I’ll be damned if I know how all you Bimmer guys keep all the iterations of them straight, unless you all have one huge cheatsheet. I have a ‘16 328i, and all I know is that it’s an E-something.......I think.
The limited slip differential in Rennie’s hand looks decidedly different—mostly because of the clutch pack—than the one inside our old differential.
Cleaned and remounted in the rear subframe, our limited slip differential now has a Powerflex mounting bushing installed.
As you probably know, a limited slip differential causes both rear wheels to power a car out of a corner, as opposed to an ‘open’ differential that just lets the wheel with the least resistance (inside wheel) try and do the work of pushing the car out of a corner. And as you must know, an open differential is not what you want in a performance car.
One of the options available in `91 (and `91 only) for the E30 318is is a factory limited slip differential. As we stated a few updates ago, ours sadly wasn’t ordered with it. If we wanted to ruffle the feathers of an E30 M3 we would need to find one, make sure it was in good condition and then install it in place of our open differential. Easy, right?
Unfortunately, the 318is uses what is called ‘the small-case differential’ and it cannot be easily switched with a larger case differential from any of the six-cylinder E30 BMWs. Bummer. So, we would need to find a unicorn: a small-case limited slip differential from another `91 318is or—even rarer—a 318 sedan in either E30 or E36 variety.
Thankfully our friend Al Taylor, from Al Taylor Sports Cars, had the differential we needed and sold it to us for the gift price of only $400. Retail price on this differential is probably more than twice that figure, especially as these cars get older, rarer and more valuable.
With our prized possession in hand, our buddy Rennie Bryant of Redline Performance then came to the shop to show us how to check and re-shim one of these differentials. While Rennie was disassembling the differential, he discovered that it had already been rebuilt. Score! He quickly put it back together and we installed it in our 318is rear subframe that we still had laying out on the bench. We used the Powerflex rear differential mount, as it is stronger, less likely to tear out and keeps the differential more stationary in hard cornering.
I’ll be damned if I know how all you Bimmer guys keep all the iterations of them straight, unless you all have one huge cheatsheet. I have a ‘16 328i, and all I know is that it’s an E-something.......I think.
Almost forgot, does anyone out there have experience with the Powerflex bushings? I’m considering them for my ‘90 Z TT, and I like the fact that they have several different durometer products available so I don’t have to live with the harsh Racer Boy units on the street.
What's not easy about swapping a six-cyl limited-slip diff? The Typ 188 "medium case" bolts right in, just needs a different rear cover. Those covers are still available, brand-new, from BMW last time I checked. You can find a wide variety of ratios in many E28, later E24 & E23, most E30. I'm told a few E30 iX were equipped with the viscous-type, and there are a few Z3 fitted with torsen types. I'm running an '00 Z3 diff in my E24 right now (well, not as I'm typing this).
Why swap in a larger, heavier diff when your power level doesn't require it?
300zxfreak said:I’ll be damned if I know how all you Bimmer guys keep all the iterations of them straight, unless you all have one huge cheatsheet. I have a ‘16 328i, and all I know is that it’s an E-something.......I think.
F30, they moved onto the F designation about 11 years ago. In case your curious....
https://store.activeautowerke.com/pages/bmw-chassis-codes-chart
In reply to z31maniac :
Is this car going to be used in parades? My guess is no...and the 'small' differential is a common point of failure on these lovely cars. Mine had had two replacements, and it's never seen a track. Other advantages of the 188mm are the large availability of ratios and a far larger selection of good used units. Furthermore, the weight penalty is very small, I believe it's twenty pounds?
There is a reason the M3 had a medium case diff. If you are making more power/torque than the M3, you need to upgrade to the medium case. Its a bolt in. In my ITA E30, I used a complete 318 rear subframe/axles/brakes with a medium case diff.
DesktopDave said:What's not easy about swapping a six-cyl limited-slip diff? The Typ 188 "medium case" bolts right in, just needs a different rear cover. Those covers are still available, brand-new, from BMW last time I checked. You can find a wide variety of ratios in many E28, later E24 & E23, most E30. I'm told a few E30 iX were equipped with the viscous-type, and there are a few Z3 fitted with torsen types. I'm running an '00 Z3 diff in my E24 right now (well, not as I'm typing this).
All iX cars had a viscous type differential as far as I know (I've owned three of them). They were only available in the US with 3.91 gears; realOEM shows there were a couple different lower numerically gear ratios available for euro iX cars, but I doubt any of them are still available.
There was also a "large case" differential used in some 5-, 6- and 7-series cars but I don't know if they can be fitted into a 3-series car.
It’s simple if you swap the rear subframe from a 6 cylinder car. I see no upside to going to the trouble of adding limited slip to the small diff. It’s like putting a viscous limited slip into a NA Miata.
Tim Suddard said:Unfortunately, the 318is uses what is called ‘the small-case differential’ and it cannot be easily switched with a larger case differential from any of the six-cylinder E30 BMWs.
huh? My 318 originally had a small case, and I have two small case diffs (3.91 original to my car and 4.10 from a '91 318is) and two medium-case (325i) diffs (3.73 and 4.10). They are all a direct swap with no modifications of any sort- all flanges bolt up directly, all mounting points bolt up directly. Just loosen the driveshaft slip-joint collar to make it the correct length since the input flange is a few mm different.
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