Speedo only works for 5 mins

[JMR99]

Hello,

Car Elan +2 1974

I'm not sure what the fix is for this but I thought you chaps might.

basically after about 5 mins the accuracy of my speedo starts to drop - when I'm doing 30mph it registers that I'm around 10mph and on the motorway I'm only doing 15mph.

The only thing I've noticed is that when I push the accelerator peddle the dial drops to almost zero and when I take my foot of the gas it starts to jump back up to around the speed I'm doing.

A previous owner has changed the speedo but this doesn't sound like a loose connection problem to me.


any ideas would be great as I'm currently using the in 4th at 2000rpm i'm doing around 30mph method to judge speed.


Cheers,


Jon

[john.p.clegg]

Joh

Sounds like a loose connection to me,try the screw fittings either end,clock first (easiest)...

John

[prezoom]

I had an unusual problem with my speedometer a while ago. The spindle from the angle drive to the speedometer gear in the transmission became unsecured from the gear in the angle drive. Not so loose as though the speedometer wouldn't work, but slipped enough to cause a slow indication of speed. A trip to my local instrument shop made things right.

Rob Walker
26-4889

[peterako]

Hi Jon,

I went about 6 months with a Speedo that progressively got more and more errattic.

Initiall, just a bit of a wobble at certin times, then slow readings after about 30 minutes driving (eg. 30mph when doing 70!).

I change:

Cable
Speedo
Right-angle drive

all to no avail.

Then, had the engine and gearbox out and we found that the worm gear that is on the output shaft on the gaerbox was not tightly held in place. This worm gear drives the right angle drive.
It's held secure with a friction fit that is tightened with the nut/bolt (sorrt can't remember which) at the UJ side of the shaft. (i.e. on the flange centre).

Tighented this up....hey presto! Perfect speedo (as perfect as a 30+ year old car can be )

After 6 months of driving by the rev counter....joy

Honourable mention to my neighbour, Cormac, who had guessed that this may have been the problem right at the start...

Best of luck,
Peter