I'm trying to determine the gear ratio on my R180. There is a number on the ring gear of ?? x 394

Does this mean 3.94:1 ? 

Should I just see how many turns of the differential input is required to make a full revolution of the ring gear?

Can anyone assist in decoding this?

Jeff

Unless you got the differential from Japan (or someone modified it), I doubt you have a 3.9 rear end.

Reference: https://www.zhome.com/ZCMnL/tech/GearRatios.html

Edited November 21, 20232 yr by SteveJ

If the numbers don't make sense then counting turns is pretty fool proof

11 minutes ago, Patcon said:

If the numbers don't make sense then counting turns is pretty fool proof

Or just count the teeth......

All the ring gears I've seen have the two tooth counts with a : between them stamped into that crown gear, like 39:10 which would be 3.9 to 1 ratio. Keep looking. 

Edited November 21, 20232 yr by zKars

just zoom in on your picture, 37:11, right there to the left of the 3 9 4 stuff. 

Standard US S30 R180 ratio for the 240 years, 3.36 to 1

I should be on CSI Calgary

Edited November 21, 20232 yr by zKars

 I'd mark a ring gear tooth and the input flange. Then count the number of flange turns it takes to turn the ring gear one full turn.

I think zKars is right. It's hard to say where the differential came from because the R180 was switched out with an R200 in the early 1980's but some time after that, it must of got switched back to an R180.

Edited November 22, 20232 yr by Jeff Berk