Replacing rear rotors on a +2 with U-joints

[thehackmechanic]

My recently-purchased '69 +2 badly needed rear rotors and pads, as both rotors were ancient, one was badly grooved, and the pads were nonexistent. The car has U-joint axles, possibly from Performance Unlimited. Obviously the factory manual refers to removing the Rotoflex couplings and has nothing about the procedure with U-joint shafts. I just kind of had at it and figured it out. I'm writing this in case it's helpful to someone else.

On these shafts, the ends have plates that adapt the four-bolt flanges of the U-joints to the three-bolt flanges of the differential and the back of the stub axles. I thought I'd try leaving the axles attached, but unbolting the outer adapter plates. Three bolts go through the holes in the stub axle flanges, capture the holes in the rotors, and thread through the adapter plates.

Unfortunately, the heads of the bolts face the outside of the car. You can reach them from underneath, but if you try to completely remove them, you find that a) there's not enough clearance to fully unthread them and pull them out, and b) even before you find that limit, you discover that if you unthread them too far, when you try to turn the rotor to access the next bolt, they hit the back of the hub housing, preventing it from turning.

Speaking of turning the rotor, the first thing I had to deal with is that my U-joints don't turn feely when the suspension is in full droop, so I put a ratchet strap from the top of the shock and spring perch to the rear corner of the lower control arm and cranked it up about 3/4 of an inch. That's the orange strap you're seeing in the pics.

The next thing was figuring out how to prevent the rotor from turning while I loosened the bolts. I had the car up on my mid-rise lift, and found that it was an easy matter to take a metal rod, clamp it in place over and under a pair of the little studs that secure the wheel, and let the rod come to rest on the lift's arm holding up the back of the car. In this photo, I'm using a C-clamp, but I found that I could use the much-quicker big clothespin-style clamp, and it secured the rod perfectly fine.

There is exactly one place where you can withdraw the bolts, and that's in the 12:00 position. Unfortunately, there's not enough clearance to loosen the bolts in that position. Not only can't you get a socket on it (and a wrench is difficult), you literally can't rotate the bolt because the bottom flat side gets trapped against the housing. All you can do at the 12:00 position is to carefully withdraw the bolts with the flat side down, once you have first loosened them from underneath.

The trick, at least for me, was to loosen the collar on the sliding splines of the half-axle, loosen the three bolts round-robin, and while doing so, push the adapter plate back toward the differential (sliding the half-axle on its splines) so the heads of the bolts didn't protrude far enough to prevent the rotor from turning. When all three bolts were free of the threads in the adapter plate, I rotated the rotor to position each bolt at 12:00 and withdraw it.

I then slid the outer half of the axle as far inward on its splines as it would go to give me space to withdraw the rotor. I had no guarantee that this would even work, as the manual said to undo the lower control arm, but I thought I'd give it a try. I was reminded of those Chinese rope-and-circle-and-rod puzzles where you swore there was no way to take them apart, then twisted them a certain way, apart they came, and you thought "wait, how did I just do that?" That was the case with both removing and installing the left rotor, but with the right one, I was more systematic about it. The recipe was to have one of the three arms of the flange on the stub axle pointed to the back of the car, so at 3:00 on the right side, and at 9:00 on the left side. This allowed just enough room to slide the rotor over that arm, which then freed up space on the forward-facing side to pass it over the other two arms.

Lastly, the rotor needed to be withdrawn from the close quarters of the rear suspension. With it in its tipped position, it was trivial to pass it between the lower control arm and the trunk floor and withdraw it from the back.

I should add that the removal of the calipers and the dust shields was the same as in the manual, except that I didn't need to disconnect the brake lines; I just hung the calipers from the lower control arms with zip ties.

I posted a shorter version of this on social media, and a friend of mine noted that if the bolts were replaced with Allen-head bolts, they could almost certainly be loosened and removed, then installed and tightened wholly from the 12:00 position. I wish I'd thought of that while things were apart. I'd do it if I ever need to pull things apart again.

As I said, I hope this is helpful to anyone else with U-joint axles tackling rear rotor replacement.

--Rob Siegel

[alan.barker]

Hi Rob,
Interresting post.
Just a few things i can suggest if that's ok.
The Bolt going through the Brake Disk should not have a Washer under it's Head.
I prefer to put a Scissor Jack under the Chapman to lift or lower it(not use ratchet strap).
Cheers
Alan

[thehackmechanic]

<<The Bolt going through the Brake Disk should not have a Washer under its head.>>

Another DIY mechanic falls victim to "well, it was in there when I disassembled it, so it's going back in."

[The Veg]

Jeez Rob, that sounds like a real nightmare, at least the first time.