GMC Seierra Drive Problems?

I have a GMC Sierra 5.3l vortec automatic 4 speed overdrive 2003 short wheelbase pickup. I put a dubble locker editon possie rear end in with 4.10 ring gear & pinion in. I had a stock rearend and 3.42 gears. Now
when I get to 110mph or a 120mph (off road) I have vibrations in the floor. I feels like it is in the drive shaft or trans. Could anyone andvise what this problem could be? Before when stock I did not have this trouble what is wrong? The gears where set up right and all new seals put back in. PLEASE ADVISE IF YOU CAN HELP ME!
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Greetings,
I'm no driveline expert, but it would seem that at the speeds you are traveling you are turning many more RPM's with the new higher ratio rear end than before so any vibration that may have been slight or unnoticeable before will be mangnified now. Of course you could also have an out-of-balance driveshaft or tailshaft or something of that order (especially if you use it off-road at such high speeds).
I'm sure someone here in the group can give you a more expert answer (also try posting at alt.autos.4x4.chevy-trucks) but it seems to me that this issue would most likely be user-induced.
Good luck - Jonathan

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Thanks, Johnathan I was told today the it might be in the dubble clutch locking system at high speeds trying to lock up the rearend and release it. If you hear any more information please advise, I'll check the other location too on my two wheel drive truck.
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DOUBLE! DOUBLE! DOUBLE! Turn that spell checkr on boy.
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Greetings,
There is a product that I believe you should look into. Their website is www.balancemasters.com and they have units for driveshafts (among other things). I know about them because I use them on my '95 Harley and love the results I've gotten. Just as a quick explanation, Balancemasters is a simple disc that has a hollow rim filled with mercury. When mounted and spinning (like on a wheel or the compensator and clutch of my Harley), the mercury acts like a fluid balancing weight and smoothes out any out-of-balance condition and vibration. Static balancing is only good up to a certain point, but after that (like at 120mph) then even a little bit out of balance can be magnified and become a problem.
Read up on their website - you just might want to give them a try.
Cheers - Jonathan

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I'll bet you lifted it too, huh?
I have a hard time believing 120mph out of a 5.31 with 4.10 gears - on or off the road, downhill with a hurricane for a tailwind.
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Mike Marlow wrote:

Have your driveshafts balanced because they are not well balance from the factory. (I do question the claimed speeds involved though because it is likely that if it does in fact record that speed on speedo, it is out of calibration))
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Mike, look I have several vehicles and this is a vehicle I just started to work on. If you knew me you would understand! This is a little project I'm working on to pick up so call "think I got a fast car person"! Just working a simple street truck for me is hard but the real horse power I can do! Just check out this site and you will see www.1320.com then if you can top this advise??? Maybe just maybe you and me can meet and play with a little pocket money! If you don't have advise please don't reply, I sometimes like to here from people who have been their and done that not just what I believe I can't do like you!
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