Moving Forward: Fixing the 4WD in my F250 - Part 1

in diy •  last month  (edited)

Here we go with another DIY post on my old '99 F250. She's generally been a reliable horse after swapping out the broken transmission and fixing the cosmetic issues that it had when I bought it off of Craigslist a couple years back, but a few things have popped up since I've owned it. With 200k miles on the clock, it's expected that some maintenance issues will pop up. My last post about this truck was changing out the worn out pinion bearings in the rear end, swapping to lower numerical ratio gears for mpg purposes and overhauling the rest of the rear end. In so doing, switching the 4.30 gears to 3.73 the 4wd capabilities were rendered useless due to the fact that 4.30 gears were still in the front axle. If you try to run such disparate gear ratios in a front and rear axle while in 4wd, unless it's extremely slick conditions like mud or ice, the resulting gear bind is going to scatter some drivetrain parts. This post is about me fixing that problem since I needed to use my truck in my sloped yard, which I'm not super interested in tearing to shreds spinning my rear tires.


In order to get the gear out, the axles need to be removed. Before tackling this job, I found the lower ball joints on both sides to be worn completely out, with lots of play. Since everything was going to be apart anyway, I took the opportunity to fix those as well and those were put on order


There are four bolts with 8mm hex heads holding the u-joint to the input yolk which were removed.


There are four more with 12mm 12-point bolts on the other end coming from the transfer case.


Next up is the tie rod end on the driver side. It has a castle nut on the bottom with a cotter key keeping it from rotating.


Then the passenger side.


I actually didn't end up taking this one joint apart because I was able to swing this whole assembly out of the way once the tie rod ends were off, but this is the least destructive way I've found to remove these tapered joints. I alternate between tapping the outside of the housing to shock the taper fit, then tap the center of the threaded area to drive it out. Sometimes it takes a few tries, but it works well and it's better than the old-school pickle fork which will destroy your boots and necessitate swapping in new parts. Penetrating oil allowed to soak in for a few minutes is usually helpful here as well, especially with something with a lot of rust.


Next out were the hub locks for manually engaging the 4-wheel drive. This snap ring came out pretty easily with a pair of needle-nose pliers


Once the snap ring is out, the locking mechanism just slides right out of the bore. I can see now why people swap in heavy duty versions of these for hardcore off-roading applications. I can't imagine those aluminum splines would last too long with the drivetrain shocks those applications tend to see at wide open throttle. This is fine for my pedestrian needs though. On the inside, the splined shaft there has another snap ring on it. This one is pretty heavy duty, so it requires a stout pair of snap ring pliers for removal. The cheap-o flimsy ones probably won't cut it.


I got a little ahead of myself on the hub locks there. These calipers and the rotors needed to come off first. Since the brackets would also be in the way of removal, it's best to just remove the bracket bolts and pull both off as an assembly for a job like this. If you look right at the top of the caliper behind where the brake line bolts in, you can see a pair of bolts. The caliper slide bolt is directly to the left of the line at this angle, and then you can see the bracket bolt behind that. That bracket bolt is what you want to remove.


Here's a little trick I learned on YouTube. This hook I used to hang the caliper up is from an old bungee cord. They work great for this. I always hang them this way instead of from the lines because you can damage the lines otherwise.


Next off after the caliper is the rotor. Even though this truck has spent most of its life in Southern Caliornia, the previous owner took it on lots of hunting and camping trips all over the US, so it's seen its share of rust-inducing mud and snow. It took a little persuasion and penetrating oil to get these off. These should get anti-sieze lubricant on them when they go back together for this reason. In fact, having grown up in the Northeast with snow and salt on the roads all winter, I've gotten into the habit of putting it on pretty much anything I take apart and put back together. It saves so much time with disassembly later on if it needs to be serviced. This is even a bit helpful in places that don't see a lot of rust. The lubrication of these parts is a nice-to-have when you go back in and remove nuts, bolts and joints like between this rotor and hub.


Next off were these hub nuts on the back of the steering knuckle.


Once the nuts were off, I was able to get the hub to break free to this point by hitting the studs on the back with a brass drift. In areas with road salt, a slide-hammer tool and even some heat might be required. With this little gap here, I was able to pry the hub the rest of the way out with a standard pry bar. A big screw driver would work too.


