I replaced all the U joints and center support bearing today on my 58 Impala and when I noticed the U joint forks were not in phase. The rear half of the drive shaft has the forks in phase and these are welded on. The front half has the forks 90 deg out of phase. I checked the shop manual and this is correct. It seems to me that this would create drive line vibration but GM must have a reason for doing it this way. Can anyone shed some light on this? Just like to understand the reason why.
U joint phasing
- Thread starter 58impala
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Ronnie, that's pretty much what the shop manual describes and they call it "in phase". It seems to me that what you have with a two piece driveshaft is in fact two drive shafts supported in the middle with a support bearing. I've built several street rods using rack & pinion connected to the steering column with miniature U joints and most of the time using three U joints and a support bearing. It seems to me the principal of operation would be the same. Borgeson and Flaming River ( I've used them both) both state that correct phasing is when both forks on the same shaft are on the same plane. They state that out of phase joints (according to their definition) causes hard spots in the steering every time the joint turns over. Since most if not all of the 348-409 cars had the two piece driveshaft I thought someone might have the explanation. Not that I'm having a vibration problem............just curious. Here's another thought..........all one piece driveshafts have the forks on the same plane.
Jim, I don't have a technical explaination. I would guess it has something to do with the splined center section. I'm sure Aubrey could explain. I do know one thing though, it is absolutely crucial that when having the front section shortened that a referance line is painted on the shaft ( or tape ) so that the shop rewelds the shaft back exactly as it was. I made that mistake many years ago and it was vibration deluxe. Couldnt keep a carrier in that car at all. Finally figured it out after using a different driveshaft. Maybe that will help someone in the future. 
I've got a computer program that's used for setting the driveline angles of large trucks. They can get pretty complicated by the time you factor in several shafts and hanger bearings. Anyway, according to this program either phasing will work but one way works a little smoother. I can't remember which was the preferred phasing but I'm guessing it was the factory setup.
When Boise Driveline did mine the stuck the whole assembly on a balancer and spun it. It is exactly like the factory setup but has small ammount of wieght in one spot.
They where the only shop here in the valley that asked for the whole assembly so the could properly balance it. That's the only way to go in my book.
They where the only shop here in the valley that asked for the whole assembly so the could properly balance it. That's the only way to go in my book.
Update on U joint phasing
I still dont have an understanding about the phasing of the forks on the front shaft............still researching that. Here's what I wound up doing. New U joints and center support bearing, added 1/8" shim under the tranny mount and removed two shims two shims on the rear upper control arm/saddle. These adjustments were necessary to bring the angles into specs because the springs have a little sag in them so the car sits lower than original. I don't plan on replacing the springs, I kinda like the "look". The car runs smooth as silk at all speeds. I'm still curious about the fork phasing...........may be one of lifes unanswered questions.
I still dont have an understanding about the phasing of the forks on the front shaft............still researching that. Here's what I wound up doing. New U joints and center support bearing, added 1/8" shim under the tranny mount and removed two shims two shims on the rear upper control arm/saddle. These adjustments were necessary to bring the angles into specs because the springs have a little sag in them so the car sits lower than original. I don't plan on replacing the springs, I kinda like the "look". The car runs smooth as silk at all speeds. I'm still curious about the fork phasing...........may be one of lifes unanswered questions.
Models916, That's great information on the links provided and thanks for posting that , but.................that still doesn't explain why the GM shop manual states in bold type that on the front shaft (two piece driveshaft) the U joint forks must be 90 deg from each other. The info on your links, unless I missed something, states the contrary. They say the yokes must be on the same plane for each shaft. I'm still confused.
Driveshafts revisited................................................
I'm in a heated discussion about my driveshaft shortening, with the company in Denver that usually does my work. Do you have a copy of the service manual about the yokes being 90 degrees off on the front driveshaft?
Thanks, Dave
belair6162
Well Known Member
DITTO !!!!
After thinking about this post for some time,last sunday i looked under the car only to find the front shaft out of phase and the support bearing trashed.
Can't say what is correct or incorrect. The magazine article cited early in this thread is authored by Doug Marion. I accept his explaination and followed the instructions in the article ( several years ago ) and have not lost a driveshaft carrier since then.
Phasing
Guys. I just talked with a retired GM teacher from training center. The front shaft yokes needs to be 90deg of phase and the rear yokes lined up with each other. Reason is the( constant velocity ). He will try to look up tech info on this and send to me and I will post... Ok 
I know where my < Vibe >is now. Had my shaft made up and they put the yokes in line. 
After all the checking and re-do etc!!! Betcha thats where it is. On a single shaft line up the yokes. Mike
Guys. I just talked with a retired GM teacher from training center. The front shaft yokes needs to be 90deg of phase and the rear yokes lined up with each other. Reason is the( constant velocity ). He will try to look up tech info on this and send to me and I will post... Ok
I know where my < Vibe >is now. Had my shaft made up and they put the yokes in line. After all the checking and re-do etc!!! Betcha thats where it is. On a single shaft line up the yokes. Mike
belair6162
Well Known Member
HOLLY CRUD !!! $600.00
Just ordered one from CPP for $199.00, should have it Tues.
http://www.classicperform.com/Store/1960_1972_Chevy_Truck/CPSSD.htm
I dont know what your billet carrier bearing has to do with it.
going to have my front section cut,turned, and rewelded, install new carrier,spicer joints, and the whole thing balanced.
and be done with it
Just ordered one from CPP for $199.00, should have it Tues.
http://www.classicperform.com/Store/1960_1972_Chevy_Truck/CPSSD.htm
I dont know what your billet carrier bearing has to do with it.
going to have my front section cut,turned, and rewelded, install new carrier,spicer joints, and the whole thing balanced.
and be done with it
Mile hi
If you have a two piece drive shaft......the front section is 90deg from one another...the rear section is lined up. no matter what.. I amgoing to the teacher tomorrow and will try to post the tech terms hope to help all here. I know mine was wrong. Thanks to 58 for prompting this discussion
If you have a two piece drive shaft......the front section is 90deg from one another...the rear section is lined up. no matter what.. I amgoing to the teacher tomorrow and will try to post the tech terms
hope to help all here. I know mine was wrong. Thanks to 58 for prompting this discussion