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Posted By: DavidP Gearbox options - 11/12/20 9:25 pm
I got home from my last ride with only fifth gear available. Opened the box to find a broken lay shaft, clean break right between 3rd and 4th. Of course this is a '72 five speed box.
I searched for lay shaft 57-4371 at a couple of vendors. The search returned with 57-4900, as if these were interchangeable. But I've read the Vintage Bike article and I don't believe that this will work with the rest of my lay shaft gears?
It looks as if I have two options.
1. Find a good used T140 five speed to swap out everything.
2. Find a good used late T150 five speed and steal the lay shaft from my '72 T150V to fix the '72 T120V.
help
Posted By: kevin Re: Gearbox options - 11/12/20 9:52 pm
you have the early five speed with the weak first gear layshaft locking dog?

if you do, i suggest locating an entire later box, as that dog will eventually go as well. that was my situation and solution too.

eBay sometimes has 5-speed gear sets for sale. they're often early gear sets and they're missing that piece . . . because it blew and they replaced the whole internals. that's only if they were able to salvage the cases.
Posted By: Adam M. Re: Gearbox options - 11/12/20 11:34 pm
Too bad David, I feel for you. I also expect you don't want to install 4 gear cluster?
Posted By: DavidP Re: Gearbox options - 11/13/20 12:47 am
Originally Posted by kevin
you have the early five speed with the weak first gear layshaft locking dog?
I assume that the gearbox is original to the bike. This is the first time I ever had it open (I've owned the bike for three years.)
After reading about the weak dog, I always free the clutch before starting and hold the clutch lever for a couple of seconds before engaging first. It engages without a clunk. I don't do wheelies or drag race, and I don't engage first while in motion.
As you say, the best option is to find someone who is parting out a T140 and get a complete later five-speed.

Originally Posted by Adam M.
Too bad David, I feel for you. I also expect you don't want to install 4 gear cluster?
That is an option. However, most of my riding is on twisty mountain roads where 3rd and 4th on the five speed are perfectly spaced. I think the only way I would be happy with a four speed is with close-ratio gears.
Posted By: kevin Re: Gearbox options - 11/13/20 12:51 am
i have pictures of both dogs so you can see what you have.

ill see if i can dig them out tomorrow.
Posted By: TR7RVMan Re: Gearbox options - 11/13/20 4:15 am
Hi DavidP, I see Bonneville Shop's $969.00 5 speed gear set is out of stock, as is the conversion kit. LF Harris made parts. Can be very hard to buy good used trans parts these days. Worn out junk can be had. Would a seller in UK have new trans in stock? Would be really bad if you used old version parts & it let go & broke the case.

I wouldn't consider converting to 4 speed. I agree 100% 3 & 4 are perfect for canyon riding. When I swap bikes with 4 speed friend I can't wait to get back on my bike with the 5 speed.
Don
Posted By: DavidP Re: Gearbox options - 11/13/20 5:24 am
Originally Posted by kevin
i have pictures of both dogs so you can see what you have.

ill see if i can dig them out tomorrow.
Thanks. Looking at the pictures in the Vintage Bike article I'm pretty certain that I have the early dog.

Originally Posted by TR7RVMan
Hi DavidP, I see Bonneville Shop's $969.00 5 speed gear set is out of stock, as is the conversion kit. LF Harris made parts. Can be very hard to buy good used trans parts these days. Worn out junk can be had. Would a seller in UK have new trans in stock? Would be really bad if you used old version parts & it let go & broke the case.
Don
The lay shafts which come up in a search at MAP and Baxter are made by Harris. I haven't checked at Burton's yet, but the Pound keeps going up and with shipping...
Posted By: DavidP Re: Gearbox options - 11/13/20 6:33 am
Looking at the Bonneville Shop site, They do have a new gear set for T150 in stock. It's over $200 more, but by the time they get the T120/140 set back in stock the price might have gone up.
If I'm gonna spend that kind of cash I'm tempted to replace the gears in my Trident and use its lay shaft assembly in the T120.
Posted By: DavidP Re: Gearbox options - 11/13/20 6:53 am
Burton's has the T140 kit in stock. At the current exchange rate it comes to about $760 + shipping.
Posted By: Tigernuts Re: Gearbox options - 11/14/20 12:16 pm
https://www.ebay.co.uk/itm/5-SPEED-GEARBOX-TRIUMPH-BONNEVILLE-T140-TR7-00-0066-FREE-UK-POSTAGE/174515541139?hash=item28a1efd493:g:0VAAAOSwa~hZZzp0

