Wonky Speedo and cruise control--totally stumped!!

[cgailey]

Just bought a '96 Taco LX 3.4 5spd with 95,xxx miles in awesome condition. Impeccable service records, same owner for 16 years, etc. etc.

Test drive was great, made the purchase, and on the drive home the speedo started to bounce around, and the cruise started to make the truck surge--it was like riding in a car driven by your grandpa who would repeatedly goose the throttle at highway speeds. If I didn't use the cruise, no surging. All was well except for the speedo.

My first thought was speedo cable, but then I drove the truck again. No problems for 20-30 minutes, then it started back with the bouncing and surging. Third trip, same deal.

I've been poring over my Haynes wiring diagrams and the interwebs and have found nothing to help me nail down a diagnosis.

My questions are:

1. Speedo is run off of a mechanical cable on this truck, correct?

2. From what I glean from the wiring diagrams, cruise runs off of VSS, and is independent of the speedo, so why does there seem to be a link between the two?

3. What am I missing?

This is really going to annoy me, so I'm going to have to fix it. I want to get a handle on the issue to see if it is something I can handle or if I need to take it to a shop. If I do take it to a shop, I would rather be in the know than be at their mercy.

Thanks in advance!!

 

[40Habits]

There is no cable , the speedometer is run off the VSS. Fix that and it should fix the cruise.

Congrats on the new Tacoma!!

 

[cgailey]

There is no cable , the speedometer is run off the VSS. Fix that and it should fix the cruise.

Congrats on the new Tacoma!!

Do you by chance know which part i need to get? Trying to find the right speed sensor is proving difficult. Dealer only came up with abs sensors. Can't determine which one is the right one online either.

Dealer schematic showed a gearing assembly similar to one that would drive a speedo cable. Confused...

Thanks.

 

[cgailey]

Manual, 4x4

 

[40Habits]

Then that is my bad. You do have a speedometer cable. The auto has a VSS and they went to VSS in the manual Tacoma's in 98. Sorry about that!!

 

[cgailey]

Any thoughts on what could be causing the issue I described? Does the cruise run off of the speedo gear in the t case?

 

[40Habits]

It is either your speedometer cable or your speedometer. The speedometer on your instrument panel is essentially a VSS and sends the signal to your cruise.

To see if it is your speedometer you can pull the gauge cluster and see if there is continuity between terminals A and B. It should be 4 times for every revolution of the speedometer shaft. Hope this helps!

 

[cgailey]

Hey thanks...that helps a lot. I couldn't figure out where the link between the speedo and cruise was. Am I correct in thinking that if the issue with the cruise doesn't occur until the speedo starts to bounce around, chances are it is the cable and not the contacts in the speedo?

 

[40Habits]

If I had to guess, I would say it is the speedo cable. Since you would have to pull the gauges to replace it you could test the speedometer then.

 

[cgailey]

Alrighty. Thanks for your help.

 

[cgailey]

Just now getting to this job and my plan was to lube the speedo cable and check the contacts at the speedometer as suggested. What would be the best option for choice of lube? I have done a search and seen all sorts of recommendations from graphite powder to synthetic bike chain lube. I have both tri-flow and a synthetic chain lube called pro-link that I use on my bikes. What do mechanics use?

Also, is the best way to lube to just pull the speedo cluster out and slide the cable out a bit to squirt the lube in, or do I have to disconnect the cable at the tranny?

Thanks again!