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Old 11-14-2016, 07:55 AM   #1
Sladek
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M42/318is Transmission/LSD Swap options - potential for use with motor swap later

I've been searching around and cant seem to find a clear answer on these couple questions:


For the transmission:
1. is there a transmission that will bolt up to the M42 to replace the getrag 240?

2. if there is, is that transmission able to directly bolt up to another common swap BMW engine (M50,S50,S52 etc)? and if so which engines?

For the LSD:
3. currently have the small case diff, when swapping to a medium case diff what exactly is needed? just a different length driveshaft?

4. with track time in mind, is swapping to a medium case diff worth it over the small case especially if there is potential for a later engine swap/moar power?
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Old 11-14-2016, 08:02 AM   #2
FredK
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The M42 has the same bolt pattern as the M50. Therefore, you may use any number of different transmissions, such as a Getrag 250 from an E36, ZF 310, ZF 320 (E36 M3, E36 328i), and newer 6 speed transmissions. These, of course, bolt up directly to the common swap engines.

Medium case diff bolts up without any modifications. The driveshaft is positioned identically. The halfshafts are also positioned identically.

Ensure, however, the medium case diff comes with a rear cover and output flanges, because the small case cover and flanges DO NOT swap over.

Finally, yes, it's worth swapping to a medium case. The small case is flimsy, and the clutches do not last anywhere close to as long as in the medium case.
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Old 11-14-2016, 08:05 AM   #3
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is there a favorite of those transmissions for heavy track use that also gets dailyed haha
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Old 11-14-2016, 08:10 AM   #4
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Sure, the ZF320 is widely available, inexpensive, and fairly lightweight (70 or 75 pounds).
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Old 11-14-2016, 08:21 AM   #5
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awesome thanks! not sure why it was so hard to find this info haha
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Old 11-14-2016, 08:23 AM   #6
Sladek
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another question, would the zf transmission require any different clutch setup or would it work fine with the stock m42 stuff?
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Old 11-14-2016, 09:52 AM   #7
bmwman91
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Consider a rebuilt or custom built diff if you are going to be tracking the car. The stock LSD's are almost all sure to be pretty worn at this point and not providing all that much torque bias. I had a custom Wavetrac unit built into a medium case by a member here for a reasonable price (not cheap, but very reasonable for what I got). Apparently the Torsen units from Z3's is also a fairly inexpensive route to go too, although you will not be happy if you lift a wheel mid-corner.
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Old 11-14-2016, 10:13 AM   #8
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Quote:
Originally Posted by Sladek View Post
another question, would the zf transmission require any different clutch setup or would it work fine with the stock m42 stuff?
I think it will, but I'm not 100% sure on that.
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Old 11-14-2016, 10:31 AM   #9
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The E36 trans has relatively close ratios, and would be nice on the track with a taller
(3.64, 3.91) diff. Especially, the 2-3 gap's not so bad.
It'd be spinning pretty fast on the highway, though, with a 1:1 5th.

As to diffs, etc- wear out what you have, first. The small case E30 diff's not particularly
weak, as BMW beefed it up significantly about the time it went into the E21.
And the M42's no torque monster- and torque is what kills diffs.

That said, don't waste money on a new small- case diff unless it's really cheap-
the mid- case is a lot more durable with 'moar power'. But it adds significant weight
and a little drag. So it's not a 'free' upgrade.
Likewise the transmission-
the stouter ones are noticably heavier, so you're going to load down that little m42 even
more by adding a bigger gearbox.

It's always about balance...

t
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Old 11-14-2016, 12:54 PM   #10
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Quote:
Originally Posted by TobyB View Post
The E36 trans has relatively close ratios, and would be nice on the track with a taller
(3.64, 3.91) diff. Especially, the 2-3 gap's not so bad.
It'd be spinning pretty fast on the highway, though, with a 1:1 5th.

As to diffs, etc- wear out what you have, first. The small case E30 diff's not particularly
weak, as BMW beefed it up significantly about the time it went into the E21.
And the M42's no torque monster- and torque is what kills diffs.

That said, don't waste money on a new small- case diff unless it's really cheap-
the mid- case is a lot more durable with 'moar power'. But it adds significant weight
and a little drag. So it's not a 'free' upgrade.
Likewise the transmission-
the stouter ones are noticably heavier, so you're going to load down that little m42 even
more by adding a bigger gearbox.

It's always about balance...

t
very good points, looking to eventually get it to a TT car so just looking for info in case a component goes bad. until then its run what i brung. i appreciate the help guys. always nice that i can get answers so quickly on r3v
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Old 11-28-2016, 07:13 AM   #11
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Quote:
Originally Posted by FredK View Post
The M42 has the same bolt pattern as the M50. Therefore, you may use any number of different transmissions, such as a Getrag 250 from an E36, ZF 310, ZF 320 (E36 M3, E36 328i), and newer 6 speed transmissions. These, of course, bolt up directly to the common swap engines.

Medium case diff bolts up without any modifications. The driveshaft is positioned identically. The halfshafts are also positioned identically.

Ensure, however, the medium case diff comes with a rear cover and output flanges, because the small case cover and flanges DO NOT swap over.

Finally, yes, it's worth swapping to a medium case. The small case is flimsy, and the clutches do not last anywhere close to as long as in the medium case.
all of the above is great advice;

if one is doing Time Trial with a M42 car it may be worthwhile to stay with a 168mm small case and just spend the money on an aftermarket LSD unit; many to choose from and they would be much better money spent long term if you are competing in TT; as lap time is of concern. lap time in sprint racing vs ultimate durability - the avail of 4,27 and 4,45 gearsets make it cheaper to run than the 188mm simply on gearing needs.

For endurance or street use pick the 188mm as its stronger and only marginally more rotating mass.


New Aftermarket LSD Cost would be alot more than sticking with used oem though; obviously a NEW item is going to be nice and new so this is not apple to apples




another issue with going to more larger more robust transmission may be driveline length; M44/M42 transmissions are shorter length than the Zf 320; perhaps someone with more 4 cylinder hands on time can chime in. the M42 e30 and m44 e36 seem to have different mounting positions of bellhousing in relation to the firewall and differnt driveline lengths; it may not direct swap in like a M50+zf5 + e36 328i driveshaft +e30 center bearing that has worked so well in the 24v enduro car

Last edited by Wanganstyle; 11-28-2016 at 07:18 AM.
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Old 12-24-2016, 08:57 AM   #12
Klug
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I just went through rebuilding and swapping over an LS into a 3.64 medium case. If you're not swapping over gearing ratios and all that and just rebuilding the LSD- I'd say it's really NOT that difficult.

I ended up removing the LSD, swapping in new dog ears and clutches (~$200-ish) and the LSD is refreshed and ready to roll. Granted I heard that you can switch (not flip) the dog ears and clutch from one side of the LS to the opposite side, since only one side of them gets worn down after heavy LS usage and age.

/a novice diff guy, it worked for me...but had to do extensive research.
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