E36 328i rear differential

[WadiM3]

Hi my 328i sport with a 3.15lsd from a m3 gave up few days ago it was always whining ever since I bought it I got scammed as I payed for something in mint condition and perfectly working but turned out some polish/Romanian bloke ripped me off. From the day I bought it, it was whining but would lock up eventually got worse and worse with the noise then last Sunday I broke down about 30 miles from
home and the propshaft was spinning freely inside the diff and all fluids leaked and there was no recovery to tow me back as it was Sunday night and everyone didn't wanna do the job. I had the car pulled by another car and I guess it lost a bit of fluid from the lsd but anyway when the car was being towed it made horrible knocking noises and the rear seemed to be jumping had the car on the ramp and replaced the diff subframe bolts were snapped along with with the diff bolt. Replaced everything and put a 2.93 open diff. I was told a while ago by Chris Bmwdirtracer I could convert any open diff into lsd by just swapping in the lsd unit from the rear, I did some research and that's true for any lsd from 3.15 and above have one offset and 3.07 and down have another. I was wondering which ratio would suit my 328i I do a lot of top end driving and also want good acceleration.

also when putting the lsd unit into an open diff has anyone got any diagrams or guides or instructions as I couldn't find any? Also if I'm just putting the lsd unit in do I need new bearings and seals and crush washers and shims? Help please couldn't get any reply from
Chris



Thanks

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Oh also are the bearings connected to the lsd or to the flanges and pinion ?

[bmwdirtracer]

The vast majority of your driving will be at, say, speeds of less than ~140 mph. Any ratio you choose will get you to that speed, and probably pretty much to the same top speed, because that will be Power-limited, not rev-limited, I'd expect.

(Don't take that wrong; my M5 will also be power-limited, I'm sure....because mathematically, 7000 rpm in 6th would be ~210 mph. 7200 is 216..... and there's no damned way I believe my car will even get close to that speed.)

A lower ratio diff (which is a higher number) will improve acceleration.

(A 3.0 diff multiplies your torque by 3...... A 4.0 diff multiplies your torque by 4. (The gear involved at any moment multiplies that torque by some additional amount. but that's another story.)

Anyway, I'm not sure what's available in the UK, but the very early U.S. 325is E36 used a 3.9 diff, limited slip. Surely there's a similar ratio available in some BMW mid-size diff in England?

When swapping the LSD unit for the spider gear set, you'll need to properly shim the unit from side to side. This SHOULD be done the correct way, with ink-spots on the gears, etc.

I said that I have successfully done this many times, judging clearances by feel. Sheer luck? Good guess? I don't know, but I can tell you I don't recommend it to someone who hasn't spun and handled a hundred diffs....It is not a good risk, really.

I have seen two different THICKNESSES of ring gear, and had to create a spacer on one of the many diffs I've done, to make the thinner gear mate to the LSD unit which was expecting the thicker gear. (I created this spacer in the custom metal shop where I worked, using lathe and mill. )

Best to just buy a diff that already has LSD. Spending an hour at realoem might point you to UK market cars with LSD, stiff-ratio diffs.

[WadiM3]

I was thinking of getting a 3.91 from a 325i automatic and putting the lsd unit in but messing around with some speed calculators says my top speed will be 120 mph at 6500 rpm in 5th and 135 mph at 7200, many said doing a 3.91 pinion and crown swap to 3.91 practically turns your 5 speed into a 4 speed as your first gear becomes pretty much useless but hey there's people who talk out of their backside and I thought Mauim3 must of got his into an m3 for a reason. I was also looking at a 3.64 pinion and crown from an e46 large case m3 but don't know which suits me best. Some ratios I was cobsidering remember this is mt daily drive and I do a lot of motorway driving


2.93
3.15
3.23
3.38
3.46
3.64
3.79
3.91

Also are ring and crown wheels swappable from small case diffs?

[WadiM3]

Its my birthday on saturday and I thought I'd treat myself to a lsd rebuild. I've found someone to rebuild it, while at the rebuild I have a few options of how many percent of lock I want on acceleration and decleration, how many clutch packs , which ramp angle. Please somebody give me a very good combo / setup!

i will potentially upgrade to a 6sp from a e36/e46 m3 and if I can't source one I will stick in a 6sp box from a 330ci with custom brackets some time in the future

[bmwdirtracer]

You cannot swap internals between the three different sizes of BMW diffs.

