Big Blue 1975 C30 --> K30 Conversion and other Upgrades.

[Honest Bob]

I am starting a thread here to document the combination of two trucks into one.

Truck #1 A blue and white 1975 GMC C35 Sierra Grande 2wd/1ton, 350/TH400 86k miles. Saved from being crushed at the junk yard.

Truck # 2 The Rat a 1977 GMC K20. 4x4 3/4 ton, 4.8 LS swapped (Comp X260 cam, ls6 valve springs, headers), turbo 350.

[Honest Bob]

The body on truck #1 is really solid for a 75 where I live but its 2wd.

Truck #2 is not solid in any way the bed is barely held on, cab supports are ready to crumble, frame is really rough behind the cab, hood is rusted and cracked by the hood latch, and one fender might be ok and the turbo 350 has 4 neutrals. Despite the bad its got some good parts in it.

[Honest Bob]

The goal is to combine the best stuff from each truck onto this CUCV frame. I've never attempted any project this large before, I've done alot of research but still have alot more to go.

I'm going to start with getting the frame rolling. I'm going to make a list here to keep things organized.

1. Verify Gear ratio's on all three axles. I'm hoping I can use the rear from the 2wd so I dont have to move spring perches and I can keep the big rear brakes. Blue has 4.10's Rat has 3.21's (I guess that's why it got so much better gas mileage!)

2. See if I can use the 2wd JB8 front calipers on the 10 bolt.

3. See if I can reuse the Rat's old ubolts. Yeah right!

4. Order ORD bolt in steering brace.

[Honest Bob]

Upon disassembly I found out that the input shaft on the 205 is what broke. The gearing mixed with the larger diameter tires was most likely the culprit.

Here is a vido of the rat on the dyno making 270whp and 291wtq.
https://www.youtube.com/watch?v=UYXwG8lXc1Y

My brother in law helped me remove the trans and motor, there isnt a whole lot more I need to pull, just exhaust gas tank and other small misc items.

[Honest Bob]

Some shots of the parts truck, you can see why it was a parts truck.

[Honest Bob]

The Rat is gone!

https://www.youtube.com/watch?v=aOkxCn0BqZM


Picked up a 10 Bolt off of the classifieds and started cleaning it up.

[Honest Bob]

Had to replace the ball joints and u joints on the one side, the other side seemed to have been done already, we will see if that comes back to bite me later on.

[Honest Bob]

Covered the gas tank in por15 along with the ORD steering braces.

[Honest Bob]

Prepping the steering box. I hope to get the front axle and a temporary rear axle under the frame this weekend.

[Honest Bob]

Steering box came out good, got the front axle under the frame.

[Honest Bob]

Got the bed off without any issues.

[Honest Bob]

Front end came off and motor was sold the same day I listed it.

[Honest Bob]

Ubolts arrived from offroad design! More prep and painting of the sway bar, gas tank brackets and 14bolt.

[Honest Bob]

Rolling frame!!!

[Honest Bob]

Trans and motor are in! Frame is off the cab and I got the hole cut out for the bolt in cover I saved from the other truck.

[Honest Bob]

Cut whole in the floor with a jigsaw and a metal blade. Worked great!

[Shifty One]

I'm watching your good work!

[Honest Bob]

Originally Posted by Shifty One

I'm watching your good work!

Thanks I cant wait to drive this truck again.

[LT7A]

Ambitious project! You are making strong efforts to keep the upper hand on corrosion in the future. Good work. I have a question. You mentioned 3.21 gears. I wasn't sure which differential you are referring to. Was it a 10 12 or 14 bolt?

[Honest Bob]

Originally Posted by LT7A

Ambitious project! You are making strong efforts to keep the upper hand on corrosion in the future. Good work. I have a question. You mentioned 3.21 gears. I wasn't sure which differential you are referring to. Was it a 10 12 or 14 bolt?

Thanks! It was a matching 10 bolt and 14 bolt full floater. I sold them and went with 4:11's.

[Honest Bob]

Got the cab on and the hole cut in the cab for the removable hump I saved from the other truck.

oh yeah and it runs!

https://www.youtube.com/watch?v=Dklt1IxL1vM

[Greenlee]

Nice work! The new body looks solid.

[Honest Bob]

Originally Posted by Greenlee

Nice work! The new body looks solid.

Thanks! Yeah the body is really solid for a 75 around here.

[Honest Bob]

Finished up the brake lines, and found out I have to modify the exhaust due to the 1 ton shocks being in different locations than the 3/4 ton.

The exhaust was a little loud on the other truck so I added some glasspacks to quiet it down. Hopefully that works.

Also cut a piece out of the spare rad support to patch up the area under the battery on the "better" one. Figured it was a good area to practice welding sheet metal before I have to do the inevitable to the kicker panels/inner rockers, outer rockers, and cab corners. I really need to get an argon tank.

[Honest Bob]

I had the throttle body gasket the wrong way around causing a vacuum leak so its running a bit better now. The Fi-Tech ecu is still learning it just needs some time I think.

https://www.youtube.com/watch?v=x5Ds6xh0Jjo