Bowden cable dust boot is partially burned......... - PeachParts Mercedes-Benz Forum

davidd · #1 10-26-2006, 11:25 PM

Hey all, I was looking under the hood of my 1983 300D today and noticed something I thought looked strange... I don't know what it is, I looked it up in the Haynes manual I have but couldn't figure it out, I am for sure new to this car.

Whatever it is, it looks quite melted... so my question is what is it? Should I be worried?

David

R Leo · #2 10-26-2006, 11:30 PM

That's just the rubber boot that protects the end of the transmission's bowden cable. All my cars with automatics look the same way but still function OK.

I don't worry about it.

dkveuro · #3 10-26-2006, 11:56 PM

Do worry about it !

It is melting because of starting ampage not getting to the starter due to a bad ground strap/mounting...they are using the kickdown cable instead.

You may find the kick down cable is softened to the point of breaking.
Need to inspect it closely.

Looking at the arm...it seems heat discolored.
You'll notice that the melted boot material has dropped onto the lower arm while the throttle was fully open as it was being cranked.....your seeing it in the closed position.

.

davidd · #4 10-27-2006, 01:16 AM

So basically to fix this I should....

Make sure the ground is fixed.... what wire is not being ground properly?? And where would it be grounded?

Replace the kick down cable (if the current one is brittle).

Replace the bowden cable and the rubber boot at the end. Where can I buy this cable?? Wait a second, after looking up bowden cable on wikipedia, it sounds like a generalized type of cable... so what is the cable leading into the rubber housing exactly??

Thanks,
David

PatricdeBoer · #5 10-27-2006, 02:25 AM

It lets the tranny know when to shift. You can adjust it to get it to shift at higher or lower rpms.

Meridivs · #6 10-27-2006, 06:52 AM

At which rpm's does it have to shift?

dkveuro · #7 10-27-2006, 10:04 AM

Quote:

Originally Posted by davidd

So basically to fix this I should....

Make sure the ground is fixed.... what wire is not being ground properly?? And where would it be grounded?

Replace the kick down cable (if the current one is brittle).

Replace the bowden cable and the rubber boot at the end. Where can I buy this cable?? Wait a second, after looking up bowden cable on wikipedia, it sounds like a generalized type of cable... so what is the cable leading into the rubber housing exactly??

Thanks,
David

There is a heavy ground strap under the car next to the transmission bell housing...grounds the engine to the chassis......check this is present and ends are clean and tight at the bolt mountings.

The ( burnt.) cable goes down into the transmission, you'll need to to drop the pan to install a new one.

If it has got really hot, the cable will have detempered and will begin to stretch causing the transmission to up shift very early.

.

.

riethoven · #8 10-27-2006, 10:55 AM

Quote:

Originally Posted by dkveuro

Do worry about it !

It is melting because of starting ampage not getting to the starter due to a bad ground strap/mounting...they are using the kickdown cable instead.

You may find the kick down cable is softened to the point of breaking.
Need to inspect it closely.

Looking at the arm...it seems heat discolored.
You'll notice that the melted boot material has dropped onto the lower arm while the throttle was fully open as it was being cranked.....your seeing it in the closed position.

.

Please help me to understand that despite the tranny and engine being bolted together, that a badly grounded engine/tranny would use the Bowden Cable as a ground wire. Doesn't the Bowden Cable go to the tranny?

davidd · #9 10-27-2006, 11:28 AM

So is the kick down cable and the bowden cable the same thing??? Or are these two different cables you guys are talking about??

David

SD Blue · #10 10-27-2006, 11:46 AM

Kickdown is provided by a switch located behind the accelerator pedal. The bowden cable is for shift points in relation to throttle position.

davidd · #11 10-27-2006, 12:24 PM

So should I replace both the bowden and the kickdown cables in a situation like this??

Also, where can I buy a bowden cable I don't see them on any of the online stores I've looked at.

Thanks everyone!

David

dkveuro · #12 10-27-2006, 02:58 PM

Okay....let's start over......The burnt cable is the modulating cable to the transmission that adjusts line pressure to change the road speed/rpm for up shifts and down shifts.

The Kick Down switch is a electric button on the floor under the throttle pedal.

The fact that the transmission and the engine are bolted together has nothing to do with the ground circuit....at least, not in this case.

The engine and transmission are sitting on RUBBER mounts.

The only way current can flow to the assembley is through a ground strap which is mounted under the drivers floor and attached to the bell housing of the transmission.

Should the ground strap be missing or there is high resistence, the electricity will seek other routes to complete the circuit.

The battery has a positive cable going to the starter and a short ground cable to the chassis near the battery tray and hood hing.

The electrical power flowing through the chassis needs to complete the circuit to the starter and at the chassis to bell housing the ground strap is there to provide high amp's route to the starter.

Most starters pull 300 amp's or more when cranking an engine.
This ampage needs a low resistence path to flow through..or it will heat up the things it can flow through....much like electricity does to the heat bars that warm your room.......if the path is restricted, the amps will seek other paths to get the job done....in your case the cable to the tranny....and also any other gound path link it can find and in doing so heat the cable and melt the rubber sleeve.

Get under the car and check the ground strap.

davidd · #13 10-27-2006, 05:55 PM

I couldn't find the ground strap, but that doesn't mean it's not there.... I wasn't really sure what I was looking for... does anyone know of a schematic that shows where it is or a photo of it??

I looked around under the driver's floor but maybe I was just looking in the wrong location. I searched the forum with no luck finding a photo nor did my Haynes manual show it.

Thanks,
David

dkveuro · #14 10-27-2006, 06:17 PM

It is usually in area between the steering box and the transmission bell housing. It is made up of a bare copper wire cable about 12mm thick and 1/2 a meter long or less, each end is bolted to the chassis/trans.

You MUST have one...this is not optional equipment.

.

Wallknight · #15 10-27-2006, 09:40 PM

So you are saying that, except for the ground wire and the bowden cable, the engine is absolutely electrically isolated from the chasis?

I've got this gunk, too, but it never worried me. I also have a braided "silver" grounding wire on the wheel well near the battery that is looks like it got chopped from its proper connection. Is this supposed to be the real ground?