Is a 3 speed really a four speed?

[WGB]

Last might I made one of my rare attendances at the West Australian Mercedes Benz Club and arrived at a workshop in Willetton for a Tech night.

The guy who owns the business who has some M-B knowledge (and owns an S600 as well as a 500SL) showed an interest in my 6.9 and stated that the 3 speed auto contains the same number of gears and clutch packs etc as a 4 speed and that only the valve body is different.

Hence it should be possible to produce a 4 speed from a 3 speed if some one can manufacture the valve body.

This was news to me and I remain unconvinced but present it for discussion.

Bill

[Big_Richard]

that's a common misconception that's been propagated thanks to the internet. Its plain wrong.

indeed it looks similar externally and has the same amount of bands, but the 4 speed has an additional planetary gear set at the very front, not found on the 3 speed. When compared side by side the transmissions have ALOT of internal variations.

[SELfor50]

I agree with MT (Manual Transmission?!)  on this one.

Someone else was trying to convince me on this last weekend.  I've spoken to many many people about the transmissions for 116's.
Naturally with my search for race pace I've gone to great extents.  And the closest I've had of anyone mentioning a 4 speed auto box in a 116/V8 was Franz from bigtoys.
He said that he'd done the conversion to a 4 Spd auto's on 6.9's before and it's very very good.  He actually recommneded it over a manual conversion.
HOWEVER, he said that it's not a modification to the valve body or existing gearbox - but a swapout to a later model 4spd Auto V8 box.  I'm guessing it's off the 560's or 500's.

Until someone shows me a step by step pictorial and proof of the modification to a standard 6.9 gearbox - then I can't believe it.

Question to pose is, if it's that easy have you done it before personally??  What was the car that had the modification.

I have a spare 6.9 transmission - so if anyone is willing to put their $$ where their  is then I'll put my spare box up for modification. 

Cam.

[WGB]

Thanks guys - I feel better now.

I was sure he was wrong.

Bill

[TJ 450]

I would guess that it may be possible to modify a 6.9 box with the parts out of a 280 4 - Speed, but I simply don't see the point. It would probably make the car slower, because you would sit there spinning the wheels.

A 126 4-Speed conversion would be a whole 'nother story.

Back to the original question, I agree that it's a load of BS. The four speed boxes do indeed have the additional planetary gear set.

Tim

[Big_Richard]

Back to the original question, I agree that it's a load of BS. The three speed boxes do indeed have the additional planetary gear set.

Tim

please correct the techincal error in your post

I for one would love a 560's 4 speed transplanted into a 6.9 - i wonder whats really involved... Electronic speedo is one thing for sure...

[TJ 450]

Whoops,... the error has now been corrected.

I reckon the the bell housing would be a bit of a problem, as I seem to recall the 6.9's version being a lot larger, as is the torque converter. The smaller engines wouldn't be too different though.

Tim

[WGB]

Having owned a 126 four speed nd a 124 four speed - both in pre-traction control days - I would be concerned about traction in first gear as well as no improvement in top gear as there is no overdrive.

I think the present 6.9 first gear launches the car reasonably well with containable wheelspin (except on wet roads) but a slightly lower first gear would help - especially if combined with a taller top gear.

Why not get adventurous and put in an ML 7 speed with 4-matic.

That would really launch well, have great traction on any surface and a great top gear.

Bill

[Big_Richard]

if your going to go overboard with technology, why stick with an old dinosaur like an m100 when MB produce much more powerful engines here and now