'Red' - '89 RC, 6BT/518 - (...at home in Virginia...) - Dodge Ram, Ramcharger, Cummins, Jeep, Durango, Power Wagon, Trailduster, all Mopar Truck & SUV Owners.

...overdrive...is good Agree

.

So, okay, here's the story. About a month ago we had some really, really cold days and nights - like -10 degrees cold. And I was working crew those three nights, and each and every morning at 5 am when i came out to fire up ole' Red...it cranked and cranked and eventually fired up and got me home. Cool. It took some coaxing, but it fired up each night, but each night it seemed to get a bit worse. Well on day 4, on my normal morning routine to work, the truck fired up, got about 200 yards, and quit. Had crank, had air, but apparantly had no fuel. Now it was still at/below 0 degrees, so I thought maybe gelling fuel...but it hadn't happened the previous three below 0* nights, so why now. Tank was full, plenty of anti-gel, etc. Checked power to the FSO - good. Hmmm. Not a good sign. Everything that should have power has it, but no fuel.......and I discovered the injection pump is leaking, badly, between the FSO and the main body. Well that can't be good....

Now, Old Red has about 300,000 miles on 'er - no joke. And apparantly the IP finally gave up the ghost. Well that's 'okay' - I gotta give props where props are due. The rig has been plenty faithful, and it's 'due' some 'issues'. So.....what do I do now? I asks myself.

Well, there were a couple options, and the obvious one was to have the IP rebuilt, and there's only one place I'll send it to have that done - up to PDR. They do it right, and it costs $1200 to do it right. When the time comes that's what I'll have done to the pump....but for ole' Red.... I had a better idea. I've been wanting to install a 518 overdrive in the rig since I bought it....and I just happened to have a fresh 518...bolted up to a pretty fresh 6bt Cummins...all from a truck previously known as Nacho......and that engine has about 160,000 less miles on it, and it works like a champ. Hmmmmm. Maybe it's time to give Red a heart traansplant i says to myself. And hey I'll get an overdrive in the process....and I won't have to pay the big bucks to have the IP rebuilt! Hey that's sounds like a bueno idea to me Agree

. So, making good use of some time off I had for the holidays, I prepped the operating table, and began open engine bay surgery.

Along the way I discovered some very interesting things, the best of which is overdrive in a 3.07-geared truck is absolute bliss Cheesy

!! Here's how it went.

First, rolled Nacho’s carcass into the shop, and my buddy Morgan and I pulled the 140,000-mile ’93 6bt/518 combo out and set it on the ground.

Then in the bay next to it I pulled Red’s high-mile ’91 6bt out, and dropped the 205 and 727 out the bottom. Note – pulling the front end/core support out was the smartest thing I ever did!

Then I compared both engine/tranny combos and swapped the fittings/lines from the old engine over to the newer engine so Red’s chassis would work as before with the new engine in place. One-for-one swap – pretty standard. Couple of interesting things tho –
First, I didn’t know the vacuum pump was different on the earlier (non-intercooled) trucks. This is a pic of the intercooled –

And this is a pic of the non-IC –

Quite a bit different. The non-IC has no oil line feed – plugged it off at the block. It also has an amazingly difficult lower mount bolt to reach. I had to get at it from below the tranny with all the 3/8 socket extensions I had. It is at least as difficult to reach that bolt as is the lower rear nut on the IP.

Then I needed to move the tranny crossmember rearward a bit so it would line up with the 518. This required drilling one-each new holes on both sides of the bottom of the frame. In order to do the conversion to the 518, the crossmember needs to be mounted about 2.5 inches rearward, while also flipping the 1/4" uber mount plate so the twin oval holes are facing forward. This gives the exact spacing necessary for the stock 3-prong 518 ‘claw’ to mount to the crossmember.

Measure between the 3 lower bolt holes, and drill a ‘forth’ hole rearward of the existing three, same spacing. Maneuver the lower main crossmember into place, install the new '1st' bolt (it’s the only one that will fit without mods), snug it up a bit, then hog out the remaining 2 more holes so the bolts will go through. It’s hard to explain but it becomes self-explanitory when yer doing it. The upper mounts have their own issue – once you move the corresponding upper bracket rearward one bolt’s worth…you can’t get the front bolt out without lifting the body up about an inch…and I didn’t feel like going through all the headache, so I just used the two remaining bolts and called it good. I did however bolt up the first one just so it wouldn’t rattle.

This is the crossmember, facing forward, with the main plate flipped once so the two holes face forward. Do this and the 518 claw mount with bolt right up…at least it did for mine.

So hardware modified and fittings swapped, my wife and I install the new engine and tranny – we chained the engine more or less standard, but used a strap to balance out the tranny. Worked great despite some clearance issues with the strap and firewall.

And the 518 installed –

Then, linkage. Had to bring the t-case shifter mount back a bit to line up with the floor. Before –

…after…

Then, bolt up the front clip. This is where things got interesting. Upon bolting up the radiator/fan shroud, I discovered another difference between a non-IC and an IC engine. Have a look –
Non IC –

IC –

Notice the fan hub location and thermostat orientation? Look again –
Non-IC –

IC –

Oh yeah, the pulleys are different too – (non-IC on left)

I simply swapped the fan and thermostat units from one engine to the other. Also, the serpentine belts do not swap from one engine to the other.

Then it was time to hook up the wiring, and the overdrive. I used the same pressure switch I used on Nacho to activate the overdrive, with a simple switch at the tip of the stock lever to cancel the o/d when I want. Overdrive kicks in right about 48 mph, and that is adjustable by 'tuning' the pressure switch setting. Works great. Agree

Next, modified both driveshafts to fit the longer tranny/t-case location. $175 and that was done. This is how much shorter a 727 is compared to a 518. Shafts need to be modified just about as much –

The result – Truck will still hum right along at 60 mph no sweat…in 3rd…but hit the od, and it has HUGE legs. 75 mph is a breeze. I can’t wait to determine the net fuel mileage increase, but I’m hoping for at least 2 mph more. By the way, these are the best shop lights you’ll ever use – without a ‘filament’ they don’t seem to want to break…at all! Sweet!

And if you’re using a sawzall without these blades you don’t know what yer missing!

Hopefully, the truck will go a 100k miles before anything else goes wrong! Been a fun 3 weeks

- Sam

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