Speedo gone wild

[SDJunkMan]

While driving my CUCV today the speedometer started making noise and jumped up to about 100 or so (even though it's only a 85mph speedo). It kept doing this even when I was just driving a few mph. I stopped and tried to disconnect it before driving any further, but was not able to, so I was going to turn around and head home. The noise stopped but the Speedo jumped around for a while, then finally settled down. Any ideas what might have caused this? I have been thinking of swapping out the Speedo because it doesn't seem like it is accurate.

 

[bucket]

If I had to guess, the speedo cable was severely binding.

 

[1987 GMC Jimmy]

Really crappy cables that don’t spin truly will do that, too, but my money’s on the binding. I’d mix some denatured alcohol and graphite powder together, pull the cluster, hook a drill to the transmission end, and pour the solution down its gullet while spinning the drill to work it down.

 

[ali_c20]

My speedo is always jumping since the original cable went south. It ends when I go 50. I had 3 different cables (cheap, cheap, not so cheap) from 3 different companies and all of them sucked. Next time I try to get some quality cable.

 

[Matt69olds]

Unhook the cable from the transmission. Pull the speedo head, unhook the cable. Pull the cable from its casing, spray lots brake clean inside. Blow out the crud, clean off the cable, grease it up with speedometer cable lube. Reinstall and reassemble. Hopefully that solves your issue

 

[Snoots]

All I've ever done was like Matt69olds said, clean out the cable with brake cleaner, wipe the cable with brake cleaner, then wipe it down with powdered graphite.

They make an adapter that fastens to one end and has a Zerk fitting. You'd pump grease through the entire length of the cable and then insert the spun cable. UGH! Whatta mess!

 

[71RAT]

While driving my CUCV today the speedometer started making noise and jumped up to about 100 or so (even though it's only a 85mph speedo). It kept doing this even when I was just driving a few mph. I stopped and tried to disconnect it before driving any further, but was not able to, so I was going to turn around and head home. The noise stopped but the Speedo jumped around for a while, then finally settled down. Any ideas what might have caused this? I have been thinking of swapping out the Speedo because it doesn't seem like it is accurate.

Mine does that too, in cold weather, it settles down once warmed up. It does jump at low speeds also since installing aftermarket cable. I just cleaned and lubed the speedo head and cable, we'll see how it works.

 

[SDJunkMan]

I guess I'll pull the cable out and clean and lube it, seems to be the general consensus. The truck has sat for a while and the PO said that he didn't drive it much so it probably is gummed up. I've never had a speedo do this so wasn't sure what to do.

Thanks for all of the responses.

 

[1987 GMC Jimmy]

My speedo is always jumping since the original cable went south. It ends when I go 50. I had 3 different cables (cheap, cheap, not so cheap) from 3 different companies and all of them sucked. Next time I try to get some quality cable.

If your speedo head is working properly, the AC Delco is okay. There’s a company that builds them in Denver, Speedometer Cables USA, that swore to me up and down that their design rivals the OEM from this period. It sounds like they’re based on an older design. Oh, and here’s the advice he gave for lubing our original cables. An 80” cable should run you about $57 dollars with them, give or take. If anyone wants to try them out, see their contact info below.

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[idahovette]

I like the "God " cleaning part!!

 

[bullmastiff]

Mine is doing the same thing but I think it is the gauge itself. I replaced the cable and worked fine, then changed the cluster and it started making sounds and jumping. Old cluster workers fine with the same cable. Sounds like little plastic gears stripping inside, but I've never opened one uonto see what's in there.

 

[Warkmeister]

Could the same problem of a gummed up cable cause the opposite symptoms? My speedo works from 0-50mph pretty well then faster than that, it’s jumping all over from 55-85.

 

[DGDamato]

Mine does that too, in cold weather, it settles down once warmed up. It does jump at low speeds also since installing aftermarket cable. I just cleaned and lubed the speedo head and cable, we'll see how it works.

Same here...when it's cold out, I can count on it acting up. It sounded like an electrical short the first time I heard it - scared the "god cleaning" right outta me!

Thanks for asking @SDJunkMan - I'll have to try to get mine cleaned out now.

 

[71RAT]

Same here...when it's cold out, I can count on it acting up. It sounded like an electrical short the first time I heard it - scared the "god cleaning" right outta me!

Thanks for asking @SDJunkMan - I'll have to try to get mine cleaned out now.

I drove it Saturday morning, over night it got down to 26 or so. Seemed to work good, it did jump a few times in the driveway. I don't know that it gotten cold enough to call it fixed or not?