I've searched for a solution to this, but not found any real info as of yet.

Anybody have any information as to what causes the speedo needle to bounce around? Seems to be linked to rough road conditions.

It throws the cruise off solid like to fix this.

 

It's either a bad connection or bad capacitors in the speedo head itself. Check the pick up wire in the rear end (assuming your car is one of those that have that type).

 

early 240s (70s to early 80s) had a mechanical speedo, a bad bowden cable can cause bouncing. newer 240's and all 7/9's have electronic speedos, so bouncing is probably what lev said.

p.s. fill in your profile with what model/year car you have so we don't have to guess.

 

yep if you have an early model with the mechanical cable - you can pull the cable off the back and try spraying down the lead with some silicone. I used to own an 84 Audi 4000Q and this was a common issue/fix for bouncy speedos due to sticky cables.

 

I've checked the connections and all is good there. What I have noticed is the smell of bad caps coming from the dash on occasion. If you know this smell, it is unmistakable.

Thanks for the replies!

 

Bad caps? I assume you mean capacitors? Can't say I ever noticed a smell on them, but, yeah, very possibly that's the problem.

 

the 91/92 740/940 speedos were particularly bad about capacitor problems. the catch-22 is, they can't be swapped with an earlier OR later year because of other changes in the instrument panel, and I've read you can't swap the whole instrument panel or your gas gauge is way off, so its a catch-22.

my 1992 740T, I pulled the speedo, carefully swapped ALL the caps with high quality panason or nichcon(?) ones bought from digikey.com, cleaning the circuit board carefully in the process, reassembled, and it STILL won't read higher than 40MPH most of the time, its accurate enough from 0-40. once in a blue moon it works for a half day, but then goes back to being stuck at peak 40ish. apparently this is due to a bad ITT speedo control chip, which is unobtanium.

 

Electronics lingo. Cap = capacitor.

Pardon.

 

Cap change is easy...I can do that in my sleep.

What's the part number on the IC (integrated circuit or chip) you need?

 

I believe its a ICT/ITT UAF-2115, and its been unobtanium for 15 years. datasheet: HTTP 301 This page has been moved

 

I can get these IC's.

Do you want me to do the work for you, or mail you the IC's?

 

hmmm, I see them on fleabay from China... must be NOS as ITT hasn't made these in 15 years.

btw, link above to datasheet must have been a temp one, here's a stable one.
http://www.odometergears.com/documen...Data_Sheet.pdf

 

I did this for a living for many years...if I can't find it, then it can't be found.

I had to source GE parts from the 60's. This IC was a breeze to source, but not from eBay. I found them from a distributor in China direct. And to be frank...the last time they were manufactured is irrelevant.

Saying they aren't obtainable isn't accurate, they are readily available as I have shown.

Don't take any of this harshly, but this line of work is my life and am 'highly' skilled and trained.

 

Bouncy speedo has been fixed.

It ended up being the sensor at the rear-end, but not the sensor itself being dirty. It was the coating on the wires that had fallen apart. The bare wires were intermittently touching and causing my grief. Hehe

So I have a brand new UAF-2115 IC if anyone wants it.