Axle Swap du Jour: Putting Early Bronco Axles Into a YJ


Good question.  Who in their right mind would take a perfectly functional 9-year-old Jeep YJ, rip out the entire undercarriage, and replace it with parts from a 25-year old Ford?  Chances are if you're reading this then you understand already, but for those of you who don't... Still not convinced?  They say a picture is worth a thousand words:
Before: Here's what it looked like before...
After: ...and here's what it looks like now...and again...and again...and again

Well, okay, but why not just go to Currie or somewhere and have some custom axles made?

Two reasons.  First, I'm a cheap bastard.  If there's an alternative to shelling out $1500-$3000 US for EACH axle from a shop like Currie or Rubicon Express, then you can be damn sure I'll take it.  Compare what I paid to buy and rebuild my axles to a quote for an identical set of axles from RE:
My Cost
Quotes from Rubicon Express
Front D44, disc brakes, limited slip
$1662 CDN
$4770 CDN ($3100 US)
Rear 9", drums, LockRite
$1800 CDN
$2615 CDN ($1700 US)

Second, that way is boring (in my opinion, anyway).  I actually enjoyed the measuring, guesstimating, shopping, and assembling that the swap required.  May not be your cup of tea, but I found it to be a great experience, and I learned a lot about the drivetrain, gearing, and braking systems in my Jeep along the way.  Also, the do-it-yourself approach gave me an intimate knowledge of every part involved, so I reckon I'm in much better shape when it comes time to fix or replace something than if I'd bought the axles complete.  There's a lot of satisfaction to be had knowing that you've done it yourself.  'Course if it breaks, there's no-one else to blame...

How did it start?

Before the swap, My Jeep was a relatively stock 1989 YJ.  It had 2.5" OME lift springs in it and 31" AT tires, and that was as far as I thought I wanted to go with lift.  Then Larry Soo (aka lars) got involved.  I remember one conversation:

Larry : "You should do a springover.  Hmm... springover with OME springs."
Me: "Uh, yeah, right.  Heh heh."

But the seed was planted.  I'd wanted to get a rear locker for a while, but didn't like the idea of throwing $$ at the stock D30 and D35 axles after hearing them bashed so often on the Jeep-L and Jeeptech lists.  Some time later, Larry told me about a friend of a friend who was selling a pair of axles from an old Bronco.  I went over to see them.  They looked TERRIBLE.  Covered in rust and some kind of green mildew, but the potential was there!  The rear end had the stock 28-spline axles, and the front had a standard-cut diff and drum brakes, but the width looked good and they had 4.10 gears in them.  The big concern at that point was that the front diff was 3-4" closer to center than the YJ D30, so I couldn't be sure if there would be a conflict with it and the oilpan.  Some ballpark measurements showed it would probably be OK, so after asking Larry to look at them I paid the man and carted them to my parents' garage the next weekend.  The guy I bought them from also gave me four ancient P.O.S. wheels with the 5x5.5 bolt pattern I was going to need, which I figured would do until I got some new wheels.

First it all came apart...

The axles sat in my parents' garage for a while, and I began my research.  At this stage, I became a real pest, bothering the likes of Larry, Rob Bryce, Rick Boiros, John Nutter, Mike Garner, and Chris Kutish with incessant questions about axle swaps, brakes, brackets, and driveshafts.  Once I had an idea of the parts I was going to need, I began pricing them out and ordering them.  I also began the tear-down of the axles.

Taking apart the old axles proved to be less difficult than I'd thought.  All the brake parts went straight into individual grocery bags after I'd made a sketch of how the rear drums went together (I planned to keep drums on the rear).  Pearl of wisdom #1: NEVER throw out anything during a project like this until at least a few months after it's all done.  Everything else came off, until the housings were bare.  Then I ground off all the brackets, which took 6-8 hours and at least eight 3" cutting wheels (used my dad's electric grinder).  The worst part of this job was the Bronco radius arm mounts on the front end.  These huge chunks of steel are welded onto the tubes and took a LOT of persuasion to remove, but it can be done with enough time and effort.  The best technique appeared to be to cut into them about 3/8" back from each weld (top and bottom).  Once one of the cuts is through, pound the ^#%[email protected] out of it until it comes off, then grind away the remaining material with a carbide bit.

