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Thread: Transmission Ramblings (Long)

  1. #1
    Join Date
    Feb 2019
    Peachtree City, GA
    My Cars
    '02 M5

    Transmission Ramblings (Long)

    I intitially posted this on M5board and didn't get much input. No indication of how much cross-talk happens between forums, so I thought I would see if anyone here has an opinion...

    In my introduction post I mentioned that I am of the opinion that the Beast is geared poorly. I also noted that I was sure that there is more to the story and that the BMW engineers knew what they were doing – after all, this is the
    Ultimate Driving Machine
    After doing a couple of hours of pecking around the ol’ interwebs, I am now convinced that BMW is just like every other car manufacturer, just on a different price point – they are all ruled by the bean counters (no offense to any accountants on the board – I know many that are very lovely people) & the engineers have to make the best they can with what they have available. Case in point is the tranny in our cars – the Getrag 420G. There is no way you can convince me that the internal gear ratios were chosen specifically for the characteristics of the S62 engine in the M5 when those internal ratios are the same for multiple engines in various chassis, all with different Q curves and curb weights.

    BMW Gear Ratios - E36 / E46 / E90 / E91 / E92 / E93 / E85 / E86 / E83 / E82 / E88

    I apologize in advance for offending anybody’s sensibilities for making the following comparing the Beast to the Ford Mustang, even though Ford has publicly stated that the e46 M3 is their target. The 2011 – 2017 Mustang GTs have a 3.7 x 3.5 V8 (5.0 liters) with variable valve timing on all 4 cams, that makes very similar numbers to the S62 engine, especially when comparing area under the curve on the dyno charts. The MT82 gearbox (also a Getrag) uses the same type of semi-remote shifter as the beast. The Mustang weighs in at ~ 400 lighter that the Beast, with a clutch that is an inch larger in diameter and a steeper rear gear (3.31).

    I know I am reviving a 10 year old thread, but the MT-82 wasn’t in existence when this thread was active, so I request some leeway on that. Thanks to CSBM5 for the link:

    I have three options for re-gearing the Beast which I think will make it more driver friendly, accelerate better, get better fuel mileage through lower RPM while cruising, reduce oil consumption (again, fewer RPM while cruising) and make the engines last longer.
    If any of the contributors to that thread still have the software available, what does it say about re-gearing the Beast as follows:

    1: 3.66
    2: 2.43
    3: 1.69
    4: 1.32
    5: 1.00
    6: .65
    Final Drive: 3.15

    The second option, albeit much more involved would be to yank the 420G and replace it with a QuickTime bellhousing, Tremec T56XL 6 speed (and associated clutch disk) and a steeper rear gear (say 3.62 from the e46 M3). The T56XL was developed as a replacement for the MT-82 because all of the Mustang hotrodders kept binding up the shift linkage when the Coyote engine was subjected to forced induction, which almost doubled the output (the chassis couldn’t handle the power and the shifter, being attached to the chassis, would bind as the engine and trans twisted in the mounts). The T56XL uses a specific tail shaft housing that puts the shifter in the same location as the stock MT-82 semi-remote shifter. This would, of course, be dependent on the length of the 420G from the bellhousing mounting face being the same as the MT-82/T-56XL. The T56XL is available in the following ratios:

    1: 2.97
    2: 2.10
    3: 1.46
    4: 1.00
    5: .80
    6: .63
    Final Drive: 3.62

    The third option that comes to mind is the Tremec TR-6060 transmission that was offered in multiple vehicles in various ratios and uses a semi-remote shifter just like the 420G.
    This would require a custom bellhousing and probably custom length shifter rods / carrier, but that shouldn’t be anything we couldn’t shame M5 Jed into making for us I would use the first generation Shelby GT500 ratios:

    1: 2.97
    2: 1.78
    3: 1.30
    4: 1.00
    5: .80
    6: .63
    Final Drive: 3.62

    Hurdles to clear:

    First Option – If the MT-82 gear set will fit in the 420G case (I have this RFI out to a Getrag Transmission specialist, but if any board members want to take it for action, then please do so), then that would by far be the most cost effective. I would get a good carbon-ceramic dual friction clutch plate because it will see more abuse, especially standing starts at max gross weight on a hill. My SWAG (Scientific Wild *** Guess) for this this option’s cost is $1500 to rebuild the transmission and buy the clutch.

    If the gear sets don’t interchange, then this option is off of the table.

    Second option – Overall lengths of the transmissions have to be the same or very, very close (a delta of
    +/- 1” or less). The bellhousing is easy, it would just take time and $$$. QuickTime already has a custom order department organized to build one-off or low production pieces. Would also need a custom clutch disk, but that is easily sourced also, just time and $$$. The last item I can see is a hybrid U-joint or CV joint to attach the T56 output yoke to the Beast’s driveshaft. The cost SWAG for this would be between $4-5K, based on the market price for Mustang T56XL swap kits.

    Update: The T56XL is 34.9" from the front of the bellhousing (back of engine) to the shifter with a 6.5" deep bellhousing. I know the shifter rod on the M5 is 14.25" (362.6mm) long, so if the 420G dimension from the front of the bellhousing to the shifter rod attachment is ~ 20", this might be viable. I know the total length of the 420G is 25", but that is to the output flange, not where the shifter rod attaches. Does anyone have any insight on this measurement?

    Third Option – a custom bellhousing, clutch disk and shifter rods. Again, all easily sourced if there is/was any interest. The cost SWAG for this option is ~ $2500 (the bellhousing would cost the same as option 2, but a used TR-6060 is much cheaper than a new T56XL).

    Lastly, the probability of me doing any of these things is slim, but I like to think about making the Beast “mine”, and this is one of the ways that I would do it. I welcome all input, so long as it is constructive. I already know that I’m a dumbass, so I don’t need any further affirmation of that fact

    Semper Fi

  2. #2
    Join Date
    Feb 2019
    Peachtree City, GA
    My Cars
    '02 M5
    The following all use 6500 as the shift RPM.

    The 420G gear spacing is not optimal (I rounded to nearest 100 for simplicity):

    1-2 shift: 3800
    2-3 shift: 4300
    3-4 shift: 4800
    4-5 shift: 5300

    MT-82 gear set isn't much better:

    1-2 shift: 4300
    2-3: 4500
    3-4: 5100
    4-5: 4900

    T56XL is the most consistent:

    1-2: 4600
    2-3: 4500
    3-4: 4500
    4-5: 5200

    Lastly, the TR-6060 GT500 variant:

    1-2: 3900
    2-3: 4800
    3-4: 5000
    4-5: 5200

    Unless you're a descendant of Ronnie Sox, manual shifting is the bane of accelerating, so why not take advantage of the VANOS and use the widest ratios with a consistant RPM drop available?
    Last edited by Foghorn37; 02-22-2019 at 09:35 AM.

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