the intriging case of the variable rate speedo

[incisor]

just to keep me interested, my 110 has decided to play tricks on me..

when cold and for the first couple kilometers my speedo runs pretty much smack on what the gps tells me i am really doing..

after about 3 or so kilometers this accuracy drifts off with the fairies...

after about 5 klms it settles out and shows 85 kph when i am really doing about 100 kph

anyone have a clue what would be causing this?

[davros]

There has been a warp in the space-time continuum. Dur to a technical error at the speedo manufacturers, a top-secret device that measures this and was disguised as a defender speedo got switched with your speedo intead of sent to the MOD.

Or perhaps there is some water or condensation in a plug/the instrument? Is it an electronic speedo or mechanical?
If mecanical, maybe a slipping drive gear or busted cable that still has some connection through friction?

Have fun!

Dave

[mike 90 RR]

Which setup do you have?? ....

A All cable connection from gearbox to speedo ...
B Short cable from gearbox to transducer ... then spark wires to speedo??

Mike

[incisor]

A. all cable i believe.

[incisor]

There has been a warp in the space-time continuum. Dur to a technical error at the speedo manufacturers, a top-secret device that measures this and was disguised as a defender speedo got switched with your speedo intead of sent to the MOD.

i'll have some of what your having :P

[mike 90 RR]

this accuracy drifts off with the fairies...

anyone have a clue what would be causing this?

British standard's ... I believe :p


A. all cable i believe.

Well ... If you chose "B" ... I could have made it easy for you ;)

But you HAD to choose "A" :eek: .....

Borrow someones speedo cable
Try another speedo
Check the gear cog at the end of the cable (gearbox end)

Mike
:D

[Bearman]

Or possibly the worm drive on the output shaft slipping. This is held by a collar and then the rear output drive flange. Check that the nut is tight on the output flange - that could explain the difference between cold and hot................Brian

[alien]

Is it there any oil in the speedo head?
Seen it twice on Jap. cars were the oil had worked it's way up the inner speedo cable.

Cheers, Kyle.

[Blknight.aus]

a, the cable slipping tho this usually shows up as jumping.

b, the magnets in the speedo are giving up with heat, if youve got the time heat the speedo up with the wifes hair drier for about 20 minutes/ half an hour before driving and if it does the fault straight up its the head unit.

No I dont have a spare one.

[Bush65]

I had this happen for a while in my rangie and on a trip back from QLD I was booked twice in the same day for speeding.

In my rangie's speedo, the spindle with the needle on it is coupled to a spindle with the driven disc by an aluminium sleeve. Both spindles are pressed into opposite ends of the sleeve.

As the temperature increased, differential expansion rates allowed one, or both spindles to slip inside the sleeve. The fix was simply to squeeze the aluminium sleeve to increase the grip on the spindles.

[JDNSW]

My guess is that Bearman has the answer. The worm gear on the transfer case that drives the speedo gear is only held to turn with the shaft by being clamped between the output yoke and the rear bearing inner race (by pressure from the nut on the end of the shaft, remove front end of propshaft to get at it). Cold the viscosity of the oily surfaces keeps it turning, but as the oil gets warmer it slips more easily. Problem is likely to be exacerbated if the speedo cable or the bearing in the speedo is dry.

John