90 Sub Speedo Issues

[LIVEAnimals]

So my speedo has been inoperative for awhile now, its got a mind of its own. Lately its been pegging itself at speeds less then 15-20 mph and anything above that is just stays put at 70 mph. What says the brethren? Anyone had a similar problem?

 

[Deuling]

I hear shady recommends speedo lube


No but for real I'm positive he or somebody mentioned a while back that lubricating the speedo cable helped.

 

[diesel4me]

My old 72 K5 did that and I tried a new cable,but it kept pegging the needle when it felt like it erratically,and the speedo head made some weird noises too--tried taking the cluster apart and see if there was anything in the speedo head that was mucking it up like rust or fuzz,etc,but the cup thing that worked the speedo head needle was looking perfect..I think its driven by a spinning magnet thing?..
I ended up just getting another dash cluster at a swap meet and put the whole thing in it...cured..

The speedo in my 82 GMC is singing the frigid weather blues now too,but still reads correctly..hoping it'll go away when it warms back up again...its hard to find a cluster for that thing here any more..I might have one from a '73 in my shed,but its probably a lot different,mine being a diesel..

 

[nvrenuf]

The speedo in a '90 (or '91) will be electric so no cable to be lubed. It's going to be a sensor or DRAC issue.

 

[LIVEAnimals]

The speedo in a '90 (or '91) will be electric so no cable to be lubed. It's going to be a sensor or DRAC issue.

Haha yea I looked for a cable to lube and saw all these motherboard looking things and I got scared and put it back together. So how do I go about troubleshooting a sensor/DRAC issue?

 

[jeff in co]

I'd check a couple things. First you might just install a new pickup sensor at the T-case and see if that fixes the problem (perhaps a bad sensor). I think it's only a $10-15 part. If that's not it, check the wiring (twisted purple and green, I think). Follow from the sensor all the way up to the DRAC box. Be sure nothing is frayed or rubbing.

 

[LIVEAnimals]

I'll do that, thanks

 

[dyeager535]

Does your cruise control work? Do you get a check engine light? Does the vehicle exhibit any driveability issues?

The VSS on the t-case, and the DRAC after that, feed the ECM and cruise. If your cruise works steady, it's not likely a DRAC/VSS issue.

 

[454Sub]

And the VSS isnt a 15$ part FYI, atleast not when I called, they wanted something like 50$ for it. I took some from the junkyard, all it is is an electromagnet, so its not a huge fail item.

 

[dyeager535]

I wouldn't trust any of the new aftermarket stuff as much as I trust a used GM piece anyway, at least not a Delco piece made in North America.

 

[LIVEAnimals]

I haven't tried the cruise in quite some time but the last time I did it wasn't working. I'll check again on the drive to work.

If the cruise isn't working as well where does that all tie in?

 

[jeff in co]

And the VSS isnt a 15$ part FYI, atleast not when I called, they wanted something like 50$ for it. I took some from the junkyard, all it is is an electromagnet, so its not a huge fail item.

Yea, I looked that part up afterward.....dang! $50-$60. I'd try out a junkyard one first. Another guy had similar problems and the new sensor fixed it.

The path:

1) Speed sensor pick-up
2) Twisted wire to DRAC box
3) From DRAC Box to:
- Computer
- ABS
- Speedo
- Cruise Control

 

[454Sub]

Yea, I thought the parts counter guy had inhaled some THC smoke when I heard that the first time.

 

[LIVEAnimals]

I need to hit the JY for an antenna assembly so I'll look for the sensor as well

 

[dyeager535]

The BEST way (IMO) is to hook up a scanner/laptop running Tunerpro RT, and see if the ECM is registering speed correctly.

You may also see some issues with how it runs as you decelerate, if the problem is not the speedometer.

As bad as the cluster connector is, my first suspicion would be the cluster connector, if I couldn't verify vehicle speed at the ECM.