Solid Rear Axle Swap

[Travis Brown]

Hey guys, I've been meaning to post on this for a while. Last summer, I decided to go all in on upgrading the off-road capability of my Explorer, with a goal of seeing what the Explorer might have been if Ford had decided to compete with the Wrangler and 4Runner 15 year before the Bronco was released. First on the chopping block was the independent rear suspension, which as you guys know, is pretty hard to lift and has pretty bad articulation anyway. So it was time for a solid rear axle swap. I haven't seen anyone else do this on a 4th gen, so I was definitely starting from scratch. Ultimately, I plan to get something with similar size and performance to a modern Bronco.

Note: The following mod is not for the faint of heart. Special shoutout to Ronin8002's coilover conversion thread Ronin8002's 4th Gen custom coilover conversion for giving me courage that I could do this and not die driving the vehicle afterwards.

Axle

I was looking for an axle that matched the 5x114.3 lug pattern of the front so I didn't have to have to deal with 2 sets wheels (front and rear). I also wanted something that would bolt up to the factory drive shaft. A Ford 8.8 out of a 1st or 2nd gen Explorer or Ranger was an obvious choice since they're easy to find in junkyards and pretty well respected for their toughness. There are two main issues

1) Older Explorer axles are about 6 inches narrower than the 3rd and 4th gen IRS (59" vs 65"). See here: Ford 8.8-Inch Rear Axle History & Specs - The Ranger Station This obviously wouldn't look good, perform well, or fit well under out 4th gen bodies.
2) More importantly older Explorers have off-center drivelines which would interfere with the gas tank on the 4th gen.

Another option is a Mustang axle, since '05-'14 used a center-drive 8.8s with a 65.5" width. Unfortunately, the Mustang axle tubes are much smaller (3" vs 3.25") and I didn't trust their strength. So the obvious answer was to use Mustang axle shafts with an extended Explorer axle and diff

^ Donor axle from 2nd gen explorer

^ Mustang axle shafts right, Explorer on the left

^ Extended Explorer axle

Frame

As everyone here knows, the 4th gen frames with their axle-through-frame design are a major headache for any serious off road mods.

^ Big chunk of frame right in the way of the axle

Thankfully, there's ample space between the top side of the frame and the body, which opens up the possibility of re-routing the frame.

^ Cutting off IRS attachment points and marking cut lines for the frame. I also cut out the cross member which served as the attachment point for the LCAs and differential.

^ Upper frame reinforcement welded in prior to cutting

^ Rerouted frame. I wish the welds had turned out better, but the fitup was really hard to get right.

^ Lots of space under there now!

 

[Travis Brown]

Suspension Design

I now had a suitable bare axle and a frame with enough clearance to mount it. I just needed to design a suspension. This was much easier said than done. The gas tank and exhaust consume any space that might be used for a triangulated 4-link, so I planned to do a parallel 4-link with Panhard bar like the Bronco. The Bronco suspension has the upper control arms inboard of the frame, which frees up outboard space to put the coilovers forward of the axle. The layout of the Explorer doesn't leave any room for this and the body would interfere with springs even if you could. That forced me to put the UCAs outboard and forward of the axle, with the coilovers behind the axle. Another problem is that the body didn't leave much room to stuff a large-travel coilover in this space. There's a small indentation on the body to give clearance for the stock strut tower. I designed the new coilover mounting point to use that space, but the axle coilover mount still had to be pretty far down. This also prevented me from moving the coilover mount any further backward, which would have made the clearance around the axle a little better. I spent a lot of time using online 4-link calculators from Pirate4x4 and stressing about anti-squat, but in the end, I kinda just had to put the attachments where they fit.

^ New 4-link attachment points

^ Complete axle, UCAs, LCAs, and Panhard bar

^ New axle installed. I used the rear cover from the stock diff and it looks pretty nice. Control arms all use Synergy Dual Durometer Bushings. I've been quite happy with their performance so far.

^I added a replacement cross member several inches above the old one. This served as a good attachment point for the Panhard bar mount. I also needed to reroute the exhaust pipe slightly to fit between the frame and the Panhard bar. This was pretty easy with a 2.5" universal exhaust kit from Amazon.

Finally done

^ Ahh yes, loving the 10" of wheel travel with Fox 2.5 X 10.0 Performance Series coilovers

 

[410Fortune]

Take that ford! Lol

Fantastic work

 

[JakePSD]

I can't say I'd ever do what you did, but man, that's cool! Excellent work!

