My GMC, a little update

Well, I just thought I'd give everbody a little update on my GMC. The 455 Olds has been sold, it was a POS motor to begin with. There's a reason why some engines come out of a junkyard, for darn sure.

I decided to put a 6.2 Detroit in there and keep the Th400 that came with the truck. Bulletproof, cheap and easy to rebuild if it needs it. I spent countless hours reading and reading about similar swaps. The 6.2 is going to do the job just fine for my intended purpose. Based on the GMC's 6.17 gears and 40" tires the motor will turn at 2200rpm at 45mph which is the max speed my town. This is perfect, because the 6.2 hits it's powerband at 2200 or so RPM. My county roads are 55mph, but I seldom have a reason to leave town these days. It will be a real simple swap. A cheap $50 adapter will mate it to the B.O.P pattern Th400 which is already been used in the truck so it's ready to rock and roll. It should deliver right around 13mpg if I drive carefully. And I plan to run 75 WVO / 25 Diesel mix in the hot summers here. It won't be a real powerhouse, the 6.2 was not designed to be. It's a fuel pincher, which is what I was looking for in a diesel for the truck. Parts are easy to find, they are simple and there's no crummy electronics like on the 6.5's.

I'll be sure to take pics when it arrives next week. It is a HMMWV take out so it's missing the usual starter and alternator. Otherwise it's complete. Was told it does indeed run good and is NOT a corre/rebuild motor. He's including other goodies such as filters, glow plugs, injectors, stuff like that. Maybe a starter if he finds one. He actually works at the company that contracts with the Military to pull the 6.2's so the Hummers can be fitted with the newer 6.5's.

I am stoked. The GMC is also getting more olive drab, ordered another case of Aervoe for it. One case at a time, I am in no rush to paint the thing.

You knew that I would say this! Keep us posted!

Sounds like a good idea and you sound like you know what your doing

Pictures pictures pictures!

Keep us updated

Hey Brother, glad to read your making progress. I appreciate your persistence in digging up information and taking the time to share your findings. I hope to spend a solid week tearing my stuff apart for 'refurbishment' next week. And like Stan has posted..... Photos, Photos, Photos!

Thank's for the support, thought of setting fire to the whole shebang many a times. Best thing you can do when you get overwhelmed or frustrated is simply walk away. She is going to look like a brand new truck when finished.

I had a long conversation with Tom at Alfa Heaven today. Tom really knows his beans, he's done every swap imaginable in these trucks. We talked a lot about the use of the Th400, 700r4, having no low range, the benefits of low range, MPG's, expected speeds, tricky spots with the swap, braking options, you name it. Tom often feels like he is preaching to the quire when it comes to this stuff, people call him to discuss motor swaps in the GMC's and they have their own ideas on what may or may not work. When in reality Tom has pretty much done it all, and will tell you right then and there if it's a good or bad idea. People would be well advised to listen to his words very carefully in this area. He's a super busy dude, so I appreciated him taking the time to talk with me.

First things first, I have to wait for my motor to arrive...Here's some pics of my powerless GMC....

"Best thing you can do when you get overwhelmed or frustrated is simply walk away. "

I've found the best thing is to start another project.

So, if you had a 700r and a TH400 just rebuilt, what would you choose and why?

Why are you watering it in pic #1? You think it will grow into a 5ton?

While things are empty, blast some OD paint onto it! You can save yourself some time and make the finished product look awesome.

This is the schizzel! i can not wait to see the finished product!! Work faster' LOL

hendersond said:

So, if you had a 700r and a TH400 just rebuilt, what would you choose and why?

Click to expand...

TH400 for sure. Over drive is nice, but expensive to make as tough as the TH400 with military gears.

Geez, I'm working as fast as I can! If only Stan lived closer, he could bring that M135 bumper mounted KEG and we could probably finish her right quick.
I agree completely OF, I like the Th400 a lot. Tom is a good guy and I respect the work he's done to these vehicles. But he likes to drive his trucks FAST. I am not that way. The joy in owning these old ladies is to slow down enough to see things you'd otherwise miss riding in another vehicle. I've actually taken the liberty of doing a great deal of degreasing, scraping, sanding, priming and painting of the truck while it's apart. I've even taken off my air lines so I can polish the copper and wrap new canvas padding around the hold down clips. How is that for attention to detail? I also modified the dash cluster to face the driver for ease of visibility while driving. My floor is no longer dented or bashed, it looks brand new after countless hours of down right tough work. I'll be cutting up a 20mm ammo can to make my center console which will house miscellenious switches, gauges, push button starter and of course the Th400 shifter. The 6.2 exhaust will be straight piped up the right side of the cab like the original 302. Only using 4.5 pipe and my childhood dream, a rain flapper!

