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 …
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.
DesktopDave said: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?
IDK I certainly wouldn't call it a "common" point of failure. My 1985 small-case LSD was original to the car and to my knowledge never opened when i got the car back in about 2011. Then I ran about 5-6 seasons of rallycross/rally with it and eventually toasted the plates (but replaced them). We usually use the 188's because of ratio availability, but the 3.91 and 4.10 were avialable in e30 small-case diffs, which are nice ratios for certain uses.
Having just moved all of my diffs across the garage today, I'd be really suprised if the difference is as much as 20lbs. Either way, a few lbs extra low in the car aligned with the rear axles is pretty much the best possible place to add weight I'd say.
Tim Suddard said: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.
twitch
chuckbaader said: There is a reason the M3 had a medium case diff.
..It was a Group A homologation special, back when "homologation" meant they had to make/sell a couple thousand street versions and the competition cars could not deviate significantly from that. If they felt that they needed the larger rear to win, they needed to put it in the homologation model.
If they were messing with final drive ratios (can't remember if it was an allowed varaiance or not), that very much will enjoy a larger rearend, because the only way to make a shorter gear (lower gear/higher ratio, however you call it) with a fixed diameter ring gear is to have a smaller pinion gear. When geometry is fixed like that, the pinion can get so small that things get weak fast. So I guess the question may not be if you plan on making M3 power, but if you plan on making competition M3 power (250-300+hp) and running 4.75:1 (example) gears?
irish44j said:DesktopDave said: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?
IDK I certainly wouldn't call it a "common" point of failure. My 1985 small-case LSD was original to the car and to my knowledge never opened when i got the car back in about 2011. Then I ran about 5-6 seasons of rallycross/rally with it and eventually toasted the plates (but replaced them). We usually use the 188's because of ratio availability, but the 3.91 and 4.10 were avialable in e30 small-case diffs, which are nice ratios for certain uses.
Having just moved all of my diffs across the garage today, I'd be really suprised if the difference is as much as 20lbs. Either way, a few lbs extra low in the car aligned with the rear axles is pretty much the best possible place to add weight I'd say.
I know it isn't, I've owned multiple E30s. I've never heard of anyone destroying multiple small case diffs in the E30 community, especially people that street drive.
I'm with you.
I think this may be akin to "these Subaru transmissions are glass" also please ignore that I did 4k clutch drops at every red light.
In reply to z31maniac :
The Subaru transmissions could reliably break things on rough roads (like stage rallies) even with nonturbo engines. Way more rad than just burning up the clutch on the street 
I have not heard of problems with the small case differentials.
And no matter what you do with an M42, it is not going to be a torque monster that readily breaks stuff.
It does depend on how you drive and how you use the car. We also know that these cars are a bit underpowered and saving every ounce of weight would be our key to success on this project.
z31maniac said:irish44j said:DesktopDave said: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?
IDK I certainly wouldn't call it a "common" point of failure. My 1985 small-case LSD was original to the car and to my knowledge never opened when i got the car back in about 2011. Then I ran about 5-6 seasons of rallycross/rally with it and eventually toasted the plates (but replaced them). We usually use the 188's because of ratio availability, but the 3.91 and 4.10 were avialable in e30 small-case diffs, which are nice ratios for certain uses.
Having just moved all of my diffs across the garage today, I'd be really suprised if the difference is as much as 20lbs. Either way, a few lbs extra low in the car aligned with the rear axles is pretty much the best possible place to add weight I'd say.
I know it isn't, I've owned multiple E30s. I've never heard of anyone destroying multiple small case diffs in the E30 community, especially people that street drive.
I'm with you.
I think this may be akin to "these Subaru transmissions are glass" also please ignore that I did 4k clutch drops at every red light.
yeah I'm one of those people who managed to get a hundred seventy thousand miles out of my WRX, tuned and driven hard, and had zero transmission problems lol. Hell my original clutch was still good at 120000 when I swapped it out
z31maniac said:irish44j said:DesktopDave said: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?
IDK I certainly wouldn't call it a "common" point of failure. My 1985 small-case LSD was original to the car and to my knowledge never opened when i got the car back in about 2011. Then I ran about 5-6 seasons of rallycross/rally with it and eventually toasted the plates (but replaced them). We usually use the 188's because of ratio availability, but the 3.91 and 4.10 were avialable in e30 small-case diffs, which are nice ratios for certain uses.
Having just moved all of my diffs across the garage today, I'd be really suprised if the difference is as much as 20lbs. Either way, a few lbs extra low in the car aligned with the rear axles is pretty much the best possible place to add weight I'd say.
I know it isn't, I've owned multiple E30s. I've never heard of anyone destroying multiple small case diffs in the E30 community, especially people that street drive.
I'm with you.
I think this may be akin to "these Subaru transmissions are glass" also please ignore that I did 4k clutch drops at every red light.
The common M5x swaps will make the small case diffs whine, they don't like the extra power. My old 318is M50TU car whined like crazy, you can ignore it until it breaks, or swap and avoid it.
Can confirm. Killed two small case diffs in my ~200 hp rather torquey M42 turbo car before I went to a medium case. I don't know what was doing the whining, but they each lasted a couple of years of track days and autocross before having zero limited slip capability and whining badly enough to motivate me to swap them out. I don't think they really die a catastrophic death, they just get really loud like the gear faces get pitted or something. I'm a very gentle driver too, no hammering shifts or anything like that.
The little Getrag 240 transmission, on the other hand, held up great.
Probably would have been fine with just street driving.
Now I want to know which 3.91 diff my rally car has. I would love to swap to an LSD, but I'm not keen on spending a bunch of money to do it.
In reply to irish44j :
Okay, an off-topic response from 4 years ago, but opposite WRX experience here--5th gear synchros went out on my 2013 WRX at 50,000 miles. When they pulled it apart they said it looked like several others were on the way out as well and replaced them all. Never tracked the car and it was rarely driven hard on the street--mostly the wife commuted in it. I definitely won by getting the extended warranty on that car. Before the transmission rebuild, the clutch fork broke at like 36,000 miles.
In reply to Berck :
The synchros are not the weak part in a Subaru 5 speed transmission. The gears shred.
It's a clamshell design of a transmission (very weak case, allows everything to spread) that dates back to when Subarus were very light 50hp cars.
In reply to Pete. (l33t FS) :
Oh. Well, in that case I guess I had a totally unrelated failure. Nothing else broke until the car got totaled with 90k miles on it... I was actually more annoyed that clutch fork breaking since it (a) left me stranded 1,000 miles from home, and (b) is such a stupid failure that I can't understand how it happened when the car was just a couple years old with so few miles. The bits rattled around in the bell housing and destroyed the clutch too. To Subaru's credit, they honored their extended warranty with no hassles, and those were the only 2 failures I had in the 5 years / 90k miles I owned it.
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