Once everything was completely disassembled, I took all the metal parts I was going to re-use down to a local metal cleaning place and had them stripped.  Everything with a bearing race or machined surface in it got chemically stripped, and the rest (like the knuckles and rear end housing) got sandblasted.  Pearl of wisdom #2: NEVER have an axle housing sandblasted.  It took a long time to get all that bloody grit out of the axle tubes - it collected in there on the thin film of old gear oil that was still inside.  Anyway, aside from that the results were incredible!  Those parts looked absolutely brand new - it was almost scary.  The chemical stripping process removed all the grease and rust from the carriers, spindles, etc. without removing any uncorroded metal at all, which is important for those kinds of parts.

Rear end parts after tear-down.  Nice shade of green, eh?Proof that the radius-arm mounts CAN be removedFresh from the cleaners

...and then it all started to come together

Assembling all the parts I'd cleaned and bought was one of the best parts of the whole project.  Brought back memories of playing with Lego and Meccano when I was a kid. It went something like this:

Brackets: This is where the real design work was.  Brackets were needed to be able to mount these axles of mine into the YJ, and they all had to be custom made.  So I did some drawings, bought some steel, and went to work.  A band saw, drill press, belt sander, and my dad's trusty grinder were all the tools needed to make front and rear shock mounts and a front track bar bracket.  The steel was all .120" hot-rolled square tubing and plate.  Since this was all custom, I made the shock brackets such that the shocks would not hang down below the axle tubes.  This was a compromise between ground clearance and shock travel.  I chose clearance, knowing that I could raise the frame mounts if necessary later.  Rather than fabbing up spring perches, I bought two pairs of adjustable clamp-type perches from Lou Feger's Racing (p/n 20232-1) in the US.  This let me get my rear pinion angle and front caster fine-tuned AFTER the axles went into the Jeep.  Since these perches are made for a 3" diameter axle tube, I had to make some shims out of 0.120" 3" steel tubing for the front end, which has a tube diameter of 2.75".  Once the brackets were made, Larry very kindly helped out by welding them onto the axle housings for me.

Note the front shock bracket and track-bar bracketMore detail of the track-bar bracketRear shock bracket and driveshaft detailNo rock-grabbing brackets here!

Paint: Two cans of Hammerite from the local General Paint went onto everything I could find.  Hammerite is a brush-on primerless metal paint, and it was the perfect stuff for a job like this.  Pearl of wisdom #3: the insides of axle tubes can be painted using a piece of rag stapled to the end of a stick.

Rear end:  Grant Klavatalks, a local truck guru and mechanic, set up the gears in my 9" third member and installed the LockRight.  A that point I wasn't interested in fooling around with gear setup, and no-one else I knew could show me how it was done, so I had a professional do it.  He found that the ring gear was badly worn, so in went a new R&P (from Precision Gear), and out came another $300 Cdn from my wallet.  Ouch.  One other thing I learned around this point about the EB 9" is that the four studs at each end that hold the backing plate and axle shafts on are 1/2" diameter on most axles, but that some have 3/8" studs.  This matters when buying axle shafts, so be sure you know which you have.  Mine were the 1/2" ones, FWIW. Oh - Grant was kind enough to swap the carrier in my 9" with a four-pinion model that I'll need as and when I upgrade to 31-spline axles shafts.  Note: the holes in the stock carrier are too small to accept the larger diameter of 31-spline axle shafts.

Front end:  Grant also set up my front gears, installed new ball joints in the knuckles, and installed the knuckles onto the axle.  He also packed my front end wheel bearings (new Timken bearings, of course) with grease and replaced every seal in both axles, as well as in the front spindles and hubs.  The carrier & pinion bearings (front and rear) and front spindle bearings were also replaced.  When I picked up the axles after Grant had finished, he told me that the front end had a factory limited slip in it.  Never having seen one before, I hadn't even noticed.  This stroke of luck almost made up for the new gears the rear end needed...

