Melted Speedo Drive Gear (in Tranny)

[dbdan]

Hi all. I've got an 84 190D with a speedo that has never worked. I read the different posts and tech threads on how to replace the gears in the instrument cluster or replace the cable.

I pulled the cluster and dissasembled it and everything looked fine. I then checked the cable by putting my drill on it and it checked out ok. I should have checked this first!

I then started the car and looked up in the transmission tailhousing and could see that the plastic rod that accepts the speedo cable wasn't turning. I finally got around to pulling it apart and this is what I found.





Both drive gears are fried. Anyone ever run into this before and know what would cause it?

There is a tube that directs ATF up over the top of the larger gear. I'm thinking this is plugged???? Any way to check it?

Once I get the parts and re-assemble, I'll post the rest of the pics in a tech. I couldn't find any other posts with this info.

I will also recommend people check the speedo cable before pulling the cluster!!!

Thanks.

Dan

[280EZRider]

My first guess is that you fried the gears by spinning the cable w/your drill. If the speedo works, then the original problem was probably a bad cable. The speedo can be spun - slowly - w/a drill to check it, but I don't believe the cable can; hence, the fried gears.

[tinypanzer]

Somehow I think if he is smart enough to get his tranny apart like that, then he's not dumb enough to spin the cable from the speedo end. Just guessing.

Is that really melted plastic on those gear teeth or just some old white grease that has hardened up and lost all of its lubricating ability? Hard to tell from the pics. Looks like cruddy old lithium grease.

I've never opened one like yours, so I just dunno.....



-tp

[babymog]

A couple of possibilities:

Possibly this was the fabled car that had the JATO rocket strapped to it and went like mach-2. The plastic gears couldn't handle the speed.

Although it looks like it was heat, could it also have been stress & heat from a seized speedometer cable then the cable was replaced but the PO never figured out or repaired the resulting problem?

One of those "might never know" failures.

[tinypanzer]

Okay, I have an hypothesis.

Let's assume that some lubrication device didn't fail, and something else caused it.

Hypothetically, what would happen if the cable were very hard to turn? I can see a scenario where a cable that was too high on friction would cause a whole bunch of extra heat to build up on the teeth of the gears. Once it gets to a point where the gear starts to deteriorate, the friction only goes up and the gears just get hotter. Eventually they melt down.

What I'm getting at is perhaps a fault in the cable, the cable routing, or the speedo caused too much of a load on that gear.

Just an hypothesis.


-tp

[pawoSD]

Yikes! I am lubing our W124's cable sometime soon!

[dbdan]

Originally Posted by 280EZRider

My first guess is that you fried the gears by spinning the cable w/your drill. If the speedo works, then the original problem was probably a bad cable. The speedo can be spun - slowly - w/a drill to check it, but I don't believe the cable can; hence, the fried gears.

HAHAHAHA...that's funny!!!! I guess I should have been more clear, I put the drill on the end of the cable that I removed from the tranny with the other end still connected to the back of the speedo, so I could actually see the needle on the speedometer move. I wouldn't be able to tell if the speedo was good if I put the drill on the end that I unplugged from the back of the speedo... (Sorry, it's been a REALLY long day, I don't mean to sound like a jerk...)

[dbdan]

Originally Posted by tinypanzer

Is that really melted plastic on those gear teeth or just some old white grease that has hardened up and lost all of its lubricating ability? Hard to tell from the pics. Looks like cruddy old lithium grease.

Tp, thanks. Yes it is actually melted plastic that is even hard to pry off with a screwdriver. Sorry for the crappy pics, my camera is old. But there were chunks of plastic in the bottom of the tail piece when I removed it. I have pics (although also crappy) on my home computer.

Dan

[dbdan]

[quote=babymog;2092715]A couple of possibilities:

Possibly this was the fabled car that had the JATO rocket strapped to it and went like mach-2. The plastic gears couldn't handle the speed.
quote]

It would have to have been some external engine to generate ANY speed in a 190D. If you've ever driven one, you'd know that it's own engine is incapable of generating any speed. Except maybe when I'm going downhill with a tailwind on ice!

[dbdan]

Originally Posted by tinypanzer

Okay, I have an hypothesis.

Let's assume that some lubrication device didn't fail, and something else caused it.

Hypothetically, what would happen if the cable were very hard to turn? I can see a scenario where a cable that was too high on friction would cause a whole bunch of extra heat to build up on the teeth of the gears. Once it gets to a point where the gear starts to deteriorate, the friction only goes up and the gears just get hotter. Eventually they melt down.

What I'm getting at is perhaps a fault in the cable, the cable routing, or the speedo caused too much of a load on that gear.

Tp, thanks again. I'll double check the cable. I appreciate the help.

Dan