vibration......

[aboesec10]

hey all, I've got a quick question, I recently had my rearend rebuilt with new bearings/seals, new gears and a posi unit. Its got 4.10 gear ratio. the issue is now that its back in the truck I'm feeling a vibration that wasn't there before. It doesn't really occur until about 60-70 mph and you can only really feel it on deceleration. Should i be concerned? Im debating taking it to a different shop and having them redo it but don't know if this is a necessary thing. Any help would be great....

[cableguy0]

If nothing else but the rear was changed I would start there. Also check the driveshaft and U joints.

[storm9c1]

A quick fix might be to unhook the driveshaft from the pinion yoke, rotate it 90 degrees and bolt it back together. I usually mark the position of the driveshaft on the yoke before I pull one apart to ensure I reinstall in the same position. Maybe the shop didn't.

Keep doing this (unbolting and rotating 90 degrees and taking for test drives) until the vibe goes away or you end up back to the original position (be sure to mark the original position so you don't forget).

Might be an easy fix.

[GASoline71]

If by chance you have a 2 piece driveshaft and it was separated and then slid back together without being lined back up exactly how it came apart (on the splines), it is now out of phase and will need to be rebalanced.

Gary

[aboesec10]

thanks guys, gonna mess with it in a few minutes, ill keep you posted

[72MARIO]

What gears were in it before the rebuild ? if you had 307 the shaft speed is much higher now than before

[aboesec10]

it was 308's, u joint looked great as it should with 700 miles on it, flipped it 180 degrees and will try that

[storm9c1]

Oh yeah going from 3.08 to 4.10. That does increase driveshaft speed significantly, which turns a small imbalance into a big one. I've been through that before. I've even had it going from 3.08 to 3.42. You may need to get the thing rebalanced if re-phasing it does not make a difference. Pretty common for doing gear changes on old iron. I've had it done at least 3 times in the past several years on different vehicles. There is a truck chassis shop about 20 minutes away from me. They can rebalance a drive shaft in about an hour for under $50. They can do car and truck drive shafts. Look for one near you. Might not be as big of a deal as it sounds to get done.

[cableguy0]

Originally Posted by storm9c1

Oh yeah going from 3.08 to 4.10. That does increase driveshaft speed significantly, which turns a small imbalance into a big one. I've been through that before. I've even had it going from 3.08 to 3.42. You may need to get the thing rebalanced if re-phasing it does not make a difference. Pretty common for doing gear changes on old iron. I've had it done at least 3 times in the past several years on different vehicles. There is a truck chassis shop about 20 minutes away from me. They can rebalance a drive shaft in about an hour for under $50. They can do car and truck drive shafts. Look for one near you. Might not be as big of a deal as it sounds to get done.

Very good point. Definitely got him going in the right direction.

Find a good driveshaft shop. Having it balanced isn't a bad idea regardless if that is the cause of your problem. Its not very expensive and making sure the driveshaft is spinning true is insurance for the rest of the drivetrain.

[aboesec10]

thanks guys, ill do that. I just had the driveline built not long ago, so ill give them a call. my main concern was if the rear diff had a problem as it was the last thing to get rebuilt and thats when the vibration started.

[Ronw435]

I have the same problem, never really noticed a vibration except for a slight vibration coming and going like pulsing. Changed to 3.73 gears on the series 3 carrier with the thick gears from Richmond. I used the pro gear set. replaced the bearings set preload and backlash. preload was around 22 inch pounds on the pinion without the ring gear installed. Specs called for 25 so figured 22 would be fine. Set backlash to .008, specs called for 7-9. Ran for about 125 miles doing the break in as instructed. First 15-20 miles pinion was running around 160 degrees. Let cool down and took it for another 15-20 miles came back measure temp and it was down to around 140 with laser temp gun. Let sit over night and ran another 30 miles this time got home and temp was around 120. Problem I am having is a vibration comes in around 55 getting pregressively worse the faster you go. Had a new drive shaft put in about 1000 miles ago. Have rotated the driveshaft 180 degrees and vibration is still there. I read where someone said to rotate 90 degrees each time. Not sure you can do that with one piece ds. It does make sense that it is worse now as the shaft is turning faster. Went from 3.07 to 3.73. Gear wear pattern after 150 miles looks great. I guess maybe I should take the driveshaft out and get it "re-balanced" again? Could the spider gears cause this. When they fell out I might not have gotten them back with the same washers as it all fell out on the floor. Gears are not making any noise at all. The vibration gets worse when I push the clutch in and coast.

Any ideas?

