Need to confirm the diff ratio of my Sierra diff that I have fitted to my Locost but the tag is missing from the casing. I think that the diff is a 3.32 or a 3.38. Is there anyway of finding the ratio with out taking the rear cover of the diff.

Turn the output shafts together through 1 complete revolution. The number of times the input shaft rotates is the ratio.

Sierra diffs come in 3.14, 3.38, 3.62 and 3.91 ratios. The above method will easily distinguish between these.

Doh! Thank you Matt, I dont know why I didnt think of that myself.