I own a '92 Bronco and yesterday while I was riding some back roads, I hit a bad bump, no worse than what I've hit before, but this time it made a funny noise.
Now whenever I decelerate, and only when I'm decelerating from above ~15 mph WITHOUT pressing the gas pedal, there is a grinding noise from under the truck.
I couldn't see anything loose or wrong under the truck or hood.
The strange thing is that it ONLY happens when I remove my foot completely from the gas pedal. If I give it even just a little bit of gas, even if I'm still decelerating it stops making the noise.
Putting it in neutral while decelerating doesn't fix it and neither does putting it in 4wd.
PLEASE HELP!!!!!!
I took it to the shop and had a mechanic ride with me, and he suggested the wheel bearings or front diff. as the possible problem.

 

I dont think your mechanic knows what hes talking about. How could it be the front diff if its not turning? (You have it when its unlocked and out of four wheel, correct) My guess is the rear diff or driveshaft. When you checked under the truck, did you have it in netral? And did you shake the driveshaft with your hand?

 

I thought the same thing, and he did say that it being only when I decelerate was throwing him off.
I plan on taking it tomorrow to the mechanic who has done work for me before, he wasn't there when I went last.
The sound is coming from the front, not the back

 

when i checked under the truck, it was in park.
yea the driveshaft felt solid
today i felt the driver's side hub, and it felt hot, but i have nothing to go on, so that could be its normal operating temp.

 

CV joint perhaps????????????

 

In your Bronco it is a double cardan joint and you would feel it when you tried to move your rear shaft. But with that said I would still bet on it or one of the joints on the rear shaft.

If it is in the front it is likely your auto hubs being F*ed up especially running 40s on them. 40s on the TTB is also going to cause you problems.

 

I only run the 40s in the mud
I run 33s 99% of the time

 

When you check the rear shaft, it must be in netral. Otherwise the shaft will be tight against the park key. About the front, with the transfer case in 2W, hubs free, reach under and spin the front drive shaft. It should turn and the front axles should turn. If they all do, then it not in the front. (unless its the brakes) If they dont turn, find out whats stoping. (either the transfer case or the hubs.)

 

what would it feel like if it was the double cardan joints

 

would taking out the rear driveshaft and driving it in 4wd work as a temp solution?
I can't take it to the garage until monday, and i need to drive it this weekend

 

yeah, you can run it in front wheel drive only

I once drove 3 hours with it that way after chewing up a rear ujoint. It'll handle slightly different but it's really not that noticeable a difference.

 

I had this problem and it was the driveshafts. The reason you only hear it when decelerating is because when you're pushing on the gas, the tension from the engine puts torsion on the shaft, keeping it still. But when you decelerate, the pressure is taken off the driveshaft and it's free to wobble. Took me quite a while to figure that one out. But yeah, like previously mentioned, the best way to check for sure is to jack the rear end of the truck up, put it in neutral, and then wobble the shaft. Otherwise the engine will hold it still and it will feel nice and sturdy.

As for driving it in front wheel, yeah, just take the rear driveshaft off and put it in 4 hi. I wouldn't do this for an extended amount of time but it should get you around just fine for a while. Just make sure to take it really easy on the gas. Stock Broncos have a chain driven transfer case and under normal conditions, your engine is putting power to the rear and the front tires in 4 wheel drive, however, with none of it going to the rear, ALL the power of your engine is going through that chain. Take it easy on it.

The only real reason you don't want to drive on pavement in 4-hi under normal conditions is because if there are slight variations in the size of the front and rear tires, it will cause them to turn at different speeds and therefore the internal gears at different speeds, which will put strain (if not damage) on your 4 wheel drive system. However, since your rears won't be turning, the internal gears will just be turning like normal, but just diverting power to the front.

I don't have them, but if you have front locking differentials, someone might have to give you more advise because it might be a different story.

 

You dont have to jack up the truck. Just put it in netral and shake the shaft. Turn it each way. (The gears in the diff will have some backlash.) You should be able to tell if its a bad u-joint. If that carden moves at all up and down, its shot. Its fine to drive on the front axle. Like he said, go EZ on it. I have lockers and I've done it. Same problem as open, just handles worse.

BY the way, Its not because of differnt tire sizes that causes the driveline bind. (although, I sappose its possible) Its because the front tires have a shorter path then the rear tires every time you turn. If you only go straight, its fine. LOL

 

So, so far he has mentioned it is coming from the front and in 2wd and his hub is hot and he runs 40" tires once in a while through the mud .I know from experiance that the hubs should only get warm, if you can't hold your hand on the hub for as long as you want then your wheel bearings are prolly full of water and mud.I am no expert but I wheel a bit and have changed my front wheel bearings lots.Bad wheel bearings can create lots of problems once they start to get hot, and they are an item that should be maintained after every wheeling trip.I don't maintain mine I just change them every year which is the wrong way to do it but there always seems to be something else that needs attention.
Anyway I am not saying that it is not the driveshaft or some other driveline part but don't forget about the simple little parts that keep your wheels rolling smoothly.

 

the mechanic said that the spider gear had come loose and chipped some teeth on the gears.
He said that he would have to replace the whole differential.
Instead of the posi-trak, he reccomended a heavier duty one, the name escapes me right now, but I was wondering if I should leave 4.88 gears or bump it up a notch?