Which Rear Diff?
Moderators: GRNSHRK, ron, bfons
- randall977
- Posts: 264
- Joined: Sun Jan 21, 2018 9:52 am
- Location: Oxford, UK
- Contact:
Which Rear Diff?
I'm trying to confirm which rear diff I have on my late '82 635 which has a Getrag 265/5 CR. None of the numbers I've found seem to tie in with the ETK numbers etc. It has the numbers 33.11-1207 984 (on the Aluminium casting) and 1.208 001 F(?) on the main case. The tag has S3### but the rest has gone.
Last edited by randall977 on Sun Feb 25, 2018 9:31 pm, edited 1 time in total.
-
- Platinum Member
- Posts: 1649
- Joined: Mon Jul 16, 2007 2:58 pm
- Location: Cheltenham, U.K.
Re: Which Rear Diff?
Should be 3.07 lsd, centre mount medium case.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
-
- Platinum Member
- Posts: 1649
- Joined: Mon Jul 16, 2007 2:58 pm
- Location: Cheltenham, U.K.
Re: Which Rear Diff?
There would have been a metal tag attached to a rear cover bolt back in the day with key details on it.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
- randall977
- Posts: 264
- Joined: Sun Jan 21, 2018 9:52 am
- Location: Oxford, UK
- Contact:
Re: Which Rear Diff?
Thanks for the reply, the tag has S3 but the rest has gone... I don't really want to open it up as it's not leaking, the oil is clean and it feels okay - should I look inside for any reason while it's out? I'm going to put new oil in, clean it up, repaint etc.
Re: Which Rear Diff?
it would normally be a LSD if originally paired with a 265/5 gearbox. This means you need to use a special LSD oil. It also means (especially given the sate of your gearbox) that it has likely seen a hard life and there is a fair chance that the LSD mechanism is worn and needs a rebuild. IIRC there is a test (detailed in the workshop manual?) you can do to see if the preload is correct or not.
cheers
cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Ralph in Socal
- Platinum Member
- Posts: 2746
- Joined: Tue Apr 14, 2009 3:32 am
- Location: High Desert of SoCal
Re: Which Rear Diff?
The torque required to break one output from the other side should be 25 ft. lbs for a healthy diff. Secure one side and find out how much torque is required to turn it separately from the other side
To determine Gear Ratio (yours ahould be 3.07 as mentioned), count how many revolutions it takes for the input to turn the output one complete turn. Very easy to do when it’s out like that.
Ralph
To determine Gear Ratio (yours ahould be 3.07 as mentioned), count how many revolutions it takes for the input to turn the output one complete turn. Very easy to do when it’s out like that.
Ralph
There is a very fine line between "Hobby" and Mental Illness.
85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
85 635csi Zinno Auto
84 528i Euro
83 635 Euro Arktik
81 528i Kastanien 5-speed
88 528e Bronzit (Granpa Car)
86 535i Auto (For Sale)
81 633 csi (retired)
- randall977
- Posts: 264
- Joined: Sun Jan 21, 2018 9:52 am
- Location: Oxford, UK
- Contact:
Re: Which Rear Diff?
Such a great forum - thanks!
Well it is 3.07. It takes around 45 ft. lbs to break one side from the other. Is 25 right? - that's not much force.
If it should be 25 ft. lbs, what does it mean if mine takes 45 ft. lbs to start slipping?
Well it is 3.07. It takes around 45 ft. lbs to break one side from the other. Is 25 right? - that's not much force.
If it should be 25 ft. lbs, what does it mean if mine takes 45 ft. lbs to start slipping?
- hornhospital
- Platinum Member
- Posts: 2931
- Joined: Sun Jul 11, 2010 6:46 pm
- Location: Silverhill, AL
- Contact:
Re: Which Rear Diff?
It may mean you have a rebuilt/upgraded diff with 40% limited slip instead of the factory normal 25%. Not a bad thing!
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
-
- Platinum Member
- Posts: 1649
- Joined: Mon Jul 16, 2007 2:58 pm
- Location: Cheltenham, U.K.
Re: Which Rear Diff?
That's cool, the "S" is the bit that confirms it's an LSD (I know you've worked this out already!), and it's quite normal for none of the tag to be legible or for it to be missing altogether.randall977 wrote: ↑Sun Feb 25, 2018 9:45 pm Thanks for the reply, the tag has S3 but the rest has gone... I don't really want to open it up as it's not leaking, the oil is clean and it feels okay - should I look inside for any reason while it's out? I'm going to put new oil in, clean it up, repaint etc.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
- randall977
- Posts: 264
- Joined: Sun Jan 21, 2018 9:52 am
- Location: Oxford, UK
- Contact:
Re: Which Rear Diff?
Just did another test - about 50ft.lbs is needed to slip. I'm amazed to find something that works - good news!