Steering:  This part was interesting. In order to use my stock YJ steering box and drag link, it worked out best to use a YJ tie rod.  The Bronco tie rod I had was bent, and it's drag link connection was way too close to center to work properly anyway.  So I bought a YJ tie rod at the local wrecker and had it shortened 4" (at the adjuster) and re-threaded.  The tapered bolts at the tie rod ends were smaller than the tapered holes in the Bronco knuckles, so I had a machinist friend make two tapered bushings to fit in between.  By the way, those tapered holes are about 1" further away from the balljoints on the Bronco knuckle than on the YJ knuckle, so I've lost a little steering radius, but it's not enough that I really notice, and the knuckles didn't really have the space to drill new holes.  Besides, having the tie rod further away is probably necessary in order for it to clear the diff cover at full lock.

Front disc brakes: The front axle had drums on it when I bought it, and there was no way I was going to keep them, so a front disc brake swap was in order.  An excellent article at showed me how.  It was almost a bolt-on swap: spindles, caliper mounts, and calipers from a '76 Chevy Blazer plus hub/rotor assemblies from a '78 Ford F150 or Bronco and the original Bronco knuckles.  A real mix-n-match affair, but it worked like a hot damn, and gave me nice big 11" discs for stopping 35" tires.  The only "rework" required is to grind away some material on the calipers, but that was pretty easy.  This method proved a lot cheaper (for me) than swapping in parts from a '78-79 Bronco or F150 D44, which was the other option.  The hub/rotor assemblies and brake pads I bought new, and the calipers I bought rebuilt.  Everything else was bought at a wreckers and cleaned up, including the caliper mounting bolts and banjo bolts, which proved surprisingly difficult to find.  Pearl of wisdom #4: get really cruddy, rusted calipers at wrecking yards for next to nothing and use them as cores to buy rebuilt ones at Napa or wherever for cheap.

Chevy spindle on the left, Bronco on the right

Rear drum brakes: The rears went together real easy.  I used all new parts, including spring kits, adjuster kits, and wheel cylinders (and shoes, of course).  I bought two lengths of hard brake line and bent them to fit between the cylinders and the tee.  Again, keeping the old parts proved to be a good idea, as I needed the old shoes as cores to get the new ones.  The sketch of the mechanisms inside the drums was useful here, as were pictures from the service manuals that I photocopied at the local library.  Pearl of wisdom #5: libraries can be your friends.  I may go to rear discs later, but I like the idea of all the static friction that drums can provide when you're trying to get your engine restarted on a 45-degree slope.  These drums are 11" in diameter, thanks to the fact that I lucked out and ended up with the "big-bearing" style 3300-lb rated 9" rear.

New 11" drums vs. old YJ 10" drums

Front hubs and axle shafts: On went a pair of Warn Premium hubs (figured I might as well not worry about them).  These required some fiddling with, but first let me explain something about D44 axle shafts.  There are two types of D44 shafts, those with small u-joints and those with large ones.  I got one of each.  Why?  Because the stock shafts for the '73 have the small u-joints, but the short one (driver's side) can be directly replaced with a shaft from an F150, which has the large u-joint, and somebody had already done that with my front end before I bought it.  Cool!  Unfortunately there's no such easy upgrade for the long side shaft, so I'll just have to keep an eye on it.  One option is to cut down and respline an F150 passenger's-side shaft, but that's more $$.  Anyway, the disc brake swap instructions say that you're supposed to keep the hub body in place with a flat washer bolted to the end of the stub shaft instead of using the c-clip that comes with the hub (this is necessary because the Chevy spindle is slightly longer than the Bronco one).  So I did that with the passenger's side, but it turned out that the F150 shaft on the driver's side has a slightly longer stub shaft, so I was able to get the c-clip on there and avoid the washer thing.  The disc brake swap lets you keep the internal type locking hubs, which are said to be stronger than the external type used on CJs and Scouts.  Yet another bonus.

The short one is the big-joint F150 shaft - note the difference in diameters

And lo and behold, I was now the proud owner of two rather impressive-looking, completely rebuilt axles ready to swap into my patiently waiting YJ.

