Nasty Vibrations!

[fourwheelinfool]

2002 Chevy 2500HD 4X4 6.0L 4L80E 4.10 75k

 

Hope someone can help me figure out what the problem is.

 

About 8 months ago I had my u-joints replaced at the dealer. Some short time after that I noticed that when going 70-75 mph or over the truck starts to vibrate, under power or coasting. I feel it primarily in the pedal but passengers feel it in the floor. I had lived with it until now because I have had neither the time or the money to deal with it. Usually cruise along at 65 anyway.

 

Since then I've got all new tires, so I know its not a tire problem.

 

Friday everything changed. I passed someone and got the vibration... it didn't drop off like it usually did, stayed with me until vehicle speed dropped to below 55 mph. I limped home.

 

My thought has been all this time that when I had the u-joints replaced the techs didn't re-install my drive shaft correctly. So I spent all of today trying to diagnose the problem as I need the truck for work.

 

1) Jack the truck up and remove the rear wheels. I didn't think it was a rim problem but I tested anyway. Brought the speed up to 55 mph, vibration still there.

 

2) Remove the rear rotors. They are in a very needy state so maybe they are the cause. Bring the speed up to 55 mph, vibration still there.

 

3) Drop the driveshaft. Greased the u-joints and splines, re-installed 180 degrees from original. Bring the speed up to 55 mph, vibration still there! Splines looked great, bright and shiny, all there. No damage that I could see. Transfer case seal looked okay. Nothing I could see wrong with the transfer case bearing.

 

4) Re-install rotors, get the truck drivable. Take it for a cruise on the highway. Yep, you guessed it, vibration still there! Just as bad as it was on Friday.

 

Let me add that this seems to be a vehicle speed issue... engine RPM has nothing to do with it, always happens at a set road speed. This is why (up to now) I have not considered the trany or t-case. Still doesn't make sense to be the trany though... Doesn't happen when in different gears, always at a set speed. No audible evidence other than when I get the vibration. Seems like the truck is fine until I hit that certain (now 55 mph) speed.

 

When I changed ATF 15k miles ago, nothing bad lurked in the pan, just fine metal powder clinging to the magnet. I also changed t-case lube at this time as well as rear differential.

 

Any thoughts?

 

 

Thanks.

[KPSNOOKA]

2002 Chevy 2500HD 4X4 6.0L 4L80E 4.10 75k

 

Hope someone can help me figure out what the problem is.

 

About 8 months ago I had my u-joints replaced at the dealer. Some short time after that I noticed that when going 70-75 mph or over the truck starts to vibrate, under power or coasting. I feel it primarily in the pedal but passengers feel it in the floor. I had lived with it until now because I have had neither the time or the money to deal with it. Usually cruise along at 65 anyway.

 

Since then I've got all new tires, so I know its not a tire problem.

 

Friday everything changed. I passed someone and got the vibration... it didn't drop off like it usually did, stayed with me until vehicle speed dropped to below 55 mph. I limped home.

 

My thought has been all this time that when I had the u-joints replaced the techs didn't re-install my drive shaft correctly. So I spent all of today trying to diagnose the problem as I need the truck for work.

 

1) Jack the truck up and remove the rear wheels. I didn't think it was a rim problem but I tested anyway. Brought the speed up to 55 mph, vibration still there.

 

2) Remove the rear rotors. They are in a very needy state so maybe they are the cause. Bring the speed up to 55 mph, vibration still there.

 

3) Drop the driveshaft. Greased the u-joints and splines, re-installed 180 degrees from original. Bring the speed up to 55 mph, vibration still there! Splines looked great, bright and shiny, all there. No damage that I could see. Transfer case seal looked okay. Nothing I could see wrong with the transfer case bearing.

 

4) Re-install rotors, get the truck drivable. Take it for a cruise on the highway. Yep, you guessed it, vibration still there! Just as bad as it was on Friday.

