Rear Brakes and Seals

Topics discussed herein -

Rob wrote - The castle nut is the only thing which holds the wheels on to the axle, and the high torque ensures there is NO freeplay in the brake drum/axle assembly so the brakes will work smoothly. It's possible for the axle splines to be damaged if the brake drum is allowed to move on the axle -- even fractionally.

With a fractionally loose brake drum, ALL the brake components would be "working" in a sideways direction when the drum moves fractionally in cornering. Having the axle nut tight ensures everything lines up as it should when the brakes are applied, and the load is in the DESIGNED direction when braking. A loose brake drum will also load the axle in a bending motion at the axle bearing (when cornering) than a tight drum, which will transfer some of the sideways load to the gearbox end of the axle. Since the axle is about 2 feet long, the leverage of that means the resultant load on the gearbox is quite light compared with the bending load on the outer bearing which is close to the brake drum. In other words -- a tight brake drum dissipates the cornering loads through leverage along the axle, instead of trying to bend the axle at the outer end.

If the car has been driven with loose axle nuts, the splines (teeth) on the drums might become damaged (anything which is allowed to move will wear -- that's why this nut needs 217 ft-lbs on it). When you get the drums off, have a good look at the splines in the drum and on the axle. The edges of the splines should be square shaped -- not rounded. I doubt you'd have a damaged axle -- that metal is STRONG, but the cast iron drum might show damage. More likely though is excessive wear on the inside of the drum where the brake lining rubs on it. If this is so, you'll feel a lip around the rubbing surface of the drum, just either side of the rubbing area of the brake linings. If this lip is tiny, and drums can be turned (machined to remove a thin layer of metal across the rubbing area and square things up again). If the drums have large wear lips, or deep scoring around the rubbing area, replacing them is a good idea anyway.

IN SUMMARY - The big castle nut on the outer end of the rear axle screws onto the splined shaft and holds the whole rear brake assembly together. If it's loose, the bearings wiggle around and the hub in the brake drum moves marginally on the shaft, causing wear. Thus the need for the castle nut to be very tight.

Someone wrote - The castle nut on the brake drum needs to be tightened 240 ft-lb of torque according to specs. I just put it on loosely, slipped the cotter pin through, and that was it.

Rob responded – The correct specification is 217 ft-lbs. I marked my nuts and axles before I took them off the very first time (about 26 years ago) so I could line up the marks when reinstalling the castle nut and thus not have to measure the torque.

The best alternative to a torque wrench is -- as you say -- get a 3/4 inch bar with 36mm socket (or 1-7/16" SAE or 7/8" Witworth (Brit standard) socket), and pull about 50 ft-lbs on it about 4 feet out from the hub. Then check the castellations and holes -- line it up with one or other hole by tightening a little more. It won't matter if its 200 or 230 ft-lbs -- so long as it's TIGHT and the pin will go through the axle. The holes in the axle are set so the torque is about right anyway.

Dave - I have a 36mm 3/4" drive socket (the size used for removing the rear brake drum) and a 3/4" swing handle and a 5-foot long piece of galvanized pipe to use as a "cheater." When "shopping" for your "cheater," make sure the inside diameter is just right for the swing handle to slide up into it.

Rob - If your cheater pipe is 18" long, you will have to exert 145 lbs on it to get 217 ft-lb on the castle nut. If it is 4-ft, you will only have to exert 54 lbs -- LOTS easier. And sometimes to "break" the nut loose you have to exert more. My "cheater" is a 5-ft pipe that I slip over the end of my 18" long 3/4" swing handle, fitted with a 1-7/16" socket. Never beat the bar with anything like a mallet --it will shock-load the axles and differential. But you can stand on the bar and gently jump up and down -- using your weight to get it to shift.

With the car on the ground and the hand brake HARD on you can get the nut off unless it's been on so long it's become stuck. Otherwise you might need someone in the car with their foot hard on the foot brake. If you have the wheel off, you need an "anti-torque" bar about 5 feet long bolted to two of the lug-bolt holes and resting on the ground so the drum can't rotate as you push down on the cheater bar (pipe over the handle). Just make sure the “anti-torque” bar is bolted to two studs adjacent to each other -- not the ones on opposite sides, or you won't be able to fit the socket on the castle nut. Obvious I know, but I've been known to do sillier things, and frustrate myself at having to start over.

Don't forget to mark the end of the nut and the axle before you start, so you can line it up again without having to measure 217 ft-lbs. Once you've got it loose the first time it will be easier the next time -- the brake shoes should be checked for wear and cleaned of brake dust about once a year, and this will be often enough so the nut doesn't freeze up.

Dave - If I position the socket on the castle nut so that the tightening force is directed downward, I shouldn't have any trouble with the car shifting off of the jack stands. With our aftermarket "custom" wheels equipped with spinners, the castle nut is not accessible with the wheels on the car. Do you think resting the brake drum on a block of wood will do it (the weight of the car holding it still), or is there a better way?

Rob - It might be enough -- especially with the hand brake applied firmly too. But of course it will be torquing the drum to run the car forward or backward, where using the anti-torque bar won't. I’m a little concerned that if the brake drum had turned unexpectedly it might pull the car off the block of wood, and with no wheel attached, it's a long way to the floor.

Dave later reported - I found that resting the brake drums on blocks of wood works nicely when removing or replacing the castle nut. Just make sure that the pressure on the "cheater" is always downward (i.e., towards the floor) when removing or replacing the castle nut.

Question regarding a loose castle nut - Should I be worried about possible damage to the bearings, and whether there is some way to tell (i.e., symptom) short of tearing everything apart?

Rob advised – You could try pull/pushing the brake drum and trying to feel for any play in the wheel bearing. Leaking from the bearing seal would be more likely too if the bearing is damaged and moving (worn). If the wheel bearing need replacing a special puller is needed to grab the outer race from between the balls -- from the inside, so to speak. Putting a new one in is easy though -- they are just a tight push fit (tap in with a block of wood and hammer). I have never had to do it on my car, despite all it's miles, probably because I replace the gearbox oil every few years so the bearings are running on clean oil (they get lubricated by gearbox oil on swing axle models). I don't know so much about the IRS models -- they have a greased bearing, and the fact that they don't have a fixed axle to spread the bearing load would mean even MORE reason to snug the axle nut up tight -- more load on the wheel bearing anyway.

Rob wrote - It's a good thing I looked at the brakes -- I found that the right rear axle seal has just started to leak, and I'll have to replace it before it leaks on to the brake linings. There is a drain tube built into the seal cover plate to prevent this, but the job has to be done soon.

The rear axle seal is on the end of the axle, outboard of the wheel bearing. Its function is to stop the gearbox oil (inside the axle tubes) from getting into the brake drums.

The seal is held in by a 'square' shaped plate with four bolts in the centre of the brake assembly. The seal (actually several pieces in a seal kit) is easily replaced, but the wheel bearing behind it is a bear -- you need a special puller which fits in between the rollers (it's a roller bearing) and grabs the outer rim of the bearing. Fortunately the wheel bearings rarely give out, but the seal does go bad occasionally.

The square retainer plate has a descending hole in the bottom of it so any oil leak is SUPPOSED to drain to the outside through the bottom part of the brake backing plate, but it gets clogged with brake dust over time, and the first you usually notice is oil streaks on the outside of the wheel, where the oil has leaked along the splines to the outside (after smearing the brake linings with oil first of course.)

So when you inspect the rear brakes next -- look at the splines, and the square cover plate around the axle. If they look wet and oily, replace the seal, and check the drain hole in the cover plate (you have to take it off anyway to see if the hole is blocked).