MTX speedo drive

[JATO]

This isn't quite an SHO problem but the source of my issue I believe is in the speedometer drive in my MTX-4 transmission. The car is my '06 Vulcan with the MTX conversion. The issue is a bouncing speedometer needle when holding a steady speed. With cruise control set, the cruise tries to counter the bouncing needle and causes the car to surge. The speedometer is electronic and is driven with the SHO VSS. I swapped out the speed sensor and the speedometer is still bouncing. Has anyone had issues with the actual speedometer drive and gear in the transmission causing "slop" in their speedometer? The only two possibilities are the drive in the trans or the speedometer it's self.

 

[Irish Pride]

I think your problem is in the cluster. You need to replace the speedo.

 

[rubydist]

the cruise controller doesn't care if the speedo needle moves at all. it looks at the pulse rate from the vss and tries to keep that at a specified rate.

if the vss has been replaced and your electronic speedo needle bounces, then the cluster is the problem like Irish Pride said.

there is no place in the vss drive on the mtx that can allow "slop" or surging - the output shaft drives the speedo drive gear, into which the vss tip goes. its not like there is a speedo cable that can wind up and then unload to cause surging.

 

[JATO]

The cruise fights the needle bounce. It accelerates the car when the needle drops and slows the car down when it advances. I'll have to check how it's all wired, the car is all 2006 Taurus for the most part except for using the SHO VSS instead of the auto's output speed sensor. The car being an '06 and CAN bus I think the cruise is tied into the speedometer, I'm going to have to pull out the diagrams for it. I had a feeling that it might be the cluster.

Edit: I just glanced through the factory wiring diagram manual and the speed control microprocessor is in the cluster.

 

[kevinspann]

Yeah, I can see my speedometer needle 'twitch'....I think it's just how it is, but its gear driven to the VSS and then cable driven to the cluster, unlike yours.

 

[JATO]

Problem solved. The issue was too much "slop" between the square hole in the end of the speedometer gear and the drive peg on the speed sensor. SHO Source sold me a good used gear but in the mean time I had to do a temp repair. What I did was flow some JB Weld into the square drive hole, installed the speed sensor, and then let it cure for 36 hours. The JB Weld set-up between the drive hole and the shaft and now it has a nice tight fit. No more speedometer needle bounce or surging cruise control.

This is just an emergency temporary repair and I expect the speed sensor will be ruined when I take it apart to fit the new speedometer gear. I used a BWD sensor from O'Reilly's and I have a new Motorcraft part in the box for when I'm ready to throw in the new gear. ****, if this repair holds I just might leave it until the next time I need to pull the trans out.

Play between the gear and the sensor might be something you guys with cable speedometers might want to look into if you have bounce that a new cable won't fix.