Speedo Question

[twithers]

I recently picked up an 88 c1500 and I've been trying to figure out why the speedo isn't working. After looking around here, I found a couple instances where people mention that the Turbo 400 tranny doesn't have a VSS that is needed to run the stock speedo. One of the PO swapped in the Turbo 400, but I'm not sure what may or may not have been done to convert the speedo system. When I was under the truck looking at the driveshaft, I noticed what looked like an orange wire that was broken toward the rear of the tranny. I assumed that this was something to do with the VSS, but now I have no idea what that wire is for.

So here are my questions:

Any idea what that wire at the rear of the tranny on the driver's side?

Is it true that the Turbo 400 is not normally compatible with my stock electronic speedo setup?

What options do I have to get my speedo to work? Manual to electronic converter, etc?

Thanks.

 

[sewlow]

T400 speedos are mechanically driven by a cable. Non-electronic.

 

[twithers]

So what's the solution? Is there some sort of adapter module for using the speedo cable tranny with an electronic speedo?

 

[sewlow]

Sorry man! No clue! Waiting for someone with knowledge to chime in.

 

[skylark]

The 400 was used in hd applications in our body style through 91. If it is the same as the 700R4 (also originally a cable) you can swap tail shaft housings and add a reluctor wheel to the output shaft as well as the speed sensor. Do a bit more research as i've only done it on the 700R4 and I'm not positive that it is the same on the 400.

 

[Truckracer]

You need this.

http://www.dakotadigital.com/index....t_id=916/category_id=311/mode=prod/prd916.htm

Dakota digital
SEN-01-128
128k GM-style High Frequency Pulse Generator

 

[twithers]

So, I got the speed sensor conversion that screws into the cable port on the tranny and has a pair of wires to connect to the VSS wiring.

I spent a couple hours digging around to try to find the vss wires but had no luck. I did the usual google search and found a couple different schematics but none seemed specific to my truck.

Does anyone know which wire I need to connect to and where it might be located? I'm assuming that a previous owner cut the wires for it when they swapped in a Turbo 400 tranny. I read somewhere that you might be able to splice into one of the wires going to the cruise control but I had no luck with that either.

Whenever I located the signal wire, I should just have to splice one wire from the new speed sensor to the original signal wire and groind the other wire, right?

One a side note the sensor I got has 1 blue and 1 gray wire. I assume that is a generic color scheme and not specific to the wire colors on the factory harness. Also, the previous owner should never be allowed near any wires again. I've spent hours removing bad electrical work and doing it right, so I definitely have an uphill battle when it comes to finding this proper wiring.

Thanks.

 

[grampadirt]

Scanned a page from my Haynes manual.Not sure what that ''buffer'' thing does or where it's located.Hopefully this will help.

 

[grampadirt]

Should've made it easier to read...

 

[skylark]

The buffer is the vehicle speed sensor buffer (vssb) and it is in the cluster on 88-91.