HLG600

Driving to meet up with a friend and these two girls last night, figured I'd have some fun on the open highway. Travelling at roughly 60 mph when I floored to kickdown. The revs went up, but the car did not acclerate anywhere near the expected punch. Tried once more, same deal. Engine revved, but the 5SP didn't downshift.

I dropped it into 3rd gear, 3/4 throttle, and wow did the car move. Shifted to 4th, with the grin on my face getting bigger.

So, why do think the auto didn't downshift when floored to kickdown? I did a transmission computer reset today...slightly better result, but still an annoying delay in WOT acceleration (auto mode). I use the gears, the V12 hammers away.

Any idea about the source of this newfound acceleration delay?

Bigdot

hows teh tranny fluid is it fresh? was the tranny cold?

99_SL_Sport

Your kickdown switch is obviously bad.

bobterry99

Actually, this can't be a possibility. The kickdown switch does not influence 5th-4th gear downshifts on the '96 and later SL600.

The problem may relate to the throttle position signal that the transmission control unit receives over the controller network from the engine control module. I think it is best evaluated by a shop that has access to Mercedes diagnostic scan tools like the HHT or SDS.

jjay911

you just need one of these...

bobterry99

Good luck in convincing anyone of that, because I have one that I would love to sell.

jjay911

Tell us about it.. WHy.. JJ

HLG600

The engine temperature was at 80-85 degrees celcius, maybe 15 minutes of moderate driving in cold weather. To my knowledge, the transmission fluid hasn't been changed. Since the car has only 43,000 miles, I don't plan on changing it until 70K, hopefully. Drove it today in automatic mode, and acceleration seemed fine (didn't go WOT due to traffic restrictions, but plan to test it out again this weekend). On a side note, I love shifting the car myself: 40 mph, downshift to 2nd, and you can feel the torque really pull.

When I get the chance, I am going to reset the transmission computer again, and take it on the highway right after. I am hoping it is just a glitch after driving in traffic alot.

SL BRABUS

Check if there any leak on the tranny...... Hope this help....... good luck.....

99_SL_Sport

How could a leak possibly cause the kickdown not to work? The transmission shifts down fine with the lever and when the car slows down.

SL BRABUS

The transmission will not shifts properly if the fluid is low or over fill when it in auto ........

99_SL_Sport

I agree, but since the car shifts fine with the lever and speed changes, doesn't that rule out the possibility that the fluid level is the cause?

SL BRABUS

Yes, I know what you mean....... But it don't hurt to check it out.........

HLG600

Thanks for the input guys.

Floored it to kickdown again today. This time, there was a one second delay in throttle followed by an onslaught of acceleration and the conquering of a hill at 80 mph. However, I have yet to reset the transmission computer again. It now appears to be just a glitch that needed a heavy foot to correct.

SL BRABUS

I think your V12 is jealous at you because you been thinking about those 2 girls instead of your car.....

SL600 V12

Our transmissions are self learning no? Maybe it just got used to not doing kickdown or doing slow kickdown from city driving.

bobterry99

Yes, the electronically-controlled transmission learns the style of the driver and adapts its shift characteristics, but this does not affect shifts at full throttle.

damaged

Since when is the kick down switch not used for kick down ???
You could have a few problems here. Fluid level is not an issue, as the transmission would shift but it would slip.
It could be a bad selector switch, kick down switch, valve body, or one of the solenoid valves in the electrical plate.
First thing to check is the floor mat. Has it curled up under throttle pedal and stopping you getting kick down??. If not have it put on an sds and have codes pulled and go from there.
Good luck

bobterry99

jjay911: I'm dumping my manual tranny '90 300SL and other R129s because I have too many cars, and there is no place to put them.

You misunderstood. I did not write that the switch is not used for kickdown. I simply noted a circumstance where beyond full throttle, engaging the switch had no bearing on what gear the transmission would shift to. This is unconditionally true for the 5-4 shift on the SL500 and SL600. In contrast, it does matter on the SL320: at high speeds the 5-4 shift will only occur if the kickdown switch is engaged.

That is all moot in HLG's case, actually. Given that he was going 60 MPH when he floored the gas, upon seeing full throttle the tranny ECU should have downshifted to 3rd gear, and once again, whether or not the kickdown switch were engaged would be irrelevant.

jjay911

jjay911: I'm dumping my manual tranny '90 300SL and other R129s because I have too many cars, and there is no place to put them.

I have storage. How much??? I want to do a project car 129 sl manual trany with a C36 engine.. What do you think of that??? JJ

bobterry99

I'm thinking I want about $9K for the car. If you are interested and want more info, email me and I will reply with pictures and more info about the car.