No Downshift, Strange Upshift!? - PeachParts Mercedes-Benz Forum

will_t · #1 02-28-2018, 10:38 AM

I have a recently acquired 1985 300TD turbo diesel North American market with a 4-speed automatic I am in the process of trying to sort out. From a stop it always starts out in 2nd gear - the only way to start it in 1st is to put the stick in L. The 2nd to 3rd shift is somewhat strange: with moderate acceleration the engine revs don't really change. It just shifts into 3rd and keeps going. It feels a little like flare but there is not a lot of perceptible loss of grip. Strange. The 3rd to 4th shift feels quite normal. Finally, it is not possible to get this car to downshift using the accelerator pedal. I don't know if it is the Klima relay (which I replaced with a used one, for what that's worth) or the kickdown switch, or both. Any ideas?

Thanks!

sixto · #2 02-28-2018, 10:43 AM

Is th control pressure cable properly adjusted?

Sixto
98 E320s sedan and wagon

Diseasel300 · #3 02-28-2018, 10:46 AM

In addition to checking the control pressure cable, you could have vacuum modulator issues too. Weird 2-3 shifting can be the K1 accumulator spring, it is widely documented on this forum and elsewhere.

Lack of downshift can be the Klima relay, but is also more likely to be the kickdown button itself being bad or the solenoid being gummed up or nonfunctional on the transmission.

tyl604 · #4 02-28-2018, 10:49 AM

It is a 300D; a 300TD is a station wagon.

Mxfrank · #5 02-28-2018, 11:47 AM

Many of them are second gear start by design. If the solenoid circuit is in good shape, you would also get first if you do a full throttle start.

To check the solenoid circuit, pull back the carpet to expose the kickdown switch. When the engine is running, there should be power going into the switch. If not, it’s the Klima or something further back: fuse or OVP relay. If there is power, then the switch itself, solenoid or wiring need a look.

Flare in third sounds like the K1 accumulator spring or piston, easy enough.

It would also be worthwhile to change the fluid and filter, you can do that when you swap springs.

will_t · #6 02-28-2018, 12:09 PM

Quote:

Originally Posted by Mxfrank

Many of them are second gear start by design. If the solenoid circuit is in good shape, you would also get first if you do a full throttle start.

To check the solenoid circuit, pull back the carpet to expose the kickdown switch. When the engine is running, there should be power going into the switch. If not, it’s the Klima or something further back: fuse or OVP relay. If there is power, then the switch itself, solenoid or wiring need a look.

Flare in third sounds like the K1 accumulator spring or piston, easy enough.

It would also be worthwhile to change the fluid and filter, you can do that when you swap springs.

I will check for power at the kickdown. The OVP fuse is good, whether or not the relay is good is anyone's guess. It is possible that the solenoid itself is bad. Is replacing the solenoid a DIY proposition? I have a lift but limited experience, and in the case of the solenoid, none.

Thanks!

will_t · #7 02-28-2018, 12:10 PM

Quote:

Originally Posted by sixto

Is th control pressure cable properly adjusted?

Sixto
98 E320s sedan and wagon

I will check the cable also. Thank you!

will_t · #8 03-02-2018, 04:45 PM

I adjusted the cable so now it will downshift 4 to 3 and also 2 to 1, but strangely, not 3 to 2.

There is no power to the kickdown switch. I put what I believe is a good Klima in it (from another car know to work) and all the fuses are fine. I am stumped. Any ideas as to why there would be no power to the kickdown switch? The elec. diagram shows only the Klima between the fuse and the switch.

Thanks!

tyl604 · #9 03-02-2018, 07:48 PM

Will - can you straighten us out? Looks like you have owned a number of station wagons per the 300TDs in your signature so you obviously know the difference between a 300D and a 300TD. But the pic is of a 300D. Are we talking about the 300D pictured or we actually talking about a TD?

will_t · #10 03-02-2018, 08:38 PM

The pic in my signature is of a CD. The car I am asking about with regard to the downshift is a TD.

Diseasel300 · #11 03-02-2018, 09:20 PM

Since this is an '85, does the tach work? A/C? The Klima relay uses the tach signal to disable the compressor and it also will disable the kickdown solenoid in certain conditions. If the tach is wonky or nonfunctional, it could explain why the KD circuit isn't energized.

Later models (late 80s) did away with the RPM dependent kickdown, and used the tach signal only for the compressor.

will_t · #12 03-02-2018, 11:52 PM

Quote:

Originally Posted by Diseasel300

Since this is an '85, does the tach work? A/C? The Klima relay uses the tach signal to disable the compressor and it also will disable the kickdown solenoid in certain conditions. If the tach is wonky or nonfunctional, it could explain why the KD circuit isn't energized.

Later models (late 80s) did away with the RPM dependent kickdown, and used the tach signal only for the compressor.

Oh my gosh I hadn't put these two things together. I have the dashboard and the center console out because I am re-doing the interior so I'm driving it around with only the left-side gauge - mostly because of the oil feed line. There is no tach! I bet you're right that the Klima is not allowing power to the kickdown. I'll have the dash back in sometime next week so then I'll be able to test it with a tach.

Thank you!

sixto · #13 03-03-2018, 12:03 AM

Maybe something’s not connected while the interior’s apart.

Sixto
98 E320s sedan and wagon

will_t · #14 03-03-2018, 11:33 AM

With an instrument cluster fully connected, and a climate control unit has been all along, everything electrical except the ashtray, radio, and glovebox light is connected. Still no downshift from the kickdown switch.

Mxfrank · #15 03-03-2018, 12:14 PM

I had a kickdown trace vaporize on the Klima circuit board. The reason ended up being that the wiring to the solenoid had torn insulation, so when kickdown was engaged it sometimes created a dead short. That was tricky to diagnose, but at least the repair was easy. Knowing that can happen, test to see if there's a short to ground in the kickdown circuit. If there is, fix the wiring before you waste another Klima.