62 W300 build. Slant 6 or V8?

[Jason Mills]

I am combining parts from two trucks to make a W300.

The Previous Owner put a V8 from a dump truck in the W300 frame. The engine was cast in 1972, and may run with a carb rebuild(thermoquad). BUT it has a center sump Oil pan, and I am guessing that is not gonna work so well. Also one freeze plug is missing... no idea why as of yet. It may be a 360, it may be a 318 I have no idea which.

My 67 D300 has a 225 in it. It runs.. has the correct oil pan, and appears to be original to the truck. It also needs a carb rebuild, and maybe some other "tune up" type stuff, as it has been a long time since it was driven on the road.

So both Engines will require work and that is acceptable. My question is which one will I be happier with when done. I expect to use the the truck with a dump bed as a summer/fall work vehicle, and on occasion haul gravel and or some other fairly heavy load such as firewood. When it is not at capacity then it will be mostly light duty work. I would guess it will be loaded 30% of the time, and close to empty 70% of the time. It may be used as a personal plow vehicle as well, although I am not decided on that yet.

I'm leaning towards the slant 6, with the thought that it will deliver better economy unloaded. At the same time I am not sure of that reasoning because if it is grossly underpowered, I won't be gaining anything, with the carb wide open all the time. I do not drive fast, and am expecting that my top speed will be around 55 on the occasion I take it to town.. When Loaded I would be happy if we could touch 45 on the flats, and downhills(assuming the brakes are up to the task of stopping the load).. and will accept 25-30 MPH on the hills..

so I guess my question is: what has your experience been with the Slant 6 as the prime mover in your Sweptline truck? And can you compare that to how a V8 performs? Any and all thoughts are welcomed.

[Aaron S]

Ok, so this is just my opinion, but I have a 68 W300 with the factory 318 and always felt that it was severely underpowered going down the road. Off road, in low gear, its fine. On the highway, running 20 mph screaming in second gear to pull a grade, not so fine. I have very little experience with slant sixes, but I would not recommend installing one in this big of a truck if you ever intend to drive it on pavement. Off road, or on dirt/gravel roads where speeds rarely exceed 30 or 40 mph it would likely be sufficient.

It sounds like you are intending to work this truck with heavy loads and drive it on the street. I would definitely go with a V8 for your application. Consider a mild performance build if you ever want to get out of third gear with a full load on the truck.

There are a lot of other factors that go into properly setting up your particular combination. You seem to have a pretty clear vision of how you want to use the truck which is an excellent start. Axle ratios, tire size, and the particular transmission you plan to use will all play a factor in optimizing the engine to meet your performance goals. I'm not talking about go-fast hot rodding here, just having enough power in the correct RPM range to make driving the truck a pleasant experience rather than a chore.

[Jason Mills]

Thank You Aaron. The experience you have shared is valuable in giving me some understanding that a 225 is going to be overworked anytime the truck has a load on, and likely overworked even when empty. (especially with 4.88 gears)

I agree that being stuck in 2nd gear on every hill when loaded, makes driving a chore. I do have a NP540 as part of this build, but even that may not be enough for the 225 to be happy even when unloaded.

[Aaron S]

You're welcome, Jason. I don't know what your experience with the W300s has been, but if you have the 4.88 gears that is a V8 truck. The sixes have 5.89s, and need them.

The NP540 is an excellent choice. I have one myself that will be going into my 68 when I get it back together (hopefully soon). My original NP435 four speed is a close ratio unit that I never liked at all. Third and fourth are too close together, requiring the drop to second to get up a hill. The 540 will have a more useable gear spread (and more synchronizers, which will be nice).

Are you planning to run the split ring Budd wheels, or are you considering a modern, tubeless wheel and tire combo?

[Jason Mills]

Ah... I had no idea that the 6 cylinder trucks were 5.89 geared. I'm very new to the swepline era trucks.. I've evolved here from 20 years with a WDX. I will need to check and determine what the gears are in the front axle of my W300 frame.

The W300 was a 62 or 63 and had the 251 in it until throwing a rod sometime in the mid 70's. The Previous owner scrapped the sheet metal, pulled the six, and put in the 360 V8. He also wanted a truck with dual Rear wheels, so it has an international rear end in it. That was as far as he got, and sold it. I'm gonna swap the rear end out and replace it with the D300 rear. Or I was thinking that is what I would do..

My 67 D300 W/ 225 slant six has a 4.88 geared (according to the data plate on the cab) dual rear wheels, 16" wheels on the rear, which may be unsafe due to corrosion, and 17.5 (I think) tubeless wheels on the front. I would run the budd wheels If I could find some... Although I have been wondering if a modern tubeless rim would be better in the long run. Read somewhere that the 2.5 ton military wheel/tire fits although that would be rather heavy and really only useful for the image conscious.. also it would seem to have a negative effect on brake performance. What is your thoughts around a modern tubeless rim, and what size tire would you choose (in the ideal world?).

[Aaron S]

I checked my service manual just to be sure, the ratios available in the Dana 70s were 4.88 and 5.87. Because it is an earlier truck that had a flathead in it, I would expect it to have the deeper gears. Of course, that doesn't necessarily mean it does...

