i replaced the VSS recently to solve a transmission problem i was having and now the speedo is jumping around at speeds greater than 55mph. it just moves back and forth a little bit. is there any cheap/free way to do a DIY fix on it?

 

I wish I knew!! Mine was doing the same thing and throwing the code for the VSS,so I replacd it with a cheap one from the parts store,still did it,replaced that one with a motorcraft one,still does it,so I don't know the answer but I would LOVE to get it fixed!!

 

The "PSOM" (Programmable Speedometer Odometer Module) might be causing it, shift problems usually present with it though.

Its occurring at speeds of 55mph and higher might be beyond point effecting trans function.

 

nah, no transmission issues here just a goofy speedometer. its completely solid at speeds less than 55mph.

 

I was having the same problem on my 97 f250 with e4od replaced my vss and still nothing got a new cluster from the junk yard and fixed my hard shifting problem completely but now my speedo jumps around alot like 30 mph at anything over 25mph so i dont know if the cluster i happen to get had a bad speedo in it or if its something else but the new cluster definitely helped my hardshifting problem.

 

I had this happen this summer as well. I used an aftermarket from O'Reilly. It jumped all over the place (like 20 mph +/-) above 55. Cruise Control relied on it so I couldn't use cruise. I put the old one back in (it was flakey but more stable than new one). I got a new one from Ford directly. It moves a little bit (maybe 1 mph), but is pretty stable. The one from O'Reilly was a Borg Warner and looked identical to the one from Ford. The guy from O'Reilly argued with me about it saying it was "OEM Spec." The new ones are different from the original. Ford changed the design a while back is what I was told from Ford.

 

They have to have a certain gap between the sensor and the tone ring in the rear diff. Searching should find all the info. If I wasn't on my phone id find all the info.

 

My was doing it also. I put a new one in from Autozone and it got worst.
I put the old one in and unhooked the rear abs black box behind the glove compartment and it fixed it. You will not have abs. It not the right way to fix it, but I do not care on my truck.

 

I had the same problem as the OP. What fixed my problem was disconnecting the RABS Module that's located behind the glove box in my 1996 F150. imgur: the simple image sharer The yellow circles are what I disconnected.

 

I'm not sure rear abs makes a huge difference anyway since most of the stopping power is in front anyway.

 

I fixed this issue on my 95 - I bought a new upgraded PSOM that has a more permissive program to eliminate the waver you describe. If this problem gets bad enough, it can cause a stall, believe it or not. I think it stems from the rear axle carrier developing play over the life of the truck. I think the waver in the speedo needle is the VSS picking up this excess play in the differential. When I'd put the truck in reverse (manual) and begin to back up, it would stall. Unplugging the vss eliminated the stall - because it disabled the PSOM. On this series of truck, the PSOM can cut back the fuel injector function if it detects excess speed - over 120 mph or so. I think for a brief moment, the carrier shifting causes the PSOM to think just that. It's so fast that the needle doesn't have time to jump, but it will stall the truck.
To bring the story to a close, after replacing the PSOM the stall was eliminated, and the needle waver was too. I plan to investigate the differential play - I'm now approaching 185k.

I will try to post the company info - I think the exchange upgraded (and odometer mileage corrected) PSOM was about $150. I had to have it to fix the stall issue. You may find one in the salvage yard cheaper, but your mileage will not be correct, and it may have the same issue.

 

RABS keeps the back end from coming around on you in hard braking situations on slick surfaces. But, since the front brakes are non-antilock, you still have to release the brake pedal when the front wheels lock to maintain steering.

Most of the time it's not an issue, but it makes a huge difference when somebody cuts you off on an icy road right before a stoplight. I've had that happen...

Jason

 

When my old VSS started failing my truck would die suddenly. The Speedo and tach would go to zero then restart about a second later. It would do it at highway speeds. Very annoying. I thought it was the CPS, so I swapped it out on our way to the Black Hills in SD. I had a spare with just in case. Even after I swapped the CPS, it still did it. Replaced the VSS because of transmission issues and it hasn't done it since. Transmission issues still exist, but the stalling and cutting out on the highway has quit. A bad VSS can affect the transmission. The computer reads the VSS and sends info to the transmission based on it.

 

the tone ring in rear end is warped, they are sensitive to heat. towing, old oil, age can warp the ring.

 

Yup, disconnected mine too. I traced the circuits out and was getting good raw input to the PSOM from the VSS, but the PSOM output signal was all f'd up til I disconnected the RABS controller. Junkyard unit did the same thing. Didn't see anything wrong with the PCB inside either one so I junked 'em both.