6.2 GMC Engine swap

[majortom]

Several people have asked if there are any specific problems with slamming a 6.2 diesel engine & trans in a GMC M series 6x6. The original 302 engine was governed at 3600 rpms giving the truck a top speed of 61 mph on 1100x20s. A 6.2 engine with the 400 turbo trans as fitted to a CUCV would be very similar except, in my opinion, you are revving the engine higher than necessary. By using a 700R4 transmission as fitted to civilian Chevys, you gain an overdrive gear and a lower 1st gear. So we now have our 6.2 engine bolted on to a 4 wheel drive 700R4 transmission and transfer. You will need to fabricate a driveshaft from the rear output of the 700 transfer to the input of the 6x6 transfer. The front axle output of the 700 transfer is not used. With this configuration you will achieve two ranges with 4 gears each and suitable engine rpms to reach 70mph. Of course there are many other items that have to be fabricated, motor mounts, linkages, etc. but the only tricky areas are clearance on the right hand exhaust & adding an air pump to the engine for the brakes. This is not extremely hard to do, you just need a good supply of beer.

 

[APM215]

Thanks Tom that clears up allot.
You are truly a GMC guerue.

 

[doghead]

I don't think the 700R4 or the NP transfercase(208 or 205) will last very long in a 13000 LB truck. I think there must be a better choice.

 

[APM215]

I don't think the 700R4 or the NP transfercase(208 or 205) will last very long in a 13000 LB truck. I think there must be a better choice.

Why not? If I'm not mistaken the transfercase on these trucks is a under drive and then the 6:17 gearing makes for some light work for that transmission.

Maybe I'm not getting why It's not a good choice help me under stand before I do this to one of my trucks.

 

[doghead]

The 700R4 and the NP 205/208 Tcases were not designed for a 13000lb truck.

 

[Westex]

The 700 R4 is a piece of Cr@!; don't even think of using it. Problems with the lockup; problems with the pump inside the unit; again, forget it. One of the worst units ever produced.

 

[Recovry4x4]

The 700 R4 is a piece of Cr@!; don't even think of using it. Problems with the lockup; problems with the pump inside the unit; again, forget it. One of the worst units ever produced.

Woah, this is 2009 not 1983. These things can be built to handle 3 times the power of a 6.2. I have one in the yard attached to a 6.2 in a 4x4 burb with 168,000 no problems. Had one go over 300,000 with just maintenance. Guess there is a chance that I got the only good ones they made.

 

[drgreg]

The 700R4 and the NP 205/208 Tcases were not designed for a 13000lb truck.

I would think the power supplied by the engine would be the main factor in this equation.

 

[Crash_AF]

Why use a transfer case? Just get a 2wd transmission for it and eliminate the extra transfer case. I don't really think the double underdrive capability would be necessary.

Later,
Joe

 

[K9Unit]

Just my 1/2. Dont waste your time or money trying to have someone build up your 700r4. I rebuilt enough of these when I was in business... Yes they can be rebuilt, extra clutches, larger output pump, adjustable gov. ect. The internals are still to small to handle a large deal of torque for a period of time.

You can think that the 6.2 doesn't put out much horsepower or torque but multiply the amount needed it will have to endure from having to turn your 6.72 gears not to mention the reduction if you ever used the transfer case just to get the 13000lb vehicle moving and thats without ever carrying a payload.

When GM first came out with the tranny it wasn't much better than the newer version today "4l60E" They first came out with the 200R4 for alot of passenger cars and proceeded to produce the 700R4 for light duty pickups and passenger vehicles after being pushed by the Gov. to make vehicles get better fuel mileage.

I wont get into all the internal problems it has but that it was never made to be put in a pickup that was supposed to be used for work " hauling loads, towing trailers ect." Most that are out there and are used for this the O/D goes first or first gear gives up the ghost. I would say probably the first time you went to pull a heavy trailer or increase the payload capacity you would twist the input shaft off like a pretzel or burn the lock up portion of the O/D.

My personal opinion, if you wanted to go this route just find a TH400 have a good rebuild done to it and run a gearvendors unit. That would still give you your underdrive and O/D and its capacity is up to 26,000lb GVW. I'm also not so sure if the np208 would hold up to the task. Its all aluminum case and chain driven. I might go with an older version np205 that were all cast iron and is all gear driven. If you didn't want to go with the gearvendors unit you could find a 4l80E. Todays overdrive version of the th400. but then you will have the headache of all the wiring as you need to purchase a stand alone comp. because its all electronic. Then I would be afraid to get in much water.... maybe this will give you a few different options if your still looking to go this route.

 

[NDT]

In my opinion the perfect swap for the G749 GMC's is the gas 366/Allison found in the 1980s/90's Chevy mediums (school bus, Uhaul truck). The first gear is low enough to approach low range on the hydramatic, and the 366 can handle 4000 rpms all day. Still will get crappy fuel economy like the 302.

 

[BugEyeBear]

In my opinion the perfect swap for the G749 GMC's is the gas 366/Allison found in the 1980s/90's Chevy mediums (school bus, Uhaul truck). The first gear is low enough to approach low range on the hydramatic, and the 366 can handle 4000 rpms all day. Still will get crappy fuel economy like the 302.

