Bad...bad...bad....bad vibrations.

[phiebert]

I am having a rear end vibration (on my car that is). I brought it into the transmission shop that put in my new 3.55 rear end and they are having a hard time figuring out what is making it shake. They test drove it and admit it is something from the gear box back. The problem is I twisted off a half-shaft around the same time I had the new rear end put in and had the half shafts replaced so either event could have caused the problem.



It only starts to be noticeable over 100 mph (and don’t say go slower!). Gets worse the faster I go. It isn’t flat spotted or unbalance tires or wheels. Someone last weekend mentioned something about the yokes coming out of the differential that attach to the u-joints needing to be lined up with each other and someone else mentioned something about the drive line having to be in a certain position when the gear is put on. If any of this rings a bell or if you have any other ideas please let me know because I really don’t want to replace half the car trying to figure out what is causing it.

Series of events.

1. Put on new rear tires, had balanced.
2. Twisted driver's side half shaft. (After market ones)
3. Put original shafts back in, took opportunity to have 3.55s installed too.
4. Under 100 mph, it seems fine, no shake.
5. Over 100mph it begins to vibrate (even with clutch pushed in) and as I get up to around 150 mph it is so bad I'm afraid something will shake loose.

U-joints look OK but could they have been knocked out of balance or something from the shaft breaking? Other thoughts?

 

[Jim Sullivan]

I had the same vibration problem after replacing the rear end a few years ago. After trying a million things and balancing everything that moved I solved my problem by looking in the service manual. It said that if I had a problem like you mentioned first thing to do would be to rotate the driveshaft 180 degrees. Tried it and it worked. I love happy endings.

 

[Mike Brunton]

I'm with Jim - most driveshafts have a marker on them that shows the "balance" orientation.

When you take it out, you need to make sure you put it back in the same way. Try rotating 180 deg, I bet it will work.

 

[99 R/T 10]

But with a NEW rear end, is there a balance orientation? I had a new rear end put in also, and I think I notice a shake, but not sure.

Mike

 

[Larry Macedo]

You guys may also want to try using hose clamps around the drive shaft to possibly eliminate the driveline vibration. You may want to check the differential bolts to ensure they are torqued to spec, especially the torque arm (ladder bar) that connects the differential to the cross bar. If the bolt holes are elongated, it may cause the differential to move ever so slightly, causing the vibration. I have a few more ideas if needed.

 

[Mike Brunton]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by wilddude:
But with a NEW rear end, is there a balance orientation? I had a new rear end put in also, and I think I notice a shake, but not sure.

Mike

<HR></BLOCKQUOTE>

When I got the driveshaft made up for my Vette, it originally had a "balance mark", and there was a corresponding mark on the input side on the diff. I ended up getting the driveshaft balanced because I replaced the rear end anyways - so my driveshaft was pretty much neutrally balanced.

Larry is probably someone to listen to - he knows his stuff. you could try rotating the driveshaft 180deg... it sure won't hurt anything.

 

[phiebert]

Thanks for all the advice. I'm rotating it 180 today and I'll let you know one way or another what happens.

 

[phiebert]

Jim, your my new hero! The 180 degree rotation worked! Smooth sailing again.

Note: Anyone changing the rear end in your car? Make sure they mark the way the shaft lined up before they take it out and put it back in that way. Viper drive lines are factory balanced and being out of balance really *****!