Used all the search features on this site, gotta love that option. Just want to confirm what I think it is.

got a 93 F350 Dually w/460 fi. Just this past weekend the speedo started bouncing and the ABS light lit up along with tranny rough shifting. Whenever the speedo started acting goofy, the truck shifted crappy and ABS light came on. was intermitted on the trip. Now when you take off speedo doesn;t respond till maybe 40 mph or faster, ABS light stays lit, and shifts crappy.

My guess is the speed sensor which using this site I come to find out why I couldn;t find the darn thing on the tranny. I am correct in thinking the speed sensor/ABS sensor in the top of the differential is the problem.

Thanks.

 

The speedo, computer(which controls the tranny and engine), and ABS system all use the same sensor in the rear axle, this would be the first thing I'd look at.

 

I just went through that with my 94. Tranny just started slamming gears. Hard slam from 1st to 2nd then 2nd to 3rd then no "drive", was like "neutral" Only way to get drive was to keep my foot in it and make it find it. Another thing I noticed was the TC locked up going slow, 25mph rolling through my local little town, like driving 25mph in 5th gear with a manual trans! lol

Got it home and checked, had code 452 (VSS) signal fault, swapped the RABS sensor on the axle with the one on my 95 as a test. Cleared codes and took it for a ride. No change and got code 452 again. (The check engine light didn't come on at any point)

Picked up a speedo unit from the bone yard and put it in, problem solved.

I've read a lot of the threads where the posters stated the speedo needle jumped around or didn't work at all for them. Odd, mine never had that problem, speedo read right and the needle was rock steady at all speeds.

Anyway yes I agree, the differential speed sensor is suspect and is the cheapest, easiest part to try but may not be the problem.

Your truck may also have a separate speed sensor on the tranny tail shaft, if you have a speedo cable, thats where you will find it. The cable runs the speedo and the PSOM and the differential speed sensor is for the RABS unit.
Also depends on if it has factory cruise control or not according to the auto parts.

 

Worded that tad wrong, didn't mean to say the cable runs the PSOM, the sensor has a cable and two wire connector for the VSS to PSOM connection.

Book says "93 to 97 F series trucks-All" but I've never seen one with a cable myself.
If you have a speedo cable the sensor should look like this,





Anyone ever seen one with a speedo cable?

 

not on a 92-96 f150.

 

Mine does not have a speedo cable, just the rear axle sensor. I just switch that and all seems well so far. only drove it 5 miles, but it was acting up just from driving down the driveway.

I did get the agruement from autozone bout how my truck has a speedo cable and a sensor inthe tranny. their books show a speed sensor in the tranny and a abs sensor in the dif. I told them just to give me the abs sensor for the dif, when they pulled the abs sensor, it was labeled on the box as a speed sensor, not a abs. funny there system doesn;t show that.

all seems good thou. easy fix if thats all it was. so far so good.