Some of you may have read my recent thread regarding a true cold air intake for my 350SLC Improvements to M116 in early 107 (true cold air intake) where I mentioned I am planning to use this car for a little motor sport, hence my search for performance improvements.

I recall hearing that the 3-speed, torque converter transmission (722.0?) in my car is virtually the same as the 4-speed unit (722.1?) fitted to the six cylinder (eg. 280E, 280SE/L, 280SL/C) W107, 116 & 123 and various diesel models of that era. I have heard that the similarity extends to the 3-speed actually having 4 ratios, with first not being accessible. I know the ratios of the 3-speed correspond with 2nd, 3rd and 4th of the 4-speed which makes for a very tall first gear in the 3-speed. My 350SLC can do a 0 to 60mph (almost 0 to 100km/h) sprint entirely in first gear!

Is it possible to modify the 3-speed (eg. valve body mods) to allow the true first gear to be accessible? Alternatively, can the 4-speed be bolted up to and used successfully with the V8 engine (iron block M116 in my case)? The addition of a lower first gear together with the torque converter would really launch this car well. It would possibly even allow the use of a taller diff than the present 3.46 to give lower cruising engine speeds with better fuel economy, yet still with good acceleration from standstill.

I had considered the possibility of trying to source the 4-speed manual transmission that was available for the 350 and 3.5 models, however they are rare in Australia and I have also heard they are very costly to repair. On the other hand, the auto transmissions of the 1970s have a very good reputation, better than either that of the fluid-coupled autos of the 1960s or the autos of the 1980s and 1990s.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

The 722.0 series has 1 less plantary gear set than the 722.1 series. No way to modify that trans & make it into a 4 speed. AS suggested the trans from a 3.5L motor does have 4 speeds.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

M.B.DOC,

Thanks for that. You have probably already guessed what question is coming next! Will the 722.1 bolt up to an M116 (3.5) or M117 (4.5) in place of the original 722.0?

I realise that the early M116 (3.5 in W108, 109, 111 and very early 107) originally came with either the 4-speed manual or the 4-speed fluid coupled auto transmission. My '73 350SLC (W107 with M116) has the 722.0 3-speed with torque converter similar (or the same) as that fitted to the M117 (4.5). Obviously the manual transmission would be nice, however they are rare (and I have heard costly to repair). The early 4-speed autos did not have a reputation for durability like the 3-speed and with a fluid coupling rather than torque converter offer no performance advantage. Therefore my interest is in the possibility of using a 722.1 with my M116.

Greg

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

No, the 722.1 has a different size torque converter & bellhousing. ALSO not rated for the torque that ANY V-8 makes!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Thanks M.B.DOC,

Guess I'm stuck with my 722.0 (3-speed) unless I want to consider substantial mods. At least the 722.0 is durable.

Regarding more serious mods, will the later (although less durable) 722.3 (4-speed auto) as fitted to the alloy M116 & M117 (and many others from the '80s and early '90s) bolt up to the '70s iron block M116 and M117? Bear in mind that my 3.5 M116 does not make much more torque than a 3.0 M103 and less than a 3.2 M104. The 3.5 gets all its performance over a narrow power band at very high rpm, hence my desire for something other than the 3-speed.

Even more serious is the possibility of adapting a non MB manual transmission (preferably a 5-speed). Anyone with any experience or knowledge of this as a possibility?

Thanks,
Greg

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

Greg,

I have the manual 4 speed on my 350SL here in Brisbane. I hunted around for about 12 months on the idea of changing it to a 5 speed, pretty much before I got the car on the road (it was a non running much neglected collection of rust particles when I first acquired it 3 years ago but thats another story).

Now that the car is finished and on the road its apparent that the 4 speed is more than sufficient, with the 3.09 diff the engine is only doing about 2300rpm at 100kph so 5th would only come in to play rarely. The hardest part is overcoming the temptation at every gear change to leave rubber all over the road. Its so completely different from an auto 350SL that you wouldnt think it was the same model. The downside is that this box is very heavy and slow through the changes - you cant manage snappy little changes like a modern japanese box. Or at least I cant so I'm not sure how hot it would be for motor sports as your considering.

I toyed with the idea of acquiring a 5spd from an M110 or similar (there are a few around if you hunt long enough) but was warned off that. Apparently its been tried more than once before with the same result everytime - meltdown! (They do apparently bolt up OK however for what its worth)

I also searched high and low for any info on kits to fit any other type of 5 speed (like the classic toyota celica conversion done to so many fords and even a few mazdas etc in the early 80's before 5 speeds were common). I drew a blank so if you do find anything I would love to know about it.

Regards,
Daryl

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'71 350SL auto
'73 350SL manual
'98 528i (yeah I know but at least its German)

'71 250CE (sold)

Thanks Daryl,

We have club members with manual 350SLs and 280SE-3.5s and I have driven a 3.5 with a manual and do remember the fairly slow and deliberate changes with long throws on the shifter and lengthy clutch travel. The 5-speed in my 190E Sportline, whilst still not the fastest shift around, is an improvement over that behind the 3.5 M116. Presumably these later manual boxes would also not be suitable. I was also not aware of the rear axle ratio you mention instead assuming the manual 350 got the same diff ratio as the autos. There is a club member with a business here in Sydney who does all sorts of interesting conversions including 6.3s with 5-speed manuals. I have been considering talking to him about the options available for the 350. I will let you know if I find out anything of interest.

Greg

__________________
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.