11/17/20 12:49 am
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Originally Posted by Lorenzo
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.[Linked Image from feked.com]

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.


1971 T120RV (R.I.P.)
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1993 Ducati 900 SS
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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.


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kevin #830083 11/17/20 3:27 am
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Originally Posted by kevin
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!

Originally Posted by DavidP
It now looks as if I can get by with a new lay shaft, complete with the new 4th and 5th gears, and new needle bearings and thrust bearings. Probably buy a new selector fork just to be certain I have the correct one.

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


1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
kevin #830090 11/17/20 5:54 am
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Originally Posted by kevin
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.
Proper gaskets are NOT optional on Triumph gearboxes. The spacing is important, kinda like the end float on an A65 lay shaft.


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Originally Posted by BikeVice
Originally Posted by Lorenzo
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.[

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

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

Last edited by L.A.B.; 11/17/20 6:34 pm.
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Originally Posted by DavidP
Originally Posted by kevin
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.
Proper gaskets are NOT optional on Triumph gearboxes. The spacing is important, kinda like the end float on an A65 lay shaft.

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


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

DavidP #830148 11/17/20 10:05 pm
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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.


[Linked Image from tbsphotos.s3.amazonaws.com]
DavidP #830149 11/17/20 10:15 pm
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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


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kevin #830158 11/18/20 12:32 am
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Originally Posted by kevin
Originally Posted by DavidP
Originally Posted by kevin
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.
Proper gaskets are NOT optional on Triumph gearboxes. The spacing is important, kinda like the end float on an A65 lay shaft.

my original april 72 gearbox didnt use any. the later layshaft iz machined slightly longer and binds the assembly without one.
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.


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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.


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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.


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71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
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