Km To Mph Speedometer

If I change my speedometer from KM to MPH do I need to change the speedometer drive gear also? my KM clock packed up and I wanted an MPH one so I have replaced it with an OMIX ADA one and its way out when I check the jeep speed with my phone app

 

Did you ever check your KM unit for accuracy?

 

Use a protractor to measure the angles of the markings on the 2 speedometer faces for comparison. There should be 1.6 KM per Mile, or .62 miles per KM.

 

10 MPH = clutch shudder heard through body rattle
20 MPH = fanbelt and generator bearings squealing
30 MPH = transfer case growl dominates over exhaust manifold leak
40 MPH = bearing knock drowned out by wind turbulence
50 MPH = tire howl and transmission scream overcome shouted conversation
60 MPH = explodey noises and sudden silence.

 

I cant say I ever did, but the new MPH speedometer is noticeably out so I would say the KM unit was more accurate

 

You'd need to check the factory parts book to see which gear is matched with your new speedometer.
Year, model, equipment? (Should be in every post).
Availability of new gears may be a problem...

 

I've done that..

 

Sounds like a typical day around here in everything I do.

 

It a 1966 Swiss M606A2 hence why it had the KM speedometer. It has an f134 and 5.38 axle ratio. The driven gear in the D18 t-case for the speedometer has 22 teeth (sw448495).

The original speedometer started making an awful noise and worked intermittently so I thought I would replace it with an mph one for use here in the UK. I think what I am going to do is clean the old km speedometer up and see If I can get it working again and see how accurate that was to start with.

 

The Omix Ida speedo is notorious for being total crap

 

Thinking about this a little ...
Presume the speedometer faces are scaled differently for MPH and KPH.
For both zero is zero, and top speed is 80 and 130 resp.
In that case, there's no change in the gears or the speedometer head mechanism.
Just change the labels to the correct scale.
That points to a defective spedometer head (usual OMIX crap).

Also, if you know the gear ratios (driving and driven gear tooth counts) you can predict the cable RPM at a given speed.
It is possble to drive the speedometer head with your electric drill and see what the needle reading is.
RPM counters are fairly inexpensive and might be nice to have in your kit.
https://www.amazon.com/rpm-counter/s?k=rpm+counter
Measure the drill rotation and compare to the predicted speed from the speedometer head.

I'd also caution - speedometer heads are delicate, like watches.
The clock spring in particular must not be mangled.
I'd try some gentle cleaning with compressed air and mild solvent, like 96% isopropanol.
Maybe use an artist's camel hair brush for the solvent.
If you take it apart, chances are it will never work again.
BTDT.

 

That's what I was thinking, NOS KM speedo are available and a lot less than an original MPH, I might ditch the OMIX unit just revert to KMs and mark the equivalent MPH on the face . It nice to know how fast your going as they have introduced a lot of 20mph zones with speed cameras here in the UK

 

According to Bob's speedometer

This means the speedometer cable speed is relative to the gearing, not the speedometer. Of course this is US, the Swedes, well

US cars and trucks came with dual KM and MP gauges in the 70's. I would compare the markings on the new unit to the one you replaced. If the placements of the numbers are the same, then you are good to go. If not, then a gear or reduction unit may be in your future.

A good read
https://www.bobsspeedometer.com/products/ratio-adapters/

 

Sounds like the problem could be in the drive cable, rather than the head.

Very typically wear, lack of lube, or misfitted length of the inner core results in erratic performance as viewed at the dial.

 

I thought the UK went Metric?

 

See post #15:
http://www.earlycj5.com/xf_cj5/index.php?threads/161841/#post-1876877

 

Love it!!