Speedo jumping/sticking

[94GTPilot]

Now that I'm starting to get a few other issues ironed out, the speedo is next on my list. To describe it best, the needle doesn't move much until about 15 mph, then quickly climbs to about 40, and by the time I hit 40 or 50, it takes off like I've got a rocket strapped to my rear end. If I keep accelerating, it will wrap itself all the way around to the back of the peg.

I've replaced the VSS, and the gear on the VSS looked fine. I'm pretty sure the next likely source is gear in the tailshaft? Am I right? I really don't feel like unbolting part of the transmission if there's something else I can throw at it first.

Any suggestions? I've scoured the internet, and 80% of what I've found is "replace the speedo cable" (coming from all the fox body guys). I know ours doesn't have one, I'm trying to figure out how many and what the components are that make our speedos spin accurately.

 

[toyman]

Is there a speedometer recalibration unit such as a Speedcal in the picture? I would be very surprised it it's the speedo drive gear. I think it's more likely to be electrical in nature.

 

[wheelyman19]

My tach would kinda do the same thing and all I did was lift the needle up from the peg a little and it worked great after that, if that doesn't work id say replace Ur speed sensor, but Idk I think those either work or don't.

 

[94GTPilot]

No, no speedcal, it's all factory as far as the speedo is concerned. I did replace the VSS a few weeks ago, and it does the exact same thing. So we can rule the VSS out. I'm about to take out the gauge cluster and see if there is a stripped gear in the back, but as far as I know, the speedo is moved electronically in that housing, correct?

And as for the speedo drive gear, is that in the tailshaft/transmission? Is it an a$$pain to get to?

 

[wheelyman19]

No other then getting the car in the air its the easy as cake. But Id try lifting the needle up a little. It's cheaper lol.

 

[toyman]

No other then getting the car in the air its the easy as cake.

That depends on whether it's an AODE or not.

 

[94GTPilot]

It's a 5speed. I will take a look at the back, and if all looks well, I'll be buying a new gear for the trans.

 

[94GTPilot]

Is there a diagram somewhere that outlines the components of the speedometer/odometer system?

 

[94GTPilot]

So I took the gauge cluster apart, took a look at the gears that drive the odometer, slapped everything together, and it has ****ing magically started working like it should. No more jumping, sticking, just moves around like it should. Granted, with 3.73 rear end gears, it's not accurate, but it's a start. Just need to find me a speedcal and see what I can do.

:censored:

 

[wheelyman19]

Did u pull the needles off?

 

[MikeH686]

Mine is doing the same thing but mine just stays jumping in a 10mph difference as im accelerating so idk if mine is the speed sensor or the voltage regulator under the dash i have a 91 lx the only thing i could say is that when i bought the car 2 weeks ago that he has a dummy shift light tied into the voltage regulator so if anyone could help point me in the right direction i would appreciate it

 

[94GTPilot]

No, I left the needles on. Just took the 3 seperate clusters out, then put them back in the assembly.

And if you have a 91, you have a seperate speedometer cable that ours don't have. You may need to change out the whole cable assembly.

 

[MikeH686]

so you think its just a worn cable?

 

[94GTPilot]

So after driving it for a few days, it's back to its old habits. I did replace the gear on the VSS with the white 23 tooth gear, just to get it in the ball park and see what happens (since I had one laying around). I guess the only 2 options left at this point are:

1) the motor on the back of the speedometer is going out, which would require me to buy a used cluster and try to swap it out

or

2) the drive gear inside the transmission is either stripped or has slid back on the shaft.

I've currently got the car at the body shop to repair my roof, replace the windshield and put a new hood on (hood latch came undone and hood flew up). When I get it back, I'm going to pull the VSS and take a look/feel inside the trans to see what I can see/feel.

Does anyone, by some random chance, happen to have a cluster laying around for some reason that wouldn't mind selling the speedometer? I'm ready to put my fist through my cluster with all the frustration it's caused.

Oh, and comments/thoughts also welcomed. ;-)

 

[revhead347]

The speedometer drive gear is plastic and pressed onto the output shaft. In order to change it, you have to drain the ransmission and pull the tail section. It's a pita and much easier to do with the transmission out of the car. The shifter bolts to the tailsection. You have to get in from the top and pop a bunch of roll pins out of the shift selector rods. Remove the speed sensor and rotate the transmission a little while looking in there with a flashlight to see if it's missing any teeth.

Kurt

 

[94GTPilot]

I was afraid of that. Guess when I get the car back from the body shop, I will take a look inside and see what the teeth look like.

I've also heard that I can hook the VSS up to a drill, with the ignition on/engine off, and see if it spins the speedo...? Any truth to that? Might that help eliminate the speedo motor if it turns without a problem?