Front......and rear (note how close the lengths are)

The Swap

Ah, the swap.  This was the best part, what I'd waited for for so long (and spent so much bloody money preparing for).  I took three days off work plus a weekend, figuring that would be enough time.  Almost made it, too.  Did I mention that my YJ is my daily driver?  Thankfully I had my sister's Topaz for emergency shopping trips, etc.  The swap went something like this:


The plan was to do a spring-over using my OME springs at the same time as the axle swap, so the spring perches went on above the tubes.  What about the rear driveshaft, I hear you saying?  Well, the YJ's notoriously short rear driveshaft was obviously a problem (especially with the low pinion on the 9"), so I bought Larry's old Currie NP231 tailshaft shortening kit (he didn't need it after his D300 swap) and a front CV shaft from a '79 Bronco.  In order to mate the two parts together, I replaced the driveshaft's CV yoke with one from a 80-something Monte Carlo, which matched the hole pattern of the CV flange on the Currie kit.  The Bronco shaft uses the same u-joint as the YJ (1310), which also happened to fit the yokes on the axles.  Gotta love it when things work out.

New (to me) Bronco shaft w/ Currie kit vs old POS YJ shaft

I also bought a pair of rear YJ OME J1R springs I found at a wreckers (woohoo!) to replace my front ones, in anticipation of the weight of a winch to come later this year.  Oh, and I got some extended brake lines from Coast Industrial on Vancouver Island.  I mailed them the necessary used YJ, Bronco, and Chevy brake line fittings, and they sent me a set of three lines made to order, with my fittings brazed onto their generic ones.  They have a woven steel core coated in rubber, nice and strong.  Thanks to Rob Bryce for this referral!

Custom brake lines from Coast Industrial

U-bolts I had made at a local spring shop for cheap, and I found spring plates at wrecking yards just by walking around until I found some with the right hole pattern.  For the swaybar mounts on the front plates, I cut the heads off two 6" long 5/8" bolts and welded the stems (is that the right word?) onto the front spring plates.  No problemo.

The transfer case:

Off came the wheels.  Then the first problem became apparent.  Pearl of wisdom #6: NEVER work on a vehicle on a sloped surface if you have to take more than two wheels off.  My parent's driveway, where all this was happening, has a mild slope to it that made for some precarious Jeep balancing during the swap.  Creative applications of firewood and jackstands made it work, but it wasn't much fun.  Anyway, I removed the D35 in short order, and went to work on the transfer case shortening kit.  This took some time to install, but there were no problems worth mentioning.  The Currie kit comes with a larger rear output bearing, which was nice to see, and the mainshaft I put in was already shortened, drilled, and tapped.  No doubt that saved a lot of time.

Most of the effort installing this kit was spent cleaning the bits of the transfer case I had to re-use, and applying lots and lots of RTV while putting it back together.  Pearl of wisdom #7: it is possible to install a YJ t-case tailshaft kit without removing the case from the vehicle.  I did it by removing one piece at a time from the back end forward, which made it a tolerable one-person job with no wrestling of heavy transfer cases required.

The rear end:

Then the rear housing went in.  I left the shafts and third member out so I could move the thing by myself, so it was easy to position under the springs and bolt on.  In went the third member, axle shafts, and drums.  There was a small delay at this point as I discovered that the 31-spline axle shafts I had ordered were actually 28 splines, which required that I take the third member and a dozen beers over to Grant's place so he could replace the side gears with the stock 28-spline ones.  Anyway, once that was taken care of I connected the vent hose and attached the brake line.  Removing the stock rear brake line was something I had been really concerned about.  If the threaded connection between the hard line and the rubber line had seized, the last thing I wanted to do was have to replace the loooong hard line that runs along the frame rail.  At any rate, it came loose with the judicious application of some vise grips and Liquid Wrench.

I hooked up my old rear shocks because they fit (with an inch or so of extension left), and measured how long the new ones would need to be.  Now that the rear end was in, I was able to accurately measure how long it needed to be, and the place that did the job only took two or three hours, so it made for a good lunch break.  I found and bought a 4" drop pitman arm on the same trip.