How easy is the swap?
Any clearance issues?
Custom motor mounts?
Overall length of engine & trans vs the stock units?
PICTURES???

"Cheers!"
-Bear-

 

[nattieleather]

IMHO I like the idea that was first proposed except that I personnaly think the 6.2L GM diesel is a dog of a motor. If (or maybe I should say when...hahaha) I get another M211 or variant I'm thinking of getting the IH Dt466 and allison trans from a school bus and dropping it in. I like the idea of the extra transfer case so that you can have the hi/lo range like the original trans.

 

[spicergear]

If you're in love with the idea of putting a 6.2 in the truck here is one way you may be able to do it- It gets mentioned now and then about the Peterson mag write up for the Chevy/ 3053A wirte up that I gave the guy all his notes for... *if* it's possible to get a 6.2 flywheel that will take the 1 ton clutch disc, then you're half way there as the gas REO's had a 12" disc in them. Get the block plate and dual pattern bell housing allowing the 3053 (3052 will fit too if you don't want OD) to be fitted to a Chevy V8 with the 'home plate' bell pattern and mount the thing. The big truck bell has mounts on it so you could, theoretically mount the deuce tranny in the same/stock location.

Or, hit a truck salvage for a 6 or 7 liter (366 or 427 TD) big block with an Allison on it and slap that in. OR a 471 Detroit with N80's in it!

 

[majortom]

i am pulling a 366 w/ alison out uf a gmc because it gets 4 mph on a good day. th400 is an excelent tranz, but top gear is 1:1. 700r4 tranys have issues, especally the early ones. i like them because the parts and knowhow to bulletproof them is out there. i have a built 700 behind a 450hp smallblock in the superburban tow truck. we haul dueces with it. i get much better mpg than the 400 it replaced. it is holding up to the abuse just fine. if you want to drive a gmc at highway speed (70mph) you must have a overdrive trany. all of the newer auto 4x4 overdrive tranys are muuuch worse than the 700. overdrive stick tranys for 4x4s are all junk too. big truck od tranys do not come with tranzcases, and there is no room to fit a redution box. the gmc has low range in the trany, it also hasa much lower 1st gear than any 3spd auto, vary simaller to the 700. i tried the idea of not having low range, with both stick and auto tranys, bad idea.i twisted driveshafts into knots, blew clutches, broke imput shafts,and ripped engines off there mounts trying to get a loaded truck moving in to high of a gear. its your truck, and you can put any thing you want under the hood. i drive big trucks fast, on road and off.i want speed,mpg, and dependability. to this hunt i have tried many engine combos in 6x6s. 454 od5spd=5mpg 70mph 413 5spd=6mpg 65mph 350 th400=5mpg70mph 8.2td 545 allison=10mpg 60mph 478torow 0d5spd=12mpg 65mph 6.2 th400=10mpg 65mph 6.2 700=12mpg 70mph i have tried other engines that turned out to be really bad ideas,355 stockcar, 671detroit, ih 345, gm235. bt4. to repower an old gmc to drive to shows, haul firewood,in general a toy, i like the 6.2, 700r4. if you think you want to try one of the gas gusslers that i did, have i got a deal for you

 

[Westech]

I remember you talking about doing this swap a couple years ago when I stopped by your shop. I think we were talking about doing it on a bobbed deuce. The 700 should hold up fine. My friend had one behind a 454 pushing well over 600 HP. Never had a problem, had many up grades and a HUGE cooler. Don't see why it would not work in a deuce of any shape. With the low 1st gear and the gears in the axle you will get some RPM's quick! Thinking about it the trans prob would have less stress then a 1/2 ton pulling a camper and loaded with all the family's toys with 3:42's or even see some 3.08 with the 700.

 

[JasonS]

overdrive stick tranys for 4x4s are all junk too.

I hope that you're not implying that the 700R4 is stronger than a NV5600, G56, or 6 speed Fuller? I know which one I wouldn't want behind my cummins.

 

[snakeater]

what would be the problem of using the 4bt or 6bt cummins with a 400 or overdrive trans. Super dependable engines, decent fuel mileage? Any takers? How about converting the origional engine to run on propane instead of gas. definately cheaper although it would be a little harder to fuel up than pulling up to the gas pump. It would be very economical for offroad use. I have also seen propane setups that were made to use the grill cylinders, those are available at any corner store or home depot. i know they aren't dot approved, but who will check? Also propane is a cleaner (greener) alternative and gives a higher octane rating than gas. Observations?

 

[nattieleather]

I was thinking about the cummins 6bt. But if I did the 6BT I would use the Dodge 46rh or 47rh (not sure on exact number) trans for the same reason the 700R4 has been mentioned. Lower first gear and a high 4th gear. But the dodge transmission is proven and tested behind the Cummins motor. I've also thought of taking the motor and trans out of a GMC Top Kick and putting that in...medium duty truck into a medium duty truck...or how about the GMC/Isuzu 6 cylinder Diesel... another medium duty truck motor for a medium duty truck. All get decent fuel miliage (though your not going to get any duce to run 20+ MPG no matter what motor you have..lol) and all modern upgrades.

 

[Chief_919]

Why not use a 4L80E with a standalone transmission computer- the same setup in newer HMMWV's behind the 6.5's, both trubo and NA?

In fact, you could almost just drop a complete M1114 drivetrain in...