This is what the axle assembly will look like with the hub and heat shield removed. I found that just pulling on this splined shaft while prying on the u-joint from behind with a pry bar was the best way to get these out. I don't recommend hitting the u-joint yoke with a hammer as I've seen suggested elsewhere. I tried this and even with a brass hammer it quickly began to deform the yoke and it didn't budge. A rubber seal is holding this into place and constant prying pressure rather than shock force works better for rubber components. Once the seal is free of the knuckle, these axle assemblies just slide right out. Since it's a full floating axle, there are no c-clips in the center section holding them in place, so it can be done even before the cover is taken off.


Next up was the ball joint nuts. The top nut is a castle nut and it's a pretty standard size. The bottom nut is enormous and will require an oversized socket set.


My Harbor Freight 3/4 inch drive set came in handy for that lower one, as the 1-5/16 inch size required was 1/16 inch bigger than anything I have in my 1/2 inch drive sets. If I was a diesel mechanic and needed these tools daily I would get a nicer set of these but considering the once-a-year use I get out of these, they do just fine. Since I didn't have my new ball joints delivered yet, I opted to coat the tapered joints with penetrating oil and leave them until later.



With the axles now out, the driveshaft off and the steering arm swung up out of the way, it was time to tear into the differential housing. This diff cover was bonded into place with RTV silicone sealant. I find that it works so well as a glue, just prying can damage a diff cover or the sealing surface, so I like to go around with a flat putty knife and sort of cut my way through the silicone. Leaving a bolt or two in place helps ensure you don't have the entire contents fly out all at once and make a mess all over the shop floor.


Loosening the bearing cap bolts for removal.


I like to back these bolts all the way out before prying on the diff. Usually there's a lot of interference on these holding them in place, but occasionally they'll just plop out of the housing when you start prying on them. I found this out the hard way when I did the rear end on my father's truck as a teenager. I had broken it on him so he made me fix it. I tried to catch it as it fell and it slammed my hand into the ground, leaving three slices into my palm where the ring gear made contact. The rest of the job was fun with that injury. Luckily I was working on the truck in the grass, and the soft soil cushioned the blow enough that no bones were broken. Since then, I leave the bearing caps on while doing my initial prying to remove diffs from their housings.


A block of wood on the gasket surface keeps it from being damaged. Once the diff was pried all the way out and hit the ends of the bolts, the bolts were removed while holding a hand on the diff to make sure it doesn't fall while doing so. This one had enough preload that it still required a little prying even after it got this far. Then the old heave-ho over to the work bench.


The last part of disassembly is removing the driveshaft yoke from the pinion. The nut can be removed with an impact. If you don't have one, this should be done with the wheels on the ground (e-brake engaged) with the hubs locked in before the axles are removed. This will hold everything in place while you torque on it. This little wheel puller works well for pulling the yoke in my experience. Once it's off the pinion can be tapped back into the housing for removal from the other side. Use a brass drift here so you don't damage the threads on the pinion.

Once the pinion was out, I moved to the knuckles. Both the upper and lower ball joints shown in the above pics are tapered joints just like on the tie rod ends and the technique for removal is the same. I alternated between tapping on the axle housing at the joint locations and tapping with a brass drift from the top where the threads are (be careful here not to damage threads if reusing the ball joints). Be careful at this stage because the knuckle can fall right out and smash your feet.

That's it for disassembly. The next post will be about swapping the new gears onto the carrier, pressing in new ball joints and reassembly of the axle. Look for that in Part 2. Until then, keep the hive buzzing!


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'Miring your shop. Your work ethic seems neither shabby. Kudos!

Thank you. I watched my father work his whole life to get something similar. I have to admit that the one I helped him nail together is dimensionally quite a bit bigger, but this one was poof'd into existence for me by the magic of localized inflation, regional arbitrage, and the willingness and ability to relocate. I am reminded of how fortunate I am every time I think about that.

I had little experience when "playing" with any kind of maintenance with my old Ford 1.4 TDCI back when I was in Portugal. And, yeah... you just made recall that fine experience the books or videos sometimes can't really explain.

Would love to play with "toys" like these... if I had a shop like yours LOL

Glad you enjoyed. We never got most of those little turbo diesels here in the US. I remember VW sold some. I always thought they would be well received, especially in small pickups, but the OEMs didn't offer them even after the wild success in the full size pickups.