Hey guys I just noticed this happening about a week or two ago, it wasn't having this problem prior. The car is an S4 NA and I'm noticing that as I drive around, any speed pretty much my speedometer needle will seem woobly / shaky / bouncy. If I hold a speed or even as I'm slowly accelerating I can watch the needle slowly bobbing up and down.

For instance if I'm holding say 40mph steady or trying to, the needle will seem to float up to 41-42 and down the 39-38 and back up over and over like it just can't seem to find 40 and stay there.

Just for the record I also noticed this problem with my FB before I stopped driving it.

Any input would be great, thanks.

 

Speedo cable is loose at the back of the cluster or the cable itself is starting to fail

 

+1 Exact symptoms I had resulting from a loos cable. Pull your gauge surround off and then remove your cluster and examine the cable if it looks good at the connection then re-attach it. If you need a new cable they are relatively inexpensive compared to most items.

 

you dont have to take out the cluster. you can easily reach under the dash and make sure it's pushed in all the way and the locking tab is secure. just trace it from the firewall and let you hand be your guide.

Matt you probably did an oil change or something and slightly tugged the speedo cable out of the firewall some. happens to alot of people.

 

I don't know if that'll be a symptom of a similiar problem.. but you may also want to check and make sure your speedometer cable is still tightly screwed into the transmission. I recently had mine come off of the transmission while I was driving, allowing the contents of the speedometer cable to fall out on the highway. After searching the forums later I discovered I wasn't the only one this has happened to.

I have since replaced the cable and noticed, with the help of a portable gps unit, that my speedometer appears to read about 10 - 15% faster than my actual speed, worse in the high end. The speedometer will report around 135mph when the gps only says 115ish. I don't know if it has always been this incorrect (in the year I've owned the car) or if something changed when the cable fell out or new one was installed.

After I installed a replacement (without taking apart the dash, got a used cable and slid the interior back into the end of the old cable), my needle was bouncy for a couple days. Now it appears to be solid again.

 

Do you have stock wheel/tire sizes and rearend??

 

I have the stock series 5 convertible wheels on it, with 205/50WR15 86W tires.
So the tires are a little smaller, but I wouldn't think they're different enough to throw it off that much?

 

Totally forgot about getting at it from behind the dash! Your right I knocked mine loose during the oil change.

 

http://www.miata.net/garage/tirecalc.html

According to this your speedo reads 10.6% faster so yea it's enough to throw it off that much

 

the same **** happened to me, and when mine fell of the tranny the little needle that pokes into the gear broke off, i bought a used one from an S4 and slapped it in.

when your checking your cable at the cluster you should also make sure that the little white plastic locking peice is clipped into the back of the cluster, it will feel like it is but turn it with your fingers, it shouldnt turn if it is in its locking place.

have fun