Hi All, Thanks for a great resource for info on our trucks. I've read several threads on this problem, but the fixes varied. I have a '96 Bronco with 154K miles, and the speedometer has started to be intermittently "jumpy" or "twitchy", along with the ABS activating when I hit the brakes. Since it's only $20, I put in a new VSS sensor. It looked to be in good shape, with no metal fragments stuck to it. I didn't inspect the tone ring. That did not cure the problem. Most of the threads indicate it is either a damaged/misaligned tone ring in the diff, or the PSOM going bad. The "twitchyness" is rather random and intermittent, not periodic as I'd expect if there were missing teeth on the tone ring. I also get the ABS light at highway speeds. Sounds like classic symptoms.

Any suggestions on further throubleshooting or testing I can do to isolate the problem? I don't mind shotgunning a $20 sensor, but the other items become more dollar and labor intensive. Thanks for the help!

HotShoe50

 

I had the same problem, which developed over a few weeks. First the ABS light, then the speedometer started having occasional siezures. That got worse and worse, swapping VSS didn't fix it. I popped of the rear differential cover and found that one side of the carrier had nearly cracked in half, and all the spider gears were chewed up. Rebuilt rear end solved the speedometer/cruise control problem, but I still have the ABS light. I'm too lazy to get that code read when I can tell they still work.

 

Whoa...a cracked carrier! I hope hope there is nothing that bad going back there. I haven't had a look yet, but sounds like I better open it up for an inspection. I haven't heard any other noises back there, like exploded spiders being ground up into nastly little bits, so I hope that's not the case.

Anyone know what symptoms I'd see if a PSOM was going out? I'm still holding our for that to be the problem. Thanks!

 

I had changed the VSS a couple of weeks before I started having real problems. It had a couple of bits of metal on it, nothing I didn't expect. Later, I started hearing a loud bang under the truck under hard acceleration or making right turns. My suggestion is to go look under the diff cover before you get stranded. The weather is still warm, so an RTV gasket on the diff cover will set up in a few hours (vice a few days for me last winter).

 

I too had the same problem. Erratic speedometer, intermittant ABS light , hard shifting, and blinking overdrive light. Changed the VSS sensor- nothing. Finally the speedo quit so I took it to local speedometer shop. They replaced the ABS computer with a used one from a junkyard and I haven't had any of the symptoms since.

 

Thanks for the responses. Well, I'm still at the diagnosing stage. I pulled the rear cover off the diff expecting to find nothing, and I found the exciter ring to have bent and chipped teeth. Not sure when that happened because the true-trac did explode a few years ago and the shop replace it all so no problems since then. No "extra" metal products in the bottom of the diff. I made a circuit to simulate the speed sensor, so will try that this weekend. If the speedo show erratic behavior with the test circuit, it's likely the problem is the speedo. If the speedo is steady, I think I'll have the exciter ring replaced. I'll advise on the progress...

Chris

 

your tone ring is fubar. get it replaced . dont go monkey rigging stuff

 

Yeah if the tone ring looks like that, you may as well replace it. You can probably locate just a ring, the ones from the open and ls diffs are the same. I had a friend with a few carriers in a box and there was one in there. Looking at about $90 for a new one.

 

It definitely is looking like the tone ring. I tested the speedo and it's rock-steady with a signal generator. What worries me is what caused the tone ring to get munched. There really wasn't any hard metal chuncks lay around the inside (that I found) which could cause the damage. I've got a Tru-Trac in there, and it's difficult to inspect, but the operation has been smooth as if there is no problem. We'll have a closer look when I get it apart. Ouch! $90 for new ring...maybe I can find a used one....

 

I think at my local ford dealer here in so cal, they have the replacement tone ring for around $36 bucks. I had the problem way back, i still haven't fixed it yet. I trying to see if i can install the ring without taking the crown out that the tone ring is installed on. To take out the crown would mean I would have to get a shop to set the crown back in so it meshes ok. Good luck.


Gabe