W126 Tranny Operation
 

I've had a question for a while and finally decided to ask. On all other cars that I've driven, if you downshift from drive to 3rd (or 2nd depending on the number of speeds) while coasting at highway speeds, the transmission shifts and the car slows via engine braking. On my MB, nothing happens unless I touch the gas in which case the tranny shifts into 3rd with the associated increase in engine speed.

Is this by design or is something wrong? If by design, why? This way I don't have the ability for engine braking at high speeds that I have in all other cars.

Thanks
jlc

In an attempt to move this up to the top and get some ideas, I'll add a bit to the question.

Yesterday I had the chance to drive another W126 (granted it was a 350SDL so the tranny is different). However, in this car when coasting down a hill, I shifted from "D" to "3" and the car noticibly downshifted. This is the type of behavior and engine braking that I'm used to in every other car I've driven.

Why am I not getting this same behavior in my 560SEL? Is it a difference of design operation or is there a problem with my particular tranny?

Thanks
jlc

Maybe the shifter linkage bushings are gone. Is your shifter loose? When you tap the gas, you shift the engine's position and maybe cause the linkage to actually find 3rd. When I replaced mine, there was 1/2 of one bushing in a linkage that required two. :)

jcantor,

This does not seem normal, but I'm not sure why yours would act this way. How are the upshifts from a stop? Are they at all harsh? Regardless, it was impressed upon me long ago that brakes are cheaper than trannies. I will limit my diesel to "3" at speeds below 45mph simply because it's better for it, but I do not forcibly downshift with the shift lever.

Goldenbear,

I would definately agree with you that brakes are cheaper than trannies however on long, steep downgrades, trannies are cheaper than my life. Along that line, though, I do know one person who brags about getting 100K out of his brakes but eventually admits that he's had the transmission rebuilt three times in 450K miles which seems like a really poor way to spend your money to me.

I only run into situations where I might downshift a few times a year. In fact, it probably took me 8 months since having the transmission rebuilt last spring to discover this issue (and I'm pretty sure the behavior was the same before the rebuild as well). Upsifts are bearly noticible under most normal conditions and moderate to hard but not harsh at WOT. Everything is certainly much better than it had been before I had the tranny rebuilt.

jlc

On a 722.3 four speed transmission if you move the shift lever from 4th to 3rd ,the Trans should down shift to 3rd gear and hold it. Take the car back if the transmission is under warranty, let them check and adjust all oil pressures. My diagnosis is that the valve body was not rebuilt.