Originally Posted by boatpuller (Post 7223110)

Well I finally got around to getting my vacuum boost system swap install yesterday. I paid a shop to do the most of the project as I'm unable to bend over the fenders anymore after 3 back surgeries and fused spine complete with rods and bolts.

Anyway, the interesting thing after this thread and talking to a few chevy truck guys. It was evident that I needed a vacuum pedal from an automatic 1/2 ton from a donor truck.
I find one for 25 bucks at a local junkyard. I go to pick the truck up and the guy that works on it tells me he spent several minutes getting the old pedal out in 90 degree heat only to find it was exactly the same as the one from the 77 c10 auto donor truck.

I thought this may be interesting to you guys that posted on this thread. My conclusion is there is no rhyme or reason to the how the factory installed pedals. Kinda what Scoti went thru in his swap.
Oh. by the way the truck now stop awesome with Cpp 11 inch booster and mc. If anyone cares I will post a pic of the final swap.

Originally Posted by boatpuller (Post 7223110)

I thought this may be interesting to you guys that posted on this thread. My conclusion is there is no rhyme or reason to the how the factory installed pedals. Kinda what Scoti went thru in his swap.

Originally Posted by Keith Seymore (Post 7224018)

I guarantee there IS a rhyme or reason for the way the factory did it.

It just may not be obvious to us, 35 years after the fact, as there may have been other constraints we cannot see now (build location, part proliferation, option constraints, interaction with other components, etc).

My friend says "Engineers do stuff for reasons". What he means is that we do not expend time or energy just to make things more difficult for themselves or others.

K

Originally Posted by boatpuller (Post 7224029)

Mine was built in California. As a diesel. I have run into a few baffling things with that truck that don't follow the book of gas engine trucks.
The short bed two piece vs one piece drive line is another example of having a hard putting a pattern together like the pedals.
Iv'e seen big block 1/2 tons with 1 and 2 piece and small block trucks with 1 or 2 piece in both long and short bed configs.....that one has always intrigued me .

Originally Posted by boatpuller (Post 7224029)

Mine was built in California. As a diesel. I have run into a few baffling things with that truck that don't follow the book of gas engine trucks.
The short bed two piece vs one piece drive line is another example of having a hard putting a pattern together like the pedals.
Iv'e seen big block 1/2 tons with 1 and 2 piece and small block trucks with 1 or 2 piece in both long and short bed configs.....that one has always intrigued me .

Originally Posted by Titomars (Post 7224612)

1 or 2 piece drive lines were always determined by total length, trans yoke to diff yoke.
if you get a drive shaft too long it has a nasty tendency to flex in the middle at high speeds.

Originally Posted by Keith Seymore (Post 5198257)

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

What you guys might be missing is that 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).

So - 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.

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 or "metal matrix" (an aluminum/carbon wrap).

K