Bizarre speedo behaviour.

[WGB]

18 months or so ago I had my speedo rebuilt with it's new AMG 300km/hr dial and it has worked accurately and reliably since then.

I went out to lunch with family friends and parked my 6.9 in the hot sun and on returning the speedo started acting very bizarrely.

It would very slowly rise and finally catch up with the correct speed about 2 to 3 minutes afterwards and then very slowly return to zero when stopped.

The odometer appeared to be behaving itself.

I drove it a week later and the speedo rose to 25km/hr and then stayed there (Including when I was flashed but not stopped by a Police Car) and also after I had stopped.

I removed the instruments and the speedo cable appeared OK and I tried the speedo with a speed adjustable Dremel attached to a short cut length of (Porsche) speedo cable and it worked fine.

I drove the car for two hours yesterday with a Tomtom attached and it worked flawlessly and accurately the whole time.

I assume it had a small piece of s##t caught between the drums w3hich I hope is now gone but would appreciate anyone who has any other wisdom.

Bill

[s class]

Thou shalt not park thy 6.9 in the sun?

[WGB]

Thou shalt not park thy 6.9 in the sun?

A bit hard to accomplish this in western Australia in summertime.

It does have a dashboard mat and I always put up a reflective windscreeen screen when I park but the interior does go into bake mode all the same.

Bill

[TJ 450]

That's an odd one. I would be going with the theory of the foreign object jamming the works. It must be local to the speedo, because the odometer was working.

Hopefully it doesn't happen again.

Regarding sun exposure... you're lucky the colour is Astral Silver, Bill.

My 6.9 is just ridiculous on a hot day in the sun because of the darker colour. That, and the scorching hot MB-Tex.

The sun is indeed pretty much unavoidable if you're going to drive the car frequently.

Tim

[oscar]

I assume it had a small piece of s##t caught between the drums

Perhaps most plausible I reckon but two other things.

- A bug in the speedo, literally. A dead something that's now been dislodged
or
- Perhaps a little more scientific.  When I innacurately recalibrated mine there's a length of speedo spring left semi coiled after the peg.  I haven't trimmed mine nor have I revisited recalibration but it's not that far off, sort of, so I've left it. 
Seeing how much was left over on mine, maybe they didn't trim your spring and maybe tucked it back somewhere underneath itself, maybe in the heat it expanded, twisted, moved and jammed the rest of the spring or contacted the shaft somehow, preventing it from moving....... maybe.   
Still, personally I think it was probably s##t somewhere.

[WGB]

Thanks Guys.

Whatever it was it is still working fine and seems quite accurate when compared to my Tomtom.

Bill

[another sad 280s]

my daily driver was doing this for abit. turned out that the needle was scraping against the window. it had been warped in the heat. (northern vic, get hot) slow to rise, slow to lower. having said that the merc is made of better stuff