Speedometer gear

[BoltTurner]

Hi

Getting tired of not really knowing how fast I'm going around town. Looking to change out the gear on the speedo cable. 33" tires with stock gears (3.5:1) and stock transfer case in a 71. How many teeth on the replacement gear to get it back in line?

Thanks
Curt

 

[jimschulz]

This is a good reference chart. You need to know the drive gear count also.

 

[broncnaz]

I dont believe there are speedo gears that will fix the gearing mis match of 33's and 3.50 gears. as the chart shows there are no gears that will work. I think with the availible gears its still around 12% off might be more or less cant recall at the moment but I've tried this in the past your only real fix is a ratio adapter with the percentage you need. a good speedo shop or a big rig transmission shop can hook you up or look on ebay or on line there are companies that sell various ratios.

 

[Steve83]

The caption of this diagram contains Ford's instructions for speedo calibration:

 

[tankhunter]

Its a waste of time messing around with swapping all those gears you never get it exactly right. Just call record your mph with a gps and look at factory speedometer reading and call these guys http://www.tacomaspeedometer.com/index/ problem solved with out getting your hands dirty.

 

[sm7mag]

I am running the same setup as you mentioned....my speedo shows 5mph slower than speed....I just keep that I my mind....I have just ran a gps on dash and just used it as speedo

 

[rguest3]

The closest you can get is to actually measure tire while on truck. A 33/12.50 is not 33" tall. Then use chart to get it close.

 

[Joe473]

Hi

Getting tired of not really knowing how fast I'm going around town. Looking to change out the gear on the speedo cable. 33" tires with stock gears (3.5:1) and stock transfer case in a 71. How many teeth on the replacement gear to get it back in line?

Thanks
Curt

Best check i was able to do is run the truck 10 measured miles down the highway and see what your odometer reads. Provided the head is working properly this allows you to calc % difference actual to read.

Viperwolf helped me identify each tooth is about a 5-7% change. I was able to get mine within 2% with 2 tests.

Also agree 33 " tires are not 33". My 30" tires in a '71 with 3.50 gears is closest with 18t tooth gear. Totally against chart but it works. 16 tooth may actually help your considerably if it currently has 19 tooth in it.