tranmission spedo gear

[47 flatbed]

I finally got a spedo cable for my truck. Using original toploader 4 spd. with cable now the spedo shows that it is off by roughly 13 mph. I have switched from the original stump puller rear 400+ series gear to drivable 355. is there a spedo gear that I can install to get a little cloer to my new gear set.

Thanks for the help

[47 flatbed]

Any know about this gear for spedo

[Ed Pitts]

What number do you have on the gear case that attaches to the torque tube? There are three different gears that I know of and each depends on the rear end used. For the standard rear 3.78 gears it has 19 teeth. A 3.54 rear will have 18 teeth, 4.11 will have 21 teeth. My 36 has a 4.11 rear end and the gear that I use has 21 teeth. Here is a pic of mine. If yours has 21 teeth, a 19 tooth gear may be what you need. Ed

[Juergen]

You are off by 13 mph but at what speed? Figure out the percent and get a gear with the same percent change.

For example let's say you were off 13 mph when going an actual 65 mph. That is 20% in error. Now look at your speedo gear teeth. Assume you had a 22 tooth gear which was correct for a stump puller 4.33 differential ratio . Ed gave you the ratios for the common car ratios. 20% off of 4.33 implies about a 3.46 gear ratio which suggests an 18 tooth speedo gear is about right for you.

[47 flatbed]

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The mph get worse the faster I go. This truck has original open drive shaft 4 spd. Not sure where to get this gear to help