Speedo & odometer inaccurate- 1977 FJ40 (1 Viewer)

Joined
May 30, 2019
Messages
26
Location
UK
Can anyone help?

I bought a restored MPH gauge cluster from the US for my Australian spec FJ40 restoration project. Previously the car had KPH cluster.

Now fitted, the MPH odometer reads high. I checked it by following my wife in her car. When mine (FJ40) clicked over for a mile, her car (2015 Discovery Sport) had only gone 6/10ths of a mile. I suspect the speedo is reading high, but haven't checked properly.

Any ideas whats wrong?

Wheels fitted are 16" from City Racer
Tyres are BF Goodrich 235 / 85-16 All Terrain
 

1911

chupacabra
Joined
Aug 11, 2006
Messages
6,182
Location
Parker County, Texas
 
 
Can anyone help?

I bought a restored MPH gauge cluster from the US for my Australian spec FJ40 restoration project. Previously the car had KPH cluster.

Now fitted, the MPH odometer reads high. I checked it by following my wife in her car. When mine (FJ40) clicked over for a mile, her car (2015 Discovery Sport) had only gone 6/10ths of a mile. I suspect the speedo is reading high, but haven't checked properly.

Any ideas whats wrong?

Wheels fitted are 16" from City Racer
Tyres are BF Goodrich 235 / 85-16 All Terrain
There are a few different sizes (# of teeth) of speedo drive gears that will affect it.

Most 40 drivers have the opposite problem; they put taller tires on and the speedo reads too low. So put the tallest tires you're ever going to want on it before doing any corrections to the drive gear.
 

Cromagnon

SILVER Star
Joined
Jun 8, 2012
Messages
218
Location
Colorado Springs, CO
 
You could have several calculation errors happening at the same time. What was the original tire (tyre) size? Also is the wife's Disco speedometer accurate? My Disco II speedo was always reading faster, with factory tires. Try using a GPS over a couple of miles to get an average and base your decisions on that instead of a single observation. Here is an online calculator to help. Speedo error calculator – speedometer error as a result of tyre size change – Speedometer calibration As stated above by @1911 there are different speedo drive gears to choose from as well.
 

Living in the Past

SILVER Star
Joined
Apr 21, 2005
Messages
19,159
 
 
 
I would pull you driven speedometer gear out and count the teeth. If it has sixteen teeth purchase 33403-69065 that has eighteen teeth. That will slow it down. Think seventeen teeth is also a option if still available. But as far off as yours is off with the eighteen teeth gear.
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top Bottom