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Rear differential upgrade what would you go with?

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  • Rear differential upgrade what would you go with?

    Thinking about a rebuilt unit with a 3:91 or 4:10 but not sure what would be the best for a weekend driver that will not see any track time. Can anyone share their experience with this mod? Any input would be helpful. 2002 E46 M3 manual.

  • #2
    I only have experience with the 3.91, so take what I say with a grain of salt... I don't see why you would want a 4.10 unless it is for track only. Everyone recommends the 4.10 but to me the 3.91 was pretty damn good and had enough traction issues.

    If fuel consumption is of zero concern, maybe jump straight into 4.10.

    MSportParts | Braymond141

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    • #3
      Thanks Braymond141 what do you mean when you say traction issues?

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      • #4
        Originally posted by SAMO View Post
        Thanks Braymond141 what do you mean when you say traction issues?
        Meaning it was very easy to get the rear end to slide with throttle. This was on street tires. 4.10 would be even more tail happy.

        The good thing is that the E46 is incredibly easy to control.

        MSportParts | Braymond141

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        • #5
          I'll comment as I've had the 4.1 for the past 8 years or so with two vastly differing power figures on the same M3. Initially it was paired with a VF570 kit, roughly 500whp on pump down here at sea level. First and second gear would break the tires loose at any rpm, with 3rd gear doing so with anything over 4500 as long as DSC was switched off. It was fun, completely ridiculous, though I wouldn't call it useful on the street as I was in lose your license territory almost immediately. I ditched the VF kit for a fiberglass CSL box that popped up in M3forum classifieds I couldn't resist trying out, very very worth it for anyone on the fence in that arena.
          I'll say the 4.1 is a LOT of fun on the street now, totally useful in the first 3 gears, though I have no experience with the 3.91's and assume they would be equally as fun, if not more, with a bit extra time in the first two. I'll agree with Brett, either is great as the e46 is so easy to control with the throttle when they do break loose, it's a good time having something you can slide around when you feel like it. For an NA M3 I would say the shorter the better if you like rowing gears, which I do.

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          • #6
            I have 4.10 on my e46 m3 honesty it’s not issue. Since we have 6 gears. BUT If we had 5speeds like the e36 yeah it would be abit annoying. But I say go 4.10 trust me🤪

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            • #7
              I love my 4.10 motorsport gears. Heck this S54 engine is a higher rev'ing engine, has an overdriven 6th gear. Years ago when deciding if to go with 3.91 or 4.10 I would hear stories from some that 4.10 was too short and 3.91 was better. Still went with the 4.10 and if I had gone with the 3.91 I would be wishing I had gone just the little extra and done the 4.10. It's 4.8% difference between the 4.10 and 3.91.
              If you do a lot of higher speed highway driving then 3.91 would be a better choice imho.

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              • #8
                I'm late to the game, but just another perspective on the gears. In 2016 I converted my car from smg to full manual and went with a UUC light weight flywheel and M5 organic clutch. The car was fun to drive so long as it was on flat ground. In stop and go traffic on a hill it was a nightmare as you had to give it more gas than normal and let the clutch slip more than you would normally like due to the reduced inertia. It was a pain and it was hard on the clutch (overheating on steep hills in stop and go traffic). Rather than go back to a steel flywheel, I decided to swap my rear with a 3.91 and a dual clutch differential. I was worried that a 4.10 would be too much. Anyway, the 3.91 made a huge difference in uphill stop and go traffic, but kind of wish I had gone with the 4.10. If you are considering going with a lightweight flywheel and clutch setup and it is your daily driver, and you have to deal with hills in your daily commute, do yourself a favor and at least get a 3.91 (If I had to do it over, I would get a 4.10). On that note, I am presently dumping the UCC flywheel setup and going to try a clutchmasters single mass steel flywheel and stage 1 organic clutch (The gear rattle is killing me!), also because I have some back issues, I am trying their hydraulic throwout bearing with a hydraulic Ram clutch pedal height adjuster. Lastly don't buy a brass fork pivot. Worst piece of crap I bought, it completely wore down (about 3/8"!) and I was having clutch release issues. Brass dust all over the inside of the bell housing. Even the stock plastic pin is better. The steel ones might be okay. Oh, by the way, I hear 3.91s are hard to get now.

