'74 Ford F-350/Cummins 6BTA

[NIsaacs]

I did this conversion back in 1990 so I have forgot most of what it required, but thought it was still relevant so I will post repairs from time to time. Maybe it will help someone now or in the future. The truck is a 1974 F-350 4x2, c/c dually, engine is a 1990 Cummins 6BTA, factory 180hp/457tq. CPL 857. In 1990, Cummins was really pushing repower of this engine and would supply just about anything you needed to make the conversion. I went with the GM application for several reasons important to my combo. The biggest issue was the engine mounted gear drive air compressor, Holset air cooled 8.5 cfm unit. It, with the power steering pump, covered up the side mount bolt casting for the motor mounts. That required the front mount at the front gear case and a need for rear mounts on the bell housing. That was the main reason for the GM, old style ('65 era) cast iron unit with motor mount castings on the bottom.

I just did a clutch job this weekend with an upgrade that it has needed, since day one. The original kit was designed more for the 4BT power than the 6BT so it always had it's issues. At the time, research was tough and repower was just getting started so it was trial and error. I also went with the Clark 280 VO 5spd overdrive transmission. It came with the GM case, input shaft and bolt pattern for the GM bell housing. At the time, all the 4x4 magazines bragged it was bullet proof...wrong! Maybe for a big block gasser but not the Cummins. In all fairness it was a recon not new, but I lost 5th twice and 3rd once over the years and 5 clutches

I think I have cured my clutch issue with an HD unit, custom built for my application 12"x1-1/8x10 spline. I never had an issue with slippage using organic facing, just too much torque for the small hub, they would break the center out and when that happened you were walking:-laf Here are some pictures of before and after, also the mod needed to the flywheel to fit the larger hub. The bore was increased from 6.5" to 7.5". You don't want to ruin this flywheel, it is still available but $900-$1100 As time goes on and if there is any interest I will post more info and pictures of the build.

Nick

 

[mwilson]

Pretty interesting stuff there Nick. Your build continues to impress me no matter how long ago it was.

I hope this clutch combo will hold up for you, it certainly looks like it might.

 

[NIsaacs]

Pretty interesting stuff there Nick. Your build continues to impress me no matter how long ago it was.

I hope this clutch combo will hold up for you, it certainly looks like it might.

Thanks Mike.

This post is for you, since you can appreciate and relate to this part of the build. When I did the rebuild and restoration of the truck in 1994, I installed a small 5" spring brake off an old Ford 750 with linkage that attaches to my E-brake cables. It even has Ford cast in the casting, even tho it is probably built by Bendix, MGM or someone. It is cool as heck when I pull in to a fuel stop and dynamite the brakes I get a lot of funny looks, but what is even funnier, is some don't even look up, it's like they don't know a 1 ton is not supposed to have that sound:-laf

Note the yellow brake valve on the floor by the seat.

Nick

 

[mwilson]

Nothing any cooler in the whole universe than a maxi brake on a 1 ton!!!

 

[mwilson]

I have saved these vin's just for you......FL70 Freightliner's with a 6BT and a Fuller 9 or 10 speed....14" pull type clutch......mounts on flywheel housing...hint...hint...

 

[DVolk]

I still have a brochure from back then about the factory repowers

 

[NIsaacs]

Thanks for thinking of me, Mike....If I were younger I would be all over those part numbers! I have thought of it a lot, especially when I started having clutch issues but I just wasn't up to it. I could barely R&R the flywheel this time, I don't remember it being that heavy the last time I had it out

A few more pic's, first one is my maxi brake, a little blurry, too close I guess.

Very dirty Spicer 3spd Aux. transmission, model 5831 with 27% under and 15% over.

And another dirty transmission, Clark 280VO 5spd overdrive, 20% over. I installed a new fork and rebuilt some of the clutch linkage.

Nick

 

[NIsaacs]

I still have a brochure from back then about the factory repowers

Does it look like this:

It is an awesome booklet with info on how to mount engines to keep NVH to a minimum, cooling requirements, fuel, intake air, exhaust pipe sizing, oil requirements, air compressors, electrical systems and just about anything you need to know about a conversion.

Nick

 

[DVolk]

No , I'd like to have that one mine is ca one page sales brochure I got at a agriculture trade show

 

[NIsaacs]

Here is a little additional info for those that might need/want it. The little Spicer 5831C auxiliary transmission is tough. They were offered in about 7 or 8 different ratio combos. Since they are getting old they are somewhat rare but parts and units are still available if you search.

The model number is for identification, with the 58 being the torque capacity, you add a 0 or now 580. That is engine torque not actual input torque, since when you are in the lower gears of your main box the engine torque multiplies several times. The 3 is speeds and the 1 means cast iron case, if it had a 0 it would be an aluminum case. The C is ratio combo.

I have had this transmission in my truck since 1985, several years before the Cummins conversion. I have only had it fail once. Pulling hard eastbound on Wolf Creek I was in 3rd and overdrive when it broke on the first hard switchback. I stopped, put it in direct and limped to the top. I had a drain pan and gear oil with me so dumped the oil and gear pieces, added new oil and drove it to Del Norte, Co my destination and rebuilt it there.

