Speedometer Needle Bounce?

I have an original (rebuilt) 356 Porsche Speedometer from North Hollywood Speedometer here in Los Angeles. The needle "bounces" when the car goes over pavement bumps. I asked the techs at NoHoSpeedo about it, they double checked that the gauge mechanism was good - it was. They gave me a new cable, which we installed, but that didn't solve the problem. John Steele and I made sure the speedo cable was secure, not being hit by anything moving under the car, etc. But the needle continues to bounce.
Anyone got a solution? I'm stumped.

disconnect the cable and hit some bumps to eliminate the cable.
its probably the resistance in the needle.

Dear Stumped,
Leave the cable attached and dont hit bumps. Opps, can't perform that test in Southern California. Sorry. I guess you could put in a cheap repo speedometer...

Bruce,
We disconnected the speedo, took it out of the dash and actually shook it. The needle didn't move. It's solid.

Dale,
Contrary to popular belief, everybody is NOT a comedian. But, thanks for playing. Geesh.

What has changed on your car recently? Did this speedo always bounce, or did it just start? Did it gradually get worse, or did it just start bouncing one day? Does it always bounce, or is it intermittant? What other changes(s) were made just before this bouncing condition started?
"Just the facts, m'am" (Joe Friday - Dragnet)
"You will tell me, my friend" (the coronor - CSI)

Car is 1200 miles new. Gauge has done it from the beginning. The only thing we've done is swap the speedo cable for a new one. Problem persisted.
I'm pretty sure the cable - or more specifically something hitting or bumping the cable - is the problem. I'm hoping someone else has run into this and has solved it. I've tried to "stabilize" the cable, but I don't know what else to do.

John, seems to me, if you changed the cable, that should eliminate the cable as a surce of trouble. As for something hitting the cable, I recently changed my speedo cable and there really ain't much on that cable path that could cause a problem. The only possible trouble area would be where the cable penetrates the front firewall. Also you could check and be sure the cable is routed safely away from the front suspension in full lock - left and right.
My cable is run off a square hole in the front wheel grease cap. Is that cap on tight? Is the cap on tight but crooked and wobbling as the wheel rotates?
If those are all negative, I would bet it's in the speedo itself. Simple test, Find a friend with a spare speedo and borrow it for an hour. It's a simple thing to hook up the new cable to a temp speedo and give it a test drive. (Can you even imagine doing that in a new car!!) Persistence, John, persistence. Best of luck.

David,
Good idea on the spare speedo swap. I'll try that, even though North Hollywood Speedometer has tested my gauge and pronounced it "perfect."
My cable goes through the firewall at the steering column. I know the steering column moves a little with the suspension flex over bumps. Maybe I should run the speedo cable through its own hole, so to speak.
Thanks for the good advice.

John, If you thump the bottom of the speedo from under the dash, when the car is stopped does the needle give a little bounce? Perhaps securing the speedo cable more securely under the dash, not to the steering column might help. Im here all week.

John:

I have had speedo needle jumping problems on various motorcycles over the years. Without exception it was caused by the cable. Usually it was not related to a damaged/kinked cable pre se, but related to how an individual cable reacted to its routing. Most times the juming was caused by the cable binding slightly during vertical wheel movement causing the cable to "wind up" on the non-speedo side of the binding area. When the vertical wheel movement returns to nominal, the cable unbound and the wound up section drove the non-wound section to cause the speedo needle to jump.

After you eliminate the speedo, I would spend some time really looking at the routing of the cable, specifically where it is anchored between the sprung and unsprung portion of the cable, trying to visualize the cable while the wheels are in vertical motion.

I hope this helps just a little.

Bill

John,

I had some cable problems this summer. In fact I lost two. On the VS, there is a crossbar under the dash that happens to run accross the most direct path to the speedo if it is mounted on the left. I was using early Super Beetle cables as they are a little longer. Anyway, I think there was just enough bind of the cable and mounting on that crossbar that it caused problems. Early on it was like you described, later it was more of a sticking issue, then it finally broke at the Speedometer. Replaced it and experienced the same issues. I moved the Speedo to the top center position and eliminated the binding.

I don't know if this is related to your glitch, but thought you might consider it. I don't recall if the pre-Super and Super Beetle cable head mounting length is the same. That would be an issue to consider too, at least on the VS crossbar. Anyone?

Jim

Might be the angle of the dangle also, anyone?

You think that it may be that the screw on connection may be alright is it possible that the cable ends from NEW cables do not match the size or squareness of the ORIGINAL speedo's?

Maybe a thin stick of electrical tape on the cable end/squares might help before you screw it on....???