Speedo Bouncing Badly

[THE "10" SILVERADO]

Does anyone else have this problem? Going about 20, it bounces from 20 to 30 constantly......almost like I was driving on one of those test courses with bumps everywhere...but on a flat road. Just started doing it lately....

Do I need a new speedo cable?

[HTX86chevy]

Mine does the same thing 20-35mph and will smooth out at faster speeds..... However, if im driving 65mph on my gps it'll show 55mph
and i have tried different gps units to double check.....
I have replaced speedo cable and the gauge itself and the problem still exists

[cjlinkster]

Mine is starting to do this same thing too. It will work fine for a minute or two and then stop working for a few seconds, and then the speedo works again.

I haven't checked, but I am thinking that it may be the plastic gear in the trans. I suspect that it should be an easy part to replace using just hand tools. Has anyone replaced this on a 4 speed?

I had already replaced my speedo cable with a new one.

[Rogue_Alphonse]

It
s probably the spring or balancer thing inside of the speedo assembly.

Don't ask why, but I got stuck having to take a regular speedo and one with a trip odometer and make one good one. Both had the same issue, and read 5 fast after 55. [I think reading faster after 55 is like... on purpose though. My 1989 F-150 did it too] I had to take the gear apparatus thing apart on the tripped one, use the shaft with the spring and balancer [and the odometer because I had the opportunity to make my speedo read the correct mileage for the truck it was being installed in], and put all these parts from a standard speedo into the trip speedo. It still bounces between 0 and 10 sometimes, or if I hit a hard dip or bump going 75, but otherwise it's good. It even reads correctly no matter what speed I'm going.

[THE "10" SILVERADO]

I just replaced the speedometer with a new one....so I don't think it's the speedometer

[Rogue_Alphonse]

Does it have that wierd module thing on the inner wheel well under the hood? The '81 my stepdad and I built had it, and we never did figure out what it was.

[cr34t3d_by_d4rkd3n]

... buy a cabel luber. go down to ur local motorcycle store. ask for cable lube. use per instructions and cable luber... also grease the ends of cable and spedo imput. grease costs mony all new guages and cables come with a slight coat... enough to take u to the motorcycle store.

[bigwheel15]

Originally Posted by Rogue_Alphonse

Does it have that wierd module thing on the inner wheel well under the hood? The '81 my stepdad and I built had it, and we never did figure out what it was.

That weird module was for cruise control equipped trucks.

[willett]

mine does it sometimes on the highway. it will start jumping all over the place really spuratically and usually it stops when i am getting ready to pull over and disconnect the spedo cable.