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Advance Adapters Rock Box install

Tech information furnished by Dave Safford



Took delivery of rock box #15 from Advance Adapters last week, and it is a nice piece of work indeed!

The box bolts between my LC 4 speed and (3-speed) transfer case, and fit and finish are really nice. AA's original plans called for the 4-speed's output shaft to be cut short, and I didn't inquire about this, so I was surprised to discover a new output shaft for my trans included in the kit.

Really surprised, because I've dis- and re-assembled every part on my 40 except the trans, and I don't have the extra-long puller required for the job. Plus, I'm a closet tranny chicken. There, I've said it! I've never, on any of several autos from street to road race to 4wd, rebuilt a transmission. I'm pretty sure I could accomplish the take-apart and put togther, but I have no faith that I could identify a substandard gear or synchro or sleeve bushing.

That was a long story to say that $200 later, I have a new output shaft in my 4speed.

The rock box install to the trans was easy, once I decided to give the input gear a rap with my brass hammer. Otherwise, I had about given up on installing the retainer clip, but tap - ching! it fell together.

The kit calls for locktite 518 sealer, and every parts store in Nashville seems to have swapped to Permatex' line exclusively. FYI, the permatex equivalent is "anaerobic sealer" and the part # starts with 518.

Once everything was together, I was pivoting the assembly on the bench and the output shaft and gears pulled right out! I finally figured out that the transfer case retains the bearing in place for this shaft. Knowing this, it made installation of the trans/box assembly easier: I removed the output shaft and gained about 10 inches of clearance.

Briggs came by to help me stab the trans, and it fell in on the first push! But he bumped the rock box shifter during bolt tightening, and a gear inside came loose, making the output shaft unfittable...relax, get a couple fingers inside the box and ooch the gear back in place, and the tailshaft went right in.

The rock box comes with a nice shifter that installs near the PTO shifter position. I also ordered the new AA twin-sick transfer shifter and their rear crossmember.

In the next installment, I'll install the transfer case and shifters, and have a report on whether my superslick custom 2.5-inch exhaust will fall victim to the crossmember! Stay tuned...

Dave Safford, TLCA #9855, STLCA Treasurer, '73 fj40 "Tin Lizard", Bunch-O-Mods


Should have included a few product info-type facts in my last post.

The gear reduction is 3.44:1. The price is $1295 for the version I bought, LC 4speed to LC transfer case. The twin stick shifter is $175 and the crossmember is $157.09.

It wouldn't be too tough to modify the stock shifter assembly, so the twin stick isn't a necessity. I don't think you would have to use the additional crossmember either, but since you do have to cut out the cruiser crossmember, the AA unit will lend a small amount of torsional resistance as well as support the weight of the extended assembly.

The rock box adds 5 inches to driveline length, so the driveshafts must be modified.

See the unit at: http://advanceadapters.com/index425.html

I ordered my unit last month, and took advantage of the introductory (read Guinea pig) pricing, so I saved a couple hundred clams over the current pricing. I called AA and gave them some feedback on the unit, and they sent me a hat, so does that make me "affiliated, yadda, yadda"?

I don't think so.

More info will follow this weekend's installation adventures.
This will be a short chapter. Having the rock box and tranny installed, I proceeded to hang the transfer. Even with my one inch body lift, there wasn't room, so I removed the rear rubber motor mounts and let the assembly rest metal-to-metal on the mounting tabs.

After several tries, I got the gear to slide onto the shaft, and the bolt-up was simple from there. Note: 37 inch MTR's and a four inch lift, plus body lift and shackles, make for a long way to lift a transfer case/ebrake assembly. I finally hooked up a come-along to the cage and winched the case into position!

Next, I installed the twin stick transfer shifter from AA. Piece of cake, everything fit beautifully with no bending, mutilating or stapling. Didn't even have to change the hole in the tunnel... actually, it was a bit too wide for the supplied shifter boot, and I had to scab in a small plate to fill the gap.

After cutting a slot in the tunnel to accommodate the rock box shifter (also nifty, no hassle), I discovered that the transfer case saver I have been running now interfered with the tunnel. Judicious framming with a brass hammer made a clever new bulge in the tunnel, and we buttoned her up.

I had been sweating the e-brake cable, thinking that the added five inches would require a work-around, but it went together with no problems. I hate hooking up the under-dash end, though ('73 style). I'd recommend pulling the drum and disconnecting from that end, much simpler.

Back in with the tank and seats, and next comes the cross member, drive shafts, and skid plate.

Bit the bullet and went to the best shop in town (Clinard's) for the drive shaft work. About $210 plus tax, all tolled.

The cross member will require trashing my new 2.5 inch exhaust system.

I was really pleased with the way the shop had run it really high next to the floor, but now it's going to have to bend around the xmember somehow.

We'll deal with that in Chapter three.

Dave Safford, TLCA #9855, STLCA Treasurer, '73 fj40 "Tin Lizard", Bunch-O-Mods


Well, the rock box is in, all is buttoned up, and here's how it went:

Got the drive shafts back from the shop, only $190 including tax. Length flange-to-flange was 34.5 for the front and 17 for the rear.

Installing the cross member was simple enough, and the brackets that weld to the frame landed right where the old cross member mounted, so I didn't have to use the scab plates provided.

AA sent a standard 4-speed tranny shift boot for the rock box shifter, but since I had installed the twin-stick transfer shifters, which came with a twin boot, I just used the old transfer boot for the rock box. Excellent fit!

The skid plate was now 5" too short, and the built-in drain holes and stamped segments didn't match up, so the guys in the shop at work came up with a solution. We cut out the center of the three-speed plate I had been using (heavier than a four-speed plate, but requires redrilling the mounting holes) and welded in a 3/16 plate, extended 5" rearward. then we bent and formed "ears" to match the contour of the stock plate and extend the sides 5".

Finally, a portion under the transfer drain and brake drum had to be removed, and a drop-down segment added to clear this area. A small relief was cut at the front to clear the drive shaft.

It was a bit complicated, but the new skid plate is truly heavy-duty.

How well does it work? Well, it's a little noisier than before, and there's a tad more slop in the drive line. Not too noticeable, because my lockrites already bonk and clunk a lot. But the crawl? Can you say sloow walk?

I'll give you a trail-test summary next week. Heading for Tellico this weekend for the STLCA annual meeting, and if the rain doesn't squelch us too badly, we'll find out if the rock box rocks on the rocks!

Dave Safford, TLCA #9855, STLCA Treasurer, '73 fj40 "Tin Lizard", Bunch-O-Mods



Posted April 15, 2003




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