If by 'Burtons' you mean Burton Bike Bits, I've had bad experiences with them and wouldn't recommend them. There are plenty of other UK Triumph spares retialers. The link above is for KBH (works out just over $750 plus postage). KBH aren;t the best price-wise, but more reliable than BBB imho.

LP Williams are likely to be more expensive but you do get excellent service. TMS are very good, as are Monty's Classics.
Posted By: The Bonneville Shop Re: Gearbox options - 11/14/20 5:10 pm
Careful here guys. Gears from triples and twins have the same numbers, but the mainshafts are very different.
Posted By: triton thrasher Re: Gearbox options - 11/14/20 5:46 pm
Not a complete kit, but I’ve always had good service from Feked.

https://www.feked.com/triumph-complete-5-speed-gearbox-cluster-650-750cc-twins.html
Posted By: Hillbilly bike Re: Gearbox options - 11/14/20 7:15 pm
I got several orders from Feked lately....5 day delivery to NY USA....shipping charges were very reasonable...
Posted By: Markie Re: Gearbox options - 11/14/20 8:45 pm
When the 5 speed box was improved, Triumph didn't change the layshaft. They did revise and improve the M/S 1st & 2nd gear, the L/S 3rd, L/S 2nd, L/S 1st, L/S drive dog and the L/S fork. I'm reading this from Triumph's service bulletin # 1/73 These all have to be changed complete, but the layshaft itself isn't.
Posted By: DavidP Re: Gearbox options - 11/15/20 4:41 am
Yes, from what I've read the original CP-1000 upgrade kit was just the lay shaft gears and dog, the two main shaft gears and a first gear shift fork.
I understand that the Trident main shaft is different. AFAIK that's the only difference between the two gearboxes. Except they never were dumb enough to use a leaf spring for indexing the Trident box.
Thanks for the links, I'll have a look. I've dealt with Burton once. The seat on my Trident came from them, good quality and service on that.
Posted By: L.A.B. Re: Gearbox options - 11/15/20 1:36 pm
Originally Posted by DavidP
Except they never were dumb enough to use a leaf spring for indexing the Trident box.

http://www.tioc.org/partsbookstriumph/pb-tri-T150-1972%2099-0955.pdf
pdf p.28 (& 29)

https://montysclassicmotorcyclessho...971-72-tr6-t120-t150-rocket-3-1386-p.asp

https://www.classicbritishspares.co...ducts/triumph-gear-box-leaf-spring-parts
Posted By: Mike Baker Re: Gearbox options - 11/15/20 1:55 pm
I believe the layshaft gained a circlip groove for high gear at some point.
Posted By: DavidP Re: Gearbox options - 11/15/20 5:26 pm
My parts book shows the leaf spring as well. My '72 T150V has the plunger. According the Stuart it was built in October of '72, perhaps they switched back by then.
Originally Posted by Mike Baker
I believe the layshaft gained a circlip groove for high gear at some point.
And it appears that mine has that circlip. For all I know this gearbox has already been upgraded?
Posted By: L.A.B. Re: Gearbox options - 11/15/20 5:49 pm
Originally Posted by DavidP
Originally Posted by Mike Baker
I believe the layshaft gained a circlip groove for high gear at some point.
And it appears that mine has that circlip. For all I know this gearbox has already been upgraded?