The front end:

The front was quite a bit more work than the rear, which makes sense in retrospect.  Larry came by at this point to lend a hand for an afternoon/evening, and his timing was perfect.  It took both of us to wrestle the D30 out from its home on top of the front springs, only to realize that we were going to replace the front springs anyway, so we should have taken them off first.  There's a pearl of wisdom in there somewhere.  So on went the J1R springs, to which we bolted the new front end.  Then we installed the axle shafts, caliper plates, spindles, and hub/rotor assemblies.  The next morning, I installed the swaybar, front hubs, and front brake lines.  Then in went the drag link.  At this point it became apparent that yes, I was going to need that drop pitman arm, but that I could get by without it for a little while, which was fortunate because I soon found that no amount of persuasion was going to convince my stock pitman arm to separate from my steering box.  Another job for later.  The track bar wouldn't go in either, because it seemed as if I had had my axle bracket welded on an inch too far to the right.

Now that the front end was in, I was able to measure the extended length of the front shocks I'd need.  I was also able to determine that the front diff cleared the oilpan just fine, but that the front driveshaft and the exhaust downpipe from the manifold were uncomfortably close.  And also that my skidplate would need a notch cut out of it in order to connect my front driveshaft to my front diff.  The front driveshaft turned out to be about 1" too short (yes, short), thanks to the D44's longer snout.

Larry Soo lends a helping handNotch cut in skidplate for driveshaft clearanceNote the scuff marks - a new exhaust pipe is a mustThe track bar and drag link turned out close to parallel

The aftermath:

So...  a few months and a few thousand $$ after it all began, what did I have?  A YJ with a really beefy pair of axles, but no front shocks, no front track bar, no drop pitman arm, no parking brake, and no wheels.  Why no wheels?  Because it turned out that the P.O.S. ones I was given with the axles weren't a matched set - one of them was a 5x4.5" bolt pattern and so was of no use to me.  A quick flurry of phone calls turned up a set of 31x10.5 tires mounted on the right rims courtesy of Ed Mah.  So on they went, and away I went on my first test drive...

It was scary.  No, it was REALLY scary.  The thing had bump steer from hell, and bounced like you wouldn't believe!  But it got me to work the following week (slowly), and nothing broke.

A little later, Larry gave me a set of stock rear shocks from an F250 or F350 that fit perfectly for my rear end, and I bought some nice long Rancho RS5012s for the front (34" extended!).  I've also had the toe-in set at an alignment shop, which also installed my drop pitman arm for me.  The front track bar went in fine once I had the Jeep on the ground (duh), and I've also cut the notch in my skidplate and installed the stock front driveshaft temporarily.  And last but not least, the YJ is sporting 35" General Grabber MTs on cheap white spoke wheels (let's not get TOO carried away).  Looks pretty good if I say so myself, and man oh man does it flex!

Check out the trail & articulation photos at my Jeep page.

What else...  oh, I've got the parking brake working, using two long-side YJ cables (and upgrading to the much-improved 90's type parking brake adjuster at the same time), and I've put in some swaybar disconnects and a hand throttle, both from RE.

Plans for the future:

Still to come is a CV-type front driveshaft and a custom exhaust pipe from the manifold to the cat.  I've recently bought a front driveshaft from a 4-cylinder TJ (at a wreckers) which has the CV joint, but I need a transfer-case yoke from a TJ to make it work, since the YJ and TJ yokes aren't compatible.  The exhaust thing I'll do once I get around to it - it hasn't been an issue on the 'wheeling trips I've made since the swap, but it does need doing.

I'll also be extending the front brake lines even further using a set of RE's hard brake line extensions, since the brake lines seem to be what's limiting my front-end flex at the moment.  Oh, and I want to get the steering stabilizer back in, but that's proven difficult so far because the tie rod comes so close to the spring perches and diff cover when the steering is at full lock.  I'll likely end up fabbing up a bracket to connect the axle end to the track bar bracket or something, and use the original hole on the tie rod for the other end.

So how much did it all cost?

Take a look here for a complete cost breakdown of the whole project (to date).


I love it!  It's a big-ass Jeep, and it performs like I've always wanted it to.  I also learned a hell of a lot in the process.

