eleazar1

First off, hello Yotatech! I'm new to the forum and new to Toyotas. I recently acquired a 1992 Pickup 3.0 4x4 manual trans, and I'm loving it.

I'm pretty capable with car work, but I do need some help with this one.
I did search for this quite a bit before posting, but I think my problem/question is fairly unique.

History:
My existing speedometer/odometer had 216,000 miles on it. The speedo would drop to 0 then return to the correct speed when I would use the turn signal.
Then, about a month ago, the odometer stopped working altogether, but the speedo still worked.
I pulled the speedo out of the instrument cluster and this is what I found:

(note the burnt circuitry at the top)

So, I got another instrument cluster from Ebay and pulled the speedo out of it. It had 218,000 miles on it, so I figured I was in good shape
with the odometer and did need to bother trying to set the mileage.
But, when I looked at the back of the new (used) speedo I found this:


It has the same burnt circuitry at the top and almost the same mileage (I'm seeing a pattern here).
Now, the new(used) speedo and odometer do work. But, they have the same problems the old one did.
Just the other day, the speedo stayed at 0 for about the first 7 minutes of my trip before returning to the correct speed.

I know other people have had similar symptoms, and the problem has been the speed sensor.
But, in my case I believe the problem to be with the circuitry in the speedometer itself.

Question:
1) Where can I find a good replacement speedometer that I know will work (i.e. not be burnt up) without paying an arm and a leg?
2) Should I still go down the speed sensor troubleshooting route before replacing the speedometer?
3) Or (this is a loaded question), can I swap a cable drive speedometer unit from a 1991 into my dash/tranny?
It looks like the gauge cluster is the same apart from the speedo, and it looks like the connection at the tranny is
almost the same as for the speed sensor with electronic speedo.

Any help would be appreciated.
Thanks

rustypigeon

I would just replace the burnt out electronic components. The components should be available at Mouser.com or Digikey.com

Can you tell us what the numbers are on the burnt out components? I can't tell from the picture.

Edit... Actually after taking another look at the picture, it looks like the circuit board itself may be damaged from the heat. Are the copper tracks on the board damaged as well?

scope103

As you point out, your symptoms point to a failing speed sensor. Burned circuit boards are never a good thing, but before you start trying to repair the boards you need to test the sensor.

This might help:


When I replaced my sensor, I first tested the cluster (VSS1 is expensive) with a function generator. Not the kind of tool most mechanics would have.

eleazar1

Thanks, rustypigeon.
Yes, the copper tracks are burnt. I'm honestly not even sure how this thing is still working. Like, everything on the speedometer/odometer head works. I thought about trying to repair the circuit board, but my electronic component level repair skills are very limited. I'm much better with mechanical components.

And, thanks, scope103. Yeah, I should check the speed sensor first. I guess I was just trying to be clever and thought I had found a unique problem when I saw the burnt circuit board. Thanks for keeping me on the right track.

And, I think I might be able to dig up a function generator. I do work with some smart technicians. However, I did just see a new VSS on Ebay for $30. I might just pick that up instead of trying to test everything.

Thanks for the help.

I'll post updates of my progress.

scope103

Uh, easy does it. If you plug in that new VSS and it works, you're golden. But what if it doesn't? Is it the wiring? The two new combination meters? The replacement VSS?

If you can get your hands on a function generator, you can do an end-for-end test of the combination meter (and testing the VSS only requires 12v, a meter and steady hands; you've probably already got those).

Give it a try; if it was easy, it wouldn't be so effective.

rustypigeon

scope103

rp -

I was trying to find that page. Remember where it came from?

rustypigeon

It's on page BE-51 of my '94 Service Manual (in the combination meter section)

The image I linked I found using google image, and it brought me to a Yotatech post...


https://www.yotatech.com/attachments...0.40.14-am.png

eleazar1

Many thanks for the instructions. I'm going to test my VSS sometime next week. I'm going camping Monday with the truck and don't want to pull any important bits off it before then.

eleazar1

So, now I feel quite humbled. I broke the speed sensor trying to get it out.
It looked so easy to get to that I did not bother looking up how to remove it. Well, hopefully I'm still teachable.

Now, I just need to find a new sensor. Hopefully that was the source of the speedometer woes in the first place.