to start off i have a 1973 F-100 390FE C6 2 piece driveshaft w/carrier bearing ford 9" 3.00 rear... every now and then after i get on it something goes rooomp rooomp rooomp, each rooomp noise is in about 1 second intervals usually during deceleration at about 20-30 mph, my thought on it is either a u-joint is going bad or brakes are making noise or the rear end or tranny is going out... i guess it may be nothing but i dunno

 

Agree with you on your first thought of U joints. Deceleration takes the load of the drive train and when spinning, lose U joints would be talkin' to ya. Check the pinion shaft too - don't be gentle!

Easy enough to check.

 

The driveshaft and UJoints spin at very high speeds. Even when going slow. Once a second is something else.

 

filthy beast what would you recommend to tighten/ check the pinion shaft? and my back u-joint is not serviceable so it might be going out.

 

its like roomp...rooomp...roomp but if you speed up it goes away and if you slow down ti goes away and going from 0-30 it's not there.

 

Check pinion shaft: Chock the tires....kick it into neutral and make sure there's some play in the driveshaft....grasp it (driveshaft) firmly by the pinion yoke and vigorously shake it side to side, up and down.

If you have noticeable play - as in it moves more than 0.25" in any direction - I would suspect the pinion berrin.

 

Why is your back u-joint not serviceable? I have the exact same set up and all u joints can be changed.

 

they can be changed, by not serviceable i meant that there is no grease zerk on the u-joint.

 

after just driving the truck i'd say in the brakes or trans it only seems to do it after getting after it in 3rd and when slowing down, however it did just do it with the engine off and in neutral... so i don't know

 

Have you checked all the U joints with the trans in neutral yet? You haven't said if you did.....

 

Oh, okay. That makes sense.

 

filthy beast to the best of my ability i did try what you said however i couldn't get the to move up or down or side to side. it would only spin... however after driving the truck the 3rd member was hotter than the rest of the axle but only a little.

 

I'm a bit confused here...do you mean (with the trans in neutral and both wheels on the deck) that the pinion yoke would "only spin?" Does that mean the driveshaft was turning also?

The Ford 9" is generally considered as bullet proof....getting hot - not as to burn the skin off your hand - is normal.....unless the fluid level is way down. Good idea to check it anyway.

 

not in complete circles spin untill the wheel hit the back chock and then if spun the other way it would hit the front chock, should my chocks have been tighter?
when i would shake it up and down it would start moving the truck, i'll go try again and let y'all know what happens.

 

Filthy there was not much play. crazy thought here... could my torque converter make this sound a few months ago the bolts had backed out enough that it would rattle i have since re-torqued the bolts but could it have affected something?