Speedometer is 20mph off

[MTownsend]

Well I have been driving my convertion for months now with the seedometer way off, I think that Proformance gear had given me a different transfer case back instead of rebuilding mine, so I figure it came from a truck that had 4:10's. If I go 55mph, I'm actuly running about 73-75. Does anyone know what gear I need or better yet, does anyone have one thay want to part with.



Thanks

mike

 

[Philip]

Did you install the ratio adapter box used on 4x4's?



This place has ratio adapters in different reduction ratios. Looks like you would need the 26% ratio box.





http://www.transmissioncenter.net/727Transmission.htm

 

[KOG]

Ratio box? How about just the speedometer drive gear? To know what gear you need what's the tire size and axle ratio? Another way is to look at the gear in it, check speedometer with GPS and change as needed.

 

[MTownsend]

it has stock tires for a 91 cummins, and 3. 55 gears it neaver had a "box" on it, but if thats what i need, ill get it

mike

 

[dpuckett]

Both my 4x4s had adaptor boxes. You need a box to get totally accurate (within 1-2%)- drive and driven gears only do so much. The box I have has 4 gears in it, with a straight offset like the 4x4s came with from the factory.



Find out how much too fast/ slow (on a percentage basis, not MPH) yor speedo is (I used mile markers on the interstate) and call a shop and tell them what you need, and they can build it for you. I had Speedometer Service in Colorado Springs build mine for about half what the dealer wanted, and I know EXACTLY what ratio it is. The straight offset is a tight fit to the transmission crossmember in a 2wd manual.



Daniel

 

[Philip]

I can get you the Dodge #. We just put one in Jeremy's truck last week. His had rusted out inside where the VSS went.



All the 4x4's had a reducer box on them.



Dodge only supplied the 4x4's with a 215 tire. If your running 235's the speedo will be off about 6 MPH with a stock Dodge box. Dodge price was $92. That is why I listed that website. They are cheaper.

 

[CGauthier]

I'm not sure if my truck came brand new with 215's or not but the tag on my door says 235's... . maybe it's a Canada thing

 

[dpuckett]

The duallies came with 215s; SRW came with 235s.



I still think you should go with the aftermarket adaptors- a) because they are half the price, b) because they are customizable to YOUR specific needs as far as ratio is concerned, and c) They are repairable. Not to say the OEM isnt, but most Dodge stuff of that sort is throwaway (if not when new, definitely when used).



DP

 

[Dieselman359]

Hummmm

I've been meaning to bring my GPS along, I thought that I felt like I was going faster than the speedo read.



For those that don't know, my W truck has 235's. I guess that I had better go out and kiss that little golden adaptor. :-laf

 

[Dieselman359]

One more thing

About the speedo, every once and a while it goes crazy. Driving at 60 it will all of the sudden go to zero, back to 60 and everywhere else in between. Then it will quit and be fine. I was wondering if that little gold priced gear that some of you have replaced in the actual speedo is the problem.

 

[dpuckett]

Check your mechanical connections to make sure they're all tight, then check your electrical connections. I believe your drive gear on the output shaft of the t-case is integrated to the shaft, is it not?



DP

 

[MTownsend]

My truck has 235/85/16 tires I'll have to take a trip to find out how far off the odometer is but I think it was nearly 30 miles off in 100 miles. Originaly when I removed the transfercase to have it rebuilt there was no "box" the speed sensor was right in the transfercase, but I have no problem getting what ever I need to make this work.