Correct Drive Shaft for a COPO

[jg4now]

Which drive shaft is correct for a 1969 - 9561 COPO?  M22 - 4.10 gear ratio.  I've read about the 20 deg offset and the in-line shafts only to be confused about which is correct for my car.  The car was in pieces when I bought it and the drive shaft was missing.  So far, I've managed to find the other missing pieces with the correct p/n's and date codes.  I'm confused about the drive shaft.  The GM Parts Manual list two possibilities.  It refers to the part numbers as before and after.  I hope someone can help. 

The car was assembled in May 1969.  Can anyone tell me what the term before and after mean?   

[william]

All 1969 Camaros built with a Muncie 4-speed used the same driveshaft: 3970521 according to a '70s P & A manual-the AIM does not list drivshaft p/ns. Automatic BBs used 3950196. 67-68 driveshafts do not interchange and are slightly longer.

Z/28s often had driveshafts with offset trunions. Non-Z/28 Muncie cars never seem to have this odd feature. In production driveshfts had painted ID stripes a foot or so back of the trans. By now they are mostly gone and no one knows their meaning anyway.

[jg4now]

Thanks William.   I do have a driveshaft that has the off-set yoke.  I just want to make sure that after the car is complete, I can say that the car is correct in every way and be truthful. 

Do you have any idea what the "Before Job & After Job" statement in the parts manual mean?  I presume it means that before a particular date the part number was 12345 and after this date, GM used a different part and that number is 678910.  So my question is; If I am correct in my presumption, how can I find the date they refer to?

Thanks again for your help.

[william]

I have worked in maunfacturing my entire career; still there. Changing a part number can indicate almost anything. The welding process may have changed, the type and gauge of the steel tubing used may have changed. They may have changed suppliers without changing the part. The new part number may look identical to the previous.

What are the job numbers?

[L78 steve]

Please explain offset trunions .

[william]

Trunions are the pieces welded to the ends of a driveshaft to locate the U-joints.

I actually stated it backwards. On an average car they are positioned randomly relative to each other. For some reason Z/28s often have them positioned identically. Since Z/28s would experience higher driveshaft speeds it may have made for easier balancing.

[L78 steve]

I have never seen shafts that were not phased .If they are out of phase they would vibrate like hell .Is it possible the shaft you looked at was twisted ?

[william]

Nope. Seen many like it over the years so it is not a fluke.

[Steve Shauger]

I have never seen shafts that were not phased .If they are out of phase they would vibrate like hell .Is it possible the shaft you looked at was twisted ?

Virtually all the hipo cars copo, ss and z28 driveshafts I have inspected are offset, as William stated, with no vibration detected. It was thought it may have been to prevent vibration harmonic, but no difinitive answer as to why. No the shafts are not twisted due to torque....

[rich69rs]

I have never seen shafts that were not phased .If they are out of phase they would vibrate like hell .Is it possible the shaft you looked at was twisted ?

Steve,

I agree - with the exception of the "69 Camaro.  Of all the research topics that CRG could pursue, understanding why Chevy did this would be top of my list.  I'm sure they had a reason.  I am also sure it was not to ensure proper driveline dynamics.  I realize that there are those that probably do not share my view, however, as a registered professional mechanical engineer for almost 30 years, I do have some understanding from whence I speak.  Chevy compromised optimizing driveline dynamics in order to accomplish something else - perhapst an attempt to affect rear end "stiffnesss" for Trans Am racing? 

Been previously discussed at the following links:

http://www.camaros.org/forum/index.php?topic=4425.0
http://www.camaros.org/forum/index.php?topic=980.0
http://www.camaros.org/forum/index.php?topic=914.0

So....from a purely engineering / driveline dynamics point of view, offset yokes are not correct.  For the dirveshaft to compensate for the differrent instantaneous angular velocities at each end, one of the three major criteria is that the yokes have to be "in phase". 

Previous discussion indicates that all '69 Camaros, with the exception of BB, TH400 cars, had yokes offset relative to one another by approximately 20 degrees.  As William previously indicated, BB, TH400 cars used driveshaft p/n 3950196, with in phase yokes - just like every other Hotchkiss suspension, rear wheel drive car I've ever seen.

My '69 RS (327 base / Powerglide) had offset yokes.  I had the driveshaft modified to in phase yokes about 15 yrs ago.  I have a dirveshaft in the garage which came out of a '69 Camaro that had a 3 speed manual.  It too has offset yokes.  As far as I know, only the BB, TH400 cars had the yokes in phase.

Seems to me we would all benefit by getting to the bottom of this.

[JohnZ]

My '69 RS (327 base / Powerglide) had offset yokes.  I had the driveshaft modified to in phase yokes about 15 yrs ago. 

Did you have that done in order to address a vibration issue? Did it make any difference?

[Jerry@CHP]

I have seen the trunions both ways too.  We did an inspection at the Camaro Nats a couple of years ago.  Most of the BB cars had them in liine and the Z28s were out of phase 90 degrees.  Larry Christensen has said for many years that he beilves that they were assembled differntly for Z28 ad BBs, but this was not proven with our research at the Camaro Nats.

Jerry 

[rich69rs]

My '69 RS (327 base / Powerglide) had offset yokes.  I had the driveshaft modified to in phase yokes about 15 yrs ago. 

Did you have that done in order to address a vibration issue? Did it make any difference?

John,

At the time, I had removed the driveshaft to install new u-joints and noticed the offset yokes.  Had the shop change the phasing simply because IMO it is the way it should be.    

The way that I drive and have driven my car since Nov 1991 when I bought it would not readily reveal a vibration issue unless something was terribly wrong - which isn't the case.  I have never had a driveline vibration issue either previous to or after modifying the yoke phasing.  My car is striclty for cruising and enjoying the view - it is never pushed very hard.  If there is a "vibration" that GM was trying to correct for by offsetting the yokes, it was at much higher rpm's than my 327/210 base engine; 2 Bbl ride will ever see.

Richard