Far Out Question: Aftermarket M5 6 speed in SL55, Physically Possible? - BMW M5 Forum and M6 Forums
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post #1 of 12 Old 6th February 2002, 10:38 PM Thread Starter
chunpng
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Lightbulb Far Out Question: Aftermarket M5 6 speed in SL55, Physically Possible?

This call goes out to Apples, Black M5, Jim Wald, Bart, TFung, and other 'Gurus of Mod'. on this board.

Is it physically possible to replace the automatic transmission in the SL55 by a 6-speed manual?

I think BMW buys their transmissions from Gertrag or some similar outfit, so it should be possible to buy a top-notch manual transmission unit and the shift linkage assembly.

The hurdles I can think of are mostly physical space limitations. But if one goes that far, it is conceiveable to modify the transmision housing/tunnel etc. to fit the tranny and the clutch asssembly. Don't know what it would do to the rigidity of the frame though. May have to move some seats to boot. Some warrenty items would be voided.

Would the engine management system have issues with the revs governed manually? Anything else that precludes this mod?

I know BMW Indivaiual will customize almost anything if we pay. Does MB offer similar programs? Or we'll have to try Renntech or Brabus to get the mod done?

There is also the road-feel issue, but I believe the dreaded 'dead road feel' is more associated with the S, E and C classes. Don't know if the SL class is equally 'dead'. But some fine-tuned suspension package might invigorate the road feel somewhat.

The costs for all these will not be small, but can't approach that of Nowack N500 or turbo-charging the M5. But if it can done, here's what you get:

You would loose a 100 lbs or so off the tansmission, which is always a good thing, and you can row your own gears. You'll have a car that can keep up with ANY supercar ANYWHERE (who would beat you, a GT2? not likely). A no-hassle convertable top, (no hard-top to lift, no soft-top to maintain) and a truly stunning looker of a car.

For me, THAT's the car to die for. Your comments, discussions, and education are welcomed.

CP

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Last edited by chunpng; 6th February 2002 at 10:52 PM.
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post #2 of 12 Old 7th February 2002, 01:25 AM
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Cool Renntech!

Quote:
Originally posted by chunpng

Is it physically possible to replace the automatic transmission in the SL55 by a 6-speed manual?
Yea, but like you said...Renntech and the $$ is crazy.

Check it out..click

Harry

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post #3 of 12 Old 7th February 2002, 02:14 AM
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that SL55 has something like 150lb ft more torque- something to consider.

from what I read about the SL55- it seems to have good road feel through the steering (rack&pinion) the real question is- does the feel get to you throough the seat? that is something that BMW has down pat.

All the best,
Jerry
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post #4 of 12 Old 7th February 2002, 02:55 AM
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nothing in impossible.. there are a few mercedes with conversions done to them to get a manual transmission in them.. I don't see why it cannot be done to the SL55... you will just need to find a compatible transmission that would hold up to the power of the engine... as more and more of the car's functions are turning electronic, I think it would get harder and harder to do this. Before, everything was mechanical, so it was simple to swap one thing out to replace it with another thing. Nowadays, you have to take into account of everything else in the car.. and in this case, I imagine that the ECU will have to be rewritten to some extent to accomadate a manual transmission...

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post #5 of 12 Old 7th February 2002, 03:25 AM Thread Starter
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Hi Terrance,

DSL up and running in the new pad already?

CP

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post #6 of 12 Old 7th February 2002, 03:29 AM
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A few years abck there was someone I knew of who had a Brabus or Renntech C-class with a BMW 8-series gearbox in it. I think it can be done with the SL. I do not feel that it is a mechanical issue, I am more concerned with ECU/Computer issues.

'Rocket
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post #7 of 12 Old 7th February 2002, 03:30 AM
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Straight up answer is yes but it's not easy, for one i'm not sure if
the gearbox is rated to that sort of power.

I've worked with guys from MB engineering being an engineer
myself even with my C32 there are little options for a box which
will

1. Fit
2. Handle the best Torque

So my guess is yes you can do it but like anything else you will
pay about $30K.

Heres another point the Lockup Torque converter on that box
is AMAZING ! Thats why firms like renntech will recommed against
it but if you want it it's 30K !!!

The other point is that the engine is designed for an Auto and the
torque curve acccordingly putting in a 6 speed will likely slow you
down a little. So the answer is yes but the tradeoff is HUGE !!!

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post #8 of 12 Old 7th February 2002, 04:11 AM
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Quote:
Originally posted by chunpng
Hi Terrance,

DSL up and running in the new pad already?

CP
nope.. still no DSL..

US Spec 2001 E39 M5 - LHD
AC Schnitzer
DFC suspension, anti-sway bars, pedals
front splitters, rear wing w/ carbon fiber

Dinan
CAI, MAFS, Throttle bodies, Velocity Stacks,
Stage 2 aluminum flywheel, front + rear strut bars,
3.45 differential

Others
Custom G-power Exhaust, Autosolutions short shifter
Supersprint Headers, Racing Cats, X-pipe
SPEC stage 3 clutch, Powerchip ECU, Schrick Cams
OZ Racing Superleggera III f19x8.5 r19x10.5, Brembo brakes
Evosport Power Pullies, Rouge transmission mounts, Plasma ignition coils
Euro interior conversion, M-technic grill with brake ducts, turbo timer
CA Automative custom carbon fiber hood


Euro Spec 1999 E39 M5 - RHD
ACS Sports Suspension, anti-sway bars, Type III Racing f19x8.5 r19x9.5


2007 Mercedes E63
2007 Corvette Z06
2008 Nissan GTR
2011 Ferrari 458
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post #9 of 12 Old 7th February 2002, 06:24 AM Thread Starter
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Upon further review, the SL 55 comes with a manual SMG type shifter. So you don't work the clutch or row the shifter, but at least you can stay in gear through redline before upshifting. The only way to enjoy the V8 tone really.

So it's not a slush box only scenerio.

CP

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post #10 of 12 Old 7th February 2002, 06:36 AM
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I believe the SL55 does not have a manual gearbox a la SMG. It is a strait-up automatic gearbox. Those button shifters are just a gimmick honestly. In those type of autoboxes, the fastest will always be leaving it in D.

I read somewhere that it will not let you hold redline.

'Rocket
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