I can safely say that EB axles make for a good swap candidate for YJ or TJ, but I'll add one caveat:  if you're going to do it, do a springover (YJ) or lift springs at the same time like I did.  Don't like the springover thing?  Then make some measurements and be REAL sure that there aren't any problems with the front diff and driveshaft touching anything.  Otherwise, this really is a good swap.  You can run the axles uncut, and with standard-offset wheels the width is perfect.  Plus you can keep your NP231 or NP207 transfer case, since the front diff's on the same side as the D30.  That's the major problem with the Scout axle swap, IMO, plus there's no fancy welding, knuckle-turning, diff-housing-grinding, or any other funky stuff required to make it work.  OTOH, the small u-joints in the front are a potential weakness, but the driver's-side shaft is easily upgraded, and the passenger's side shaft can be upgraded with a little work.  See Larry Soo's Scout axle swap page for his arguments.

Since I got the rear pinion angle set right, I have had NO driveline vibrations, which is a relief.  The rear shaft is running at about a 21-degree angle relative to the t-case output shaft, which is steep even for a CV, but it doesn't bind when the rear axle is articulating, and I haven't worn out any u-joints yet...

Axle wrap has surprisingly not been a huge problem.  It's there, and I do plan to fabricate and install a rear anti-wrap bar in the near future, but truth be told it's not as necessary as I thought it would be.  Spring sag has also been very minimal; the progressive-rate OME springs have held up really well, but I'm careful not to bounce too hard on them, to avoid taking them into negative arch.  Some extended bumpstops are in my plans for the near future as well, probably just some pieces of rectangular tubing bolted to the ends of my u-bolts on each spring plate.

The front D44 was (I think) set up with about 4-5 degrees of caster.  When I had the brackets welded on, I positioned them such that I'd have around 8 degrees, which seemed to be the conventional-wisdom figure for springovers.  That left the pinion pointing upwards about 4 degrees.  Not great, but I figured the caster was more important than the front pinion angle, and now that I'm planning to use a front CV shaft it may actually be about right, since you're supposed to have the pinion pointing at the t-case yoke for a CV shaft.  The Jeep handles fine on the freeway - no wander at all.  It ought to be even better when the steering stabilizer is back in.

4.10 gears with 35" tires and a carbuereted 258 engine leaves something to be desired in the power department.  It is better than the 3.07's with 31" tires, though.  It crawls pretty well, but it ain't great on the highway - I still almost never see fifth gear.  4.56's would probably be ideal, but were never a stock option for EBs.  Obviously, the only solution is an MPI conversion next year sometime <g>.

Bump steer is still noticeable, but putting the front track bar back in made a HUGE difference.  Definitely a must for this configuration.  The Jeep stops and starts in a straight line now.  I've used a 7/16" clevis pin to connect the track bar to the axle bracket for a quick disconnect (thanks to Dave Gray for that idea).  With the bump steer under control, the Jeep rides quite well - softer than stock, and the swaybar does a decent job of controlling body roll.   I do get nervous on sidehills with it disconnected, but I haven't rolled it (yet).

The stock YJ master cylinder appears to be up to the task of stopping the Chevy discs and Bronco drums, but it could use a little more oomph.  I may look at swapping in an F150 M/C later on, but for now I have no real complaints about the braking.

The only thing I might have done differently would be to use axles from a '78 or '79 Bronco, since then you'd get the front disc brakes and (so I hear) a reverse-cut D44 up front.  I'm not sure if the higher pinion on that front end would be a good thing or not - it might actually make the driveshaft conflict worse, so measure and measure again if you're thinking about it.  Also, it's MUCH easier to get 31-spline shafts for the '78-era 9" rear end.  I'm not sure what the cut-off year is, but in order for me to upgrade, I'll have to have custom shafts made by Dutchman or Moser or someplace like that.  Again, the fact that there's a difference may imply that the track width or diff position in the later rear ends is different, so break out the tape measure before committing yourself.

Pearl of wisdom #8: axle swaps are expensive.  Sure I saved a chunk of money doing it myself, but be aware that it isn't a cheap venture, and that it WILL cost you more than you think.  No amount of planning will entirely prevent Murphy's Law and lots of little hidden costs from creeping up and biting you when you least expect them.

Thank you...

I'd like to take a second and thanks the following people for their help, patience, and advice during this whole thing:
Larry Soo (aka lars, the Jeep God)
Rob Bryce
Ed Mah
Grant Klavatalks
Rick Boiros
John Nutter
Mike Garner
Chris Kutish

Questions?  E-mail me
Chris Waterman

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