Building a Full Floating Ford 9" Axle
Written by Andrew Horvath
All Ford 9" axles are a semi-floating design, which simply means that the axle must support the weight of the vehicle which is usually done by a bearing at the outer end of each axle shaft. This design works well but is not as strong as a full floating design. A full floating design means that the axle does not support any vehicle weight; the axle shafts only need to turn the tires. Sure, a semi-floater works fine with stock vehicles but a modified 4x4 adds additional stress in the former of larger tires, lower gearing, differential lockers, and additional weight (body armour, bumpers, winch, heavy duty drivetrain parts, etc.). With these additions, the semi-floating axle's dual role of both supporting AND propelling the vehicle often times results in snapped axle shafts after a few seasons of hard four-wheeling. A full-floater axle literally takes the load off the axle shafts by using spindles and hubs to support the vehicle's weight. The only stress a full-floater axle shaft sees is the torsional force used to drive the wheels. Besides improving the durability of the axle shaft, a full-floater design also makes it much easier to deal with a snapped axle shaft. Simply unbolt the drive flange and pull out the axle shaft. That's all there is to it. With other axle designs such as the C-clip and semi-floater, you would have to replace the shaft on the spot because without it, you could not safely expect the wheel to stay on the vehicle.
Most front axles you find under 4x4's are full-floater axles and the rears are semi-floaters with the exception of some ¾ ton and larger trucks which use a rear full-floating design. The reason for this are the strength advantages mentioned above.
You are probably going to ask yourself why I didn't just swap in a full-floater Dana 60 from a ¾ ton truck instead of going through all the hassles of making a full-floater 9". Well, the reasons are plain and simple: in the end it came down to the ground clearance and weight-to-strength ratio advantages of the 9" over the Dana 60.
In order to make a full-floater axle there are a few very important items you must have. One of these is a spindle that is attached to the axle tube which lead to the start of the brainstorming process. Front Dana 44 parts (ie: spindles and hubs) seem to be very easy to find at the local wreckers so it made sense to use as many of them as possible. With that very rough plan in place we (Chris Waterman and I) needed a way to attach a Dana 44 spindle to the axle tube and at the same time have a seal that would seal against the axle shaft to keep junk from mixing with the gear oil (and to keep the gear oil inside the axle housing where it belongs). After mulling over a lot of ideas and advice from various sources we decided on designing a flange that would be welded to the axle tube and allow a spindle to bolt to it. After that, all we would need was to toss on some hubs, caliper plates, calipers and a double-splined axle shaft to achieve our full-floating goal. Seemed easy enough to me.
Since I was going through all the trouble of building a full-floater I didn't want to hold back with the housing. There are a few different housing designs that Ford put under their vehicles. Some of the housings are fairly weak and some are extremely strong. The one that is most desirable was factory equipment on Lincoln Continentals. This housing has the exact same shape of the Currie heavy-duty housing. The resemblance is so close that even the weld that surrounds the back of the center section stops in exactly the same spot. Hmmm, sort of makes you wonder, hey! One thing that is a little different about the two housings is that the Currie one contains 0.188" walled axle
Flanges and Alignment Jig
After a lot of talking with people, Chris and I chose to design the flanges to be butt-welded to the housing rather than using a press fit design. If the idea of butt-welding the flanges on to the axle tubes worries you, don't let it. All stock 9" housings have the flanges butt-welded to the housing. Probably the most important reason you need to butt-weld to the housing is that it allows for the use of an alignment jig. A jig is a must when making a rear end because the carrier bearings MUST run totally true to the spindle-mounting surface. If you are a little off then the axle shaft will not spin true in the spindle and damage to some your shaft is very likely. The alignment jig was a fairly simple design in that it only included four aluminum pucks and a steel rod. Two of the pucks were machined to fit in place of the carrier bearings. The other two were machined to fit into the recess on the flanges where the spindles would mount. The way the jig worked was that the carrier bearing pucks were installed into a gutted third member and the outer pucks were installed into the flanges. Next, the rod would be passed through all the pucks which would align the flanges perfectly. Remember that the pucks must have as little play around the rod and flanges as possible to ensure total accuracy. Now that we had a plan for how to align the flanges, we needed to get them made!
It turned out that a buddy of mine owns a CNC machine shop and he was willing to give us a hand. Now that we had a place to get the flanges machined we needed to work out one more small detail: how to seal the flange to the shaft. A simple solution was to have a part bored into the center of the flange to accept a seal. After a few calls to Moser and Dutchman it turned out we needed a seal that sealed against a 1.313" surface. So off I went to Lordco to find a seal. The seal Chris ended up finding sealed against a 1.313" surface and had a 2.500" outside diameter. So with that settled, we needed to have a section of the flange bored to 2.505" which was not a problem with a CNC machine. The bore hole for the spindle was made very precisely to allow a perfect press fit. When I first got the flanges in hand I wanted to test the spindle fit so I cleaned up my spindles I was not able to slide the spindle in the flange if it wasn't totally aligned. But after I got the spindle in the flange it would spin totally freely. Around the outer part of the flange, six holes were drilled and tapped to use 3/8" fine thread grade 8 bolts. This part of the flange was very important because if the spindle did not fit perfectly into the flange the load on the spindle would be on the bolts instead of the flange. I think the coolest thing about the making of the flanges was that they were created from scratch on a computer screen. The program my buddy used enabled us to see the flanges in 3D from any angle, which really helped to fine tune everything. After we were satisfied he clamped a solid chunk of hardened steel in his CNC and pressed [Enter]…well not quite but you get the idea!
