Differential Question

[Moto-Mucci]

I've been told that when the rear end is in the air and you spin one wheel - the wheels will spin opposite directions when you have a LSD, and the same direction when it's an open diff.

Is this true or is it the opposite way around?

I had my rear up the other day and my wheels both spin the same direction when spinning one. Is it possible for this to happen with a LSD?

The tag on the diff is illegible - all rusted up.

[Jean]

Other way. You might have a big "S" in white stamped on the diff case itself as well as the tag.

[TooTall90]

wheels spinning same way = LSD

[Moto-Mucci]

good to know, thanks.

Also, is there another way besides the tag to tell which LSD I have? The PO replaced a bunch of things so I'm wondering if its the stock one.

[Adrian_Visser]

Well the vin will tell you every option the car left the factory with but the list stops there.

[Dozyproductions]

push one wheel. see how many times the other one spins to every one full rotation to the one you're pushing. That can give you a rough estimate.... I think ;)

[SamE30e]

good to know, thanks.

Also, is there another way besides the tag to tell which LSD I have? The PO replaced a bunch of things so I'm wondering if its the stock one.

There is the easy way...

Step by Step instructions by Sam

1. Goto a empty straight road
2. Look around for police
3. Stop vehicle
4. Depress the clutch pedal
5. Select first gear
6. Bring the engine speed to 5000rpm
7. Rapidly release the clutch pedal while simultaniously going WOT and hold for 2 Mississippi's, (The vehicle will lunge forward at a fast rate (Unless you're driving a 318i or ETA)
8. Stop vehicle
9. Get out of vehicle
10. If there are 2 rubber marks you have a LSD, if only 1, you have a Open diff or a POSLSD.

Sam

[rThor432]

^^I think he was asking how to tell which LSD ratio he has...

Also, is there another way besides the tag to tell which LSD I have? The PO replaced a bunch of things so I'm wondering if its the stock one.

Mark the tire/tires. Rotate the driveshaft and count the number of rotations of the driveshaft for one full rotation of a the tire/tires that are rotating.

Driveshaft rotations/rotation of tire=diff ratio.

Ex-- driveshaft/input flange/pinion rotate 3.46 times and the tire rotates once. The ratio is 3.46:1.

push one wheel. see how many times the other one spins to every one full rotation to the one you're pushing. That can give you a rough estimate.... I think

Haha no...

[Wh33lhop]

There is the easy way...

Step by Step instructions by Sam

1. Goto a empty straight road
2. Look around for police
3. Stop vehicle
4. Depress the clutch pedal
5. Select first gear
6. Bring the engine speed to 5000rpm
7. Rapidly release the clutch pedal while simultaniously going WOT and hold for 2 Mississippi's, (The vehicle will lunge forward at a fast rate (Unless you're driving a 318i or ETA)
8. Stop vehicle
9. Get out of vehicle
10. If there are 2 rubber marks you have a LSD, if only 1, you have a Open diff or a POSLSD.

Sam

I have left two marks plenty a time with an open diff.

As far as the ratio, there should be a little metal tag held on by one of the diff cover bolts. If it's still there (no one has gotten rid of it) it'll say something like "S3.73" if you clean it off. If there's an S, it's a regular (clutch pack) LSD, V denotes a viscous LSD (for the ix) and no letter means it's open; obviously the number is the final drive ratio.

If you don't have a tag or you want to double check it, do the wheel spinning trick. Same way = LSD, opposite way = open. Then, check what sort of revs you're turning over on the highway (this is assuming you've got a G260, so 325e or i, 5 speed). If you're at about 3300rpm at 80mph then you're 3.73. If you're at 3600ish, then you're 4.10. If you're at 2600 then you're 2.93. But you should probably have the 3.73 if you're a 325i or is, 2.93 (or 2.73) if you're an eta and 4.10 if you're a 318i.

If you've got a G240 (318i) the 5th gear will be a tiny bit shorter (.83 instead of .81) and revs will be a bit higher. But then you've probably got a 4.10 anyway. If you're auto, I don't know the ratios off the top of my head so I can't help ya.

[SamE30e]

I have left two marks plenty a time with an open diff.

As far as the ratio, there should be a little metal tag held on by one of the diff cover bolts. If it's still there (no one has gotten rid of it) it'll say something like "S3.73" if you clean it off. If there's an S, it's a regular (clutch pack) LSD, V denotes a viscous LSD (for the ix) and no letter means it's open; obviously the number is the final drive ratio.

If you don't have a tag or you want to double check it, do the wheel spinning trick. Same way = LSD, opposite way = open. Then, check what sort of revs you're turning over on the highway (this is assuming you've got a G260, so 325e or i, 5 speed). If you're at about 3300rpm at 80mph then you're 3.73. If you're at 3600ish, then you're 4.10. If you're at 2600 then you're 2.93. But you should probably have the 3.73 if you're a 325i or is, 2.93 (or 2.73) if you're an eta and 4.10 if you're a 318i.

If you've got a G240 (318i) the 5th gear will be a tiny bit shorter (.83 instead of .81) and revs will be a bit higher. But then you've probably got a 4.10 anyway. If you're auto, I don't know the ratios off the top of my head so I can't help ya.

Thats in like the most ideal conditions. On dry pavement it will most likely spin 1 wheel if it's open.

[Wh33lhop]

Thats in like the most ideal conditions. On dry pavement it will most likely spin 1 wheel if it's open.

If you're on flat pavement going straight it'll generally spin both for at least a few feet. I didn't do a lot of tire spinning before I got my LSD (none actually) but in my last car I've finished off a set of tires with an open diff, and I've seen plenty of open diff launches that spin 'em both.

All I'm saying, if both tires spin, doesn't mean it's an LSD. Jacking up the car and turning one wheel is a better indication, although admittedly not as fun. :p

[b*saint]

^^I think he was asking how to tell which LSD ratio he has...
Mark the tire/tires. Rotate the driveshaft and count the number of rotations of the driveshaft for one full rotation of a the tire/tires that are rotating.

Driveshaft rotations/rotation of tire=diff ratio.

Ex-- driveshaft/input flange/pinion rotate 3.46 times and the tire rotates once. The ratio is 3.46:1.



Haha no...

How do you know its rotated 3.46 times. Do I have to bust out trig to figure it out? I dont think you can tell the difference between 3.46 and 3.73.

[Wh33lhop]

You can't tell the difference between three and a half and three and 3/4?

I would just read the tag, or do the highway rev trick.

[yberther]

The tag on the diff is illegible - all rusted up.

Let us know what you figure out.

[Wh33lhop]

Let us know what you figure out.

Haha, I didn't even see that.

Still, the easiest solution is just to get on the highway and check the rev counter in 5th.