MoparFins

Techical Discussions => Tech- - DRIVE TRAIN => Topic started by: John B. on September 27, 2008, 05:48:49 PM

Title: driveshaft balancing
Post by: John B. on September 27, 2008, 05:48:49 PM
Hi fellas; I'm about to do the U-joints on my 69,300. the question is, should  the driveshaft be balanced? I seem to recall there is a certain way to install it to avoid vibration and such! am I on the right track here? thanks, John (http://moparfins.com/forum/smileys/smiley2.gif)
Title: driveshaft balancing
Post by: Stan Paralikis on September 27, 2008, 06:02:16 PM
Never heard of that one.
The driveshaft itself is balanced. Replacing U-joints doesn't affect anything.
 
I think.
Title: driveshaft balancing
Post by: Stitcherbob on September 27, 2008, 06:45:57 PM

You are supposed to mark the driveshaft before removing it so you won't develop any vibrations that you didn't have before. Tire crayon works well, just mark a line on the shaft ends , a line on the trans extension and the yoke. That way if you accidentally spin the rear axle, you can put the front splined end into the trans right where it was, and then rotate the rear yoke back to position to hook up the u-joint the same as it was.

I think the installation trick you  were thinking of has to do with u-joints that have a grease fitting vs ones that don't. The school of thought here is that you should install the joint so that the hole drilled in it for the fitting is constantly under compression during power cycles. If it is installed under tension, it could rip the joint apart at the hole. This is a drag racing thing and might never matter on a street car, but our C bodies do have big blocks with lot's o torque!
The other thing about grease fitting vs none is the theory that  non-greaseable joints are made of better materials because they won't ever get a drink of grease.

stitcherbob2008-09-27 23:52:51
Title: driveshaft balancing
Post by: chuck lowe on September 28, 2008, 04:11:37 AM
if a driveshaft is REinstalled and tested with a vibration , remove and reinstall turned 180* ----------------------later60 dart2008-09-28 09:12:26
Title: driveshaft balancing
Post by: Guests on September 28, 2008, 07:27:36 AM
As long as you press them out and press them in you should be fine (HO HAMMERS) make sure if you use grease able ones that the fitting is in the proper direction so that it can be greased after installed unless it's on an end cap
Title: driveshaft balancing
Post by: Mike on September 28, 2008, 12:17:14 PM
My experience is the same as Stan's, the drive shaft itself is balanced
and you should not experiece any vibration after you reinstall it with
new U-Joints.

Title: driveshaft balancing
Post by: Bill Mounteer on September 28, 2008, 06:27:06 PM
Usually there is in index mark on the slip yoke and the drive shaft.  If you can't find one, make one using a small chisel. This index is important so that the axis of the front and rear u-joints are lined up and balance each other.

Title: driveshaft balancing
Post by: John B. on September 28, 2008, 07:23:38 PM
hey guy's; thanks for all the help!! Bill, are the index marks there from the factory? I'm asking cause the trans. was rebuilt a while back , and I suspect they may have not looked for those when putting things together! John
Title: driveshaft balancing
Post by: Bill Mounteer on September 28, 2008, 11:39:39 PM
Drive shafts were "phased" in the factory, some have punched index marks but many just got a yellow or other coloured paint dab to designate the phasing.  So if yours was marked with paint, the marks may not have survived.

You can tell if you get it wrong, you'll feel a slight vibraton almost like you get from a bad U-joint.




Title: driveshaft balancing
Post by: John B. on September 29, 2008, 09:45:37 AM
Hi Bill; So the comment on turning the shaft 180 degrees may be necessary? John
Title: driveshaft balancing
Post by: Bill Mounteer on September 29, 2008, 10:39:25 AM
Yes.  Here is a link (http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml#Phasing) that talks about 4x4's but the basic info applies to our cars.

Title: driveshaft balancing
Post by: John B. on September 29, 2008, 03:47:50 PM
Hi Bill; Thanks for the "driveshaft school". That explains a lot, and I can see why the "Phasing" is so important! John (http://moparfins.com/forum/smileys/smiley2.gif)
Title: driveshaft balancing
Post by: Bill Mounteer on September 29, 2008, 04:19:10 PM
 I ran into this on a 4x4 that had a persistent drive shaft vibration, I replace a bunch of U-joints but the problem didn't go away. As luck would have it I managed to bend the drive shaft and when I took it in to get a new tube welded in the shop asked me to also bring in the sliding yoke.  When I asked why, he explained about phasing and the need to restamp the index marks. As they say "the light went on" ! (http://www.moparfins.com/forum/smileys/smiley4.gif)

Title: driveshaft balancing
Post by: Rich on September 30, 2008, 08:22:29 PM
Has anybody here ever bent a drive shaft?  I learned my mechanical skills on my father's 57' Chrysler 300 (had that huge 392 Hemi).  That car loved to twist the driveshafts into pretzels, then it would then vibrate and shake like crazy. We ended up putting on a great big pinion snubber and had a huge 4" diameter driveshaft made. Stopped all the problems.
Title: driveshaft balancing
Post by: Snotty on October 01, 2008, 12:18:00 PM
Have not done so, but did have a ball-n-trunion U-Joint freeze up onve.  Car shook like crazy under power but smooth as silk on idle or coasting.
Sheesh!
Title: driveshaft balancing
Post by: Bill Mounteer on October 01, 2008, 01:39:09 PM
Never managed to bend one on a car, but bent quite a few on my 4x4's.  Usually going over the crest of a hill or on a river crossing and managed to hit a big rock! (http://www.moparfins.com/forum/smileys/smiley17.gif)

I once had to drive nearly 50 miles home at about 10 mph with a bent drive shaft, they really do vibrate when bent like a bannana! (http://www.moparfins.com/forum/smileys/smiley18.gif)