I notice a couple times while driving today, that the Bronco makes a faint rattling sound from underneath as I'm driving very slowly or decelarating. Then, it'll make a 'clunk' before I come to a stop. It did this twice, any ideas what it could be?

I havn't had the bronco very long and havn't put it in 4wd very much, but I did put it in 4wd hi briefly today. It was back in 2wd when it made the sound. Could it be something hung up with the transfer case?

Brakes maybe?

1990 Bronco EB

 

A good place to start looking is universal joints. You said it wasnt in 4wd, but check the front joints anyway (if you have auto hubs, they might not be disengaged, therefore front axles could still be spinning) also check the joints on the drive shaft for any play.

 

I was having this problem in my Bronco too. It had me confused for a while, but made sense after I thought about it. When I had my foot on the gas, there wasn't any sound, but when I let off, that's when it would clunk and make noise. It turned out to be the driveshafts and universal joints in them. When your foot is on the gas, it puts torque and tension on them, keeping them still, but when you let off, then they're free to wobble and make noise.
I had both my front and rear drive shaft completely rebuilt in and out and the total came to around $300. Not bad considering your truck is useless without them.

 

"Then, it'll make a 'clunk' before I come to a stop."

Lube the slip joint in the middle of the rear drive shaft. Slip the boot back and lube the splines well. It is better to pull it apart by dropping the driveshaft from either end but this fixed mine. Mine made a clunk both starting and stopping.

 

Yes it will probably be in the drive line. But I have had my front wheel bearings go out and made me think the same thing, so don't exclude front bearings. It is an easy check.