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Any recommendations for diff rebuild?

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  • Any recommendations for diff rebuild?

    So with the 6 speed conversion coming in at far more than I anticipated, Ive decided to get the diff done before Xmas and get the gearbox done in the new year.

    Currently looking at taking the diff off the motor myself and sending it to someone to convert to 3.91 ratio, stripped down and rebuilt with new seals and bearings, clutches as required with 40%lock and new backplate seal.

    Any recommendations for any techs out there that can do this job at a decent price?

    Cheers

  • #2
    Iridium?

    http://www.z3mcoupe.com/forum/showth...t=10611&page=2 #13

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    • #3
      Why 3.91??
      [GROWING OLD IS COMPULSARY ---- GROWING UP IS OPTIONAL

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      • #4
        Originally posted by ragerover View Post
        Why 3.91??
        Yeah, 3.91 seems a bit high. Had it in M3 with 6 spd and found it a bit too much.

        A think 3.46 or 3.64 is ideal - especially if you spice it with a custom tune with higher rev limit. Otherwise it is just feel fast but not so fast at all.

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        • #5
          Originally posted by ragerover View Post
          Why 3.91??
          Purely because the yellow z I sold to Pete was such a hoot with the 3.91. Do you reckon a 3.46 would be enough to dispense with the standard giraffe ratio?!!

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          • #6
            I recon a 3.91 will be too high
            You will actually be slower off the mark as
            As soon as your off the line you will be changing gear
            Top speed will be restricted and it'll be recon its tits off on the motorway at 80
            When you change the box it will be the same in the lower gears
            But better in too as you've got 6th

            I went for the 3.64 which has all the benefits
            But was still too revvy in 5th but with the 6 speed box it's great
            Best of all worlds
            [GROWING OLD IS COMPULSARY ---- GROWING UP IS OPTIONAL

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            • #7
              I had a 3.9 in my m3 compact great around knockhill a tire some every where else.

              I know a guy rebuilds diff to any spec you want for around 400-500 bearings, clutch packs, seals, ramp angles etc.
              BMW e21 track car
              Z3M (S62)
              2.8 Z3 Coupe
              Ariel Atom
              GT86 race car
              Ferrari 348 Challenge
              Merc G500

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              • #8
                Definintely stick with 3.46 or 3.64. If you're going for a 6-speed then a 3.64 will be great and you know will still cruise fine on the motorway with your 6th gear.

                3.46 is perhaps a good ratio for stickign with the 5speed gearbox.

                Echo comments about the 3.91 being too short, the problem isn't particularly the diff but the BMW gearbox ratios aren't particularly good 1st-3rd, especially 1st which is too short so when you drop the diff it'll do no more than your average diesel. Ideally 1st and 2nd ratio should be a touch longer so 1/2/3 are closer and you're not left with a really short 1st. My 205 1.9 GTi would do around 45 in 1st!!

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                • #9
                  Cheers gents

                  I spoke to Sean at Iridium. He feels finding a diff on eBay with a 3.46 or 3.64 ratio is the cheaper solution

                  What cars do these come off so I don't end up buying the wrong diff??!?

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                  • #10
                    You could try Automac for a diff,

                    http://www.automac.co.uk/

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                    • #11
                      Originally posted by M400DPC View Post
                      Cheers gents

                      I spoke to Sean at Iridium. He feels finding a diff on eBay with a 3.46 or 3.64 ratio is the cheaper solution

                      What cars do these come off so I don't end up buying the wrong diff??!?
                      E30 Sports 3.64 diff ratio are perhaps the most common. 3.45 and 3.46 are very rare (and usually older). But I think with the 6-speed I'd go for the 3.64, it will make the biggest difference and really transform the car.

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                      • #12
                        Originally posted by c_w View Post
                        E30 Sports 3.64 diff ratio are perhaps the most common. 3.45 and 3.46 are very rare (and usually older). But I think with the 6-speed I'd go for the 3.64, it will make the biggest difference and really transform the car.
                        What sort of performance difference do you think it makes in terms of 0-60 and 0-100 mph?
                        2002 '52 S54 - Titanium Silver with 18" BBS LMs, AP Racing BBK, KW V3, H&R anti roll bars & ACS flippers (previously 2000 'X' S50 - Arctic Silver)

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                        • #13
                          Probably not a lot outright performance; it's all about in-gear flexibility. The engine feels so much more alive and the car feels lighter with the lower gearing. It's up there as the best mod IMO.

                          I'd go for a 3.64 IF I had a 6-speed gearbox.

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                          • #14
                            Originally posted by c_w View Post
                            Probably not a lot outright performance; it's all about in-gear flexibility. The engine feels so much more alive and the car feels lighter with the lower gearing. It's up there as the best mod IMO.

                            I'd go for a 3.64 IF I had a 6-speed gearbox.
                            I have and I did

                            It would be interesting against the stopwatch but feels much faster

                            I've had a go against an MC an MR and a few M3's and come off best
                            But that could be just being in the right gear at the right time
                            [GROWING OLD IS COMPULSARY ---- GROWING UP IS OPTIONAL

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                            • #15
                              Originally posted by ragerover View Post
                              I have and I did

                              It would be interesting against the stopwatch but feels much faster

                              I've had a go against an MC an MR and a few M3's and come off best
                              But that could be just being in the right gear at the right time
                              You'd be surprised how irrelevant it is according the time e.g. 100-200kph. It feels faster, but it actually isn't faster at all. Sometimes you are in upper gear and you accelerate slower, and when you're in the same gear you accelerate better compared to stock final drive. I have some measurements somewhere which actually show no significant difference (3.15 vs 3.46).

                              Chris is spot on here - it's all about the flexibility of gears and bands.

                              I still think best is combo:
                              6-speed + 3.64 + higher rev limiter
                              or slightly worse 6-speed + 3.46

                              I personally hate when the gearing is so short you keep hitting rev limiter in 2nd on powersliding out of tight corners, one of the reasons I avoided or 3.64 and taller.

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