vibration in driveline. help please!

[Wtfan18]

hey guys i need some thoughts or advice. i took the truck to town last night and on my way home about 11pm i decided i wanted to see what the truck would do. so from about a 55 roll i stuffed it in 3rd held it. shifted 4th and when i hit 100 or so there was a really loud, strong vibration up through the shifter... the driveline on this thing has been an absolute nightmare... from blowing u joints and denting drive shafts. etc etc. etc. here's is what i have done to try to correct the issue 2 weeks ago...

i put a magnetic degree finder on the rear end while on a lift and it gave me -10 degrees... obviously off if its supposed to be -3... well i had already gotten 4 degree shims so i put them in. put the truck on the ground and with all the weight on the suspension it read a -5... still off i know... ive driven the truck 250 miles and i have put a driveshaft from a 98 c-1500 auto 4.3 in it and it FIT PERFECT there was plenty of clearance on the front yoke and i have a brand new ujoint in the rear. the drive shaft has no dents in it and i HAVE NO CLUE WTF THE PROBLEM IS. i know -5degress is not -3 but would it really cause that much vibration? could the drive shaft be unbalanced? i have no idea what the deal is and could really use some suggestions. thanks guys.

[RedHeartbeat]

Have it balanced just to get that question out of your mind. Also, double check that the rear pinion yoke has not come loose.

[Wtfan18]

alright. thanks greg. ill probably have to find a drive shaft shop to have the balancing done? i hope the rear pinion yoke isnt loose. we did just change the rear end out 2 weekends ago though...

[RedHeartbeat]

I take mine to a big truck driveline company, they do small stuff too.

[tanz45]

I doubt a couple of degrees would do that, but shouldn't you measure it on the ground? idk just askin. Bad axle bearings or a tooth off the ring gear can give you some really bad vibes. Is that 4 wheel drive? My front shaft spins all the time, just front diff disconnect. Check front shaft u-jouints as well.

[Wtfan18]

I doubt a couple of degrees would do that, but shouldn't you measure it on the ground? idk just askin. Bad axle bearings or a tooth off the ring gear can give you some really bad vibes. Is that 4 wheel drive? My front shaft spins all the time, just front diff disconnect. Check front shaft u-jouints as well.

yeah it was hard to get under it the first time it was the end result i was really worried about which was measured on the ground with all the trucks weight on the suspension and ended up with a -5 degrees. all the stuff in my rear end isnt even 2 weeks old. i jsut installed a auburn LSD and 4:56's with all brand new seals,bearings,races... you name it i got a master install kit. its a 2wd truck.

the front u joint is the original in the shaft so i guess i can check that. i just am a bit perplexed at the moment... the truck feels great the driveline is the only thing that worries me... i know the tranny is built to handle a lot but the shaft it self is the 1 piece that really just bothers me and eats at me. even though it looks fine and has no issues im just waiting to hear a loud bang from something and hear grinding and dragging lol... after blowing those 2 u joints it really leaves that sound in your head....

[tanz45]

Yeah, nothing beats a driveshaft flying up through the bed or under the centerconsole like in my buddy's CJ. I think i saw someone say check the pinion/yoke. Pretty sure there should be 12 inch pounds of rotational drag.

[Wtfan18]

yeah well it already messed up my corsa pretty damn good! i think i might end up building a housing for it... so it cant destroy everything should it ever happen again... how would you measure the 12 inch pounds of rotational friction?

[tanz45]

There are torque wrenches that are in inch pounds rather than foot pounds. Jack up truck, take off tires and drums/calipers(they create more drag) Take off drive shaft and use the wrench with the proper socket to rotate the pinion. You have to use the torque wrench that has the needle style indicator, not the click style. As you rotate the pinion, the needle will stay at 12 inch pounds. I am almost positive that GM is 12 inch pounds. But don't quote me. I am sure the other members here would know, or GM.

[tanz45]

outlaw king confirmed 12 inch pounds.