I heard a rumor

[SCOTI]

New modified pedal installed this weekend. I sure hope this combination works....

[chevak20]

I got concerned with the difference in pedals when considering a future brake vacuum to hydraulic booster swap. So I got myself a pedal from a Suburban K20 Diesel -89 with th 400. This truck had the booster rod code 71217 and the stud measured 14.1mm or a hair from 9/16 (14.4mm).
Underneath the green plastic bushing there is a steel bushing also.
I got the spring also that pulls the pedal back in position.
The pedal has number 355561 stamp in it.

[SCOTI]

This truck had the booster rod code 71217 and the stud measured 14.1mm or a hair from 9/16 (14.4mm).

What is the "booster rod code"? What or where did you learn this info?
355561 is the pedal # from my Hydraboost/7.4l/auto trans equipped cc dually as well.

[chevak20]

On Autozone homepage here is a link to hydroboost #71117
http://bit.ly/1vMQE8o
The code is stamped in on the rod at the flat part just before the "ring" on a oem rod.
You can put in any car or truck model on Autozone webpage along with a valid zip code and search parts that will fit or even compare between different years by adding a new vehicle search.

I have bought for my own 1982 K20 Suburban diesel with JD7 brakes, a replacement hydroboost with # 52-7248, and that rod that comes with it is 14.2mm big in the "ring", so it should fit over the pin/stud just about perfect. So the difference between #52-7248 for an -82 or newer and the #71117, I don't know. The #71117 is not supposed to fit my -82 with JD7 brakes according to Autozone webpages. Maybe a Difference between attachment points at the firewall maybe?

[chevak20]

Correcting here, sorry too many tabs open at once and to little sleep.
For my -82 with JD7 brakes the hydroboost # 52-7307 is what I have bought, And I was wrong the #71117 do fit my -82 also.

[boatpuller]

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.

[SCOTI]

Originally Posted by boatpuller

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.

I would venture to guess yours having the same pedal had something to do w/it being 1/2 ton.

I drove mine over to work last week a couple of times to free up shop space for another project & it seems to stop fine. But, I was basically just idling along (I can walk from my shop to my work in under 2mins so it's not a long drive). I still need to replace the master cylinder & then will see if my combo of parts now will work w/o damaging the master cylinder.

[Keith Seymore]

Originally Posted by boatpuller

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.

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

[boatpuller]

Originally Posted by Keith Seymore

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

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 .

[jsavage977]

for what its worth I swapped in a pedal ass. from a 82 2wd single cab shortbed manual with vacume into my 88 gmc auto 4x4 crew with hydo and they where the exact same besides one being the wide foot rest and the new one the skinny foot rest.

[jsavage977]

^^^^ ha ha oops, my post probably didnt help too much, i didnt realize this post was 3 pages long! sorry still new to online forums

[Titomars]

Originally Posted by boatpuller

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 .

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.

[Keith Seymore]

Originally Posted by boatpuller

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

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.

Almost -

there's a little more to it than that.

K

Originally Posted by Keith Seymore

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