Making Everything Straight
After I had the alignment pucks and the 3rd member jig in the housing I made sure everything was straight. Well, not to my surprise the housing was not straight, damn. At this point, I had two options: 1) find another housing and 2) straighten the housing myself. Being the cheap guy that I am, I chose to straighten the housing myself. My housing was only out about 3/16", which was enough to make me concerned. The easiest way to straighten any housing is to heat the one side that the housing needs to bent towards. So it was just a matter of getting out a torch and heating the one side and then letting it cool. This process will bend the axle tube about 1/8" to the direction the heat was applied. Well for me there was a little problem, I didn't have a torch. The way I managed to get around this was to lay a nice long and hot bead of weld along the top of the axle tube. After this I let the tube completely cool and to my luck the housing was now straight.
The next step was to grind off the entire weld that was on the tube with my angle grinder. Then I measured the axle and 3rd member to figure out where I needed to do my final cuts to achieve a centered pinion as well as my desired WMS-WMS (WMS = Wheel Mating Surface) width. This was not too difficult if you are somewhat math literate. Before you start anything you need to figure out if you want the pinion to be centered or offset to one side. For my application I chose to make the pinion exactly centered which meant the 3rd member needed to be offset to the passenger side by 2.5". This caused the passenger side axle tube to be 2.5" longer than the driver side tube. With that in mind I measured how much distance the flanges, spindles and wheel hubs would take up by actually assembling all the parts. With that number in the back of my mind it was time to choose the WMS-WMS distance. I wanted to make my axle around 63" wide to make up for the added height of my larger tires and lift. I figured this would give me a little more stability when put in off camber situations. For the final measurements I factored in all the numbers and prior measurements. With my final measurements in hand (and triple checked) I made the first cut in the housing. You must make sure these cuts are totally square or else you will not be able to get a solid butt weld. After both axle tubes were cut square and to the perfect length I ground away a little bit of the outer edge of the tubes to make a nice chamfered surface to weld the flange to. Now it was time for the most important part of the whole project: welding on the flanges. Don't rush this process as one mistake may cost a lot of time and money in the future. The first step was to bolt in the 3rd member with the alignment pucks clamped in place. Then I slid the rod through the two pucks and placed the flanges over the rod with the outer pucks slid in the spindle borehole. Make sure the holes in the flanges are in the same orientation or else the caliper brackets will not be oriented at the same height, which will cause the calipers to be at different heights. I then made sure everything was nice and tight and not sloppy to ensure total alignment. I was now ready to tack weld the flanges in place and run a test. When tacking the flanges in place I made sure I did four small tacks on opposite sides of the flange then double-checked everything was still aligned. By total fluke the rod that I used to run through the jig had about a 1/16" clearance around it when a Dana 44 spindle was slid over it. How perfect was that? I then bolted the spindles to the flanges to see if everything looked good and the rod was totally centered in the spindle. To do the final welds you want to make sure you know what you are doing. So DO NOT attempt to do the welding with a 130 amp welder. Make sure you have plenty of power to zap it all together. If you are uncomfortable with welding this part take the safe route and take the housing with the jig in it to a shop for the final butt weld. This will give you a little assurance if you ever get nervous about the strength of the butt weld.
All the Other Parts
To finish off my 9" I needed to assemble the outers and then order some axle shafts from a company like Dutchman or Moser. After I installed my new 4.56 gears and 31-spline Detroit in the 3rd member, it was time to think about the outers. One question I needed to ask myself was if I wanted to run a 19-spline or 30-spline outer axle shaft. Both had their advantages and both had their disadvantages. For the 19-spline outer I could use cheap drive flanges from the wrecker that were used in Jeep Wagoneers and Chevys that had a front Dana 44 with full time 4x4. The disadvantage was the splines were coarse, which meant they were machined deeper into the axle shaft. The 30-spline outer axle was the way to go for me mainly because I had an extra 200 bucks to cough up for the Warn 30-spline drive flanges. The 30-spline outer had the same spline diameter that could be found on all front Dana 60 axles so the strength gain was evident. If you do go with the 30-spline outer (like me) you will need to bore out your spindles to 1.350" from 1.275" for clearance issues. In both cases you will not be using the little Torrington bearings found in the inner end of the spindle. The outers I used in order to maintain a 5 on 5.5 bolt pattern were the same items used for a disc brake swap on a early model Bronco Dana 44. These parts included 73-76 Chevy ½ ton spindles, caliper backing plates and calipers, 78-79 Bronco rotors and any F150 (TTB or Dana 44) hubs. Then all I needed were the wheel bearings and drive flanges. To attach the hard lines on the axle to the caliper I needed a short brake hose that had the proper fittings on both ends. After looking around I found one that worked perfectly (Raybestos part #BH38421). Lastly, after everything was assembled I needed to take the measurements for my shafts. The best way to do this was to slide a rod down the inside of the axle tube and measure the distance from the inner end of the carrier splines to the end of the hub. With that measurement I called Dutchman and talked to them about the specifics. When I ordered my axle shafts I made sure I specified that I needed a 1.313" seal surface machined into the axle. This was the point where the seal in the flange would rest against the axle shaft. The last thing that needed to be addressed was the lack of an e-brake. I was not worried about this because I was going to make a t-case e-brake anyway.
