3 broken speedometer cables in a month! - PeachParts Mercedes-Benz Forum

#1 09-02-2002, 03:12 PM

Hi everyone!

This problem is getting a bit too frustrating... About a month ago, the years old speedometer in my '76 123 200D cable broke. Having served 2 years or so (maybe even more, cant remember really), I simply thought that it was rather normal that it did. So in my usual DIY method, I replaced it with a similar 'slightly used' cable.

After about 3 weeks, the same problem appeared. Thinking that the cable was more than just slightly used, this time I bought a new one so as to make sure that this rather irritating problem should go away for good. To my surprise, this NEW one broke in less than a week! Something must really be wrong! And im too frustrated to know what it is... What happens is that it will operate smoothly and then without warning, the speedometer will rise instantaneously and then will just drop dead.

As I read somewhere, I did lubricate the cables before installing them (although it seems as if they were pre-lubricated or something). I used an ATF because of its fluidity. The whole installation is not a cumbersome or complicated process so I think I've done it right. But the results indicate otherwise...

The cables seem to break at the point near the transmission (not at the instrument panel part) but not at the very end. The cable broke at about 2-3 inches from the 'transmission end part'.

Sorry for my usually long posts, just didn't want to leave what might be pertinent details as regards the problem. Hope you guys can help me out, as always. Thanks in advance!

thebern · #2 09-02-2002, 05:40 PM

Is it ppossible that you have the cable incorrectly routed causing it to 'kink'? Are their any 'hangers' to support the cable you may have missed? These are the only things that to me would seem to cause this problem.

God luck, thebern

#3 09-03-2002, 07:46 AM

Fortunately on the 123s, there's a lot of room for the cable to run through without having to kink it. I did follow the natural 'bending tendency' of the cable, which seems to follow the original path anyways (them 'little-belt-like-holders/hangers' seem to be in the right place, didnt have to remove/replace them).

My dad said that it could be that the speedometer gauge mechanism itself is sticking due to old age and lack of lubrication (this car is 25+years old, afterall). This prevents the cable from spinning freely hence creating the tension which ultimately breaks the cable. I did notice that the speedometer reading seems a bit off. It registers slower-than-actual speed before it breaks. But no noticeable sound was present which would have indicated lack of lubrication (not sure whether it should have creaked or squeaked at the least anyways).

So, is this 'gauge' thing probable? Is the job of cleaning/lubricating the gauge a DIYer? Im afraid disassembling the whole gauge panel might be a bit too complicated. And I wouldn't wanna fix what aint broken. Any Ideas?

Thanks,

DON

rickg · #4 09-03-2002, 10:23 AM

Audis of the early '80s had this problem big time. I've owned three of them, and every one did the same thing. What I finally did on the Coupe I currently have after going thru three cables in about six months, was to take apart the speedo and take out one of the drive gears from the odometer mechanism. Now I have a speedo so I can tell how fast I'm going, but have to guess my oil change intervals. The only sure fix is to have the speedo unit either repaired or replaced. Even after I took apart the speedo unit, I couldn't tell what exactly was causing the problem. You need to be a watch repair man to actually repair these things I think. Must be a german thing!

ATLD · #5 09-03-2002, 12:47 PM

Did you notice whether or not the trip or main odometer were near a multiple of ten? Typically when the odometer's break, they will break right before one of them (usually the trip) hits 9.9, 19.9, 199.9 etc as this requires muck more power to turn rather than simply the 1/10mi dials.

Also remember that you should always reset the trip odometer when stopped!

I had a problem with my trip odometer, as it's primary gear broke free from it's powering shaft. I imagine that if the gear didn't break free it could have broken the cable. Used superglue and adjsuted spring tension to fix. That has worked for the last three years.

Otherwise, I agree that It's most likely some type of kink. Also, I'd use standard gear oil to lubricate the cable, not ATF, as ATF has other conditioners.

if you remove the speedometer, you can turn the female cable acceptor with a drill equipped with a square drive bit. Use this to see if it all looks like it's working right.

ATLD

#6 09-04-2002, 06:58 PM

Thanks guys!

Thank you for that warning as regards the complexity of the inner mechanisms.

Also, I haven't reset the tripmeter, and it DID stop on 9kms! I guess the problem might really be on the gauge itself.

Wish I could figure out a way to repair the cable too, as those things aren't cheap around here...

