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2-1 downshift

1K views 9 replies 5 participants last post by  fatherfixit 
#1 ·
98 C280. I recently replaced the trans with a used one with about 100K on it. When should the trans downshift to 1st when braking to a stop (at what speed)? Mine doesn't go into 1st until its essentially stopped, like less than 2 mph. If I do a rolling stop and take off before it drops into 1st, the downshift is rather abrupt. Its a good solid shift - just not smooth. I don't recall this occurring with the original transmission. Is this normal?
 
#3 ·
#5 ·
Well the best thing to do when a transmission wears out is to rebuild it. You know you've got a good transmission, why would you buy a used one that could have problems? Anyway, replace the fluid and filter, if there is no dipstick tube, you will need to install one. Then, replace the transmission connector seal (also called the pilot bushing), and make sure no ATF has found its way up the wiring to the TCM. If what I just said sounds like chinese, there is tons of information on this website (check out the W210, W140 sections) and on this transmission (722.6) and all its problems.

And for the future, if you have a transmission that lasts 350 000 miles, you don't replace it, you rebuild it (even if you don't do the work yourself, it's a little more expensive, but then you don't end up with problems)!
 
#6 ·
used trans vs rebuilt

This was an economic decision. If I had wanted a rebuilt I would have bought one from Mercedes. At any rate, its a relatively minor problem. Had it into the dealer in Sacramento today, and the mechanic (who seems pretty knowledgeable by the way) took it out for a drive and thinks it's working pretty well and that he could reprogram it but didn't think it was worth the cost, so I'll drive it awhile longer as-is and make a decision down the road.
 
#7 ·
Not a fix but here is my experience.

Bought a 2000 C280 with 35m, now 142m.

A handful of times, it would do that harsh downshift from 2nd to 1st. It would happen with that slow rolling stop, typically on a cold tranny. The kind of stop where you could have approached at greater speed and braked but for whatever reason just decided to coast to it. I live in a hilly area and there is a stop at the bottom of a hill about 1 1/2 blocks from my driveway. Sooooooooooo, I just stopped doing that slow rolling kind of stop. If I was particularly worried, I would change to (W) mode and the car would then start in 2nd gear all the time and skip 1st altogether. I would chamge back to (S) mode whenever I felt more fuel conscious.

Tranny still fine at 142m, nothing done other than a few fluid changes and a wire plug or two.
 
#8 ·
This is a guess,

Since your TB uses the drive by wire and not a cable, the throttle position "thinks" your old transmission is still back there. The new transmission "thinks" it's still reacting to throttle inputs that may not be the same. Possibly your inputs are more aggressive when viewed as the transmission rather than your actual pedal position.

I believe if you disconnect your battery for 10-15 minutes... then reconnect it, switch the car on (but do not start it) and allow it to sit for at least 5 minutes in that condition.

This should allow the TPS to relearn the idle position with zero input....and your transmission can then be on the same page as far as expected level of input.

Again, this is just a guess, but the fix might just involve a 11 mm wrench and a cup of coffee. Can't hurt.
 
#9 ·
Actually, there is a reset procedure for the throttle position sensor, I don't remember it off the top of my head (but it doesn't involve disconnecting the battery, something about pressing the accelerator with key on engine off, switching key off while accelerator is still pressed and keeping it that way for a bit before restarting the car). Do a search for it, you will find it, it might indeed help.
 
#10 ·
Thanks to all for the suggestions. I would definitely say that the trans works better warm than cold, but I think that was true when the car was brand new. I have tried the procedure mentioned by Patman1, and I didn't notice any difference. The dealer informs me there is an "adaptation" procedure they can do in the shop with a computer, but afer test driving the car the tech did not think the problem was serious enough to warrant the expense. For now I'm just driving it. I'm pretty sure it will last as long as I have the car, which now has 360,000 miles on it.
 
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