One of the benefits of these Dana axles is that a variety of gears, and even some carriers are available for them. On the other hand, things like hubs, brake drums, and axle shafts that are specific to these trucks are hard to come by. Fortunately they are stout and rarely need replacing. Axle shafts (rear ones anyway) can be made and disc brake conversions can be done, although none of this is particularly easy or cheap. Your D300 rear should work.

The deuce and a half wheels will not fit. They are similar in appearance but have a much larger bolt circle. The Kaiser/Jeep M715 wheels will fit, as they have the same 6 on 7 1/4" bolt pattern. The tricky bit will be if you wish to keep the dual rear wheels, as that will severely limit your wheel and tire options. The 16" split ring and 17.5" tubeless Budds in dually offset do exist, but they are not all that common. There may even be some dually offset 19.5" wheels out there, but I have never seen them.

I have had modern 16" tubeless wheels built for all of my trucks and I have no regrets. Being able to go to any tire shop and have them worked on makes life much easier. I have bought wheels from Stockton Wheel and Diamond Racing Wheels, I personally feel that Diamond makes a better product at a better price. I have also seen 16.5" Hummer wheels recentered for these trucks. If you choose to have wheels built, you should be able work out the center offset so that the front and rear wheels line up front to back without spacers or hub modification, like a "super single" layout, if you're willing to run a reasonably wide rim (10" or so).

I have been very pleased running 38" tall Pit Bull Mad Dog radial tires on my trucks with 4.88 gears. I chose this tire because it was the closest thing to an 11x16 Michelin that was readily available. They have very good road manners, a good traction tread for off road work, and a much higher load capacity than most other off road tires. They are also tough as nails.

One other thing I will recommend is to find out if there is a shop in your area that offers a tire truing service and strobe balancing. Basically, they shave the tire until it is perfectly round and then balance it, all with the tire on the truck, so that it balances the whole rotating assembly. The difference is like night and day, and the tires will wear more evenly and last longer.

[Jason Mills]

Oh wow. Course correction occurring. I may not need dual wheels on the rear.

Those Mad Dog tires do have an very good load rating, as in 700 LBS more per tire than I have ever seen. I do have the spacers, and such to convert to a single rear wheel, and it reduces weight. . that is an insightful bit of knowledge.

I came to wanting a W300 because of the D70's it wears. Rugged, to the point of almost making the WDX axles appear to be a standard duty axle. I've had no problems with my WDX, but the solidity that the W300 offers is appealing. Also the option for 4.88 gears, the NP540, and the enjoyment of learning about and creating a usable truck has been alluring me for a while. I've got a fairly large amount of body work to do, but I hope to have a really nice usable (3 season) work truck when I am done. It may serve plow duty in the winter, but will not be taken off property until the town salt truck gets put away in the spring.

At this moment I may look into finding one M715 rim, as that will give me a complete set. Then in time as needed I may choose to have some custom rims made.

Now that you mention it, I remember Doc Dave writing about having his tires shaved and balanced.. and I will begin to ask around here, to see who does such work. Very valuable insights

Thank you Aaron for sharing your experiences and knowledge on these less common vehicles. I'm reminded that getting a copy of the shop service manual will be helpful. So far I am only in the beginning stages, but all of a sudden there will be real work being done on the brakes, electrical work, and having a parts manual and shop manual will be helpful.

[Aaron S]

If you get an M715 wheel (or several, they're usually not real expensive and are very sturdy, with the centers welded in rather than riveted as on a standard Power Wagon wheel) take a stepped drill bit and open up the lug holes 1/16" or so. The military, in their infinite wisdom, specified the holes be exactly the size of the lugs. The tolerances are so tight that in their natural form the only way to change a front tire is to take the hub off, lay it on the ground, place the wheel on the hub, and then install the whole assembly on the spindle. I have personally encountered this phenomenon, it is astonishing.

If you decide to run the Mad Dogs, I would encourage you to have wheels built. Its not all that expensive in the grand scheme of things, and I'm not entirely sure that it would be safe to run those tires on a split ring rim. They are a wider tire than the military Michelins, and I don't know that they have the correct bead design to accept and properly seat the retaining ring. I run them on a 10" wide rim, and I think that is about the minimum for those tires... the sidewalls tuck in enough that the rims don't get beaten on rocks. They would probably fit a little bit better and have a little bit flatter contact patch on a 12" rim, but the 10's were a little less expensive and have been a very good combination for me.

I have this set up on my 58 W300, which has a dump hoist under the factory 9ft Utiline bed. I routinely haul three to four yard or so loads (a full bed) of dirt, gravel, road base, masonry sand, whatever I need around the ranch, with no complaints from the tires.

[Jason Mills]

Good Point: I have heard some comments about the split rim really only working for a tire of the correct sidewall, and width. When I go to the Mad Dog's I will dive all the way in and get custom rims.

Your experience with the M715 wheel is easy to believe, and hard to imagine how someone thought it was a good idea. Truth is often stranger than fiction!