Thanks again,

DON

ATLD · #7 09-05-2002, 10:34 AM

What exactly broke with your cables, one side turns while the other doesn't (internal fracture), or something else? If you can remove the cable core, you might be able to have the fractured part welded (as long as the weld won't be in tight turn) and it is ground smooth after. Just a thought...You'd be amazed how fast that cable turns when the car's dooing 50+mph; I believe about ~2000+rpm, so it has to be done right.

Anyway, time to start looking for a new odometer; if you can't fix it. Take out the odometer and look at whichever odometer is stuck around the 10 multiple and check for wear or anything out of place. Sometimes a little bit of teflon grease on the gears and pushers/slides will do the trick; unless something is actually broken or cracked. If you decide to try lubrication, do it carefully so you don't see splots on your odometer's numbers; a small cuetip, or toothpick might work.

ATLD

ATLD · #8 09-05-2002, 10:35 AM

Oh, yeah; make sure that the new/fixed cable is well lubricated: I mean dripping with oil!

ATLD

lrg · #9 09-05-2002, 02:44 PM

For what it's worth I was told by a speedo rebuilder never to oil a speedo cable, always use graphite powder. The tendancy of oil to hold dirt and ultimately end up at the bottom end of the cable leaving the upper part dry will often lead to premature failure. Also, in most cases a broken core cable can be made up new. I've had this done a couple of times and they were pretty inexpensive. Check out a local shop if you have one otherwise look in Hemmings, I've seen a few ads there.

ATLD · #10 09-06-2002, 12:34 PM

I agree; I'd still either use a heavy gear oil or graphite; never both. I didn't mean 5w-40 or something that will leak out, when I said oil. Perhaps if you have some mobile 1 synthetic hydropoid gear oil left from the differential, I'd use that.

I wouldn't use ATF in any case, as it's less of a lubricant oil and more of a fluid; hydraulic oil, though it does some lubricating and cleaning naturally. Way too fluid!

ATLD

P.S> I don't know how easily graphite would flow through the cable as it's really light. It's important to make sure that however you lubricate the cable, it's lubricated thoroughly: remember it spins really fast!

kerry · #11 09-06-2002, 12:41 PM

Speedometer shops around here make up cables to fit. They are not very expensive. I had my odometer out last night and they are not that hard to figure out. If the problem lies in the trip odometer you should be able to remove the gear that joins the two odometers and just use the top one. In my 85 td the speedo cable drives the top odometer and a small plastic gear connects the top one to the trip odometer. To test mine, I chucked a square drive bit in a drill and it fit in place of the speedo cable. I had to run the drill backwards to turn the mechanism the correct direction.

lrg · #12 09-06-2002, 02:53 PM

If you are lubricating a cable you should lightly coat the core cable with graphite as you feed the core into the outer jacket. Start the end of the core that goes to the tranny end and feed it into the end at the top of the jacket by the instrument cluster. It can be pretty messy so you may want to have someone help to keep from getting the graphite,grit all over. I you do it this way you'll end up with a bit more lube at the top end that will gradually work it's way down the cable.

#13 09-07-2002, 08:45 AM

Hi guys!

I know its kinda dumb, but... i don't know how to properly lubricate the cable.

When I lubricated the last one, I used ATF because of its fluidity. What I did was to 'fill' the top end of the cable then blow air into it to force the oil inside. I didn't (and still dont) know that the cable can be disassembled without destroying it. How is that?

As to the brooken cables, I think they can be repaired/welded because, afterall, they broke at a part which is nearest to the end part where the cable is straight.

Thanks a lot!

DON

kerry · #14 09-07-2002, 09:46 AM

Given what an independent speedometer shop charged me to make a new cable, I would think it would be cheaper to get a new one than to get the old one welded.
To lubricate the cable, grab the cable itself (not the sheath in which it rides) with a pair of pliers once you;ve removed the instrument panel and disconnected it from the speedo. Then push it back into the sheath, lubricating it as you go.

Fisherman · #15 03-05-2003, 10:03 AM

Found this old thread while searching around on speedos.
I just replaced the speedo in my 300 with a 1979 version and though it now reds much closer to my actual speed I am getting some noise and a slight bounce to the needle at around 40 mph.
My question is this:
Since the old speedo worked (albeit rather poorly) and I did not have any noise from teh cable prior to this changeover is it possible that this speedo has some binding in it? Secondly, is it possible to lubricatethe speedo mechanism wihout tearing it apart? It looks to be a sealed unit with no visible means of lubrication but I did not really go over it prior to install wiht a magnifying glass or anything. Also if you can lubricate it what would you use?

Lubing the cable is no big deal as a first step but while I have it out again I'd like to ensure that I do not need to do this R&R again and again and again...