Need to fix my transmission issues!! - PeachParts Mercedes-Benz Forum

braverichard · #1 12-29-2004, 08:28 PM

Hi again all,

I need help with certain things relating to the transmission in my '84 Euro 500SEL which was actually taken from an '88 420SEL.

First of all, when I take off from a stop lightly, the transmission shifts at 20mph. It zooms off with great power but once that shift occurs, it slows down and crawls to 40mph where it shifts again and then starts zooming powerfully into the high speeds. When I floor the gas pedal from a stop, the exact same things happen. No difference! I've been told here that I need to adjust my TV Bowden Cable, however I've had no luck in locating it. Not knowing much about the whole "kickdown" mechanism, I decided to explore things before even consulting the factory service manual. I found the kickdown switch right under the accelerator pedal. In fact, when I found it, I laughed a bit as I didn't expect to see that the accelerator pedal literally hits that switch. Anyway, I disconnected what looked like its power supply, and I drove the car and nothing changed. The car drove just like it did with the kickdown switch connected.

To summarize, I need these issues cleared:
1) Does the result of my adventure with the kickdown switch indicate that it doesn't work?
2) Can someone who owns this same car post a picture of the TV Bowden Cable that I'm supposed to tighten?

jp928 · #2 12-29-2004, 10:14 PM

Gearbox behaviour is modified by lots of things, including how much throttle you have in. There will be a connection from the throttle to the box by a cable somewhere. The kickdown switch will come in when you press MORE after reaching WOT, to tell the box you want to go down a gear for some more pick up. If you werent pressing the throttle right to the boards, it wont be relevant to your problem. You should find 3 connections to throttle at engine - actual throttle, moved by the pedal, cruise control cable or similar, and another going down to the box. Sounds like the gearbox connection is loose or broken or jammed in its casing. The gearbox is also supplied by a vacuum connection (dont know your model, maybe wrong here), which if broken will give hard shifts as though you are WOT, and a poor idle on the side.
HTH
jp

BenzMatic · #3 12-29-2004, 10:47 PM

It sounds like TV Bowden cable adjustment issue, this adjust the shift timing on your tranny. I am attaching the pics from a 87 420SEL, it should be the same for your car. The cable come from tranny to the back of the air filter and attaches to the Accelerator/throttle linkage. Try adjusting it to your choice of shifting.

Good luck

deanyel · #4 12-29-2004, 11:09 PM

For an 87 that is a clean car. Looks like a Michigan 04.

braverichard · #5 12-30-2004, 11:08 PM

BenzMatic,

Thanks for the pics. Attached are the pictures of the setup in my car. I've found the components on your picture but which is the cable? I tried moving that piece of medal that is connected to the throttle linkage and all I did was rev the engine as a result.

And why don't you think the kickdown switch has a part in all this? I mean, after I disconnected its power, there was no change in the way the car behaves when I floor the accelerator.

BenzMatic · #6 12-31-2004, 12:28 PM

The cable is under the linkage, sort of, I can see the black rubber boot for the cable in your pic. It is probably a white color cable going away from you, standing from dirver side.
What do you mean by "rev engine in result", do you mean it rev. high before it shifts the gear? please explain. You might be having a "flaring" problem, in that case may be you need to adjust the "vacuum modulator" on your tranny.

All you have to do is losen the screw (make sure to mark the current location, so you can always return back if it do not work), and slide the metal part a bit and re-tight the screw and test drive. This adjustment changes the shift points with respect to the engine rpm.
As for kick down switch is concern, it only activates when you floor the pedal and all it does is down shift one gear.
The problem you posted do not exhibit any co-relation to the kickdown function. You can reconncet the switch and floor the pedal,press the kickdown switch, and you check if it is working or not. It should downshift the gear, rev the rpm high and give you a great pickup right away.

jp928 · #7 01-01-2005, 02:58 AM

Moving the cable fitting while it is locked up will obviously open throttle and lift revs. The point is to change the relationship of the cable to the gearbox with the throttle position - hence unlock screw, move fitting a couple of mm, lock up screw, test drive.
Take the two wires from the kickdown switch, turn ign on, but dont start it, short the wires together - you should hear a click from the tranny underneath as the solenoid fires, to open the kickdown valve. If no click, check for +12V on one of the wires- if 0V on both, start looking at fuses. Many Porsche 928 drivers (also have MB Auto trans) wire a parallel kickdown switch so they can kick the box down a gear (by closing switch) without having to floor throttle.
jp

braverichard · #8 03-07-2005, 08:55 PM

HA HA HA !! The transmission is [probably] dead!!

Here's the story. I left work early today since I'm having some work done on the office building. Got home and the weather was nice so I decided to attend to this transmission. I ruled out the kickdown switch: I put its kickdown switch in my 300SD and it kicked down fine. The one from my 300SD, when put in the 500SEL, didn't make a difference. Since I knew it was working, I ruled out the kickdown switch as the source of the problem.

Then I got on the Bowden Cable. I adjusted it fully. Took the car for a test drive. It was shifting late indeed. In fact, flooring the car from a stop would spin the rear tires like hell. I decided to drive up to the lake about 5 minutes from my house to complete the test drive. I got there, went round twice and then I decided to reverse. I reversed over, say 500 ft, came to a complete stop and then tried to drive off but the car wouldn't move forward or backwards! The engine was running, but when I moved the gear selector nothing happened.

I thought the shifter bushings may have been shot or something, but I concluded the transmission just crapped out because when in park, the car would stay at about 900rpm, but once I put it in drive it would drop to 500rpm. Also, when in park, I couldn't push the car, but when I put it in drive I was able to push it out of the road at the lake and into a parking spot. I couldn't even call my girlfriend to come and pick me up from my house as I left my cellphone at home. However a gentleman in the area had his phone so he kindly let me use it to call my girl for a ride.

So there you have it. Since my garage is full of stuff that I don't want to move around in order to accomodate the car in there and since the temperature will be cold here for the rest of the week such that I can't work outside, I have no choice but to have the car towed to my indie and have him determine if the transmission is dead or the bushings need replacement. What do you guys think based on the rpm information in the above paragraph? I'm thinking the transmission is dead but I'll find out what is really the case tomorrow or on Wednesday. One thing's for sure: if it is the transmission, I'll just sell off the car for parts!

braverichard · #9 03-10-2005, 05:51 PM

Just like I suspected. The transmission has been declared toast(dead) by the mechanic. Steve (C32AMG), thanks for your generous price offer to rebuild it. However, this one will be for parts. I'm parting out the sucka. I'll be starting a new thread in the parts section soon for this.