bumping under floorboard

If you can move the yoke in and out of the tranny, but not the rear, where's the slop coming from? U-joint straps tight? Did you do the joints or did you have it done? Check the shaft yoke ears, and make sure the holes aren't elongated.. If they are, the steel is stressed and you'll have to have it rebuilt soon or you'll start to eat u joints. That movement is probably not causing the bump, but it's related to what is. Find where the slop is and let us know...

Matt {peace}

and this is why i love this place....cause i cant even think to connect the dots about play on one end and not the other.
well, i will crawl under there again but im not hopeful about seeing anything i missed the 1st time.

Have you checked for monkeys with hammers?

Brian

well, usually, I'm the monkey with the hammer!

you might want to check and see if the u joint are in line the extra slak or the yolk is probly it but they need to be in line

ok your not a monkey#1 have had a sim. prob. it was 1 st tranny mounts, 2 nd both engine mounts bad... if you havent checked them,, could be /// quinn GL

Yeah, my guess would also be the motor mounts, and/or transmission mount allowing the engine to flex to one side.

This is fairly dangerous, but you can put the nose of the truck against a very solid object (mountain side, wall backed by dirt, VERY large tree...) and in gear, with the hood open, apply some throttle and watch to see if the engne lifts or shifts... to prove a broken motor mount.

would the driveshaft need greasing? when i had an underbody clunk, it turned out to be an exhaust heat shield hitting the floor board. just a simple tac weld and the problem was fixed.

ive got a 3inch body lift on my r/c, and it does the same kind of clunk, i havent figured it out yet either

have you checked the slip joint on the driveshaft? could be worn.
also, are you sure it is the rear shaft, if this a 4wd could be a bad ujoint in the cv joint on front shaft, i had one of these go out on me at 70 mph and i thought the truck was coming apart, sounded like someone was under there with a 10 pound sledge just a whaling away

eric

Does the clunking have a pattern to it (does it vary with an engine speed) or is it irregular??

What you describe is typical of a wasted shockmount or a loose shock bolt if it is irregular.

19464

Smokey said:

Yeah, my guess would also be the motor mounts, and/or transmission mount allowing the engine to flex to one side.

This is fairly dangerous, but you can put the nose of the truck against a very solid object (mountain side, wall backed by dirt, VERY large tree...) and in gear, with the hood open, apply some throttle and watch to see if the engne lifts or shifts... to prove a broken motor mount.

Click to expand...

Why can't you just power brake it to check the motor/tranny mounts. No, I wouldn't stand in front of the truck either...

-SM

i had a bump under the truck once. turned out to be a loose exhaust pipe. usually is the simplest things

ChargingRam said:

Have you checked for monkeys with hammers?

Brian

Click to expand...

Hehe... I was going to suggest he check for dead pedestrians lodged in the drivetrain...

i heard a clunk under my truck once it turned out to be a volkswagon

Well, on mine, the trans/tcase mounting bolts had come loose and the tcase would rise about 1" if ya got on it hard. There are rubber bushings that wear out on the mounts. Check them out. There is a steel sleeve inside the mounts, so just tightening them may not be enough.

It could also be a bad motor mount. Yes, power braking will show it. Just watch the engine with the hood up. Make sure to do it in reverse too.

Also check to be sure the trans is still bolted securely to the engine.