CEL speed sensor circuit. Pulling the T-Case?

[Macross]

First off I have a 95 hardbody sev6 4x4 at.

 

I bought this truck about a year ago and really haven't had many issues with it. I repaired the frame, replaced the entire fuel system, all of the brake, and the entire exhaust system. It's a pretty nice little truck. The speedometer has always been about 10mph high at around 60mph, so it'll read 70 when going 60. anyway, I've put about 15k miles on it since I bought it with 145k miles, it's right at 160k miles.

 

So I was driving the other day merging from one expressway onto another accelleating from about 30mph up to about 80mph when all of the sudden my speedometer drops to zero. about a minute later the CEL pops on. I drive it to my local shop and theres one code in the system stating vehicle speed sensor circuit.

 

They try to remove the speed sensor, and it comes out in about 3 different pieces. The main mechanic who I think is pretty good, threaded a tap into it, welded a stud to that, then put a socket over it creating a puller and managed to pull the speed sensor out. The blue 18 tooth gear was completely intact. The local parts store had a 4x4 speed sensor in stock but it was for the non 31" tire model and was sold without the gear. it looked exactly like the one I pulled out, sensor, plug, and all. I figured the normal one would be better since my speedo had always read 10mph high. We swapped the old gear to the new sensor, installed it, and no luck, still no speedo, still same CEL.

 

The next day I drive over to my friends work and pull the working cluster out of my old 95 hardbody sev6 4x4 at... YES this is my second one lol. I swap his known good cluster into my truck and the speedo is still inop an the CEL comes on. I take the truck back to the shop where we trace down the red and white wires from the cluster to the sensor for continuity and there is. They remove the speed sensor and turn it by hand AND THE SPEEDO WORKS AND THE CEL GOES OUT.... reinstall the sensor, NO SPEEDO, and about a mile down the rd. the CEL comes back on.

 

I'm now looking at pulling the transfer case and splitting it open....

 

IS THIS VERY COMMON? I've heard of the sensor and cluster issues, but I've never heard of this issue? can the gear that drives the speedo gear on the output shaft come off, or slide down? meanwhile leaving the speedo gear intact? is there anything else I can try?

 

I appreciate all of your help

 

Nick

 

 

[Slartibartfast]

Sounds like you've pretty well narrowed things down. I'd have a look in through the hole in the transfer at the gear to verify whether the gear inside is borked, though at this point I can't think of much else it could be.