Thanks
Ron

[aboesec10]

sounds like the same setup i used ronw435, I haven't been able to get mine up to speed and see if anything changed after the 180 swap on the ujoint but hopefully this evening. Im running a new 1 piece shaft that i had built when i did the motor swap, The vibration didn't show up until the diff was rebuilt and regeared. Also had the rear wheels rehooped to set the backspacing where i wanted it. I think if it was the wheels id feel it more often though?

[Ironangel]

Originally Posted by aboesec10

sounds like the same setup i used ronw435, I haven't been able to get mine up to speed and see if anything changed after the 180 swap on the ujoint but hopefully this evening. Im running a new 1 piece shaft that i had built when i did the motor swap, The vibration didn't show up until the diff was rebuilt and regeared. Also had the rear wheels rehooped to set the backspacing where i wanted it. I think if it was the wheels id feel it more often though?

Changing over to a one piece drive shaft opens up a whole new can of worms such as "pinion angle" and "critical speed"...Mix those two elements with gear changes, lowering or raising the suspension, properly balanced wheels and tires, can all contribute to a vibration. If your just a little bit off in one or more off the above factors, high speed vibration will result and can be very difficult to pinpoint because harmonics between components can go beyond a balanced drive shaft... Changing gears in a properly rebuilt rear end dont usually cause vibrations, but if that shaft wasn't balanced by a reputable shop, pinion angles checked and understood, then that's where I would start. A worn ball joint with an almost balanced or worn tire can have you looking out back for a vibrations. http://www.wallaceracing.com/driveshaftspeed.htm http://r.search.yahoo.com/_ylt=A0LEV...AdAswdSzmSIq8-

[crazy longhorn]

Originally Posted by Ironangel

Changing over to a one piece drive shaft opens up a whole new can of worms such as "pinion angle" and "critical speed"...Mix those two elements with gear changes, lowering or raising the suspension, properly balanced wheels and tires, can all contribute to a vibration. If your just a little bit off in one or more off the above factors, high speed vibration will result and can be very difficult to pinpoint because harmonics between components can go beyond a balanced drive shaft... Changing gears in a properly rebuilt rear end dont usually cause vibrations, but if that shaft wasn't balanced by a reputable shop, pinion angles checked and understood, then that's where I would start. A worn ball joint with an almost balanced or worn tire can have you looking out back for a vibrations. http://www.wallaceracing.com/driveshaftspeed.htm http://r.search.yahoo.com/_ylt=A0LEV...AdAswdSzmSIq8-

Totally agree , with angles & critical speed....add an OD gear to that, then the shaft spins faster than the engine (been there,did that)!
If you are off anything on the on the balance or driveline angles, you will find a vib, that you never saw ,even @ 100 mph +! longhorn

[storm9c1]

If you have any doubts about the wheels, get them balanced. It could be an issue that only shows up at higher speeds.

[aboesec10]

took the wheels down to get the balance checked. guy said they were definately off. Will drive it to work tomorrow and see if that was the culprit

[aboesec10]

wheels and tires weren't the issue, driveshaft gets rebalanced tomorrow........

[storm9c1]

Sounds like the tires needed balanced anyways. So that will at least help them (and your suspension) last longer. Keep us posted.

[GASoline71]

Getting closer.

Gary

[aboesec10]

ok! vibration is gone.... stupid simple issue. I didn't realize it but somehow the joint caps, which have a teflon washer at the end of the cap, got switched around during the reassembly. Not a big deal except somehow the teflon washers both ended up in 1 cap. Obviously that throws the joint out of center......... Ez fix though and now i can drive it again

[GASoline71]

Sweet!

Gary

[Ronw435]

Wow good for you aboesec10. Took driveshaft out again and took it to be "re-balanced". They told me I had a bad rear ujoint and re balanced the drive shaft. The ujoints were new about 5k miles ago. Put the ds back in took for a ride and it is a little better but the vibration is still there. Has anyone had any problems with wheels from LMC? I have the six hole chrome blade wheels and replaced one because it seemed to be out of round when I got the tires balanced. You could actually see the out of round on the machine. I know this could contribute to the vibration problem but was wondering if anyone has had any problems with their(LMC) wheels?

[storm9c1]

Can you try swapping a known good set of wheels and tires from another truck? Otherwise you may be chasing your tail...

[Ronw435]

Storm I really dont know anyone that has a set of 6 lug wheels near me.

[aboesec10]

I agree with storm, thats a quick way to tell if thats the culprit. Newer gm 6 lugs will fit your truck as well.