M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: DaneD on August 10, 2009, 09:22:53 PM
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Hey all, recently broke my 4.10 open diff being stupid on a sharp left hand turn.
Anyway, i'm looking to put a new diff in, looking for pro's cons of different ratio's.
Have already sourced a 3.9 diff locally (waiting on price) and a 4.10 open for $330AUD.
Also have the option of a larger (medium?) 6 bolt 4.10 LSD for $1100AUD.
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While I have no experience with 3.9 vs 4.1, a medium case 4.10 LSD would be the best.
I do have an open small case 4.1 I am interested in selling for $150. I am in Canberra.
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3.73 medium case is the ideal choice for the M42. It will get you to 100kph in second gear and not make your ears bleed on the highway.
http://www.m42club.com/forums/showpost.php?p=26477&postcount=28
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3.73 medium case is the deal choice for the M42. It will get you to 100kph in second gear and not make your ears bleed on the highway.
http://www.m42club.com/forums/showpost.php?p=26477&postcount=28
Thanks for the tip and the link.
Anyone have any idea how much work is needed to match the speedo up to different diffs?
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While I have no experience with 3.9 vs 4.1, a medium case 4.10 LSD would be the best.
I do have an open small case 4.1 I am interested in selling for $150. I am in Canberra.
Any idea on shipping to Devonport Tasmania (7310)?
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Thanks for the tip and the link.
Anyone have any idea how much work is needed to match the speedo up to different diffs?
You won't need to do anything to the speedometer.
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4.45 would be my ideal choice...
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I should probably mention that this car is highway driven for over an hour approx 4 times per week, from what I understand a higher number diff = more RPMs at highway speed?
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higher number diff = more RPMs at highway speed?
Yes.
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+1 on the 3.73. I swapped a 325is medium case that bolted right up. Much better for highway use. Not noticeably slower either. If you end up not liking it, get lower profile (smaller circumference) tires.
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+1 on the 3.73. I swapped a 325is medium case that bolted right up. Much better for highway use. Not noticeably slower either. If you end up not liking it, get lower profile (smaller circumference) tires.
Hey so you didn't have to do anything for the diff swap? I'm looking at a 3.73 right now and would like the extra hwy mpgs. It was a direct bolt up half shafts and all?
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Yep - bolted right up. The bigger diff is about 20# heavier, but it should also last a lot longer. The new one is also an LSD unit, so I get a bit more traction.
The difference in fuel mileage is very slight. I'd estimate only 2%. You also give up a bit of first gear grunt, and steep highway grades will force you to downshift more often. Still - IMHO - this makes the car SO much better on the highway. It makes 3rd and 4th MUCH better for passing - the gear spreads widen out a bit and you can hold it in each gear a lot longer.
It's been a long time since I did this, but IIRC I had to bend the rear diff mount a good bit to line it all up. I also had a stuck bolt on the speedo sender and couldn't swap it out (the earlier speedo sensors use a different style plug but are functionally identical - you might also want to grab the wiring pigtail just in case). I ended up splicing the old-style connector into the wiring harness.
There was only one easy way to do this too. I had to drop the diff twice to line it all up right. If you can drop the rear exhaust pipe (I couldn't - bolts too rusted) that will help tremendously. I also ended up pulling off the heat shield to re-adjust the driveshaft length, then had to pre-load the CSB again. It was much more work than I'd anticipated. If I had to do it again, I'd replace the guibo & CSB while I was under there.
From what I remember, carefully line up the diff snout with the driveshaft and lift it into place with a jack. Start the four 17mm main carrier bolts into the top of the diff 4-5 turns, but leave them loose - just enough so the diff doesn't drop... Then get the four nuts onto the driveshaft yoke studs a few turns, but don't tighten them all the way either. Then get the diff 'ear' mounted to the car. Finally, tighten up the yoke, carrier bolts & ear. Finally, reconnect the half-shafts and the speedo plug.
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I am using a 4.27 from a 316i in my 318is (M44B19) and the acceleration is just great! I have a lot of fun with this diff :))
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i went from a 410open to a 373LSD and was pretty stoked. big difference
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I have the 427 LSD and it works well in the city but the highway is not good. After installing the supercharger the car pulls in 5th going up hill like crazy. I do mostly city driving but given the choice I would like to have a small case 391 lsd.