speedo milometer issue

[underkut]

Today I had planned to go out for a little drive in my mk 1 S and realised I was in for a special treat as the milometer was going to click over to 2000 miles (not from new before you start)
As I was diving with 1 eye on the speedo and the other on the road, it finally went, only to get stuck!!!!.
I am only guessing the mechanism is stiff so my question is has any one got an easy tip to rectify this or does it need to be removed.
the speedo side works fine but I guess the longer I leave it the more wear the milometer will take.
Any ideas?

[Andrew1967]

More than likely it will be the little nylon arm that pushes the odometer round.

The speedo will need to be taken out of the casing and the arm replaced for one that isn't worn.

A five minute job once you get the speedo out of the car and separated from the casing.

[69k1100]

Were the the early ones nylon? I thought they were steel arms on an eccentric shaft. The gear on the odometer might be worn though, that is plastic.

[Andrew1967]

Some had a metal arm but most of the Mini ones i have seen (and have had this problem with) have nylon arms.

A replacement arm that is not worn should cure the problem.

[ianh1968]

WARNING:

Be very careful if you take your speedo apart.

If the spiral spring on the needle unwinds itself, you may never get the
speed to read correct again....

The needle can sometimes jump over the stop pin, spin around about
50 times and then laugh at you as you curse it!


The speed needle works by some kind of eddy-current effect where
there is a kind of induced magnetism into a circular ally disk on the
needle spindle. It's all completely above me, but what I normally do
is very carefully sellotape the ally disk so that it cannot move...

I do the job of unjamming the mileage gubbins, then very carefully
remove the tape, taking great care not to change the proximity of the
disk to the rest of the mechanism.

It is normally possible to reset the mileage using wooden or plastic
cocktail sticks - These do not tend to scratch the number barrels up!

You might be lucky and find that it is a "one-off" jam.

It is possible to "recalibrate" the speed, to a limited extent:
Say, you want to make the speedo read 70mph where it currently
reads 75mph - carefully pull the needle round to 75mph, next, whilst
holding the ally disk so that it cannot move, twist the needle back to
70mph. Obviously, you can make it read "correct" at the point that
you selected but will have to take a view on how it reads everywhere
else on the scale. You might feel confident enough to increase or
reduce the turns on the spring, but I never have...

Most needles that I have found are loose enough on the shaft that
you can move them, just don't pull the needle right off unless you have
taped the shaft up.

Ian

[Andrew1967]

Yes, they are a precision instrument for sure and care is needed but...

There is no need to touch the speedo needle spring to replace the odometer arm.

Take the chrome rim off and undo the two screws that hold the innards to the casing. Withdraw innards and remove a small spring clip that holds the arm on. Fit replacement arm and reassemble speedo.

I've done this quite a few times on Mini speedos in the past with no further sticking problems.

[ianh1968]

There is no need to touch the speedo needle spring to replace the odometer arm.

You are correct, but what I have found with both of the speedo's pictured
in my other post is that there is no fixed connection between the central
boss assembly and the rest of the scale with all the numbers on it. When
it is put together, the two screws through the back of the case pull the
central boss back into the housing, which, in turn sort of clamps the outer
scale into position.

When I talk about the "central boss", I am referring to part of the face that
is immediately inside the I II III gear change marks, ie everything inwards
from and including the inner chrome bezel ring...

Pictures are here:-
viewtopic.php?f=3&t=9919

What this means is that once you have removed the main bezel and glass
and undone the two screws from the back, the outer scale is no longer
fixed to the rest of the assembly. The outer scale is now free to flop
about, and as the outer scale has the stop pin attached to it, it is easy for
the needle to jump over it and unravel the spring.

For types where the entire face and scale are one item, or are at least
semi-permanently connected, this self-destruction should not be an issue.

This is just something to be aware of for the benefit of those who have
not taken one of these apart before...


Andrew, where do you get those odo arms from - I've always "fixed" a
jammed odo the expensive way by buying a whole new speedo and then
putting my old faces back on...


Ian

[Andrew1967]

Ian,

Yes, you are right about the central part of the face flopping around separate to the outer face with the mph markings.

I seem to recall that there are a few small lugs on the outer face that clip into cut-outs on the casing to hold it into place. Maybe I have been lucky in managing to keep the needle the correct side of the stop pin.

I cannibalise other Smiths speedos (Minis, Morris Minors etc) for good nylon arms. Providing there is no or VERY little visual wear to the face that turns the odometer drum, there is no further problem.

My Mk2 Cooper's speedo had problems at 90000 and I repaired it as above. I thought it would have problems at 100000 but it worked fine.

No need to buy a new speedo Ian