Spicer also made the 6031/41, 7031/41, 8331/41 and the twin counter shaft 1241. The 60 and 70 series are small enough for pickups but not the larger ones.

Nick

 

[NIsaacs]

After my conversion, my (twin I beam) oem front coil springs would not hold up the weight of the Cummins. Even after the heaviest spring I could buy, it would still sag, so in '94 I installed a mono beam axle from a '76 Dodge motorhome with leaf springs and the steering box. It uses the 17.5 wheels to clear the large disk brakes. Note in the picture, the flat faced lug nuts. Keep in mind the wheel is not hub centric, it is lug centric. I carry two coined lug nuts to center/snug up the wheel, then zap the flat ones down tight. I always wondered if you were not in the know, what did most people do about mounting them to the rig?

Note the sag of before:

And after:

Picture of the axle and steering box:

Nick

 

[NIsaacs]

Over the years I have had several rear axles in this truck. The original D-70 4.10 geared axle I removed in about '85 when I installed the 3 spd. aux. transmission and installed a 14 bolt dually axle from a GM truck. It had the 4.56 gears which I needed off highway. I like the GM application because of the larger brakes than the Ford for that era. The Ford are 12"x3", GM is 13"x3.5".

Then on my first load after the Cummins install I roasted that gear set towing a load of scrap to Phoenix. The first big pull out of Miami, right by the Catholic Shrine it was almost on fire. I unhooked the trailer and after it cooled off I limped it back home. I needed it bad, so I found a set of 4.10's in a salvage yard and installed them. I was kinda glad in a way because 4.56 was too slow now. When I returned to my trailer most of the load was gone:-laf. I had 3 junker pickup beds on my flatbed, full of batteries, radiators and scrap steel. The batteries and radiators were all gone.

When I did the rebuild in '94, I pulled the GM axle and installed a D-70 HD out of a GM truck and installed 4.10's, it had 3.50's. The HD is rated 10k v/s the 14 bolt at 7500. It has not given me any trouble at all, even with the little 1350 U-joint.

Nick

 

[NIsaacs]

Here is a better picture of the front wheel/lug nuts, and some pictures of the before and after.

My 428 gasser, note the AC pump, it was for compressed air.

Nick

 

[NIsaacs]

Some finished pictures:

You can't see it in the picture, but there is a gooseneck hitch door and battery box door on the back of the bed. The large box on the front of the bed is my fuel tank, 48 gallon and on the other side is a matching tool box.

Nick

 

[Shadrach]

I like repowers, especially if it involves a Cummins. I have seen lots of Fummins around.

 

[Wayne M.]

Thanks Nick! I've always wondered about the details of your truck. I was impressed about a lot of things, but especially the I beam front axle. I thought some Fords, like the first Super duty's of the late '80's had em, along with those Budd wheels. You're referring to the alternating conical seats stamped into the wheels, and the bell wheel nuts, right? I had em on my first truck, a '81 D350 Dually I saved from the scrapper.

 

[NIsaacs]

Thanks Nick! I've always wondered about the details of your truck. I was impressed about a lot of things, but especially the I beam front axle. I thought some Fords, like the first Super duty's of the late '80's had em, along with those Budd wheels. You're referring to the alternating conical seats stamped into the wheels, and the bell wheel nuts, right? I had em on my first truck, a '81 D350 Dually I saved from the scrapper.

Yes, the Super Duty and GM 3500 HD's had the single beam axles but I couldn't find anything that new. I did almost buy an axle out of a 1410 IHC, about a '69 I think. It had the big 5 bolt Budd 19.5 wheels but it was so old it had drum brakes. That was an awesome truck for the day, about 1.25 ton with pickup cab. It also had a big Rockwell rear axle but it had a crack right at the spring perch on the right hand side, oil was all over it.

Here is a picture of the wheel, just like you remember. Another thing the old Ford and Dodge duallys had were left hand threads on the left rear. Lots of young tire guys were like, what?

They require this type nut and I carry two of them to center the wheel:

But, for some reason they have this type, I like them so I kept them. They are not totally flat on the back side, they have a small dished taper to clear the (4) raised part on the wheel.

I never liked this type wheel, I had a tandem dually trailer with them. GM had hub center wheels from way back, way better system.

Nick

 

[JR]

That is interesting about the front wheels. Not hub centric, not lug centric (although it appears as though every other hole is on the wheel in the pic?)
This is where proper clamping force really comes into play!
What is the extra hole in the wheel for?

Edit: Never mind, just realized that picture is of a dually wheel. I initially thought it was a picture of your front wheel.

 

[NIsaacs]

Edit: Never mind, just realized that picture is of a dually wheel. I initially thought it was a picture of your front wheel.

It is the same as what is on my truck. They originally used 8x17.5 10 ply but I went to 215/75x17.5 16 ply.

Nick

 

[Wayne M.]

Nick, it's the bottom nut for all locations. I can show the shop manual I think I still have.
When I got my '81, it taught me a bit of driveline basics. You couldn't go over 35 when I got it. The 2 things wrong was the driveshafts were out of phase, and the rear wheels had the wheel cones butted on both sides and kept shifting. IIRC the nut torque is high- better than 200 ft/lb.