New Driveshafts to Prevent Vibration?

[TheWhiteElephant]

I lifted my 1973 K20 long bed with a 4" all spring Rough Country lift a few years ago. I have had no driveshaft work at all. Truck is street driven with street tires. There is a noticeable vibration in the higher speeds, maybe 45mph+. Didn't bother me too much at first, but now that I'm driving the truck more, I'd really like to address the issue.

I'd like to get input from those of you who have no vibration with 4"+ lifted trucks, mainly from those of you who have had driveshaft work. What exactly did you do? I'd like to possibly purchase a set of double cardan driveshafts from one of the online vendors, but I want to make sure that I will have as smooth/vibration-free ride as possible before I drop that much money.

Any of you running double cardan driveshafts and noticed a big difference from stock/OEM?

Thanks in advance.

[obijuan]

Rear ujoint angles should be equal and opposite which is doable on a long bed truck. Or point the pinion directly at the tcase with a 1-2* pitch down and use a cv. What does the truck currently show for angles at the tcase and at the rear pinion?

[TheWhiteElephant]

Originally Posted by obijuan

Rear ujoint angles should be equal and opposite which is doable on a long bed truck. Or point the pinion directly at the tcase with a 1-2* pitch down and use a cv. What does the truck currently show for angles at the tcase and at the rear pinion?

I haven't checked yet, but I was thinking the vibrations are mainly due to the increased angle of the front driveshaft, correct? Would lengthening the rear driveshaft be "necessary"?

[obijuan]

You have locking hubs so it shouldn't be spinning really in 2wd. Lengthening of the rear is really dependant on the truck and the lift. Being the year and if it is all oe it's probably ok with your rear springs. Look to see if there is a wedge on the rear springs. That may be the issue all together.

[TheWhiteElephant]

ah yes!

I did install a wedge in the rear springs, but last I checked they were both a bit off-center. Thanks for the input.

[andrewmp6]

Are the wheels balanced good and have you tried rotating the tires to rule them out?How are your ball joints or king pins whichever you got?And how are the front wheel bearings?

[special-K]

I've never done anything to driveshafts with the 4" lifts I've done and never had vibration issues. When I lifted the '85 Jimmy 4" and installed the 14-bolt SF I used a conversion u-joint temporarily till I had the Suburban (rear was from) driveshaft shortened. I never did that, just stayed with the conversion u-joint. It never vibrated at all. I have also never used wedges.
It must be in your main/rear drivetrain. How are the u-joints and or the splines on the shaft & yoke? Beyond those being worn, it could be pinion or transfer case output bearing(s). I'd think the associated seal would be leaking if it was one of those. The other big one would be if your driveshaft is not true.

[CrewCab59]

Does your shafts have any play on the slip yoke splines , the splines do wear and as they do you will have vibrations. Can you tell if any weight slugs cam off the shafts , it will be spot welded on.

[TheWhiteElephant]

Originally Posted by andrewmp6

Are the wheels balanced good and have you tried rotating the tires to rule them out?How are your ball joints or king pins whichever you got?And how are the front wheel bearings?

All bearings/ball joints were replaced, tires/wheels balanced. Thanks for the input, Andrew.

[TheWhiteElephant]

Originally Posted by special-K

I've never done anything to driveshafts with the 4" lifts I've done and never had vibration issues. When I lifted the '85 Jimmy 4" and installed the 14-bolt SF I used a conversion u-joint temporarily till I had the Suburban (rear was from) driveshaft shortened. I never did that, just stayed with the conversion u-joint. It never vibrated at all. I have also never used wedges.
It must be in your main/rear drivetrain. How are the u-joints and or the splines on the shaft & yoke? Beyond those being worn, it could be pinion or transfer case output bearing(s). I'd think the associated seal would be leaking if it was one of those. The other big one would be if your driveshaft is not true.

The ONLY thing I haven't done to the driveline is replace the driveshaft U-joints. I had the intention of replacing driveshafts, but I'm thinking I should go ahead and replace the u-joints because they definitely look like they need replacing. Yep, the pinion seal is leaking a little as well. I'm gonna get to work on all that, I appreciate your knowledge and input. Thanks.

[TheWhiteElephant]

Originally Posted by CrewCab59

Does your shafts have any play on the slip yoke splines , the splines do wear and as they do you will have vibrations. Can you tell if any weight slugs cam off the shafts , it will be spot welded on.

Thank you, I have to get to checking all that. There is an intermittent clunk when I let go of the gas, though.

[special-K]

Do you have a locker in the rear? If drivetrain gets loose in it's mounts you will get clunks when maneuvering, such as into a parking space in a parking lot. Has it gotten worse since you've had it?

If splines are good on the drive shaft, you can have it checked for alignment and balance by a machine shop or place that services shafts

[TheWhiteElephant]

Originally Posted by special-K

Do you have a locker in the rear? If drivetrain gets loose in it's mounts you will get clunks when maneuvering, such as into a parking space in a parking lot. Has it gotten worse since you've had it?

If splines are good on the drive shaft, you can have it checked for alignment and balance by a machine shop or place that services shafts

Tim, when I installed my 4" lift I also put in the aluminum pinion angle shims in the rear. I've noticed one has shifted. I'm thinking these shims are unnecessary/not really helpful on a long bed. What do you think?

[special-K]

I have never used any shims on a 4" or 6" lift. Never had issues from that.

[1redbowtie3]

I have an '86 3/4 with a 6" lift with shims, stock length rear driveshaft, no vibrations at all. If it's making sounds off the gas you have slop somewhere, bad u-joint maybe? ...

[brad_man_72]

If the shafts need ujoints.... Take them to a driveshaft shop to check the condition of the rest of the shaft. The driveshafts SHOULD be balanced after new ujoints anyways.
You can have other issues for sure but it sounds like the driveshafts need attention. A little piece of mind...