1991 850i Automatic... What is the best Limited Slip and Rear End Ratios to use?

[execmalibu]

1991 850i Automatic... What is the best Limited Slip and Ratios to use?

I think that the 850i Auto already have a pretty short rear end ratio... (3:65) I want to accellerate out of the hole better if possible with an Auto.

I am used to my SL65 that accelerates effortlessly like a rocket-sled...

I read about an 750il large case LS and that you need to change the input shaft and rear cover...



Input?

[olinjohnston]

I told you (in your other thread asking this) that your upgrade diff will be the 3.91 LSD out of an E34 M5 since your existing one is a 3.64 open diff.

[execmalibu]

Sorry I missed that in the other post...

Is that the whole third member assembly? What is involved in the swap... DIY?
I am pretty tooled up and have experience with Vintage Porsche, Ferrari, Mercedes, BMW, and Vintage Bikes etc etc.....

I changed the rear end in my 2001 Viper.

[smc850ci]

your upgrade diff will be the 3.91 LSD out of an E34 M5 since your existing one is a 3.64 open diff.

That's what I did, and yes I had to change the input flange, rear cover, and the output flanges. It is REAL FUN now!

[olinjohnston]

I have a diff swap DIY in the stickies section that is applicable to all E31s. For mine, I also swapped the rear cover (which is how it mounts in an E31) and the input flange from my original one.

[Ahmed303]

I am still looking for that gray market 3.73:1

[Imndeep]

I am still looking for that gray market 3.73:1

That sounds like a better ratio to me too.

[m6bigdog]

I am still looking for that gray market 3.73:1

The 3.73:1 LSD is also a US 92-93, M5 diff ratio. Given the rareness of the M5 (1500 total import into US in 91-93) it may be a mute point

[Ahmed303]

The 3.73:1 LSD is also a US 92-93, M5 diff ratio. Given the rareness of the M5 (1500 total import into US in 91-93) it may be a mute point

I know. I need help from my euro brothers. Anyone?

[execmalibu]

Will an E32 3:91 Limited Slip work or only an E34 unit??

[olinjohnston]

Will an E32 3:91 Limited Slip work or only an E34 unit??

I wasn't aware that any E32 came with that ratio?

Basically, the diffs that will physically bolt on will be the 210mm "large case" units from a V8 or V12 E32, an E34 540i, or M5, and any E31...But the M5 one is the only one that will give you shorter gearing.

E31 850i - 3.64 (4-speed auto)
E31 850i - 2.65 (6-speed manual)
E31 850CSi - 2.93LS (6-speed of course)
E31 840Ci - 2.93 (M60 5-speed auto)
E31 840Ci - 2.81 (M62 5-speed auto)

E32 740i/iL - 2.93 (M60 5-speed auto)
E32 750iL - 3.15LS (88-91 4-speed auto)

E34 540i - 2.93 (M60 5-speed auto)
E34 540i - 2.81? (M60 6-speed manual)
E34 M5 - 3.91LS/3.73LS (changed 7/1991 to the 3.73 for NA) These will be your only "off the rack" upgrades going from a 3.64.

These are all US-spec figures. European models are often different. I just wanted to let you know what donor diffs are going to be for sale...

Of course if you can fit it in your budget, you can have any ratio made for you.

[02540ico]

I thought the large case was 210mm. Its 280mm?

[execmalibu]

Anyone have an E34 M5 Limited Slip with a 3:91 for sale?

How much are they worth?

[Ahmed303]

Depending on your luck and the condition of the unit, it can go from $500 ~ $1800 on ebay.

[smc850ci]

Anyone have an E34 M5 Limited Slip with a 3:91?

I do. Paid $500 on Craig's List a couple of years ago. Local guy, so no shipping.

[olinjohnston]

I thought the large case was 210mm. Its 280mm?

You are correct! Eek...(corrected my post)

Large case diffs are 210mm.

[rockytt]

I do. Paid $500 on Craig's List a couple of years ago. Local guy, so no shipping.

I think he meant "does anyone have one for sale?"

[execmalibu]

GOT ONE!!

One of my E9 parts sources had one... $500

Thanks...

[Ahmed303]

GOT ONE!!

One of my E9 parts sources had one... $500

Thanks...

Congrats! Happy for you and I am sure you will like it. Would it be too much to ask if you could check with your sources and see if you can find a 3:73:1 for me please? Thanks in advance.

[execmalibu]

I will ask...

- - - Updated - - -

I still can NOT upload photos?... "I shows drag your files here" and when I drag a jpg photo it seems to load but when I save there is still NO photo attached?? I am on a Mac?

[IcemanBHE]

Photobucket. [IMG] Tags. Paste. Boom.

[thelongeride]

In rebuilding an LSD such as a 3.15, could the gears from an open (non-lsd) 2.93 or any other gear set from a 210mm large case be used?

[TedBobo]

GOT ONE!! One of my E9 parts sources had one... $500

Thanks...

Gr8 price....mine migrated from Chicago, with shipping it was substantially more than $500. You'll be pleased with the upgrade.

[Ed Lyerly]

Euro M635's ('84-'86) had 3.73 LSD big case 210mm diffs. Also US Spec M6's ('87-'89) had 3.91 LSD. You will need to swap out your rear cover .... but these will also work. The US spec cars got the 3.91's to compensate for the 30 HP lost and 300 or so lbs that were added (diving board bumpers, steel door beams, catalytic converter, and rear A/C).