66 driveshafts

[lswonmatt]

So I thought for sure my 66 gmc long bed would habe a 2 piece drive shaft but today i was going to unbolt the bed to remove it to start the bodywork on cab corners and got to looking and it is a 1 piece drive shaft .... did long beds come with one piece drive shafts or has mine been swapped out sometime in its life i just thought it was odd I always hear about 2 piece shafts on long beds and find out mine has a 1 piece

[Cooper197]

I have a 66 Chev C20 long bed and it's a 2 pc driveshaft.

[DPowers]

My 66 LWB is a two piece as well. Is there a place where a carrier bearing was at some point?

[Captainfab]

I have seen 2 longbeds with a 1pc driveshaft from the factory. I really don't know what the deciding factor was.

[lswonmatt]

No places to bolt or mount a carrier bearing just a drive shaft straight from the trans to the rear end is all I got

[61K10]

what transmission do you have?

[lswonmatt]

Originally Posted by 61K10

what transmission do you have?

3 speed , stamped ( GM 11 ) ( 3830210 ) looks like ( H4 5) stamped below can't tell if there's an x or something stamped after the 5 or the casting is worn down but that's all the numbers i see

[65chevysub]

Can you post a picture of the one piece shaft? I had one made several years ago, but it caused more vibration than it was worth, so I went back to my 2 piece.

[lswonmatt]

Originally Posted by 65chevysub

Can you post a picture of the one piece shaft? I had one made several years ago, but it caused more vibration than it was worth, so I went back to my 2 piece.

I don't have one on my phone at the moment but I will get one and post it but now that you say that I do have alot of vibration when taking off in first or reverse or under a load going up a hill from a dead stop but goes away after taking off or picking up speed I figured it was the clutch going bad and not enough power from the engine dying down

[65chevysub]

Originally Posted by lswonmatt

I don't have one on my phone at the moment but I will get one and post it but now that you say that I do have alot of vibration when taking off in first or reverse or under a load going up a hill from a dead stop but goes away after taking off or picking up speed I figured it was the clutch going bad and not enough power from the engine dying down

I think my vibration was from a bad balance job on the shaft.
Thanks for getting a picture.

[lswonmatt]

it looks like the cross member is set up for trailing arms even though i have leaf springs but here are the photos as promised



(Photos below in another post photobucket pics wouldn't show up )

[The Rocknrod]

Your posts pics have been photo-bucketed.

[lswonmatt]

put them in attachments maybe that will work and someone will be able to at least see something

[Keith Seymore]

Originally Posted by Captainfab

I have seen 2 longbeds with a 1pc driveshaft from the factory. I really don't know what the deciding factor was.

It has to do with propshaft (aka "driveshaft") critical speed.

Propshaft critical speed not just based on wheelbase but is also based on trans type (length), rear axle ratio, tire size, and engine type (larger engines allowing a higher top speed) AND/OR any strange resonances in that particular combination (camping out on that resonance will break the trans/transfer case tailshaft housing).

One other comment - critical speed is not directly related to balance, but rigidity. When the shaft exceeds it's critical speed it begins to bow in the middle and swing like a jump rope. Hence the disturbance and durability concerns.

You can get around it by going to a larger diameter steel tube - or more expensive alternative materials like aluminum, carbon fiber, an aluminum/carbon wrap, or exotic materials like "metal matrix" (aluminum impregnated with other metals) - or - the cheap way out is to limit the vehicle top speed via ignition or fuel cut off above a certain engine rpm.

So - given two otherwise identical appearing trucks - there could be a tire difference that put it over the edge, or perhaps a different horsepower rating which would allow for a higher top speed, or some unseen bending resonance that shows itself during testing which would drive the truck to get a one piece shaft vs a two piece. A long wheelbase truck with a low (numerical) rear axle ratio spins the shaft slower and might get a one piece, but an otherwise comparable truck with a high rear axle ratio might get a two piece.

K

[lswonmatt]

So with the holes in this cross member could it be used for trailing arms if I had the arms the mounting brackets and a pan hard bar?

[Captainfab]

Yes.......

Originally Posted by lswonmatt

So with the holes in this cross member could it be used for trailing arms if I had the arms the mounting brackets and a pan hard bar?

[rideblue00]

1 pc a GMC thing?

[Captainfab]

Not exclusively.

Originally Posted by rideblue00

1 pc a GMC thing?