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                • #9
                  Originally posted by Tig368 View Post
                  I'm late to the game, but just another perspective on the gears. In 2016 I converted my car from smg to full manual and went with a UUC light weight flywheel and M5 organic clutch. The car was fun to drive so long as it was on flat ground. In stop and go traffic on a hill it was a nightmare as you had to give it more gas than normal and let the clutch slip more than you would normally like due to the reduced inertia. It was a pain and it was hard on the clutch (overheating on steep hills in stop and go traffic). Rather than go back to a steel flywheel, I decided to swap my rear with a 3.91 and a dual clutch differential. I was worried that a 4.10 would be too much. Anyway, the 3.91 made a huge difference in uphill stop and go traffic, but kind of wish I had gone with the 4.10. If you are considering going with a lightweight flywheel and clutch setup and it is your daily driver, and you have to deal with hills in your daily commute, do yourself a favor and at least get a 3.91 (If I had to do it over, I would get a 4.10). On that note, I am presently dumping the UCC flywheel setup and going to try a clutchmasters single mass steel flywheel and stage 1 organic clutch (The gear rattle is killing me!), also because I have some back issues, I am trying their hydraulic throwout bearing with a hydraulic Ram clutch pedal height adjuster. Lastly don't buy a brass fork pivot. Worst piece of crap I bought, it completely wore down (about 3/8"!) and I was having clutch release issues. Brass dust all over the inside of the bell housing. Even the stock plastic pin is better. The steel ones might be okay. Oh, by the way, I hear 3.91s are hard to get now.
                  BMW sells a stainless steel pin that you can be assured is up to the job. https://www.turnermotorsport.com/p-1...uine-bmw-part/

                  +1 on brass being a STUPID choice. I really wish retailers would get rid of this from their sites.

                  I don't think the new setup will alleviate your gearbox rattle. The 420G rattles with a stock dual mass flywheel (faintly).

                  MSportParts | Braymond141

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                  • #10
                    Well I went with the 3.91 I'm pleased with my choice feels great on the highway most of all with a new LSD and Powerflex bushings the whole car feels very well planted. I also put a set of Firestone Firehawk Indy 500 tires on it Great tire for the Money.

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                    • #11
                      I was in the minority of people who actually liked the stock gearing, but I had a 3.91 in my s/c car so l decided to swap. Overall, it made the car (n/a) much more fun. It was overkill on the s/c car, which spun the tires too much but dare I say the n/a car kind of needed it. RPM's on the highway are not *totally* unbearable, but I do miss the 3.62 cruising at 80mph so the upgrade does come with a compromise. Would not consider a 4.10 for this reason alone but be aware that both 3.91 and 4.10 are Motorsport gearsets so they are cut a little straighter and have a slight whine at times... YMMV.

                      I may swap to a 3.85 (stock E92 M3 gearset) to get rid of the whine, or a 3.73 (E34 M5) down the road to find my happy medium. But the 3.91 definitely woke the car up quite a bit! Also, I am running 275/30-19 which will affect the ratio a little too.

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                      • #12
                        If you won't see any track time and it will be a fun weekend car and don't do too much long freeway driving, go with the 4.10. I actually didn't mind 3.62, it's got a nice "build up" when going through the RPMs. I just installed my dinan 3.91, I'm pretty happy with it. It's got good driveability but I wasn't super impressed. Maybe my expectation was too high. But I track the car too (it's built as a street/track car) so I didn't want to go 4.10 and have to shift too much with some of the tracks here in CA.

                        But if you want to have fun on the street, go with the 4.10.

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