Troubleshooting speedometer

[Jharsman]

How's everyone doing today? I have a small problem that is causing a lot of headache, I have been searching the forums since around 10am and haven't quiet found the answer I'm looking for.
First off, this post is about a 1990 Laser rs
Earlier today my speedometer would dive to 0 in between shifts and any time I let off the throttle at all. Thinking it was just a bug i let it be for the time being. A little later I went back out for a drive around the block to find out if it was still jacked up, and sure as shit the speedometer doesn't work at all.
The first thing I did was pull the cable out of the trans and spun it by hand, verified that my tiny fingers could spin the speedometer 15mph the cable is good. I hooked it back up thinking maybe it had loosened its self and took another drive, this time I had my laptop with me, through ecm link I could see that the computer was seeing 0mph the whole time too.

My question(s) is/are
What is the piece that the cable end thread onto in the transmission? Is that the vss? I am wondering because there are no wires that connect to it at all, it is only held in by a 10mm bolt.
If that is the vss there should be wires on it?
If that is not the vss (which I'm assuming its not) then where would that be located? From what I have found using the search, it should be right under the intake manifold, but I'm not seeing anything.

Also as stated it is a 90 laser, the ecm is rewired and out of a 91 or 92 and the transmission is a 92 and up (although I have no idea what the difference is besides the amount of teeth on the axle splines, which is just a guess)

Any help would be appreciated, I am trying to go to the track tonight at 6...time is ticking away for me

 

[nelliott500]

You have a mechanical VSS so I don't think the ECU can read your speed.

When you pulled the VSS out of the trans and spun the cog by hand, you saw 15mph on the speedo? If that's the case, the VSS is good, the speedo cable is good, and the gauge cluster is good. Did you look inside the trans where the VSS slides in? I would think it has to be trans-related if everything else works.

 

[Jharsman]

I didn't actually pull the VSS(I wasnt sure if that is what the cable hooked into), just disconnected the cable from it.and spun the actual cable end. So far i have only verified the cable is good. I was having problems getting the VSS out so I figured I would get on here and see if that was actually the VSS, or if it was something different. I have data logged with this car before, and speed is was one of the parameters that was working. That's why this is confusing me because from what I have found searching, like you said, it is a mechanical VSS.

 

[nelliott500]

Ahh, alright. Then I would think the issue is the VSS. Maybe the plastic teeth are all chewed up. I had trouble getting mine out and couldn't find much information about it. Take out the bolt and try to wiggle the VSS out. It didn't work for me. I took a long pry bar and a hammer and just tapped the flange of the VSS (the wing that the bolt goes through) to rotate it until the wing was turned far enough so that I could tap it out from under the car.

 

[Jharsman]

Thanks for the help, I wasnt sure if that was the VSS or not. I'll get back out there and see what I can do. I was also reading that some of the VSS's split into 2 different pieces. Is this true for a 1g 5speed turbo? I would hate for something to fall in the trans and have to pull it out and apart.

 

[nelliott500]

Not that I'm aware of. Here's a pic of a 2g VSS and 1g VSS. The 1g is on the bottom.

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[Jharsman]

Does anyone know how the mechanical VSS actually works? I'm asking because like I said, I could monitor vehicle speed through ecmlink even though it is a mechanical sensor. Since this problem started I have not been able to see speed on link, which is making me think it could be something else since I don't know how the mechanical VSS converts to an electrical signal for the ecm to see.

 

[Jharsman]

Also since this has happened the car backfires loud and hard under under boost. Its almost feels like hitting fuel cut but not nearly under enough boost for that to be it. Any ideas??

 

[Jharsman]

After doing MORE research last night, it seems like the VSS is actually on the back of the speedometer. Can anyone verify this? Digging through posts that are years old what I think I figured out is that the part that the speedometer cable screws onto in the transmission is purely a gear that only spins the cable, and at the other end (speedometer) where is screws in, the end of the cable spins the electronic VSS and relays that information to the ECU. Does this sound right to anyone?

 

[nelliott500]

You may be right. The repair manual calls that part the "speedometer driven gear assembly". Part #12:

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[nelliott500]

Does your car have ABS? ABS cars have a speed sensor at the wheel hub (part #4):

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[nelliott500]

If you need repair manuals, let me know.

 

[Jharsman]

I do not have ABS. Ill be ordering the speedometer driven gear assembly and see if that fixes my problem. Thanks for all the info!! I do need a manual, where did you find an online version?

 

[Tiny]

have you figured out what the problem was?

 

[Jharsman]

have you figured out what the problem was?

Yes, it was the speedo drive gear assembly in the transmission. That plastic gear was shaped like a bow tie when I pulled it out.