My 78 has original riveted brake rotors. Its been sitting in a barn for 30+ years so I'm replacing the entire system. The fronts were easy; I pulled the spindles, drilled on press and pressed out the rivets. Since the car only has 20k miles, I decided on the rear to drill out on the car. My question is...can I leave these rivet "stumps" in the axle hubs? In the front I first tried to knock them out with a hammer and punch, but needed to use the hydraulic press. I assume to extract them fully, I would need to pull the axles?


Can I leave rivet stumps?

 

You can finish drilling them out to remove them. You do not need to remove the axel to remove the rivets. I would remove them because they could become dislodged and create a problem with the parking brake system. I drilled and tapped mine and replaced them with 3/8"X24 Stainless steel bolts. The trick is to make sure the bolt head does not stick up above the rotor hat. The bottom line is that you do not need the rivets or bolts to hold the rotor in place. The wheel lugs will do that. Jerry

 

Be sure to measure the runout of the new rotors and shim as needed to get it down to under 0.002” or you will risk having brake problems down the road.

 

Are you using the old rotors?
If so, be sure to put them in the same position when they came off.

 

As long as the parking brake adjustment holes in the rotor and hub are aligned, and, you've kept the rotor on the side it came from, it'll all mate as it did when new. No special gyrations like marking a stud to the rotor are necessary to replicate the position.

 

I would at least grind the rivets flush so there is not a burr sticking out. If you drill through them with a small drill bit, like a.250" then you should be able to drive them out. I just did this yesterday during an arm rebuild.
Check the endplay in the bearings and the action of the parking brake while you have the rotor off.
The rotor only goes on in one correct position, yes you can install it in 5 different locations but the parking brake holes will be covered up. For years rebuilders would not dial in rotors and told people to index them to get the best runout, that is a hack way to do it. Do it right and it will perform better. I set mine up for runout under 003" the closer to 0 the better.

 

I'm replacing the entire brake system with the exception of the hard lines. The lines appear to have minimal corrosion, seem to be clear and was able to unthread without issue. The car sat in a barn in Michigan for many years (20-30?), so I was concerned with anything rubber or seals.

Why GM riveted rotors makes zero sense to me. The only technical reason I can think must have something to do with the non-floating calipers. The argument about assembly or runout just doesn't make sense given every other disc brake system I've experienced. I'm sure I'm wrong or missing something...worked at GM as an engineer and can tell you they are too cost conscience to add such complexity for no reason. That said, they did have a different mindset is 60's and 70's.

I have two more questions:
1) The new calipers didn't come with any of the copper crush washers. I assume I can just pick up new at the local auto parts?
2) what should I do with the original calipers and rotors? Do they have any value to anyone? There was no core exchange when my new parts.


LF original vs new

 

The fixed caliper design is exactly the reason they were riveted. The hub and rotor were machined as a unit so that excessive run-out wouldn't cause the brake pistons to pump on each rotation.

Only the front calipers use the copper washers and, yes, just pick a couple up from NAPA or the like. As for your originals, you could offer them on the classified forum. Perhaps contact Lone Star in Texas to see if they're interested.

 

Your old cores are Delco Moraine. It is hard to tell if your new ones are Delco. If you are a belt and suspenders type of person, consider tearing down your originals and cleaning them up and saving them. I would check to see if they have been sleeved in stainless steel. If so, all the more reason to keep them for a possible rebuild. Jerry

 

If it was me, Id toss the caliper and rotors in a storage tote. Calipers are rebuildable, good OEM rotors are not impossible to come by, but dont grow on trees either.

Id keep them, for awhile anyway.

 

Just a thought. Since you're doing all this work, I'd at least check the steel line between the 2 rear wheels - that goes across the width of the car. I found hidden corrosion under one of the line clamps when I completely replaced all of mine as part of a complete restoration of everything under the belt line of our '68. It looked perfectly fine. When I removed the clamp and un-threaded the two ends (with no issue), the line essentially broke apart - in the area that was under the clamp - as I removed it. It's not that bad to replace the lines. Best, Paul

 

Any idea why the rears don't have crush washers?

 

The rear has a proper flared hard line attaching to the caliper. The flexible line is upstream on the swingarm, but it also has flared interfaces at both ends.

 

Direct flared line to the rear calipers.

 

I would pop off the rubber piston gaskets. Take out the piston and see how much corrosion. If not much buy a 3 spring hone and some spare stones from NApa and hone it out using Acetone and clean up well with brake fluid spray. I restored my calipers and replaced with O ring kits. If you need help let me know
I think your calipers are 547???

Grant

 

Almost every other disc brake system uses floating calipers, so the rotors can have some runout. The caliper housing can oscillate a few thousandths as the rotor turns. And they have steel pistons with a seal in the caliper housing.

The C2/C3 fixed hard mounted caliper design is very sensitive to rotor runout. zero is best. or .001-.003. Any runout causes the pistons to pump in/out as the rotors turn. Note that you can not true the rotors on a bench because the hubs are not true to start with. The the piston design contributes to the problem. The lip seals will pump in a little air or water as the pistons oscillate. If it pumps air in, you will have a spongy brake pedal. The double seal design will trap water in between the seals. Then unlike almost every other caliper design, the seals are on the pistons themselves and the smooth bore is on the housing itself, and the bore is cast iron in this case. Corroded/pitted iron housing results, Then leaking calipers. Oscillating pistons just make it happen faster.

Various fixes include some or all the following: Stainless steel sleeved caliper bores, o-ring seals, zero runout rotors by shimming, or on-car rotror/hub truing as the factory did, machine shop trued hubs, aluminum calipers, or Wilwood calipers. The Wilwoods have aluminum construction and the seals are reversed and on the housing, and run against smooth steel pistons.

Solve enough of the corrosion issue and you will have reliable leak-free brakes. But IMO that requires getting rid of the iron bore surface. Even if it is mirror smooth, it will not stay that way forever, and may not last very long at all.

Your factory 20k mile rotors were probably just fine, thickness wise. And true. Most of these problems begin when factory rotors are removed. But in your case there are very few shops around anymore that can turn rotors on the car, to remove the rust that you had.