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Diff Ratios / LSD
Posted: Thu Oct 18, 2007 1:43 pm
by Trento
Goodafternoon could some of you help me with some advise on the following please.
My 318IS has a noisy Diff, I beleive its a 4.10
1) how do I tell by looking at it if its a LSD or not
2) If is a open diff 4.10 and i change it for a open diff 4.27 do i have to do anything or change anything to the speedo reading etc.
3) I am told a 3.91 LSD from a 325i would fit but I would have to change the drive shafts. Is that all I would have to change and again would it effect the speedo reading.
Thanks guys
Posted: Thu Oct 18, 2007 1:53 pm
by StuBeeDoo
You don't have to change the driveshafts. What you do have to do is drop the exhaust and heatshield(s) and undo the big nut by the prop centre bearing to allow the prop to slide forward.
You don't have to correct the speedo reading as it's taken from the RH driveshaft.
There should be a tag attached to one of the rear cover bolts. If the diff is a slipper, the first character punched into the tag will be an S. You may be lucky and have one of the tags that actually has the ratio stamped in. If not, the next part of the identification will be 2 digits - this is the number of crown wheel teeth. They will be followed by another 2 digits - the pinion teeth. Divide the first number by the second and you'll have the ratio.
The rest if the digits on the tag will be the date code for when the diff was first assembled.
Jack the rear of the car, let the handbrake off, then spin one wheel. If the wheel the other side turns the same way, the diff is a slipper (or the diff's been welded!!). If the opposite wheel goes the other way, it's an open diff.
HTH
Stuart.
Re: Diff Ratios / LSD
Posted: Thu Oct 18, 2007 1:54 pm
by Ziggy
Trento wrote:Goodafternoon could some of you help me with some advise on the following please.
My 318IS has a noisy Diff, I beleive its a 4.10
1) how do I tell by looking at it if its a LSD or not
2) If is a open diff 4.10 and i change it for a open diff 4.27 do i have to do anything or change anything to the speedo reading etc.
3) I am told a 3.91 LSD from a 325i would fit but I would have to change the drive shafts. Is that all I would have to change and again would it effect the speedo reading.
Thanks guys
1) look at the tag - if the first character's an 'S' then it's an LSD.
2) Nope.
3) AFAIK, you don't even have to change the driveshafts, but don't hold me to that. Just need to adjust the prop slightly, no change to the speedo.
Re: Diff Ratios / LSD
Posted: Thu Oct 18, 2007 4:43 pm
by Trento
Thanks for this info guys