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

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.

Re: Big Blue
 

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.

Re: Big Blue
 

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.

Re: Big Blue
 

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.

Re: Big Blue
 

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

Re: Big Blue
 

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.

Re: Big Blue
 

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.

Re: Big Blue
 

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

Re: Big Blue
 

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

Re: Big Blue
 

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

Re: Big Blue
 

Got the bed off without any issues.

Re: Big Blue
 

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

Re: Big Blue
 

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

Re: Big Blue
 

Rolling frame!!!

Re: Big Blue
 

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.

Re: Big Blue
 

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

Re: Big Blue
 

I'm watching your good work! :chevy:

Re: Big Blue
 

Thanks I cant wait to drive this truck again.

Re: Big Blue
 

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?

Re: Big Blue
 

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

Re: Big Blue
 

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

Re: Big Blue
 

Nice work! The new body looks solid.

Re: Big Blue
 

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

Re: Big Blue
 

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.

Re: Big Blue
 

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

Re: Big Blue
 

Looking great! You are doing solid work for what appears to be a fairly small shop, I know the feeling well!

Re: Big Blue
 

Thanks! Its a 20x20 this weekend I hope to get the 7' 11" truck out of the 8' garage door. I really could have used a bit more room during this project, but I cant move until the truck is back on the road.

Re: Big Blue
 

I ran into that problem before and ended up having to air down all of the tires to get it to fit! Good luck.

Re: Big Blue
 

Big progress but not alot of pictures since its been dark when I get home. Got the front end and bed on. The passenger fender to door alignment really spun me for a loop. Apparently I needed a spacer under the front passenger side of the cab mount (luckily found it laying on the old frame still!). Spent a good 12 hours on it.

Replaced the lap belts with three point belts from the other truck. Just had to drill a new hole in the floor.

Re: Big Blue
 

Rest of those pictures.

Re: Big Blue
 

I got to take the truck out for a spin but it wont shift out of first in d or manually (reverse works). I've tried just about everything. I have vacuum at the modulator, I replaced the modulator with another I had, the kickdown solenoid (that I just replaced) clicks when supplied 12v, tried running with the kickdown solenoid unplugged all with no difference.

I did install the new kickdown solenoid using the original metal gasket which I am beginning to think I should not have used and could be my problem.

https://cdn11.bigcommerce.com/s-6y2b...145009.JPG?c=2

Gotta drop the pan again. :waah:

It will give me the chance to replace the leaking trans cooling line and speedometer gear. I got a deep transmission pan with a drain plug on it in case I need to go back in again.

Otherwise the motor seems to be running great. :metal:

Re: Big Blue
 

Removing the kickdown solenoid gasket didnt solve anything. Trans fluid had a whole lot of clutch material in it for driving it around the block.

The transfer case fluid had some water in it and rust (I should have tore it apart before...), I found some ground teeth and shift rails are kinda chewed up.

What to do.. after about a month or so of going over my options I decided to go with a 4l80e and rebuilding the np205 (I have another np205 to scavenge some parts from) with a twin stick. I picked up a 4l80e from a 2003 savanna with 163k on it, hopefully its got a couple more miles left on it.

Re: Big Blue
 

I managed to come across a Dana 60 with the correct gear ratio that I couldnt pass up.

Re: Big Blue
 

More pictures of the transfer case work.

Re: Big Blue
 

Finally got the NP205 back together with new bearings shift forks and shift collars. Got the PML trans pan on the 4l80e. Just waiting on some good weather to throw this stuff in the truck. Oh yeah and I went with the JB customs twin stick for the hell of it.

Re: Big Blue
 

I had to swap out the rear backing plates to the 80's type to match the m1010 frame ebrake setup. These were a hard to find item (the 1 ton 3.5" backing plates are not being reproduced as far as I could find) but ebay to the rescue.

The transfer case has been installed removed and installed again (forgot to install the gasket between the np205 and trans the first time causing a massive leak).

I put together an exhaust system using some ebay knock off hooker ls swap manifolds, Hooker manifold to exhaust adapter 520-70701403-R, Hooker 520-16526 exhaust system with some Hooker 520-21005 mufflers and a Jegs H pipe kit. It fit suprisingly well and was even able to fit a stock sized spare tire.

Re: Big Blue
 

I had to make some more exhaust hangars to match the rest. The tailgate needed some love to get the levers on the sides to move again.

Re: Big Blue
 

I was able to drive the truck to work last week, the drive in was great but upon walking out to the truck after work I noticed a puddle of brake fluid under the proportioning valve. I was able to limp it home and order another proportioning valve. It ran great otherwise.

https://www.youtube.com/watch?v=QC_I-zdQI8k

Re: Big Blue
 

I don't mean to sound unsympathetic or over-simplify anything, but I think I have spotted the problem. If you look in the upper left hand corner, it is cleverly camouflaged, but it appears that there was a wrench in the works...

Re: Big Blue
 

On a serious note, you have done a great job of building a very capable truck. I hope you keep going with the level of detail that you have been attaining -- It's cool to watch!