Can you help me diagnose a noise?

[boliviancruiser]

Ok,
So about 4 months ago I bought a 1997 80 with lockers. Bought in Bolivia but imported from the states. Thought I got with with 80k miles but really got of from a dishonest importer and it has almost 200k. (In Bolivia almost no one will show you the vin plate until you have bought the vehicle... not cool.) Anyways I did an oil change and lube, etc and put about 2500 miles I noticed a bit of a squeak and had the notorious drive-line thump. I checked the u-joints and one of the front ones was bad so I changed the u-joints on the front shaft. I also did the rear brakes at this time but the front ones were only about 25% worn. About 1000 miles later the sound showed up again this time it came at a low speed while driving in town and what a much lower pitch (varies with drive train speed not engine rpm). After further reading I decided it was time for a birf repack etc. In the end I changed the birfs both of them, one of the shafts, all of the bearing and seals etc. I have a good line on oem parts here and the stuff showed reasonable wear, since I do alot of remote travel seemed better safe than sorry. Unfortunatly it did not solve the problem which showed up again very shortly. I put a CDL switch in and pulled the front shaft, drove 600 miles without hearing it then it showed up once or twice and went away. I reinstalled the front shaft and have driven for a month with no sound and today it came back worse than normal. Now my wife says today she was driving and it made this grind/vibration and the abs light came on for a second. I am confused as it should be impossible for the abs to engage if the brakes are not being applied (right?). Anyways now the sound is gone but I just feel like I can't trust the vehicle and don't know what to think. One mechanic said he thought it was the front output bearing on the center diff (transfer case) another some thing else. Anyways I am at a loss and could really use your knowedge, I have read every post I can find.


Thanks alot in advance,
Warren

[Trunk Monkey]

Originally Posted by boliviancruiser

After further reading I decided it was time for a birf repack etc. In the end I changed the birfs both of them, one of the shafts, all of the bearing and seals etc. Now my wife says today she was driving and it made this grind/vibration and the abs light came on for a second. I am confused as it should be impossible for the abs to engage if the brakes are not being applied (right?).

The ABS activates if it senses a differential in the contact rings on the birfs during braking. If you've got shavings or metal bits that have collected on the magnetic sensors, then the ABS system may have an error (ABS light on, sometimes activates during normal braking). Try cleaning the sensors front and rear. Also check if any of the ABS sensor wiring has stretched or looks broken. And finally, if the light comes on and stays, you can pull a code for the ABS and see exactly what's up.

[boliviancruiser]

Thanks for the reply. Does that mean that the ABS can engage even when you are not under breaking at all? I have never heard of that happening?

[fj80toyman]

Check both of your front ABS sensors, sounds like it might have eaten one of them. It's easy to do, pull them out the top of the housing. You shouldn't see any metal/shavings on them.

ABS doesn't 'engage' per se, it 'activates' when as T/Monkey said, the speed differential between any of the wheels senses one is locked up or going slower than a threshold speed. In your case, sounds like you've got some damage that needs taking care of.

That's the best part of finding a strange sound - if you leave it alone long enough, it'll find you!

Post up what you find.

[Fly Rod]

Originally Posted by boliviancruiser

Thanks for the reply. Does that mean that the ABS can engage even when you are not under breaking at all? I have never heard of that happening?

No, what you are probably experiencing is a failure in the ABS sensors some where. Clean them all up and check all the wiring. While you are down there check everything you can see that moves for wear. If you and you wife heard grinding look for the source. Jack your truck up and check your front wheels for play. Make sure your wheel bearing adjustment didn't loosen up. Check all your exhaust hangers. They can grind and squeek at random times.

Good luck!