6.9 5 speed manual trans - anybody done it?

[daantjie]

Hi guys

I know this topic has been bounced around before, but I think it falls under the "sounds much easier than it is" category

I think the 3 speed in the 6.9 is really not up to the task, and the multiple issues most owners experience over time supports my viewpoint.  I have some anecdotal evidence that being a 4 speed box made into a 3 speed was kind of a band-aid at the time by Benz and really the box is out of it's depth with the 6.9.  Perhaps for the 107 450 it was fine but not for the 6.9.

So...anybody know of a successful manual trans swap?  I've read that the older BMW M5 manual box (Getrag?) would be an ideal candidate.

Thoughts?

Cheers

[raueda1]

Not an answer, but a bit of info to pass along FWIW.....

In the course of my transmission problems my transmission guy commented that the 3 speed internals were substantially beefier than their counterparts in the 4 speed.  This is possible because there are simply fewer parts to fill the volume of the transmission case allowing the stuff that's there to made larger/stronger.  He showed me a couple internal components (planetary gear carriers and bands if I recall) and the difference was pretty obvious.  The clutch bands were significantly bigger than the 4 speed.  The point is, it isn't just a 3 speed version of the 4 speed.

Does it matter?  Is transmission still under-designed?  I can't say but I thought it was a worthwhile tidbit.  A 5-speed stick is a fascinating idea...   

[Squiggle Dog]

I recently rebuilt a 3-speed Fordomatic transmission. Apples to oranges, I know, but it was SO much simpler than the 4-speed W126 350SDL transmission I did. I also had the good fortune of finding a Getrag 5-speed manual in a wrecking yard. As soon as people knew I had it, they were on me like vultures.

With as interchangeable as Mercedes parts are, I'm pretty sure a 5-speed would bolt up without too much fuss. Heck, an OM617 turbo diesel bolted right up to the 4-speed column shift in my fintail wagon. EBay Deutschland seems to have W116 clutch pedal sets from time to time, though I think W115 or W123 pedal sets work in a pinch.

[daantjie]

Not an answer, but a bit of info to pass along FWIW.....

In the course of my transmission problems my transmission guy commented that the 3 speed internals were substantially beefier than their counterparts in the 4 speed.  This is possible because there are simply fewer parts to fill the volume of the transmission case allowing the stuff that's there to made larger/stronger.  He showed me a couple internal components (planetary gear carriers and bands if I recall) and the difference was pretty obvious.  The clutch bands were significantly bigger than the 4 speed.  The point is, it isn't just a 3 speed version of the 4 speed.

Does it matter?  Is transmission still under-designed?  I can't say but I thought it was a worthwhile tidbit.  A 5-speed stick is a fascinating idea...   

Dave as far as I know the stator shaft is the weak spot.  It uses the same shaft as most other boxes used in the 116.  The splines get sheared off and then you are done for.  My transmission knowledge is pretty much nil so I defer to the experts for the most part.  Agree if well maintained and not abused the box "should" last forever  Interestingly this box was also used in the 928 Porsche.  I wonder how it held up in that setup

[Mattr]

Hi guys

I know this topic has been bounced around before, but I think it falls under the "sounds much easier than it is" category

I think the 3 speed in the 6.9 is really not up to the task, and the multiple issues most owners experience over time supports my viewpoint.  I have some anecdotal evidence that being a 4 speed box made into a 3 speed was kind of a band-aid at the time by Benz and really the box is out of it's depth with the 6.9.  Perhaps for the 107 450 it was fine but not for the 6.9.

So...anybody know of a successful manual trans swap?  I've read that the older BMW M5 manual box (Getrag?) would be an ideal candidate.

Thoughts?

Cheers

I started a discussion about this on M-100. It has been done, and there's an Australian who makes an adapter kit for I think GM 4 or 5 speed transmission. I thought about it a lot, and realized that in the dream of maintaining the 'cruiser' atmosphere this car has, I'd much rather upgrade to a 5-6 speed automatic than having to shift this car myself. I do agree with you about the 3 speed, though. It's a dog of a transmission, and adding more gears would probably help with the horrific fuel consumption as well.

If life will ever cut me a break, I'm going to buy another M100 motor, rebuild the injection system, and then work on getting a 5-6 speed auto setup.

