Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
My '70 Fury has u-joints at both ends of thed driveshaft. AFAIK any driveshaft with one or more u-joints with anything other than zero offset between input and output shafts will tend to vibrate. When a u-joint rotates with zero offset, the joint rotates at a constant speed, however as an angular offset is introduced, the average speed remains, but the actual speed varies with the outside of the angle moving faster than the inside. Sorry, I'm not doing a very good job with my description, use Google to search "u-joint phasing" for many much better descriptions. Below is a graph showing the speed fluctuation as a function of angular offset. This graph is for a single u-joint. Phasing means you make the peaks 180 deg different on the second joint and the peaks will cancel out. The solution in some applicaions is a special "constant velocity u-joint". Some driveshafts require 3 u-joints with the end joints phased and the center one a constant velocity type.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Hmm. There is a sliding yoke on the end of the transmission output shaft, at least there is on my 727 trany. Without a sliding joint somewhere in the system, vertical rear axle movement would put a variable tension/compression load on the u-joint, which it's not designed for.
Joined: Sat Mar 29 2008, 03:36PM
Location: North eastern Wis.
Posts: 1638
Yes there is a slip joint in the trans but it has no effect on the relationship of the two u-joints on a C body car... Although the slip joint might be the culprit if the bushing is worn out. You can test it by simply trying to move it up and down. There should be no movement just like in the pinion bearing.
I have to admit, I almost ran out to check my van,
as it has a similar problem. Upon reading the statement of the solid single shaft, I realized that can not happen. I am going to have my drive shaft balanced and if that isn't it, the only other thing I haven't checked would be the front pump in the transmission. Here's hoping we get this settled so we can enjoy our rides this summer.
Joined: Thu May 01 2008, 11:15AM
Location: Chicago,IL
Posts: 2868
bboogieart wrote ...
Yes there is a slip joint in the trans but it has no effect on the relationship of the two u-joints on a C body car... Although the slip joint might be the culprit if the bushing is worn out. You can test it by simply trying to move it up and down. There should be no movement just like in the pinion bearing.
I have to admit, I almost ran out to check my van,
as it has a similar problem. Upon reading the statement of the solid single shaft, I realized that can not happen. I am going to have my drive shaft balanced and if that isn't it, the only other thing I haven't checked would be the front pump in the transmission. Here's hoping we get this settled so we can enjoy our rides this summer.
Good, I'm not crazy I had my shaft balanced over the winter but I haven't driven it yet. I have a cyclical vibration that doesn't feel like wheels/tires or a wheel bearing and everything below is tight
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Sorry for my misguided advice!
Where I went wrong was to note that phasing is only important on drive shafts that have one u-joint mounted on a sliding pinon that slides on the end of the drive shaft. A pinon that slides within the transmission can't alter phasing because the yokes are welded and fixed to the drive shaft ends.
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Small world, many torn u-joints and/or bent, twisted drive shafts on my '78 IHC Scout taught me all about phasing. I just never looked at my Fury close enough to realize it was a different animal altogether. Lived and learn.
Joined: Sat Mar 29 2008, 03:36PM
Location: North eastern Wis.
Posts: 1638
furious70 wrote ... Good, I'm not crazy I had my shaft balanced over the winter but I haven't driven it yet. I have a cyclical vibration that doesn't feel like wheels/tires or a wheel bearing and everything below is tight
I get what your saying. Not a balance issue with the wheels and I've checked the wheel bearings in front and back. Rear axle bearings too. All good there. Mine is a rotational growl that is rpm related. Rrrrrm, Rrrrrm, Rrrrrm, type thing. It seems to be right under foot, but a van is just a big empty box. Also doesn't start up until things get warmed up a tad. Then if I keep it under 40 mph nothing, but the faster I go the more it growls. Let off the gas and no noise while coasting. I am really leaning toward the front pump in the trans.
I had my shaft balanced over the winter but I haven't driven it yet. I have a cyclical vibration that doesn't feel like wheels/tires or a wheel bearing and everything below is tight
