Differential, Ratios, and Tags

[aaron_silva]

Here is a picture of the "tag" that is on a differential.


The numbers at the begining tell you what the ratio is. For example, a diff that starts off with 4,27 #### would be a 4.27.

When the tag starts off with a "S", then it is a limited slip unit. For example, S 3,73 #### would be a 3.73 LSD.

Aaron

-any more quality info would be appreciated.

[randomtask37]

it wont always be on that one bolt. it could have gotten switched around over time. wherever its placed it will be on the cover off the diff if its still attached.

[aaron_silva]

I've always wondered what this "tag" looked like

A ton of people have been asking about it so I thought it would help. :roll:

Aaron

[Jand3rson]

The tags on mine have always been on the bottom of the diff.

[randomtask37]

also if u ever get the diff out of the car it will also be branded on one side saying what kind it is.

[ACS325ic]

Decoding the Diff's Dogtag

The differential's "dogtag" is located on the right side by the speedometer pulse sender on a large diff, and on the top left by the diff mount on a small differential from the factory.
The "dogtag" is an aluminum strip with numbers and perhaps letters imprinted on it. It's approximately 2"x.5" in size.
It'll be held on to the differential by one of the cover's bolts.
In the case of a BMW Replacement differential, the "dogtag" reads differently. It will have four numbers and then an A followed by the manufacturing code numbers and perhaps the Limited Slip indicator.
Example 1141A405S would be a 41 ring teeth divided by 11pinion teeth which decodes as a 3.73 ratio. The S at the END of the code in the Replacement codes means it's a Limited Slip unit. So BMW Replacement code 1141A405S means it's a Limited Slip 3.73 ratio.
So for Factory Replacement differentials, you divide the 2nd set of numbers by the first set to find your ratio. Replacement Diff's have an A in the middle of their code, and will have the S for Limited Slip as a SUFFIX not a Prefix as the regular Diff's code reads. Limited Slip Differentials also will have a large stenciled S painted on the top of the differential's case.
If there is no "dogtag" for which to read and the diff is out, the only BMW Approved method is to remove the cover and count the ring and pinion teeth on the gears and divide as before explained to find your ratio.

[finch]

also if u ever get the diff out of the car it will also be branded on one side saying what kind it is.

can you read this with out removing the diff..?
cos i cant find the dogtag...

[finch]

also if u ever get the diff out of the car it will also be branded on one side saying what kind it is.

can you read this with out removing the diff..?
cos i cant find the dogtag...

[mikeedler]

and for a bit of extra info, a big V will be on the top, and a V will be on the tag for a visco sperre diff.

[slowman]

can you read this with out removing the diff..?
cos i cant find the dogtag...

There are three ways to find out if you have a LS or not...

1. Jack the car up in the air and get both back tires up in the air. Leave it in neutral with the parking brake off. Now turn one of the back tires. If the other tire turns the same way, you have a LS. If it turns the opposite way, you have an open diff.

2. Again, jack the car up in the air, but get only one back tire off the ground. Try to turn it. If it doesn't turn, you have a LS. If it does turn, you have an open diff.

3. Do a burnout... one black strip generally means you have a gay open diff (unless you manage to launch it perfectly straight, with both tires having the same amount of grip). Two nice black strips means a LS.

[imsotyerred]

Can someone explain the ratios on the differential, for example, i picked up a 293S for my 325e, but i keep seeing 410 and 373 and the like floating around the boards...

[E30 Wagen]

Which differential rations are best for things like off the line quickness, or top speed?

[erik325i]

Which differential rations are best for things like off the line quickness, or top speed?

A lower gear ratio (higher numerical #) will help accelleration. (4.10 LSD)

A taller gear ratio (lower numerical #) will give you a higher theoretical top speed. (2.93 LSD)