CBC (Chassis Broadcast Copy) Prop. Shaft information

[bcmiller]

OK need some help here in regards to possibly refining the CRG Driveshaft Report.  As with anything, we are always looking for new data and we update reports as we get new solid confirmed information.

Some recent information has surfaced that is suggesting there is yet another driveshaft that needs to be documented for 1967 and another for 1969.

If you have a Chassis Broadcast Copy (CBC) for 67,68 or 69 Camaro we would appreciate your help. These are quite rare, but they do surface sometimes. Would be interested in a clear photo of the whole sheet, or if you want to just include the 2 letter code and the propeller shaft (driveshaft) box, that is fine too.  For 69s it is box 230. 

Thanks in advance.

You can post here or email me direct.

[bcmiller]

Any CBCs with a six cylinder engine in 67, COPO or L78 in 69 would be the most helpful but we will take any information you can provide.

[asm69]

Hi,

I have 1969 Camaro z28 October 1968 Van Nuys build. I have the Chassis Broadcast Copy sheet.
Box 230 has the letters "WN".  I have attached an image.

[bcmiller]

Got it. Thank you!

[firstgenaddict]

The first ZL1 with auto is GL - sheet is known.

[bcmiller]

Correct.  But we do not have COPO with manual transmission verified.

[bcmiller]

Was able to get a sheet recently that confirms for 1969 that an L35 with M20 does use the same driveshaft as a Z28, other small blocks and L6. 

http://www.camaros.org/driveshaft.shtml

There is some question though whether other big blocks with manual transmission received the same driveshaft. Evidence is leaning toward something different.

[KurtS]

I know of 5 BB Muncie cars that all have the same WN driveshaft (L6, SB, BB with powerglide or manual).
1 BB Muncie with a different driveshaft - why is unknown.

[bcmiller]

I have 3 examples indicating a different driveshaft was used for a 427 with a Muncie.

Thus the reason for the thread.

[rich69rs]

http://www.camaros.org/driveshaft.shtml

I would like to have a serious discussion as to why GM/Chevy offset the yokes 32 degrees on some applications and not others.  From a pure engineering perspective this makes absolutely no sense.

No engineering/technical reference will state that this is how you design a double cardan propeller/driveshaft.

For a double cardan driveshaft to function with minimal vibration, the yokes have to be in phase in order to maintain the same operating angle at both ends.  In phase yokes will also accommodate a certain degree of side to side mis-alignment.

At a minimum, offsetting the yokes will stiffen and introduce both a 2X and torsional vibration into the driveline.  Any significant side to side mis-alignment would aggravate the issue.  (Retired now, but during my 45+ years of experience as a registered professional mechanical engineer, root cause analysis of vibration in rotating machinery was an area of my expertise.)

Did the SCCA Trans-Am series have anything to do with it?

Richard

[bcmiller]

This thread is not the place for a discussion like you want. Obviously I didn't do the designs - but apparently the engineers back in the day knew what they were doing. So does it REALLY matter WHY?

Some of the big block driveshafts have inline yokes/trunnions because of how the engine is slightly offset toward the passenger side.

[rich69rs]

....... - but apparently the engineers back in the day knew what they were doing. So does it REALLY matter WHY?

I'm going to make the following comments, and then I'll move on....

Yes it matters, at least to me....from both an engineering as well as a historical perspective.  For the sake of completeness of the CRG report, I would hope that it matters as well - if nothing more than to add a footnote in the report noting that 32 deg out of phasing of the yokes is well outside of normative engineering practice and at this time the reason(s) are not known.

I have been pondering why this happened for almost 30 years; since July 1992 when I had the driveshaft in my '69RS corrected to in phase yokes.  I would simply ask that you take 2-1/2 minutes to watch the following video from Spicer:
      https://www.youtube.com/watch?app=desktop&v=Idk3BVDVHq4

The demonstrator they use in the video, both visually as well as audibly, shows the effect of:
                         1) not maintaining the same operating output angle between driveshaft ends (first two minutes) and 
                         2) what happens when you change the yokes from in phase to out of phase.

I don't doubt that the engineers knew what they were doing.......one possibility is that they had discovered a high rpm driveshaft resonance problem.  An inexpensive fix for a driveshaft resonance issue could have been to offset the yokes which would effectively stiffen the driveshaft and shift a resonance frequency(ies). 

They could have accomplished the same thing by changing the diameter/thickness of the driveshaft tube material, but that would probably be a more expensive route to take. 

Of course the downside of knowingly offsetting the yokes would be that they were fully aware that they would be introducing a 2X vibration into the driveshaft along with both inertial and torsional forces and resulting vibration(s).  One could argue that as long as the driveline lasted the length of a race or for 5 years for the general public.....   

Richard

[bcmiller]

Richard I appreciate your insight.

The only way you are going to get an answer is build a time machine, go back to the 60s and ask the design engineers. It's in the design drawings that way.

[Hans L]

CBC from my 04B VN Built '69 Camaro Z/28 - pretty deteriorated at the edge unfortunately.   Best guess - WN...

[bcmiller]

CBC from my 04B VN Built '69 Camaro Z/28 - pretty deteriorated at the edge unfortunately.   Best guess - WN...

Thank you. Yes WN seems correct.