Checking which diff is fitted

[Forkie]

I must be your worst customer !!!! So further to the 'front brakes' post, and the ' carb rebuild' post - as i am still chasing faults - during the latter it was suggested i check what diff is fitted to my Auto 2500S - although i know what should be fitted !!!!
So i set aside this evening for some more poking around, tests etc, first of which was checking the diff ratio by what was suggested ; 3 and 1/2 turns of the prop should equal one full turn of the rear wheel. Here is what we did and what we got ;
Jacked up N/S rear. I chose to mark with tippex on the gearbox end - easier to see - so a mark on the shaft, and a mark on the tail housing. Made a point of marking when one section of the U/J was facing directly downwards , just so i could keep track of quarters, halves three quarters. Tippex marked the tyre, on the outside, relevant to a brick directly underneath it, after taking up the slack, to make it easier - so i am watching the prop whilst the lad is turning the road wheel. We did this three times.
One complete revolution of the roadwheel, mark to mark, gives 1 and 3/4 turns of the prop - so i read that as being halve of what it should be. What are we doing wrong.....

[Forkie]

Just a thought - we had one wheel off the ground, one wheel on the ground - and we have albut half the turns - should both wheels of been off the ground? What difference?

[johnnydog]

Because the Triumphs have a 'open' diff (the wheels turn in opposite directions with both wheels off the ground) as opposed to a fixed or 'limited slip diff (where both wheels turn in the same direction), the road wheel should be turned two full revolutions to do the diff ratio check.
I think you already figured that out with your second post! It seems like you do have the correct diff (1.75 x 2 = 3.5 (near as damn it to 3.45 !).
Maybe the info on how to check it was a bit misleading, but at least you have got the correct result!

[Forkie]

Yes, it was !!!!! Took me an hour or so of thinking ' why am i only getting half of the prop turns to one full wheel rotation' !!!!! And yes it is nice to confirm i do indeed have my correct diff in place. Back to the brakes it is then !!!