Speed sensor at 1989 suburban Speedometer retrofit

[ratrod47]

Project car is 1932 Essex coupe hot rod. I have installed a complete 350 with 700r4 ( mechanical speedometer drive) and complete wiring harness/ ECM from donor truck which was my daily driver. Has any one taken the vss from stock speedometer and retrofitted to another mechanical speedometer ( 62 Studebaker lark) ? I am trying to avoid the expense of buying a JTR speed sensor 2prs adapter.

Any information would be much appreciated? I have not tried to open the back of the speedometer cluster yet.

[majabr]

Project car is 1932 Essex coupe hot rod. I have installed a complete 350 with 700r4 ( mechanical speedometer drive) and complete wiring harness/ ECM from donor truck which was my daily driver. Has any one taken the vss from stock speedometer and retrofitted to another mechanical speedometer ( 62 Studebaker lark) ? I am trying to avoid the expense of buying a JTR speed sensor 2prs adapter.

Any information would be much appreciated? I have not tried to open the back of the speedometer cluster yet.

Hi Ratrod47,
I recently completed a TPI conversion on a 1984 5.0L K10 pickup truck and ran into a similar issue. On this conversion, I was able to connect the vss signal wiring via a "conditioning module" from the built-in speed sensor and wire it into the speed sensor input (vss) to the ECM (1227165). In this vehicle the vss generator is embedded in the speedometer display assembly and that signal was ultimately used as the speed sensor signal input to the ECM.
I was unable to do a tear down of the speedometer display assembly and determine exactly what kind of circuit is embedded in the speedometer to generate the vss pulses. I suspect that it is a type of magnet/transistor (hall effect) device, since the output of the vss pulses from the speedometer are fed into 12VDC powered module (amplifier) and then this output was used to connect the vss signal to the ECM.
The speedometer on the K10 is made from a brittle plastic and I determined that any further disassembly of the speedometer could only be done by destroying the speedometer. Fortunately, the conditioned vss signal that I used from the speedometer was able to satisfy the input requirements of the ECM vss circuit and worked okay with the 1227165 ECM.
I suppose that you could try to retrofit an older type of speedometer with the built-in vss sensor, but you would also have to install the vss conditioning module that the output of the speedometer plugs into. There again I do not see that the speedometer could be disassembled in such a way as to be able to reuse only the speedometer dial and the internal vss sensor.
Even though I had success with converting the vss output signal to the 1227165 ECM, I already determined that if that did not work, I would just have to bite the bullet and add a speed sensor that the ECM could recognize. There was another reason that I was willing to purchase a newer speed sensor adapter for this conversion and that is the resolution on the newer speed sensors offer twice the resolution as the older speed sensor. For example, the older speed sensor gives a maximum pulse count of two pulses per speedometer cable revolution while the newer aftermarket speed sensor outputs four pulses per revolution of the speedometer cable.
Hope this helps.

[ratrod47]

Thank you. I am using a cable drive speedometer from a1962 Studebaker Lark in my hot rod. What i was interested in if there is away to retrofit the vss internals from the 1989 speedo cluster. I do not mind sacrificing the cluster if I was sure it could be done or has been done by someone. Using the ECM 1227747
Do you have a picture of the VSS condition module, Or is that the green plastic thing attached by wire to vss speedometer ? I do not think I saved the matching plug on the harness end going to the ECM for that at least I have not found it. I think it was a dark blue wire to the ECM. I had original planned on getting the JTR Stealth 2PRS speed sensor per the info I had read about. Probably will have to get the 2PRS seems like it would be a lot easier in the long run and simpler for me to figure out . What did you purchase as the 4 pulse sensor?

[majabr]

Thank you. I am using a cable drive speedometer from a1962 Studebaker Lark in my hot rod. What i was interested in if there is away to retrofit the vss internals from the 1989 speedo cluster. I do not mind sacrificing the cluster if I was sure it could be done or has been done by someone. Using the ECM 1227747
Do you have a picture of the VSS condition module, Or is that the green plastic thing attached by wire to vss speedometer ? I do not think I saved the matching plug on the harness end going to the ECM for that at least I have not found it. I think it was a dark blue wire to the ECM. I had original planned on getting the JTR Stealth 2PRS speed sensor per the info I had read about. Probably will have to get the 2PRS seems like it would be a lot easier in the long run and simpler for me to figure out . What did you purchase as the 4 pulse sensor?

Hi Ratrod47,

This item on eBay is the type of interface that is connected from the back of instrument cluster to the ECM on the K10 pickup truck. IIRC, the black connector (it looks like an optical interface and not a hall effect transducer as I mentioned earlier) in the link plugs into the back of the instrument cluster and the signal out of the green module drives the cruise control, is split and sent to the ECM as the speed sensor (vss) input.

As I stated in my earlier message, I did not have to purchase and install the third party vss adapter for my project, since I was able to use the existing vss instrument cluster output interface.

I don't see any way to retrofit the older Studebaker speedometer to output the required vss signal to the ECM.
Here is a picture of the 1984 C/K 10 speedometer vss interface.

[ratrod47]

Based On your words of " I don't see any way to retrofit the older Studebaker speedometer " that is good with me I will just buy the 2PRS speed sensor. After all what is $120 to get this build on the road after many years of work to get there.

Thank you majabr for your time, information and efforts to educate an old school guy. I am sure others on here will find this interesting and help full.