[daantjie]

I love driving stick so for me a 5 speed manual would be the biz.
My DD is a 5 speed manual Civic and I love revving it out every now and then. I pretty much hate the idea of not being in total control of shift points but then again I'm a control freak by nature so take that as you wish

[nathan]

I thought the stator shaft was unique for the 6.9, TJ will advise as he has rebuilt his transmission.  I think his difficulty was finding one of these shafts to replace it. 
There doesn't seem to have been many major issues with transmissions ive heard of amongst 6.9 owners.
These cars with massive power are 40 years old, so I would imagine most transmissions should receive some attention after all this time. 
Most 70s cars had either 3 or 4 speeds, and MB would have known people shelling out the original prices had no interest in a manual.
The Australian group who reportedly made adaptors for the transmissions were Big Boys Toys (in NSW?), I dont even know if they still exist - the conversation came up about 10 years ago but no one ever tried their product.

[76116]

I love driving stick so for me a 5 speed manual would be the biz.
My DD is a 5 speed manual Civic and I love revving it out every now and then. I pretty much hate the idea of not being in total control of shift points but then again I'm a control freak by nature so take that as you wish

AFAIK, the 3-spd in the 6.9 can be shifted manually....

[karmann_20v]

Anything can be adapted, if you throw enough money at it...

I would say in terms of transmissions, you want either an E39 M5 6 spd, any GM 6 spd (either Corvette, Camaro, Cadillac CTS-V, etc), Ford Mustang GT, maybe Dodge Challenger too - all these cars came with more power and torque than the 6.9, so you know you won't grenade it . Making it fie onto the M100 and modify the drive shaft is the real task here. I would think you can still find the pedal cluster from a manual 280/350, but not that easily these days (107 would probably work too?). Shifter assembly from a manual 116 may not work, depending on the transmission type.

Then there is this, you know you want it:

http://www.tremec.com/anexos/TREMEC_DCT_0318.pdf

Jag guys have it so easy:
http://www.vintagejag.com/Parts/Transmission_Conversions.html
http://www.jag-lovers.org/e-type/5speed.html

At the end of the day, if you were to swap your own manual into the 6.9 you could theoretically develop a kit not unlike the Jag links above. I'm sure you would find a couple ppl interested in the conversion to recoup some of the costs.

[TJ 450]

There's nothing weak about the 3-speed, although the stator shaft does wear, even on the smaller engines cars. Complete failure would be rare, but it has happened. I ended up with a part for the Porsche 928 trans which has a V profile spline which may or may not be an improvement.

The are two different versions of shaft though, one is pressed in and the other is clipped in, this I understand is more of a early vs. late thing. They require a different bell housing.

With regards to the 4 vs. 3 speed thing, even on the 6.3 the trans is effectively still operating as a 3-speed unless you kick it down apparently just like on later cars. Of course this is a completely different trans however.

Tim

[daantjie]

Thanks guys.
I guess this also falls into the "if you have the money honey I have the time" category   or is that "I have the transmission"

[3l33ter]

I've thought a lot about how to "wake up" a 6.9 - more compression (or a supercharger), standalone with port injection, higher redline, etc. But I think what the car needs more than anything is a better gear set. I like autos and manuals equally, and I can't say which one I'd prefer on a 6.9 until I try one of each ( haha) but I think the gearing is the key factor to choosing the right transmission in either case.

There's also the issue of space, as MB transmission tend to be on the small side, so any other transmission won't easily fit in its place. Just speculating - correct me if I'm wrong!

[oversize]

I've discussed this issue many times on another site.  Personally I don't think the 6.9 suits a manual transmission since it's not a motor that loves to rev.  That's unless you're going to spend lots of time and money shedding weight by replacing the rods and pistons with new much lighter components.  Followed by lightening the crankshaft and using various other racing-like methods.

Personally I think there's value in exploring another auto that has an overdrive and a high ratio 1st gear.  And one that can cope with all that torque (plus more if you're planning engine mods).  So it comes down to a ratio comparison, in addition to what's the easiest to fit in place of the old box.  Most of the new boxes require an ECU to function, so that will rule out many modern options unless you can find one that can cope with a stand alone ECU and limited sensor input from the 6.9 engine.

I like the ratios and torque capability of the Torqueflite 48RE (4 speed) but it may not fit in the tunnel.  The ratios are very similar to the 6.9 box, so it may not justify all the effort, but it does have an OD which the 6.9 lacks.

The GM Hydramatic 6L80E is a 6 speed box with a higher ratio 1st gear than even the 6.3 (4.03 vs 3.98) plus 2 x OD ratios.  That's one of the reasons the 6.3 is so fast off the line.  However, I'm unsure if there's stand-alone ECUs available for the GM box.

I've heard there's an MB 5 speed box that was fitted to the V12 biturbo and Chrysler 300C that might suit, but I'll have to do more research.