[Aaron S]

Please keep us updated on your progress. This sounds like a very interesting build (at least to me), and would likely make a good article (or series of articles) for the magazine. I imagine that there are many folks who would enjoy reading about how you solve the puzzles which will present themselves in the course of this build.

I hope to have one to submit soon myself, about installing a 354 Hemi from a 56 Imperial into a 58 W300 Power Giant. It is looking good, but I need to know how the story ends before I can write it.

If there is anything you think I may be able to help you with along the way, please do not hesitate to ask. I do not claim to have all the answers (or even most of them) but I have always found this forum to be an invaluable resource for sharing information, and I imagine that between all of us on here there will not be too many unanswerable questions.

[Jason Mills]

That sounds like a fun idea! I will take some pictures, before I get started, and see if I can find a way to make them interesting or unusual as well as informative.

Quite sure I will have more questions along the way as well. Thank you for sharing your knowledge and experience with me. You have answered questions I had not even though of asking yet, but would have come up upon at some point.

What engine does your 58 W300 have in it right now? Does it have the wide ratio NP435 as well?

[Aaron S]

The 58 had a 315 Poly, which was a pretty good little motor until it seized up going down the highway last October. It looks like the oil pump drive gave it up and the idiot light didn't come on until it was too late... it will get actual gauges with the new engine. Progress is being made, so it shouldn't be long now.

The transmission is a wide ratio NP420. The gear spread is much more useable than the close ratio NP435 I have. Interestingly, this is a heavy truck unit, and has a much larger input shaft than the standard unit... similar to an NP540. This has made finding clutch parts kind of interesting. Fortunately the old disc was in decent shape and I was able to send it out to be rebuilt with modern friction materials. I am trying to do every little thing I can think of now, in the hope that I will never have to take the truck apart again, ever.

[Hobcobble]

I am combining parts from two trucks to make a W300.

The Previous Owner put a V8 from a dump truck in the W300 frame. The engine was cast in 1972, and may run with a carb rebuild(thermoquad). BUT it has a center sump Oil pan, and I am guessing that is not gonna work so well. Also one freeze plug is missing... no idea why as of yet. It may be a 360, it may be a 318 I have no idea which.

My 67 D300 has a 225 in it. It runs.. has the correct oil pan, and appears to be original to the truck. It also needs a carb rebuild, and maybe some other "tune up" type stuff, as it has been a long time since it was driven on the road.

So both Engines will require work and that is acceptable. My question is which one will I be happier with when done. I expect to use the the truck with a dump bed as a summer/fall work vehicle, and on occasion haul gravel and or some other fairly heavy load such as firewood. When it is not at capacity then it will be mostly light duty work. I would guess it will be loaded 30% of the time, and close to empty 70% of the time. It may be used as a personal plow vehicle as well, although I am not decided on that yet.

I'm leaning towards the slant 6, with the thought that it will deliver better economy unloaded. At the same time I am not sure of that reasoning because if it is grossly underpowered, I won't be gaining anything, with the carb wide open all the time. I do not drive fast, and am expecting that my top speed will be around 55 on the occasion I take it to town.. When Loaded I would be happy if we could touch 45 on the flats, and downhills(assuming the brakes are up to the task of stopping the load).. and will accept 25-30 MPH on the hills..

so I guess my question is: what has your experience been with the Slant 6 as the prime mover in your Sweptline truck? And can you compare that to how a V8 performs? Any and all thoughts are welcomed.

I'd stick with a V8. There was a decent ~50K mile A318 [Poly] available in Moosup, CT
not too long ago. If its set up for a manual tranny, you could find the correct hydraulic
clutch flywheel and clutch components [www.hrclutch.com]. An LA318 would be another
easy option. As for power, these trucks, in their day, did quite well with the Slant Six and
small block V8s..... but life [and traffic] moved a bit slower then too....

A front sump 318 oil pan and sump tube wouldn't be too hard to find. The 4.88 gear
isn't too bad on the road. I have a '68 W200 with the 4.88/4.89 gear coupled with an
LA318/NP435 and its tolerable at 55-60mph. At minimum, you're picking up 37hp
by keeping with the A or LA 318 vs the Slant Six.... that's somewhere in the 25%
increase range.

The pre-'69 D & W 300s came with the 6 lug hub/drum assemblies which are basically
non-existent these days. Make sure your drums are decent and take good care of them.

The 300 series steering box [Gemmer?] is, to my recollection, not a unit that can be
rebuilt. The 100/200 series Saginaw boxes were..... so make sure your steering box
is in good condition and, if possible, keep any eye out for one or two "backups" through
your local bone yard or the Parts For Sale / Wanted sections on this site.

There's a guy by the name of Bud Thorp in Washington state that can likely help you
out with hard to find used parts. He's pretty active over at the www.sweptline.org
site. I've dealt with Bud for many years. He's got 40+ years experience in truck parts
which will benefit you when help is needed.

If your truck needs some attention to the cab, you can't go wrong with Kenny Exline
at www.exlinecustomauto.com .

John

[Jason Mills]

Thanks John,

Good information and likely I will put ALL of your links provided to use. That sheet metal by Kenny Exline is nice and will be helpful!