 

Let me add that this seems to be a vehicle speed issue... engine RPM has nothing to do with it, always happens at a set road speed. This is why (up to now) I have not considered the trany or t-case. Still doesn't make sense to be the trany though... Doesn't happen when in different gears, always at a set speed. No audible evidence other than when I get the vibration. Seems like the truck is fine until I hit that certain (now 55 mph) speed.

 

When I changed ATF 15k miles ago, nothing bad lurked in the pan, just fine metal powder clinging to the magnet. I also changed t-case lube at this time as well as rear differential.

 

Any thoughts?

 

 

Thanks.

 

MAYBE WHEN THEY WERE WORKING ON YOUR U-JOINTS THEY MIGHT HAVE KNOCKED OFF A BALANCING WEIGHT. I WOULD GET THE DRIVE SHAFT REBALANCED AND CHECKED FOR STRAIGHTNESS. AN UNBALANCED DRIVE SHAFT WILL VIBRATE JUST LIKE AN UNBALANCED TIRE.

[fourwheelinfool]

Yes. I think you are correct.

 

Today I went out and bought new U-joints. Figured what the hell, might as well try replacing them. The old ones didn't seem bad, but I did notice the yoke to the t-case seemed to be vibrating a bit at idle.

 

So I buy new joints and drop the shaft... whops wrong size. Put the shaft back on, go back to the parts store, get the right size joints.

 

Drop the shaft again. Have a hell of a time getting the old joints out. All the bearings looked good and nothing really wrong with the old ones. HRM. At this point I dont think replacing the joints will fix my problem. Now I have to.

 

As I remove loose scale from the drive shaft I notice an odd rectangular area with a light rust rather than a more pitted rust like the rest of the shaft. HRM. Measure area. Measure one of the other wieghts... exactly the same size! Now that I think of it, I seem to remember a weight in the middle of the shaft where the bald spot is.

 

So... I made a weight out of lead (calculated to be the same weight as the one that had a matching size) and epoxied it on. It's in the process of curing now. Gonna wait until tomorrow and put the new joints on.

[fourwheelinfool]

Holy U-Joint Batman!

 

That was... fun. Lets call it fun.

 

So I learned the difficult way how to install a u-joint. The trick is to put one bearing cap in just so that its flush with the inside of the yoke. Take the joint, stick the opposite end without the bearing cap in the other side of the yoke, then push the mating side into the cap you installed. Then press the bearing cap and spider in until the opposite end is flush with the outside of the yoke. Slip the other bearing cap on and press the joint together. Keep moving it back until you have just enough space remaining to install the snap ring. Be careful and go slow! I knocked the bearings out on my first attempt and had to remove the joint with both caps installed. Not fun.

 

Here is the lead weight that I made and epoxied onto the shaft where the old one was once located. I'm also applying rust transforming primer in this pic:

 

 

I got lucky in that my 8" C-clamps were exactly the same diameter as the bearing caps. Made installation a breeze... once I learned the proper technique:

 

 

In the end, my joints ended up pretty stiff. I whacked the yoke a few times to spring the bearing caps but it didn't help that much. Before putting on each cap I made sure to grease the spider ends. After complete assembly I greased each U-joint, greased the yoke splines and installed the shaft. Looks mighty fine:

 

 

I know you're not supposed to coat the driveshaft with anything as it affects balance, but I figured I was already taking chances by figuring out a weight and putting it on with epoxy. One coat of primer and two of regal red. I'm planning to undercoat the whole chassis. Here it is installed:

 

 

Went for test drive... MUCH better! I can still notice a very slight vibration around 75 mph but really not bad and it passes quickly. All in all, I'm fairly happy.

 

After I took it for a drive, noticed the joints were squeaking a little so I sprayed them with WD-40 and greased them again. After a second drive the squeaking had stopped. The one thing I don't like is the stiffness of the joints, but they were pretty stiff to begin with from the package. Not nearly a free floating as my old ones (which were still good I believe).

 

See all the trouble a missing weight can make you go through?!

 

Just in case you don't believe it worked: