Back asking for help again on my close to 'completed' crew cab long bed conversion, this time with the speedometer. I have a series of punchlist items and this one is bothering me.

My speedometer doesn't work whatsoever. Every other gauge on my dash is working perfectly. I swapped in an NV4500, and it seems to have the same output for speed as the old Getrag - correct? The little setup with gears to turn the signal into voltage that the gauge needs? Well, I put a new VSS on, and hooked a drill to it and spun it both directions as fast as the drill would go and get no flicker on the needle. The gauge worked before the conversion on the Getrag. I feel like it's something simple, but I haven't been able to find it. If all my other gauges are working it means they're all plugged in, correct? There's no way just the speedometer is unplugged somewhere? Any other ideas? Thanks,

Spruce

 

In all my decades of working on things with engines, including swaps/conversion, nothing ever goes exactly perfect. Like pinching a wire for example. Or yanking on a wire to make it longer. Also consider how old our trucks are now. Insulation gets stiff and breaks, wire break from bending and vibration. Break out the ohm meter and jumper leads and start tracking wires.

 

If it is a 2wd the speedo port is in the transmission you will need to swap the speedo unit around.
If it is a 4x4 then it should stay in the same NP-205 that came with the Getrag donor.

Which gauge cluster are you using? The cummins donor truck or the old crew cab one?
I have done it where I re-used the '85 crew cabs, manual speedo cable driven, cluster. The other 12v crew build I used ALL the Cummins donor trucks wiring, gauges and cluster.

More details of this build would help me, help you.

 

Sorry, was late when I typed this up. Here's a few more details: the conversion was a 93 W250 that I stretched and put a 72 cab on. I reused the dash from the 93. I also reused the NP205 transfer case, and my speed sensor is hooked up to that. So all the gauges in my 93 dash are working except for the speedo. Even the odometer and trip meter is working.

Cougar - me and ohms don't get along too well... and I'm not that good at following wiring diagrams, but I guess I'll start probing.

If I take the VSS, and spin it with a drill, I should be able to see volts coming out of the VSS with a multimeter right? Has anyone tried that and know what kind of range it should be in? Thanks,

 

IIf the ODO and trip meter are working, it tells me the VSS is working.
My guess is the speedo gear is your problem.

 

Agree...
The speedo 'gear' being the guts in the cluster. Both the speedo and odo are electric. The more common failure is the odo, and the speedo keeps working.

 

Having just recently sourced a new gear adapter (I dropped my np205 taking it out). I will tell you I'm amazed that the system even works . The little baby pins for the gear adapters can very easily sheer off. I got mine from PATC and I believe they sell just the drive pins. Square on one/ side peened on the other. Luckily I didn't have to replace the internal to the np205 section, but I believe those are avaliable as well.

 

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