My 2nd case of paint should arrive any day now so I can finish painting. I'll get pics tomorrow to keep this thread alive.

Please keep in mind that the pictures will show hundreds of parts laying all around. Some parts are yet to be replaced, repainted or fixed, etc. I was born with a curse called OCD and as such I've spent over $450 in body work so far. Guess i'm kind of funny that way. Pics tomorrow, like I said.

if in the future you need low range you can swap in a ww2 t case .the 700r4 is a good tranny.the early production ones had some problems but were corrected.make sure the tv cable is hooked up right.

Hi,
Have you considered changing the transfer case to a two speed. Boyce used to have the parts for this altough I have no idea as to cost or difficulty.

I've thought about the 700, but I don't have the need to drive at highway speeds right now. The Th400's 1:1 3rd gear puts me at 2200RPM's at 45mph which is max speed for Yuma. 2200 is also where the 6.2 produces the most power while delivering the best fuel economy you'll ever get, i.e it's powerband. A WWII CCKW Tcase requires a lot of work to fit in, re-fabricating propeller shafts to make up for the length difference, and the CCKW Tcase is not near as strong as the M211 Tcase. Most of all it's more work than I wish to do in my grandparents backyard.

Truck nut, I heard it's doable? I saw it on a post here that was really old. The guy took a piece out of the M211 tcase and machined a bushing to fit in it's place. It converted the Tcase to a 2 speed. I'll call memphis, though this is something I'd be interested in doing at a later time.

I like the 700r4 because it has a lower 1st gear than the Th400 and the higher 4th gear. That would be my reason for going with the 700r4 over the Th400, but as you said you are not looking to run any faster than the truck did when it was new so that will be a good combo for you. Keep the pics comming.

It is true that the 700R4 has a wider spread of gears. And there are rebuilders who can make them almost bullet proof. But the cost of up-toughening is considerable. The basic TH400 is pretty stout from the get-go and it does not cost too much to do some stoutness upgrades. Changing the rear thrust bushing to a tinnerman style will help and I have made the TH400 in one of my motor homes into a TH475 by changing from the helical planetary to one with square gears. It makes some low gear whine, but much stouter. The single best thing you can do for a TH400 is to keep the oil filter clean and make sure the oil temps do not get too high. The TH400 uses an internal screen that is finer in mesh size than a TH350 or 700R4 and they tend to clog and cut oil flow. In my motor home I had the screen removed and I use an external spin on filter that I can change with each engine oil change. I also use an external transmission cooler of very large size.

Have you thought about using 11.00 x 20's rather than 9.00 x 20's ?

I appreciate the information, Bob! I was going to run the biggest cooler I can get my hands on. I may do the external filter as well, it would really simplify things. For tires, I will be putting a few new 9.00's on. I don't have the $1100 to do a full 11.00 swap, but that is more than like what i'll end up doing when I ditch the 9.00's. I wanted to put on the Michelin 395's, but I don't feel like selling my left...kidney to get 6 of them.

I got a little more info on my motor today, it's shipping out on Monday and will be here Wednesday or Thursday. It's coming on a skid pallet and has all the alternator brackets and a complete engine service pack. It was re- built back to standard in 2004 by the Military and has under 6,000 miles on it. He said he's sending it to the paint department of his shop before it ships too. Even more amazing, this guy isn't getting a single thing out of this deal but the satisfaction in knowing it's going to a good home. What I am trading him for the motor, he is giving to the young son of a friend of his. He's even out shipping from Louisiana to AZ. Needless to say, no good deed ever goes unpunished. I just try my best to pass it on whenever I can, to those less fortunate than I.

I am speechless. I didn't know what to tell the guy other than a big thanks for this 25 years of Marine Corps service and an even bigger thanks for what he's doing for me.

My motor arrived today! Got it sitting ontop of the engine hoist legs. Took a lot of redneck ingenuity to get it into the backyard, ended up having to use a hand winch attatched to the hoist and truck bumper to pull the hoist through the dirt. Those tiny little iron wheels don't like dirt. Where there's a will there's certainly a way.



Pics tomorrow when I get some light!