I acquired a differential unit from a R-Ltd some years ago which has (according to my research) a ratio of 4.3:1. Ideally I need a 3.9:1 ratio diff. Before I dispose and re-purchase, is there any way of physically checking the ratio? Many thanks, in anticipation.
Ken Stanbury. Northamptonshire Area
Its easy if you have access to a lift or can get the back wheels off the ground. Or easier still if the diff is sitting in front of you.
Put a chalk mark on each wheel (or drive coupling), on the inside where it can be seen from near the diff and next to a convenient reference mark on the body (or diff), and also on the propshaft and a reference mark on the diff.
Rotate the propshaft (car out of gear of course) and count how many and a bit turns it needs to make both wheels rotate together just exactly once. That is the ratio.
Or, if you jack up just one wheel, then it is how many propshaft turns to make the one wheel rotate twice.
If you are really enthusiastic and want ultimate accuracy, keep on turning the propshaft until its marker meets its reference at the same time as the wheel markers meet theirs, while counting both wheel turns and prop turns, and do the sum.
It is usually easier to turn the propshaft and count that for one wheel turn, rather than try to watch and count the propshaft while turning the wheel(s). I first did this years ago when I ended up with a bitsa car and tried to find out what speedo drive it needed.
Thanks Richard, but might it be a tad difficult to distinguish between 3.9, 4.1 and 4.3? However, if I multiply it all up by, say, 10 times, then hopefully I will ensure some accuracy. I’ll give it a go. Thanks again.