Speedo Electrical Signal

[sperold]

My speedometer is not working in my 90 SHO. I can get my speed from a GPS App on my phone.

I wonder what is the affect of not having the electrical signal that I think goes to my ECM. I have been driving the car and there does not seem to be any difference from the old days when my plastic gear on the transmission was still spinning.

Going to fix this gear thing, I am just wondering what is happening in the meantime.

Does anyone know what this speed signal is used for in the car's ECM, or wherever the signal goes?

Thanks.

 

[zoomlater]

Are you referring to the speedometer cable? That's a mechanical cable that is connector to the speedometer in the dash. There is an upper and lower speedometer cable. When my speedometer stopped working, I eventually had to replace the lower cable. The VSS sensor appeared to work fine without it.

The thread below has some background on the VSS sensor

https://shoforum.com/index.php?threads/half-throttle-woes.120706/#post-1332468

 

[Irish Pride]

The VSS is used for the cruise control.

 

[NoSlo]

The speedometer is mechanical. The cable screws into the back of the VSS, and connects through it to the little transmission gear. If the gears in the transmission are stripped or missing from the end of the VSS, you get neither speedo nor VSS signal.

On the MTX SHO, the VSS is an input to the EEC-IV computer, which then runs the cruise servo. There is no VAPS nor cruise relay box on 92 SHO.

The only other likely use of the VSS in EEC is determining when the vehicle speed is sufficient so air conditioning doesn't command additional radiator fan speed.

 

[sperold]

Yes, it is the little cast aluminum assembly that is broken to the point that the end of the speedometer cable does not connect. It is bolted to the transmission and has the nylon gear inside it. The VSS part fits on this thing and the 2 piece cable completes the system. Since my part is broke, I do not know if the bottom section and the VSS part were once one piece.

I hear they are a bear to get out as the bolt is only 7mm and it is hard to reach (and see).

I have a good cable, including the VSS part that the electrical wire connects into, so that part of the system is fine.

Does anyone have a part number for this assembly, (or a used one) as I need one to fix this issue.

 

[luigisho]

https://www.fordpartsgiant.com/part...ar=1990&Submodel=&Filter=(e=6_cyl_3_0l;t=5mt)

this is the vss part. You have a diagram of the other stuff?

 

[sperold]

^^^^ Thanks for the picture, the part# and the price!!!!

Thanks to everyone.

The picture shows that my part which I thought was 2 pieces is actually 1 piece. You probably have to take the thing apart to change the plastic gear, back in the day when you could buy it separately.

Thanks again. I appreciate the help.

 

[NoSlo]

If the cable won't go into the VSS, and the cable end looks undamaged, then a new and correct VSS should fix that. Digital cluster, for example, uses a different VSS. Also, you may need to twist and play with the cable to get it to go in properly, as the square cable end must align and fit into the square receptacle deep in the VSS.

If the VSS square end is not engaging inside the transmission with the plastic speedometer driven gear, it may have once been installed wrong, breaking the gear. They are about $15, but are on the "pull the tranny" category as far as replacing (just due to space).

This whole assembly below is what comes out of the transmission if you need to service the gear. The driven gear itself is a "17271" part number, but I didn't immediately find the full part number or color (probably beige) for the SHO's MTX-IV. Don't lose the o-ring.

 

[BaySHO Performance]

The VSS can be removed by dropping the Y Pipe IIRC. The transmission doesn't have to be removed.

 

[PaulTAutoX]

The speedometer is mechanical. The cable screws into the back of the VSS, and connects through it to the little transmission gear. If the gears in the transmission are stripped or missing from the end of the VSS, you get neither speedo nor VSS signal.

On the MTX SHO, the VSS is an input to the EEC-IV computer, which then runs the cruise servo. There is no VAPS nor cruise relay box on 92 SHO.

The only other likely use of the VSS in EEC is determining when the vehicle speed is sufficient so air conditioning doesn't command additional radiator fan speed.

FWIW I have a '92 and it has both cruise and VAPS. It was probably a late '92 (I didn't buy it until Jan of '93).