Eaton Fuller Intermediate Companion Flange
*New! GM/Chevy passenger drop 6 bolt round now available for preorder!*
Order a companion flange, as a substitute for housing preorder.
By purchasing the companion flange, you will be considered as a preorder for a housing. Once all of the (qty 10Female Eaton Fuller & 6 Ford male) companion flanges are out of stock, you will only be able to preorder an adapter, indicating your desire for one on the next run. The housing qty scheduled for the next production run will be finalized November 3rd. *UPDATE*Currently there are more housings scheduled than female companions available, the next companion production will be Jan 2026.
FSO-64x4 adapter Companion Flanges
Two required for a complete setup.
Offerings Available:
Transmission Side 38 Spline Female
Transfer case Side 34 Spline Male
"350HP" 38 Spline Female *reduced price*
"350HP" 34 Spline Male *reduced price*
The 38 Spline Female has been tapped to accept a M12X1.75 bolt. The bolt pattern is square 8 on a 3.5" Bolt Center. Eight grade 12.9 Bolts will be supplied with this companion.
LocTite Red 271 @ 100ft/lbs torque is required for all eight M12 bolts
LocTite Red 271 @ 150ft/lbs torque is required for tailshaft yoke nut(supplied by customer)
Companion Torque Rating Simple Explanation
Reduced price "350HP" companions.
Four of the first female companions, had four of the eight holes, drilled on the wrong Bolt Circle Diameter. They are too close to the outside edge, and the bolt head/shoulder hangs over the flange interfering with the billet housing. This is easily fixed by grind the heads down on four of the eight bolts. Because of this, they are at a reduced price and therefore have been 'Rated' for a lower 350HP. This is because of the reduction in clamp force, after grinding part of the bolt head down.
They are still well over rated for even the highest power applications. Below is a brief explanation given with rounded numbers of Torque.
Four m12 bolts torqued to 100ft/lbs creates 5,000 ft/lbs clamping force between the two companions. This is related to the contact surface area between the two companions. When that clamping force is overcome, the bolts will then act in single shear. They are rated at 40,000 lbs sheer each.
A well tuned 350HP diesel, should have double the torque for 700/ft/lbs. The first gear ratio of 7:1 from the overdrive units, gives a output factor of 700 x 7 = 4,900ft/lbs force at the output. If you have an instantaneous load in first gear high range, like bouncing off the ground with all four tires and then back down onto all four tires with perfect traction. Exceeding the 5,000ft/lb clamp force can happen, and will move into sheer. This is why the other four bolts are still used, with clearanced head/shoulders. They do still add clamp force, and will also provide sheer support in the unlikely chance that you exceed the minimum number of 5,000ft/lbs four bolts provides.
Further analysis shows that: Eight M12 bolts provide 9,000ft/lbs clamp force. NP271/273f is Rated for 8,000ft/lbs torque input. NP205 is rated for 6,500ft/lbs torque input .
If you have a 500HP engine, with 1000ft/lbs torque, and a 9:1 non overdrive first gear. You can produce over 9,000ft/lbs force. This exceeds the largest commonly available transfer cases with 34 spline inputs. If you shift to second gear 5.21:1 ratio, you're only producing 5,200ft/lbs torque input at the companion flange.
Moral of the story is, your Transfer Case and the 34spline shafts it uses are load rated below the bolts and the clamping forces, not to mention the sheer ratings.
WixomWorksLLC doesn't currently have a warranty plan in affect. In case of unforeseen breakage, we do have a back supply of companions available to overnight ship. Realistic exploration and communication about any failures will be required to ensure breakage doesn't happen again. We ask that you are realistic about the power your running and the benefits of having a transmission that will handle it. Remember, this adapter drops a 2" diameter 38 spline output from a medium duty truck, to a 1.5" diameter 34spline from a lite duty truck. The T-case is the lowest rated component in the system, and the supplied parts are in excess of this. Breaking a 34spline output will be considered accordingly.
Loctite Red 271 @ 100ft/lbs. torque is required for all eight M12 bolts
Loctite Red 271 @ 150ft/lbs. torque is required for tail shaft yoke nut (supplied by customer)
Additional Information and Build your own?
This is a two-piece setup. It requires two separate companion flanges, to transmit power to a Transfer Case. It also utilizes the yoke nut, used on factory end yokes. Loctite Red 271 @ 100ft/lbs. torque is required for all eight M12 boltsLoctite Red 271 @ 150ft/lbs. torque is required for tail shaft yoke nut (supplied by customer)
It is possible to use only the Transmission side companion and make your own Transfer Case side. For those using anything less than a 34 spline T-case, or for those wanting to save on total costs, you will have to make your own until 32 and 31 spline production is ready.
Another option to transmit power from an Eaton Fuller transmission, is to make your own "Spud Shaft". This is viable because the adapter housing sets main shaft endplay, not the output yoke. The involute splines don't require a register or end yoke nut. This is usually done with an old output yoke, lathed down to a concentric shape, that is then welded to an old transmission output shaft cut to length. This must be done by both a competent lathe operator and welder. Concentricity is key, so that the hub seal surface does not leak, eliminating vibrations.
If you already own both the output yoke, can scrounge a burnt-up transmission to donate an output shaft, an have the skills to do so you'll be money ahead. Otherwise, Eaton Fuller output yokes are usually $250-450 if available.
https://www.northerndrivetrain.com/category/cat_flanges_SplinedBore_38Spline_1-998-38invol.html
https://www.northerndrivetrain.com/mm5/merchant.mvc?Session_ID=0ad369f6a5280c0e7ed25eca99d16d79&