Another work post, for those so inclined to skip it.
BTW, I should also mention that most of what I've been doing to the car recently falls under the category of "routine maintenance" and not actual repairs. There's just a lot more to maintain on an old car than on a new car.
I wrote up the brake job a page or so back, but said I didn't want to tackle the rotors despite having them on hand.
For anyone who's done a brake job on a modern car, you know that changing the rotors isn't much more involved than just changing pads. Typically, you'll unbolt the entire caliper mounting bracket(which is normally two bolts separate from the ones you take out to just swap the pads) and move it out of the way. From the factory, a lot of cars will have a screw or two holding the rotors to the hub, but it's my understanding that their main function is to keep the rotors in place as the car moves through the assembly line. If something crazy happens like one strips out or is stuck, I've never stressed over replacing it if I had to drill it out. In any case, though, if those screws are present and removed, the rotor just pulls right off the wheel studs. In operation, it's held in place by being "sandwiched" between the hub and wheels and consequently just held on the studs by the lug nuts.
The MG uses an arrangement that I understand is common to older disk brake systems of any origin. Basically, rather than resting in front of the hub, the rotor is bolted to the back of it, and consequently replacing the rotor requires removing the hub.
This actually isn't a huge deal. If you've only dealt with newer cars, you've probably never serviced hubs, but maybe replaced them they wore really badly. On modern cars(and by modern I'm stretching back to probably the 80s on some designs-what was left mostly went away in the 90s), they're a sealed unit that is just replaced in its entirety if it ever wears out. In reality, unless something crazy happens to physically damage it, a sealed hub will easily make 400K+ miles.
There again, this isn't a setup unique to MGs, but is something that was used on American cars and I'm sure others from probably the 50s going forward. Basically, the entire hub assembly fits onto something called a "stub axle" that, in operation, is held under tension. Riding on the stub axle are a pair of tapered roller bearing races along with spacers and the like to keep everything where it should be. The hubs, in turn, have the outer bearing races pressed into them, so the hub turns on the bearings. The entire assembly is grease packed, so it's a good idea to occasionally break it down, clean out the old grease, and repack it with fresh grease. Replacing the rotors is a good time to do that since you're taking it apart anyway.
So, here's how all of this works:
Once the caliper is removed(in this photo I have it zip tied to the top of the suspension A-arm), the dust cap in the center of the hub needs to be removed also. This exposes a castle nut, also called a castellated nut, that is helded from turning by a cotter pin that fits in the grooves of the "castle" and through a hole in the stub axle. Notice also that there's a lot of grease in there.
After removing the cotter pin, the castle nut is unscrewed, and the hub pulled off. I didn't photograph everything, but basically you get these parts off
Not shown here are the bearing races, as I handled those separately. There are two, an inner and outer. Also, somehow or another, I missed photographing the spacer.
That leaves behind the stub axle. Normally the brake backing plate is here also, but I removed it to clean it up and paint it.
I'm showing it here with a grease gun attached to one of the Zerks(grease nipples) on the kingpins. The kingpins are the swiveling part of the steering knuckle, and need to be greased periodically. This is done by connecting a grease gun to each of the Zerks in turn and forcing grease in. As fresh grease is forced in, old grease will be seen oozing out of any joint it can find. When fresh, clean grease starts oozing out, you know you've added enough. There are 3 Zerks on this car's kingpin, and I opted to do them here since they're easy to access and see. I had a bit of a diversion in that when pumping grease into the center Zerk, I got a nice steady stream out of the bottom one. Fortunately, these are a generic part, and $3 bought a half dozen of the correct replacements from NAPA.
I spent a while working on intermediate steps that I didn't photograph, but basically I decided to wirebrush, de-rust, and paint both the backing plate and the hub. That took a while, but I'm happy with the results even with my messy rattle can paint job. I'm more going for rust prevention than anything.
The bearings need a bit of extra attention. First of all, I'd bought replacement outers at Autozone since they were $7 each. On advice, though, I opted instead to clean and reuse the original Timken "Made in England" bearings.
Timken invented this type of bearing, and these stay well enough greased that they're unlikely to go bad. Modern bearings, even those marked Timken, are of unknown origin and quality.
I cleaned these by soaking in kerosene and then blowing out with compressed air. Once clean and dry, they can be packed with grease. They can actually be packed by hand rather easily(you put grease in your palm and force it into the bearing), but why do that when there's a tool for it?
These are not very expensive, and basically hold the bearing while you use a grease gun to inject grease around the bottom of the race and through the top, the same way it would be done by hand.
Finally, I bolted the new rotor to the hub.
I opted for fresh hardware, which was another adventure. The bolts holding the rotor to the hub are 5/16 UNF(5/16-24). I went to the hardware store, and in general the only fine bolts they have are grade 8. Grade 8 fasteners are overkill, but at the same time I'm okay with using a fastener that's stronger than needed. I needed 1 1/4" long bolts, but the ones they had didn't have shoulder. The 1 1/2" ones did, but they only had 7 in stock(I need 8, 4 per side). I debated a bit and gambled on 1 3/4" not being too long, and fortunately I was correct.
As the repair manuals say, assembly is the reverse of disassembly
The most difficult part was getting the hub seal seated correctly, but fortunately it didn't take too much persuasion.
From there comes reinstalling the castle nut. On a typical American front suspension, the procedure for installing this is to tighten the nut until the hub locks, the back off until the cotter pin lines up. The workshop manual for the MGB specifies a bit of a different procedure-the nut should be torqued to 60 ft-lbs and checked for free rotation and also endplay. It should "tunk" slightly when pulled on. If it doesn't under this amount of torque, the shims between the bearings are adjusted. Too much freeplay requires removing shims, while too little requires adding them. Fortunately, mine was dead-on at 60 ft-lbs.
