Tom928

On my 84S, I replaced the trans about 1500 miles ago.
Since then the tranny has been operating fine.

It started shifting 1-2-3-4 right in a row. By 30 mph, I'm in 4th gear and I have no kickdown even if I floor the pedal.

I checked the fluid level and it is between the min / max lines on the reservoir.

I checked the vacuum and it it good, when the trans shifts it is smooth and normal.

The bowden cable is just a little loose. It barely slips on the ball, but there is just a little slack. Is the cable THAT sensitive?

I was reading in the WSM and found that the solenoid valve has a fuse in it, but I don't seem to find it in the wiring diagrams. Does anyone know where the fuse is or if the 84 had a fuse?

Any tips or troubleshooting ideas would be appreciated.
TIA,

Landseer

The bowden is a mechanical connection to a hydraulic circuit.

Yes, it is that sensitive. Go thru a set of tightening iterations and see if you can solve it that way. Should.

To tighten on the 84 requires some spiderman arms, or at least removing air housing and using a long screwdriver and/or long angled needle nose pliers.

Kickdown relay exists, not sure of the exact circuit. Should be some simple test procedures to test operation of switch, relay and actuator.

Floor kickdown is mechanical linkage acutation of electric actuation of hydraulics, bowden kickdown is mechanical actuation of hydraulics, they are I think pretty much separate.

Tom928

I will go thru tightening the cable and see what effect it has.
I know what you mean about working on the cable.

Thanks Landseer

Calgary Ole

What you describe sounds like the bowden cable is disconected, maybe check that it is attatched at the tranny first. Also, keep track of the revolutions you adjusted so you can return to the original location if its not the problem. It took me weeks of adjusting to get mine back to the proper place.

Tom928

I have begun to wonder about this.
The trans was working fine to begin and shifting normally with kickdown.

Something changed. If the cable was loose enough to get diconnected OR has broken, it sounds like that could be the problem.

Another question is the kickdown switch under the gas peddle. What is the symptom if it goes bad?

Calgary Ole

Yes under the gas pedal but I am not familiar with trouble shooting the kickdown.
When I was having trouble adjusting the Bowden cable I disconnected and took it for a spin and had the quick shifting you described.

Tom928

Update: So I adjusted the kickdown cable. Tightened by 7 turns and loosened by 3 turns - no change.
I checked to see that the cable is connected. If I pull, it does stop and pulls itself back when let go.

I checked the kickdown switch under the gas pedal and it is working. As Wally P. suggested in an old post, I can put the car in D, turn on the ignition and press the gas pedal and hear the solenoid click with the depression on the gas pedal engaging the kick down switch.

Fluid level is fine between the min/max marks.

It still shifts fast, by 20 mph I am in 4th gear with no kickdown when floored or no downsift when slowing down, I have to manually downshift. I can be going 20 mph and have to manually downshift from 4th to 3rd, then to 2nd the trans will not do it unless I come to a stop.

There is no slippage, when I put it in a gear and accelerate, it jumps and goes but solidly.
Upshift's are very, very quick. 1-2 is by 5mpg, 2-3 is like 2 seconds after and 3-4 is by 20mph!

Ideas???

IcemanG17

my 1st thought is the kickdown solenoid at the tranny (not the switch under the pedal) is not working....unlike chebby automatics, the mercedes unit determines shift RPM by the bowden cable and the kickdown solenoid...the solenoid at the tranny can fail and cause problems similar to what you describe

Another test is this...disconnect the bowden cable completely...I do it at the throttle body...this will cause the transmission to always want the highest gear possible... If you do this and the tranny stays the same....then maybe the bowden cable is no longer hooked up inside the tranny....odd but could happen...we run the lemons racer this way.....this way we determine when it shifts gears....prior to this with the bowden hooked up it would hold WAY to high RPM's before it would shift.....think 6500rpm....

Landseer

I don't know enough about the hydraulic and electric kickdown features to help much.

Best I can do is give you some visuals. Maybe this well spur more discussion and get you to a solution. (Am speculating about a blockage in the valve body, maybe the valve acuated by the bowden, but have no experience with this at all.)

Here are some pictures of my 84 auto transmission during disassembly.

They show where the bowden cable attaches and what it actuates.
At the end, I'll also show the electric kickdown actuator referenced by Brian.

I don't know if the electric solenoid could cause your Bowden downshift problem, I don't think so.

But, I know it must work to achieve kickdown via switch the floor switch beneath pedal.

Landseer

For completeness, here's one more that shows the business end of the 84 bowden cable.
(Sorry for the Newfoundland dog hair, its everywhere, including my cereal bowl and coffee.)

And one that shows the other end of the bowden, as it attaches to the throttle body.

Last picture is governer unit.

(Would be great if you could say, hey Chris, I did the same thing you did at first, tightened the cruise cable and wondered why the transmission wasn't affected)


You need somebody knowledgeable to help on this. I've heard about issues also with governors causing shift problems. A28 troubleshooting guide is a little cryptic, maybe WSM is better.

I wish more people would post about troubleshooting these transmissions. They will increase in focus as our cars age.

Mrmerlin

Might be a good idea to get under the car and remove the white bowden cable housing from the trans and lift it up about 1 inch if the cable is connected it will not let the housing up more than an inch or so and you should see the rod come up with the cable portion capturing the rod, make sure that the rod wants to return into the trans body with some spring pressure as previously posted.
If the cable has come undone then you may need a small set of needle nose pliers , a small mirror and to disconnect the ball from the throttle quadrant to give yourself some extra cable to reattach the cable

Tom928

Thanks for all the help guys.
I will do some more checking tonight and see what I can find.

Tom928

I was able to get the transmission working again. Looks like there were 2 problems.

1) The kickdown solenoid was stuck in the ON position even without power to it.
After replacing the solenoid I now have kickdown.

2) Valves in the valve body were dirty and sticking. Upon disassembly I found a lot of buildup on the surfaces.
Alot of varnish like stuff on the valves and the valve bores. I did replace the K1 springs just to be on the safe side; however, I did not replace any other springs.
After disassembly, cleaning and reassembing the valve body, the car now shifts different than it did when I first replaced the transmission.
Now 1st > 2nd shift is quicker, 2nd > 3rd is quicker(and a little harder??), but 3rd > 4th waits longer and is very smooth. The downshifts are later but smooth.

I don't think I have it dialed in but at least I'm back on the road again.
BTW - does anyone have any recommendations for a gauge set to measure pressures?

Thanks to Steve C. and everyone on the thread for helping.


Cheers,

M. Requin

Tom, have you learned anything about a gauge set? It looks like it wouldn't be too difficult to put together if you had info on the fittings. I'm interested in doing this myself.

Tom928

Hi Martin,

So far this is what I have;

1) Advanced Tool Design Model ATD-5550 Automatic Transmission and Engine Oil Pressure Gauge Kit
http://www.amazon.com/Advanced-ATD-5.../dp/B000OUZBZ0
It's a single gauge with fittings and hose. My concern is that the hose is only 6ft and would likely not attached to the trans and come up into the car far enough to check pressure while driving if a person needed to do that. It could be extended I guess. ~$30 x 2 plus then have to make a holder.

2) Transmission Pressure Gauge Set
www.baumtools.com/pdf/10903.pdf
This was more like what I was looking for; however, it lists for $189 according to the lady I talked with a Baum tools and it is NLA.

So far this is all I have learned.
Sounds like just buying the gauges, some hose and fittings then making a custom set for the 928 trans might be the best option.
I was going to give the local MB transmission guys a call today and see if they can help.

Also, I will start a new thread on this.

Cheers,