Speedometer after changing rear diffs.

[general]

Anyone know how to re sync speedometer? Changed rear diffs from 391’ to 294’s.Think my Speedo is about 10-15 miles to slow.1967 Dodge D100. Got a feeling this might be a pain in the arse,lol.

[BigBlockTrucks]

With my 65 I went from 4:88 gears to 4:10 I was off by about the same. I used a gear reduction box from an old Chevrolet. It screwed between the transfer case and to speedometer cable. It is accurate now.

[BigBlockTrucks]

If your truck is an automatic it’s a mater of changing speedometer gears. They are easy to change but can be hard to find the gears.

[PwrWgnDrvr]

You can also easily change gears on a std tranny. Step by step instructions are in the FSM.

[martincom]

There are charts in the service manual that indicate the number of teeth the speedometer pinion should have fro a given rear axle ratio and tire size combination. There also charts and calculators online that will yield the same results. Speedometer pinions are available from places like Year One and Ebay.

[general]

Thanks for the info.It’s a 4-speed,maybe that makes it easier.

[general]

Hello PwrWgnDriver. This may seem like a stupid question,but what is the FSM?

[PwrWgnDrvr]

Factory Service Manual
Reprints available from Bishko, better quality than new!

[general]

Thanks,I'll check it out.

[martincom]

Manual or automatic, the speedometer pinion is the same.

Tip: Only lift truck from the rear when changing. In this manner, all the fluid/lubricant will flow to front of the transmission and you won't need to drain anything (or get a bath) when you remove the pinion.