Hi all,

I just recently learned that MB sold the W124 in Europe with a 5-speed automatic tranny (722.5xx). I was also told that the 300SL/SL320 5-speed will work in the 124, with either a custom driveshaft, or (I presume) the Euro 124/5sp shaft. Has anyone heard of this swap being done in the USA? Any known "gotchas" involved? The 5-speed stick swap is very complex and nearly impossible without a donor car (i.e., a donor that comes with the manual trans & all the required parts!), but the 5-speed auto should (?) be simpler. And I don't really want a manual trans in this car.

The advantage would be allowing a lower axle ratio (change my stock 2.65 to a 3.07 LSD from a 16V) for very strong off-the-line power, and around town it should be snappier in general, if kept in 3rd or 4th gear. The 5th gear is a 0.75 overdrive which would end up being a little *taller* than the stock final drive, for even nicer freeway cruising, and a little higher top speed (about 140mph instead of stock/rated 129mph, assuming there is power to push it up there.) The 5sp shift gate, etc, are all parts that can come from Europe. The only downside I've seen so far is that used 5sp trannies are expensive! Probably $1500+... ouch ... plus the diff. But the performance should be impressive, the LSD will pretty much be a requirement along with fat tires to make the thing hook up off the line. (buwaahahahahaaa!)

The gear ratios for the 4sp and 5sp are in this PDF file:
http://www.meimann.com/docs/mercedes/Tranny_ratios.pdf

Side note: The donor tranny would have to come from a gas engine. Can the valve body be tweaked (different springs, etc) to get the shift quality correct in a diesel? Or will it shift OK "as-is"? IIRC, the M104 makes about as much torque as the OM603 so there should not be a strength/reliability issue.


Regards,

__________________
Dave
Boise, ID
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Dave: don't forget you'll need the tranny module/computer to engage that 5th gear.

BTW: according to two different Mercedes techs I know, they both said the 5-speed automatic (722.5xx) are problematic and have reliability/longevity/durability issues since the 5th gear was an afterthought (that's why it's an electro-hydraulic hybrid tranny) and NEVER offerred for the V8's.

:-) neil

Yes - I'd make sure the donor tranny comes with all wiring and associated computers. I'm not too worried about longevity, I don't expect to put 200k on it or anything. Durability shouldn't be a problem with the relatively low-HP diesel (torque is probably similar to the M104). Reliability, well, I'd like it to be reliable! Too bad there's not more options available.

In Australia, all 300CE-24, 320CE and E320 coupes (ie. W124 coupes with the M104) came with 5 speed autos. The final drive ratio was actually much shorter than you suggest due to 5th being an overdrive. My father owns a '93 E320 coupe which has the 5 speed auto and runs a 3.69 (yes, 3.69) rear axle ratio. First gear starts at full throttle (normal starts use 2nd gear) are a tyre smoking exercise! When you actually get the power down to the road acceleration is impressive (0 to 100km/h or 62mph in the low to mid 7s, I think). Overdrive 5th is sufficiently tall to allow economical cruising at reasonably low engine revs, even with the 3.69 diff. I believe the transmission is the 5 speed auto originally used in the R129. The replacement filter I purchased for my father's car carried a 129 part number. It was also much more expensive than the filter for the 4 speed in my '90 300TE. The 5 speed also has a reputation of poorer reliability than the 4 speed. There are M104 powered W124 coupes getting around in Oz with 4 speed retrofits following the failure of the 5 speed. Most still have the short diff ratio which makes for high revs when cruising in 4th.

__________________
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.

Unfortunately I don't have any info beyond what I'm posting here, but my dad purchased (and later sold to me) a used 1983 300D (123 chassis) turbo, which we determined had a 5-speed transmission installed in it. If you started it in 1st, and manually shifted up, you could feel 4 distinct shifts. (I am familiar with torque converter lockup, and this was not TC lockup).

When we discovered that, we spend a week or so trading it back and forth feeling the shifting. We knew that the car had had the transmission replaced at some point in it's life, but we didn't know why.

Some other oddities were that at roughly 80mph the speedometer read only around 60mph. Some of that was that it had tires that were a bit taller than stock, but obviously the gearing was a bit different from stock somewhere (it also had the speedometer replaced at around 30k miles for some reason - so that might have been the reason for the speedo error).

It was also fairly easy to spin both rear tires when starting from a stoplight in the rain. I've driven several 123 bodied diesels (and a couple of 126s) and have never experienced that except in that car.

I don't know about the reliability of those transmissions, but my family collectively put 100-120k miles on it, and it had been in the car for at least 50k miles by the time that we bought it.

-Tad