MauiM3Mania has a six speed, and can use the much higher revs of an S50B32 Euro engine.

Many of the E24 and E28 cars had LSDs in 3.46 and 3.64 ratios These are medium diffs and should swap right into an E36 with just a cover swap. (because the E36 diff uses it's cover for mounting, as I recall)

It all comes down to what's important to you: top speed, or acceleration. When swapping diff ratios, you trade one for the other.

In the US, I 'd likely just pick up a used diff from the right car, for a couple hundred bucks, rather than pay the big money for a race rebuild, unless the car was being built for racing.

My 2 cents.....

[328 Power 04]

In my opinion 3.38 or 3.46 will be the best blend of acceleration and comfortable high speed. 3.23 would be best choice if doing 75-80mph often.
I have a 3.64 torsen limited slip in my Z3M, and it's very annoying on any longer drives. I can't imagine a 3.91 on a daily car.

[shadowpuck]

I have to ask - it's a street car right? Why do you care about top speed unless you are at the track?

I've had experience with a variety of ratios in an e36. 3.91 is great on track but annoying on the street.
3.46 is the ratio to have but that means a custom diff.

[WadiM3]

I very often go to Scotland from and the a74m is the straightest piece of road god has ever let man made and it's so empty and I often find my self at full tilt. Finding an LSD is so rare now in the uk and the only ones we usually see are 2.93 3.15 or a large 2.93 and they go for about £600 now a days second hand meaning clutches most likely worn and it's a blind. It like my first lsd as they all take them out of the car before sale.. so I bought a low mileage 3.15 open diff with all the hopes of swapping the carriers around lol but as you guys scaring me with the shim business I might pay someone 500 to do the rebuild

[shadowpuck]

my opinion:
1) it's a street car, talking about top speed on a diff/gearing is useless and a waste of time. we (you and i) have had that conversation more than once.
2) $500 for a rebuild sounds way too cheap to me based on what diffsonline and other pros charge.

[WadiM3]

No 500£ for new seals, bearings and clutch friction plates and dog collars. If I want a custom ratio it would be an extra £150-200. How many percent of lock do I need or want and what ramp angles ?? I thought for a split second to get a 3.91 as its the poor mans supercharger lol but that means I would defo need 6th gear and also a top speed of 148mph at 6th. And 131 at 5th at 6500 rpm

[WadiM3]

Oh how noticeable is the 3.91 in acceleration. Like would I feel it or can I accelerate with some m3's for a few seconds lol ?

[WadiM3]

So if I get a doner open diff 3.15 and swap my carrier with the lsd and put everything back together exactly how it was wouldn't work ?

[bmwdirtracer]

It would be sheer luck, if the spacing was correct. There are dozens of different shim thicknesses for adjustment.

[WadiM3]

I mean I just want to basically swap a carrier and as far as I know the shims are by the output flange and I wouldn't mess with them I'll put them back the same way they where ?

[bmwdirtracer]

No. The center sections vary slightly , and need to be accurately spaced with shims.

[MauiM3Mania]

As powered, your car can't be both quick sprinter and high speed demon. Take your pick, I'd suggest go for the sprinter as high speed is going to either end your existence or your possession of a drivers license.

My 99 M3 has a 3.91 LSD, which is out of a 92 325i with the winter package as I recall. I can get half way through an intersection and it's time to shift into second unless I'm going to draw attention by getting the engine into the 4-5k range. As Chris mentioned, I have a six speed so my highway rpm/mph is about the same as the stock 3.23 with the five speed. And I don't have roadways suitable for anything remotely resembling high speeds and this is not my daily driver.

Check off a few boxes here. http://diffsonline.com/bmw-e36-m3-32...l#.WZE65VGGPDc The one I want would be about $4500. :-)

Consider a 2.93 diff and a turbo. Go read up in the Forced Induction sub-forum for details.

[WadiM3]

This is my favourite sub forum! I to often take a peek into the selling one and the forced induction but it's anal sex for me as I have the steering rack in the way so really hard to turbo!