w116 2.65 differential into a W123

[sleeeper]

OK,
I've got myself into a bit of a pickle and could use some suggestions. several weeks ago durring a half price weekend at the local picnpull I scored a 2.65 diff from a 1980 116 450sel with about 100k miles on it. Everything looked like it would be compatable with the 123 chasis, the dimensions, the mounting points. Well today an axle going bad on my 1982 300td inspired me to do the swap. As it turns out the diff bolts in just fine except the holes in the flange where the diff bolts to the rear flex disc are slightly farther apart than the 123 flex disc. I am not ready to admit defeat yet and can think of three possible solutions, 1) maybe the rear section of the 116 driveshaft can swap with the one in the wagon at the center bearing if they are the same length and I can just use the 116 flex disk? does anyone know if the universal joints in the drive shaft can be dissassembled and put back together? 2) Take the rear sections of both the SEL and 300TD drive shafts to a driveshaft shop and have them weld the SEL flange to the 300TD shaft and balance the whole deal-any ideas on what that might cost? 3) Even crazier, maybe there is a way to have a custom flex disk made that will work as an adapter? Does anyone know what other models have similar flex disks to the 116 ? Thanks in advance!

-On a side note the axles from the 116 look identical to the 123 exept they are about an inch too long.

[sleeeper]

I just thought of one more possibility,
can you remove the differentail flange? maybe I could just swap the flanges between the differentials. This would be the best solution, any ideas on how to go about it or what is involved in removing the differential to flex disk flange?

[MTUpower]

I asked about w126 diff in a w123 and dieseldiehard gave me this answer-

Hi As I recall, the diff cases were different in widths. The wider SD part caused the axles to push the wheel assy furhter out so the edges of the tires were wearing (because it changed the Caster?)
A look at the microfice showed different part numbers for the differential assembly even though the gearing was the same. I don't know if the SD the diff came from was a 116 or 126 chassis but the mechanic fixed the problem by using spacers of the right thickness, they are available as a set from Mercedes which cost about $50 (for a bunch of little steel discs!?)
Anyhow the problem was real and fortunately the solution was simple. I hope this saves you from the tire wear problem that I had following the diff swap in my wagon. Its been fine since the right spacers were installed.

perhaps a search "easter egg" not kidding or other key words will help
William

[sleeeper]

So in case anyone cares,
The 2.65 w116 chassis differential is not a straightforward swap into the 123 chassis. I managed to make two special sockets by grinding and welding some cheap ones in order to be able to remove the "universal flange" (piece that bolts to flex disk) on each diff used a gear puller to remove flanges and then swaped.
I was a little perplexed about how to remove the pinion nut as it is locked in place at the factory by bending over a tab into a grove on the pinion and there was nothing to grab onto to unbend it. So I tightened the nut a little bit to unbend it a smidge so I could bend it back. I really wish I hadn't done that. I found out after the fact that there is a crush spacer in there and that if you over tighten the pinion nut it will screw up clearances. The tightening torque spec'd for that nut is 100-150 Ncm or about 0.75 ft/lbs! I swaped flanges and replaced the nut and did my best to tighten it to spec-which is pretty much finger tight! I think/hope it will be OK but would probably have shied away from all of this if I had not already spent $80 on the differential. Other than the different flange one other noteable difference between the differentials is that the 116 unit located the driveshaft ~1/4" lower than the stock unit. So... for all of you 123 diff swapers you may want to skip the 116 chassis. I will update this once I have tested it on the road.
Cheers

[sleeeper]

Well,
Things took a better turn today, I got the 2.65 diff into the wagon and replaced the noisy axle while I was at it. Man, getting the mounting studs on the diff to line up with the holes in the car was a serious pain, It took a lot of manuvering and attempts and then it jus finally went right in. I still need to recalibrate the speedo but the axles seem to fit well-using the spacers from the 123 differential. I just got back from the first test drive , no weird noises plenty of accelleration and it is much quieter on the highway. So it looks like this might just work out. The best HWY mpg I got before was 27mpg-I can't wait to see what kind of a difference the differential makes. So, besides swaping the pinion flange the 116 differential will fit in a 123. Interestingly the gears on the 116 unit are a bit larger than those on the 123, and on the test drive I could almost swear there was a little lsd action going on. does anyone know if the w116 bodied 450sel came with limited slip? I would have thought it would be obvious from looking at the ring gear?

[t walgamuth]

yes i think it should be readily apparent if you know what to look for. (on the posi. ) look for pictures in a book.

i would have discouraged this very drastic change in ratios. but you should get really good mileage at the price of slower take offs. i have done a number of rear end changes and the % change in the engine speed vs the car speed is pretty much the change in the mileage in a diesel. in gas cars it is not so clear. good luck. ps you will need to find a way to make the speedo read right too. did you get one with the diff? and will it interchange?

[sleeeper]

On driving the car it seems to do fine on take-offs, actually I am surprised it didn't slow things down more. I have yet to take it up a really steep hill though. the cruising on the highway is really where it shines though, quite and plenty of power.

As for the speedometer, I found what I believe was the speedo from the same car but somebody had mangled it up, but I did take the gears out of the unit and checked to see if they will swap into the wagon and that looks good, unfortunately I can’t remember if it was a 120 mph speedo like the one in my wagon so now I’m not sure. I found this 116 speedo on ebay:

This auction is for a good used speedometer used on the 107 and 116 chassis Mercedes-Benz. This would include models such as 280S, 280SE, 300SD. 450SE, 450SEL, 450SL, 450SLC, 6.9 and others. This unit has been tested and all functions do work including the odometer. Reads up to 125mph and odometer reads 40K miles. Unit is calibrated to W=1155…

But I am dubious about the claimed calibration as a lot of the models listed had different rear ratios. Does anybody know what calibrated to W=1155 means? I emailed the seller but so far no reply….

The difference in ratios is ~13.7% if I could improve my mpg that much I will be very happy! –That’s ~3.5mpg! I didn’t think the change was so drastic as other forum members have switched from 3.07 to the 2.47 ratio and been quite happy-that’s a 19.5% change!

[Benzawy]

How is the performance now?

By the way, what model w123 do you have (year and motor size)

[snookwhaler]

It sounds like the swap went well. That is great. I replaced a diff. in 123 last year. Not that big of a deal. I remember lining up those 4 studs to the holes was a bit of a PITA.

I'm not sure if the MB is any different... But on most diff.'s you are supposed to measure the rotational torque of the pinion with a "needle type" torque wrench. You make a note of this torque before removing the pinion nut. Then you always install a new crush washer and set the nut back to a torque value (specified in the shop manual). Then you check your rotational torque again and so on. If it is not done properly, your diff. will be short lived.

[charmalu]

Welcome to the forum

This thread is from 05, and the guy`s last activity is 1-5-09. so not around.

here is a thread of setting and determining the friction preload.

www.peachparts.com/shopforum/showthread.php?t=233540

there is a ton of info on doing the diff swaps. if you do one. remember, the spedo is matched to the differential, not the transmission. besure to grab the spedo.

Charlie

[Doktor Bert]

Couldn't you just swap the flex disc????

[vstech]

the bolt pattern on the flex discs are too wide for just swapping the disc.
they don't make a disc with two different patterns. it would weaken the disc.

[Doktor Bert]

Ahhhhhh.....

So changing input yoke is job #1...

How to get around the axle issues????

[Doktor Bert]

When I do this swap, I won't have a back-up car, so I must plan ahead. Sorry for all the questions....

[Doktor Bert]

So, what else, exactly, will I need?????