How to designate what diff I have?

[sharky]

OK well the 3:25 is going in with the S52 but the one coming out I bought with the car. The car had a little work done to it when bought so I would venture to guess maybe he swapped diffs at some point. It was a 87 325is manual. Are there any #'s on the casing to tell me what ratio it is. It has a S stamp so I know its LSD but is there anything else because I need to sell it and find out what ratio.

[MikeK]

its most likely a 3.73 LSD

[FredK]

If it wasn't broken off and the rear cover hasn't been touched, there is a metal tag on the upper right bolt that has the diff ratio stamped into it.

It should be a S3.73 stock, but it may have been upgraded to a S4.10.

EDIT: Thanks for stealing my thunder Mike.

[thedeal]

there is a metal tag attached to one of the bolts. It probably has a bit of rust on it. Take it off and hit it w/ some simple green and scotchbrite. should say something like S3,73 followed by some other numbers and letters. the 3,73 means your ratio is 3.73.

EDIT: Thanks for stealing my thunder FredK

[sharky]

Ah ha, that's what that tag was, everyones thunder was appreciated, will take a look when I get home

[Ben Carufel]

You don't need Simple Green and a Scotchbrite pad to clean the tag. Scrape it with something (chisel, large flatblade) and the numbers will be easy to read.

Much quicker and easier.

[E30 Wagen]

there is a metal tag attached to one of the bolts. It probably has a bit of rust on it. Take it off and hit it w/ some simple green and scotchbrite. should say something like S3,73 followed by some other numbers and letters. the 3,73 means your ratio is 3.73.

EDIT: Thanks for stealing my thunder FredK

I sometimes forget that they switch the commas and periods in Europe. So confusing...

However, let's say the tag is present but it is so rusted that there are no numbers left? Is there any other way to distinguish, other than disassembling the diff?

[thedeal]

I sometimes forget that they switch the commas and periods in Europe. So confusing...

However, let's say the tag is present but it is so rusted that there are no numbers left? Is there any other way to distinguish, other than disassembling the diff?

You could count the number of revolutions of the drive shaft compared to one revolution of the drive axle....