Bad exciter ring?

[JSchuricht]

Working on a 96 350 DRW 5SP for a friend and having a issue with the speedometer jumping around at speeds above 30mph. So far I have replaced the VSS and visually checked the wires. I don't see any related DTC's, and have seen the ABS light come on once. I attempted to capture the behavior with my AE scanner, but I don't think it is quite quick enough to catch everything I see on the speedometer. Unfortunately I don't have a breakout box or o-scope, but my thoughts are that it is the exciter ring. Anything else I should check before I tell him to get out his check book?

[superduty4x4]

It could be the PSOM (small computer module integral to the speedo). You can try swapping it with a known good unit to rule it out. If the PSOM is bad there are a few things to keep in mind:
Swapping the whole cluster is easiest but you can disassemble the cluster and swap just the speedo/PSOM. If you do a full cluster swap it has to be out of a same year rig because there are minor wiring differences among the years.
PSOM stores mileage, so whatever mileage the donor truck had will show on your truck. You can get them reprogrammed for correct mileage but its not cheap.

[alberta 7.3]

I'd say you may want to pull the diff cover and inspect the tone/exciter ring. There may be gear damage and the shrapnel ripped/dinged some teeth on the ring. It doesn't take much, I had a few teeth that had slight damage and my ABS was completely shut out, and the speedo was jittery.

[superduty4x4]

Originally Posted by alberta 7.3

I'd say you may want to pull the diff cover and inspect the tone/exciter ring. There may be gear damage and the shrapnel ripped/dinged some teeth on the ring. It doesn't take much, I had a few teeth that had slight damage and my ABS was completely shut out, and the speedo was jittery.

Anything more than a dark grey metallic fuzz on the VSS when you pull it out indicates trouble. Fine metal fuzz is normal.