speedo trouble

[jake27081991]

hi all,

finaly got round to trying to fix my speedo reading, currently it reads around 30mph when it should be reading around 60,

it works as it should except for this, as in it is proportional to apparent speed, its just that it seems to be around half what it is meant to be at all times.

can i tighten the spring inside the speedo to fix this, if so how? if not.... any other ideas??

thanks in advance

jake

[bmcecosse]

If you think it is the correct speedo - for the final drive ratio in the rear axle, and the 'miles' reads more or less correctly - then yes, the needle can be removed from the spindle and refitted to increase the spring force. But - it's a bit hit-or-miss, and very delicate too! What tpm is the speedo - and what's the spec of the car ?

[mike.perry]

How fast do you have to go before the needle lifts off the stop?

[jake27081991]

how do i find out the tpm? (does that mean turns per minute????)

how can i go about removing the needle, or even the face?

also, dont know what speed the needle lifts up... dont have a gps.. sorry... how would this affect it?

thanks

jake

[bmcecosse]

Turns per mile is listed on the face of the speedo - 4 small numbers - often next to the mileage reading. Face unclips after easing back the tabs - needle is just gently pulled off as i remember! It probably just needs a good cleaning - since you say it's reading low.

[mike.perry]

If you were doing approx. 20mph before the needle lifted off then you could turn the wheel inside the speedo until the needle was at 20mph then holding the wheel steady move the needle back to zero which would reduce the speedo error. This is assuming that you have the correct speedo for the car.
What engine/diff is in the car and what is the Serial no. or TPM of the speedo?

[jake27081991]

theres a chance that it isnt the correct speedo, i think it orrigianly had a 1098 in it but has been replaced with a 948,

not entirely sure on these details however.... i will post engine numbers etc later,

thanks

[bmcecosse]

The engine wouldn't matter - it's the final drive ratio that affects speedo accuracy. But not usually to the extent you say!

[jake27081991]

now it has completly stopped working.... time to rip it out and take propper look...

it has a few numbers on it, one is SN4406/00, which sounds like 'serial number'??

and the other is 1525

[bmcecosse]

Well -1525 tpm is not a standard Minor speedo - however it shouldn't be all that far away - certainly not to the extent you were reporting!

[mike.perry]

SN 4406/00 1525 is listed on my records as a 948 option, the normal 948 is 1504 but that should make very little difference.
What year and model car have you got?

[jake27081991]

it a 58van....

[mike.perry]

It should have a 4.55 diff so a 4406/00 1525 speedo is probably correct, unless anyone with a 948 LCV knows different?
Back to the original problem which was speedo overreading.
The speedo could be faulty, try another one with a tpm of around 1504
Check the diff ratio, by turning the wheel and counting the propshaft turns. There are some instructions somewhere. If the ratio works out at 4.55 then you have the correct speedo. If not then consult the speedo chart.

[jake27081991]

is the a more accurate/easier way to check the diff ratio??

[kittyfell]

Yes, you can pull the diff and look at the markings on the gears. Seems easier to me to jack up one wheel and turn the prop.

[MarkyB]

If it's a van you could remove the rear wooden floor and read the numbers off the top of the diff, I think.

[mike.perry]

The ratio may be stamped on the diff casing, it is definately on the crown wheel but that means finding out the hard way.

[kittyfell]

Does the diff have an oil filler plug in the differential itself? That's the first clue.

[jake27081991]

yes the filler is in the back of the diff, which i believe makes it the 8/43 ratio...

what do the two screws on the back of the speedo do? is there a way to adjust the spring tension?

[jake27081991]

i took the speedo apart and there doesnt seem to be any means of adjustment..

now i guess it is time to get a new speedo...'''

how do i determine the correct speedo to get?