My '91 300SE turns 3500 rpm at 70. This is finally starting to bug me, and it eats up water pumps, alternators, tensioners, etc. I had the idea of regearing it 10 years ago, but never got around to it.

I thought about trading the 3.73 diff gear for a 2.80.
Then modifying the tranny so it starts off in low gear.
Modifying the speedo would be the last part.
I really think the engine could pull the car down the road at 2700 rather
than 3500, with acceleration just a downshift away if required.
I live in Texas, so I don't need the "Granny" low gearing.

So, questions:

1. Anyone ever heard of doing this?
2. Can I buy ring/pinion gears for my diff anywhere, or do I need
to find a complete diff that would bolt into my late 126 chassis?
3. Would I need to find the exact speedo, with the proper internal gearing?
Or can the electronic speedo somehow be adjusted to match different gearing?

thanks,
DG

I think the axle ratio is 3.46:1.

The problem you have is a nearly 4000 pound car with a 3L engine that produces about 175 lb-ft of torque at 4000 RPM.

If you regear, it will probably be a slug, even with first gear starts, and the cost would be very high relative to the value of the car.

You're better off just driving it into the ground or selling it and getting a V-8 S-class.

Most of the M103 engine cars with automatics are turning 3000 or more revs at 70 except for the later 300Es with 2.87:1 axles.

The manual transmission versions are much more relaxed with their overdrive fifth gear.

Duke

I own one of these cars and Duke hit the nail on the head. You'd spend a fortune reengineering a car to do something that's not feasible given it's weight.

You'd be better off selling it and looking for a 420 or 560 if the revs are bothering you.

In spite of 3450 rpms @ 70mph, I think this is one of the best cars MB ever built. You get the simplicity of the M103 system and the ride/size/comfort of the W126 body/chassis and in my case, 20-22mpg on the highway. Not bad for a big beast.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

I agree. These inline sixes are quiet and smooth as silk. Don't worry about the revs. They are designed for sustained high revs. If you have to, cover up the tach.

Duke

Thanks guys. Yeah, you're probably right. If I did it the poor engine would probably downshift just to fight a 5 mph headwind.
But you gotta admit, even 15 years ago, a tranny with no overdrive, no lockup, and a 2nd gear start was kinda silly. Of course, it's still working perfectly after 160k, and probably will for twice that.

DG

I use my SE for highway driving and find a it a superb high speed car.

I cruise at 90 effortlessly and the low gearing allows for great throttle response at 70mph and up, unlike other cars where you are either coasting or downshifting.

267k of high revving and it still spins right up to 6500rpm in the first three gears.

Great sounds from this motor too- a nice mechanical purr.

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

[QUOTE=Duke2.6]I think the axle ratio is 3.46:1.

I have a 82 300D none turbo and I didn't like the rpm at 60mph in it . it had a 3.56 gear set so on e-bay I found a 3.07 rear end complet for 85$ and it had 130k on it when it arived I checked the ring and pinon and the spider gears, thay all looked good so put it in and gained 8 mph so at 60 now I'm doing 68.
it's a slightly slower off the line but I stay in gear longer and didnt affect the
freeway power at all and the engine now sounds like it should at 65mph.pluss I gained 3mpg on a tank.I had a gear changer put in the speedo cable to correct the calibration.