Why do people use other Triumph diffs in the Stag

[sujitroy]

This weekend I removed a third diff off a part Stag. I needed the quill shaft off it. The diff is not from a Stag, but starts with the letter C. Is this from a TR6? We don't recall is the Triumph 2000 was imported into USA, but I have seen one or 2. One diff cover bolt doesn't line up. it very close but you can't put a bolt on it. The diff shell has subtle differences too. Assuming your Stag diff is OK, do people swap diff from another Triumph because of the difference in rations? Is the TR6 diff the same as a TR4, 5, TR250 diff?
Sujit

[flying farmer]

UK TR6 and TR5 use a 3.45 ratio

I am pretty sure the TR250 is a 3.7 the same as the stag, but it is 29 years since I took the diff off my TR250 and it was missing several teeth so it went in the scrap pile. I used a spare PI saloon casing with a Dolomite Sprint 3.45 diff unit from an axle with a cracked casing.

TT250 has a CD prefix, I think USA TR6 is CF, but don't know the ratio. Wouldn't be surprised if it was 3.7 as they were equally asthmatic as the TR250.

Everything about the Stag diff is different, casing (hence the different bolt spacing), crownwheel carrier and pinion shaft bearings. Output shafts are the same.

I read somewhere the diff used in the stag came from an earlier Standard model and was deemed to be stronger than the Triumph diff. The Stag crownwheel carrier has slightly thicker webs than the saloon/TR item, but the outer pinion bearing is significantly smaller and seems to go first in my experience. The crownwheel thrust bearings are the same in both.

I think the usual reason for change is the original diff has gone noisy, years ago there were plenty of spare ones about. I got fed up with swapping second hand diffs in the early 90s and took to rebuilding them at the first sounds of distress, before the crownwheel and pinion got damaged.

Neril

[Motorsport Micky]

The Triumph saloon ratio of 3.45 is popular because it reduces the standard diff ratio and gives little lower cruising revs and better economy.

Mick Richards

[stag8manod]

Hi, The 3.45 diff in my Stag has a MG prefix(from a PI saloon). A fellow club member has a 4.4 Rover in his Stag and had to change the diff to a BMW because the Triumph diffs (changed several) couldn't handle the torque.
Cheers Ian A

[sujitroy]

I'm mentally preparing to have my diff rebuilt sometime. A fellow Triumph TR6 owner had his diff rebuilt for $1500 at a local British car specialist. (Ouch)
Mine is an auto and I will consider having my Stag one rebuilt with a 3.45 ratio wheel and pinion.
Thanks all.
Sujit

[stag8manod]

Hi Sujit, Do it,don't even think about it. The auto Stag should have left the factory with a 3.45 and is a major improvement second to a 4 speed.. I converted mine, but it's a manod. I was concerned it would overgear it but as my hoon days are just about over its fine.I kept the 3.7 complete so if I wasn't happy I could rechange and always a spare. I also changed the speedo drive to one from a 2.5 PI and the speedo is spot on at 100k and 2350 revs. I also used a rear diff cover from either a Mk1 saloon, or Estate as they are the same as the Stag with the right bolt pattern.
Cheers Ian A