My speedometer will only read up to about 15 MPH until I drive the truck for about 15 minutes. (I will check that time period and update in the next few days.) After that it will read a few MPH under the actual speed shown on the GPS. The ABS and "Brake" light are illuminated on the dash.
Details of the truck:
'96 Dodge Ram 1500
5.2 Engine
NV3500 5 speed
NV231 Transfer case doubler
NP205 Transfer case
5.13 Gears (rear axle is a Dana 70 from a '96 Ram 2500)
43" Super Swamper SX tires
I made an adapter to attach the speed sensor from the output of the NV231 to work on the speedometer cable output of the NP205. I can understand if the speedometer read consistently off and by adjusting the tooth count on the gear it can change the speed displayed. I'm confused as to why it will read up to 15 MPH until the truck is driven for roughly 15 minutes.
The CEL is not lit and I have not found any codes related to the ABS and "Brake" light saved. Am I missing something? Does anyone have any ideas why the speedo will read slowly and then "warm up" and start working? Thanks in advance for your help.

 

ABS and brake lites are probably on because the rear wheel speed sensor doesn't agree with the vehicle speed sensor, and they get confused. On the 96, the VSS is gear driven in any event. How is it working off the 205? I would be interested to see if they used the same housing on both t-cases, that would make life real easy.

 

Is the issue temperature related or purely time ? In other words, if you have driven for a while, turn the truck off and 2 minutes later drive again does it show the same symptom ?

In 96 the speedometer and the PCM share the output from the VSS (literally via a splice). Maybe there is a way to show what speed the PCM sees, depending on scantool and if that is even implemented in the PCM. That could point to either the speedometer itself or the VSS.
I don't think the ABS controller and the PCM talk to each other so the lights are likely a "normal" ABS problem (rear sensor or module error).

 

 

HeyYou, I posted the picture showing the adapter between the VSS and the speedometer cable output of the NP205. It has a section of the drive cable extended to drive off the Ford speedo gear to the VSS. I will check to see if it is temperature related per DerTruck's suggestion. Thanks for the replies.

 

If you don't mind me asking why did you use a NP205?

 

It's all cast iron, it's gear drive, (no chain) and essentially indestructible. Of course, it is also quite heavy.......

 

Twin-Stick. 205 can be easily modified to have 2 wd rear low, 2 wd front low or high including the normal 4 wd hi/lo.

 

Yeah but the strength isn't as good as the 231. I just put an Atlas in mine. I didn't even know people still used the 205, good to know though!

 

I used the NP205 with a NV231 doubler because the Atlas wasn't in my budget and I wanted gear choices to wheel the different terrain I see in the North East.