 

[allmyEXes]

Your rear frame mods make me wonder how well a Gen 2 full chassis would fit under a Gen 3 Explorer body or a 2001-2005 Sport Trac for that matter. Build a run ready 5.0 or 5.8 chassis then add later year body?
Here is a couple of axle widths with same year F-150 axle width in the middle. Gen 2 Explorer 59.81". 1977 to 1986 E-150 69.25. Van rear end is 9.44 inches wider. Lug/stud pattern may need adjusted.
Nice job!

 

[boominXplorer]

Something I figured was possible someone finally did! Looks good with the 4 link! I would have picked a more fitting axle but you definitely made it work! Good job!

 

[Fix4Dirt]

Fantastic work, never expected this to be done on a 4g. A+! Cant wait to see what else this rig will do

 

[Travis Brown]

Thanks guys. I took it up Rattlesnake Canyon with a big group yesterday and she fit right in with all the jeeps and toyotas. I've still got some issues with the tires rubbing the trim when fully stuffed into the wheel well, but other than that, the rear axel is performing flawlessly. The front suspension on the other hand needs some work. I did a 3" spacer lift to match the rear and the the thing handles like a scared chicken on the freeway. Very twitchy. I'm still trying to figure out what's wrong

 

[dvdswan]

I did a 3" spacer lift to match the rear and the the thing handles like a scared chicken on the freeway. Very twitchy. I'm still trying to figure out what's wrong

Since doing the spacer, did that bring in the track width to the same as the rear track width? It might be worth installing 1" hub spacers to see if it changes the fronts attitude. Just a thought.

 

[Travis Brown]

Since doing the spacer, did that bring in the track width to the same as the rear track width? It might be worth installing 1" hub spacers to see if it changes the fronts attitude. Just a thought.

After doing a bunch of online research, I think the problem is probably the very wide tires (285/75/17), and the reduced caster from the 3" lift. I'm going to try to give it a bit more caster and see if that calms things down.

 

[Turdle]

This answers all of the questions on the forum . Nothing else needed.

Yes. It'll fit.

Nice job sir.

 

[dvdswan]

After doing a bunch of online research, I think the problem is probably the very wide tires (285/75/17), and the reduced caster from the 3" lift. I'm going to try to give it a bit more caster and see if that calms things down.

I'm not sure it's caster since the knuckle does shift forwards or backwards when the suspension cycles and the UCA/LCA keep the knuckles in the correct position that way. Camber on the other hand, in/out movement from the frame is affected. (Giving the tires the lean in at the top).

Have you done a 4-wheel alignment? Since doing the 4 link have you measured the distance to the front wheels or known point on the frame to ensure the axle is square to the frame? This would affect your track causing a sideways dog track. This would not necessarily cause your twitch.

Is the track bar flat or at an angle? I know this matters with steering linkage being equal to the track bar but not sure about the rear. On my 3-link rear the track bar is flat and level with the axle.

When you feel the twitchiness, do you feel it in the steering or your butt? Have you ever felt the "Death wobble"? If so, how does this compare to that.

 

[Travis Brown]

I'm not sure it's caster since the knuckle does shift forwards or backwards when the suspension cycles

The shock tower is angled so the upper ball joint actually moves slightly forward as the UCA rotates downward. Normally it's negligible, but with a 3" lift, it's significant. I need to measure it, but I think it's something like a 1/4" or more (~1 deg)

Have you done a 4-wheel alignment?

I tried, but the tech said he couldn't get the caster in spec. The best he could do was 3.9 deg

Is the track bar flat or at an angle?

Yeah, I was pretty careful to get it flat in the design. Don't want any bump steer.

When you feel the twitchiness, do you feel it in the steering or your butt? Have you ever felt the "Death wobble"?

It's all in the steering wheel like the car is trying to drive itself every time i hit a bump or groove in the road. I think the right term for it is tramlining. I found another possible explanation online. The wheels I put on have zero offset, so the contact patch moved a couple inches outward compared to stock. Maybe the scrub radius is what's causing the problem.

 

[allmyEXes]

To gain more camber adjustment, as drastic a task, remove the UCA brackets out a 1/2" or so. That would involve disconnecting the UCA, Sawzall each of the two brackets, cleanly, prep them and the frame spots and mig weld them back on.

 

[dvdswan]

I tried, but the tech said he couldn't get the caster in spec. The best he could do was 3.9 deg

It's all in the steering wheel like the car is trying to drive itself every time i hit a bump or groove in the road. I think the right term for it is tramlining. I found another possible explanation online. The wheels I put on have zero offset, so the contact patch moved a couple inches outward compared to stock. Maybe the scrub radius is what's causing the problem.

I know on a solid front axle you want 6-8 deg. Anything less you will get the death wobble. Is there any room in the UCA/LCA slots to install washers to bring the UCA back or LCA forward? I don't think there is but...