so the needle on my speedo bounced kinda bad around 50 60 70and it wouldnt let me use cruise so i pruchesed a new one from napa. vss319. The new ones plastic old ones metal i replaced it and it now bounces anyware above 10 or 20. So today i tore the diff cover off cleaned all the crap out of the dif put new fluid it and now i think its actully worse any help or ideas?

 

Get one from ford i went through 3 aftermarket ones before i got one from ford.

 

You have rust on the surface of the axle where the VSS mounts ....

 

x2 with rick on this.

VSS having issues, might be dirty.

 

you dont think its grounding properly i take it then?

 

i pulled and cleaned the sensor and looked at the ring attached to the ring gear and that looked good. ill have to look in to a grounding issue

 

its a hall effect sensor.

Rust can build up under it and cause it to move. or you could have metal shavings on it.

Be careful removing it, its easiest with the diff cover off, cause anything you scrape wont fall in.

might be replacing the fluid again. =(

if they break, you gotta pull the diff cover and push it out from the inside.

 

Rust on the mounting surface makes the unit set too far away from the tone ring.. Cant read properly ..

 

Thanks for saying that better than me. haha.

 

You can more find details in TSB 96-21-11, too.

 

PSOM Pointer Waiver TSB 96-21-11 by Ford for 92-96
Programmable Speedometer/Odometer Module Pointer Waiver Article No. 96-21-11
ISSUE: The speedometer needle may waver and/or a light surge may occur on some vehicles when speed control is used
at highway speeds between 80-113 km/h (50-70 mph). This may be due to slight dents/chips in either the exciter ring
or the Vehicle Speed Sensor (VSS) and air gaps between the VSS and the exciter ring.
ACTION: Replace the Programmable Speedometer/Odometer Module (PSOM) if required. New PSOM's come with increased immunity to system
variability. Refer to the following Diagnostic Procedure for details.
DIAGNOSTIC PROCEDURE
BRONCO/F-SERIES - Perform normal PSOM diagnostics per Pinpoint Tests "H" and "J" of the 1996 F-Series/Bronco
Body/Chassis Service Manual, Pages 13-01-30 through 13-01-32 and Pinpoint "B" of the 1996 Powertrain/Drivetrain Service Manual,
Page 10-03-11.
1. Any slight dents, chips, etc., in either the exciter ring or VSS will create needle waver. Measure air gap between
the VSS and exciter ring. It should be 0.38-0.51 mm (0.015-0.020").
2. Check exciter ring runout per the same ring gear backface runout procedure of the appropriate model 1996
Powertrain/Drivetrain Service Manual, Section 05-00. Make sure the exciter ring is mounted correctly to the
ring gear. If runout is more than 0.1 mm (0.004"), perform the differential runout check per the procedure in the
appropriate model 1996 Powertrain/Drivetrain Service Manual, Section 05-02A or 05-02D, to find cause and repair as needed.
3. If all items listed above check good, replace the Instrument Cluster Assembly. Obtain the correct service part number from the Parts Catalogue
and then contact the Electronic Odometer Exchange Center at (800) 259-9700 for U.S. Dealers and (800) 663-9974 for Canadian Dealers.
NOTE: DEALERSHIP MUST TELL THE ODOMETER EXCHANGE CENTER THAT YOU NEED A PSOM3 LEVEL CLUSTER FOR A SPEEDOMETER NEEDLE WAVER CONCERN.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage
Bronco 962111B Replace Programmable 0.7 Hr.
BASIC PART NO. CODE 10849 06
OASIS CODES: 204000, 204100, 204200, 205000

 

#2 in Ricks post above is the most common reasons I've seen for a bouncing speedo. It doesn't take much to knock it out of tolerance, (.004"). Look through the sensor hole vs. removing the cover again to check it.

 

I've only seen this 2 times & both times it was from rust build up under the sensor . If the tone ring is screwed up , there may be a really good (bad ) reason for it ...

 

There is more info & pics about what Jim was talking about .. here https://www.ford-trucks.com/forums/9...ch-issues.html