4.10 How can I tell by Teeth or Rotation?

[GT BMW E30]

I am looking for the thread or post explaining how to count the teeth and rotation to tell if you have a 4.10 diff or not. Diff has surface rust on top and bottom. No stamp, no tag. Car comes with a 4.10. I want to confirm it.

[LJ851]

4.10 is the ratio. If lsd, measure how many rotations of the input it takes to turn the outputs 1 rev.

If non lsd (open), hold one output stationary and measure how many rotations of the input it takes to turn the other output 1 rev.

[Wanganstyle]

Pull cover if its out.

The ring gear of a 188mm 4,10 ratio gearset is stamped "h21"


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[GT BMW E30]

great. going to check now.

[cabriodster87]

Count the teeth on the ring gear and pinion then divide. Example 45/11= 4.09