Putting it All Together
Now that I had all the parts to build and finish my full-floater it was time to put it all together. The first thing that I did in this process was to install the 3rd member in the housing. Then what I did might be a little out of order but I slid the housing and 3rd member under my jeep and tack welded the spring perches after setting up the pinion angle. I also tacked the shock mounts on so I could do all the welding at once. I will explain why I did this later on in the article. With the housing back out of my Jeep I finished welding on the perches and shock mounts. I made sure I did a nice job here!!! Broken welds on the trail are no fun to deal with. Originally my plan was to install the axle seal into the flanges and then just slide the shaft through. Well that plan needed to be changed after I received the shafts from Dutchman. The diameter of the shaft was darn close to 1.5" before it necked down at each end so sliding the entire shaft through the seal would have surely damaged it. To get around that I simply slid the shaft in and then slid the oiled seal over the shaft and tapped the seal into the seal bore in the flange.
After I had the seal installed, I slid the bored-out spindles over the shafts. I also used a little RTV silicon between the flange and the spindle to help make a good seal. With that done I slid the caliper brackets over the spindles and oriented them so the bleeder hole on the calipers would be pointing up after the calipers were installed. This was very important if I wanted to be able to bleed my brakes. I then threaded the grade 8 3/8" bolts and lock washers through the caliper plates and into the flanges. I also used a little blue Loc-Tite to secure the bolts. If I remember correctly the bolts were 1.5" long which turned out to be the perfect length. If you are a little worried about the thought of your spindle bolts taking all the weight of the vehicle don't worry about it. The weight of the vehicle is actually placed on the spindle bore of the flange and the bolts simply keep the spindle in the bore. With all the bolts tightened up it was time to slide my hub and rotor onto the spindle with the new hub seals and bearings in place. Then I assembled the lock nuts the same way I would on a front Dana 44. Now it was time to slide my drive flanges in but before I did this I needed to slide in two little 'wear washers' (as Warn calls then) over the axle shaft. Then I slid the nice heavy-duty 30-spline drive flange over the shaft.
With the drive flange tapped all the way in I installed the rest of the drive flange components. This included the tapped retaining plate and external snap ring that was included in the warn drive flange kit. I applied some silicon to the o-ring on the cap just to make sure no junk would get into my hub assembly after I bolted it in place. Now the last thing I needed to deal with were the brake lines and hoses. With the calipers and pads installed I loosely screwed the banjo bolt through the brake hose and into the caliper. This was when having the spring perches welded on made my life a lot easier, because I didn't have to guess about where the best spot to weld the brake hose tabs was. Or more importantly, I knew where I shouldn't weld them. I then got out the little metal tabs that I pulled off a Dodge truck that allowed a brake hose to pass though and be secured with a little c-clip. The reason I wanted to get ones from the wrecker over making my own was because the hole in the middle wasn't just a hole; it was actually a toothed hole that prevents the brake hose from spinning when I threaded the hard line into it. After I made sure there was not going to be any interference with the u-bolts or rocks I welded the tabs in place. I then ran hard line to the top of the diff where I welded a bolt to allow me to bolt down the brake line 'T' junction block. Then it was just a matter of getting some new u-bolts, installing the 9" and bleeding the brakes.
Considering This Swap?
If you want to get in contact with my friend that made the flanges his name is JP and can be reached at firstname.lastname@example.org. Also if you are wanting to keep your Dana 44 or Dana 60 but want to convert it to a full-floater just contact JP and he will be able to modify or create the perfect flanges for your needs. And just to forewarn you, here is my approximate total cost including taxes, in Canadian dollars: $2350.00. Your cost will probably be different from mine. It all depends on how good you are at haggling and how skilled you are at scavenging in the wrecking yards.
A special thanks goes out to Chris Waterman for the problem-solving ideas and solutions, Chris Siebert for the use of his alignment jig and JP Baron for his unbelievable CNC machine work and design of the flanges.
If you still have some questions about this project I can be reached at email@example.com
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