[Linked Image from i.postimg.cc]

https://www.britishmotorcycleparts.co.nz/57-4900-layshaft-assy-inc-4th-5th-gears-5-speed
Posted By: DavidP Re: Gearbox options - 11/15/20 6:23 pm
From looking at Kevin's post from 2018 about upgrading, it appears that I already have the later 1st gear dog.
The lay shaft broke flush with the fourth gear. If I can get dimensions for the gears I could be certain.
Sure would be easier to just replace the lay shaft with those two gears pressed on.

Attached picture Dog1.jpg
Attached picture Dog2.jpg
Posted By: Markie Re: Gearbox options - 11/15/20 9:11 pm
Thats the new layshaft dog. The other gears should be stamped with different numbers if your box has been upgraded. m/s 1st & 2nd 57-4653, l/s 3rd 57-4647, l/s 2nd 57-4657, l/s 1st 57-4654, l/s fork 57-4660. As I wrote before, these parts are supposed to be installed all at the same time. If your box wasn't upgraded and you have the new l/s dog, could that be why your l/s broke?
Posted By: koan58 Re: Gearbox options - 11/15/20 11:07 pm
Triumph layshafts aren’t known to break, this is the first one I’ve heard of.
Of course there can always be a faulty one, but I think it more likely that a fragment chipped off during a gear change and unfortunately found its way between between 2 gears, levering them apart such that the shaft could not cope.
That’s only a guess, who could know for sure?
Posted By: DavidP Re: Gearbox options - 11/16/20 12:06 am
Okay, I have a partial upgrade.
LS 1st, 2nd, and 3rd are later parts, but 4th is the old number.
MS 1st/2nd is later, 3rd is early. I think the upgrade kit only changed 1st/2nd on the main shaft?
I can't see a number on the selector fork.
Maybe some bozo just put the newer gears on the old lay shaft?
Posted By: kevin Re: Gearbox options - 11/16/20 1:27 am
new job, no time until now.

here are pictures of two of the early 5-speed locking dogs:

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]


notice the recess in the back side that isn't poresent in the new ones.

also, it's only 0.393-inches thick:

[Linked Image from i.imgur.com]

my machine was an april 1972, T120RV DG . . . . it had the leaf spring.
Posted By: DavidP Re: Gearbox options - 11/16/20 1:51 am
Thanks,
I noticed the recess in the back of your broken one from your earlier post. That was the clue that mine might be the later version.
Mine is an EG model, just a month later. Still has the leaf spring. I only get a false neutral shifting down from 3rd. Perhaps that will improve with a new lay shaft.
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.
Posted By: Lorenzo Re: Gearbox options - 11/16/20 1:34 pm
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) ?
Posted By: Markie Re: Gearbox options - 11/16/20 7:28 pm
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.
Posted By: Lorenzo Re: Gearbox options - 11/16/20 11:40 pm
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]
Posted By: DavidP Re: Gearbox options - 11/17/20 12:40 am
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.

Attached picture GBbooboo.jpg
Posted By: BikeVice Re: Gearbox options - 11/17/20 12:49 am
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.
Posted By: kevin Re: Gearbox options - 11/17/20 2:01 am
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.
Posted By: BikeVice Re: Gearbox options - 11/17/20 3:27 am
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
Posted By: DavidP Re: Gearbox options - 11/17/20 5:54 am
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.
Posted By: L.A.B. Re: Gearbox options - 11/17/20 11:28 am
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
Posted By: kevin Re: Gearbox options - 11/17/20 3:35 pm
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.
Posted By: Markie Re: Gearbox options - 11/17/20 5:43 pm
Wow! Just when I thought I had a handle on it.
Posted By: The Bonneville Shop Re: Gearbox options - 11/17/20 10:05 pm
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.
Posted By: kevin Re: Gearbox options - 11/17/20 10:15 pm
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
Posted By: DavidP Re: Gearbox options - 11/18/20 12:32 am
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.
Posted By: kevin Re: Gearbox options - 11/18/20 1:36 am
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.
Posted By: DavidP Re: Gearbox options - 11/18/20 5:38 am
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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