I need to calibrate my ETB speedo and ETB can tell me the right numbers to set if I can tell them my diff ratio and wheel/tyre size.

Diff came straight from my 89 Sierra 2.0L saphire with a carb'd pinto engine. Any idea what the diff ratio is likely to be or how I can identify it?

Cheers
Nick

Hold one wheel stationary and turn the other 1 full turn. Count the number of times the input flange turns and thats will be the ratio of your diff. Easier said than done though.

Or get the code letter from the ID tage attached to the diff.

My guess is that it will be a 3.62 or 3.92

Have you looked at ETB`s website?
www.etbinstruments.com
Go to the technical help section and then FAQ`s. Item No.5 tells you about performing the `cardboard disc test`. Very easy and very accurate. They never asked me for my diff ratio, I just gave them the test results and how far out my speedo was after it failed at the SVA, together with my tyre size. They recalibrated on that and 2nd time at SVA passed.
Nick

Mr F Monkey, shouldn't that be 2 full turns....??
Like you said, easier said than done - popping the back off & reading the writing on the crownwheel is much more reliable.
Bob

According to the Sierra's VIN plate I have a "U" diff which is 3.38 - seems strange to me?

I guess I'll have to get under my boot tray and see if I can get it off the diff tag

Nick,

My '86 2.0gl had a 3.38 in it, the tags can't be relied on to be correct,.

If it's a 3.38 whip it out and flog it and pop in a 3.62 or 3.92 will make it a lot livlier to drive and should get a few quid out of it

Ned.