Packard Forum Index » Post-War (1946-54)

Very interesting.....Bolt on, stock brake pedal and Master Cyl and Packard wheels on my 51-200
also the same bolt on and my 53 with power brakes. I have seen dozens of questions and answers about the feasibility of front disc brake setups, there's usually talk of pedal geometry and stroke, bore size, relocating or changing size and placement of master cyls. etc..
Please don't let this subject die, I'm very interested and would like to hear from everyone that has a thought, pro/con and feasibility.
Now that there appears to be a straight add on disc brake setup, I'm wondering now, since this setup is available, do I really, really need to change?

If your issue is fade, then disc can help. If the issue is stopping distance, they may help you get closer to wheel lock-up without doing it but the relatively small tire patches for a heavy car will likely still be the limit.

Because this conversation conversation came up on FB I was looking at what Wilwood has. I'm not really a fan of modifying braking systems, and don't really think it's necessary on my Cavalier, but Wilwood has front disks brakes that bolt on, are designed to use the factory master cylinder, and will maintain front to rear brake bias. Not on my to do list, but it's interesting.
wilwood.com/BrakeKits/BrakeKitSearch?yea ... =Packard&model=Cavalier&option=2602+All&axle=Front+Kit

Stopping distance won't improve unless you also install radial tires.

Quote:

Amen. Physics do not change with discs.

It seems like some people get it in their mind that they need to change the brakes to make their car safe. Disk brakes & dual master cylinders seem to be the popular mods. I suppose the fade resistance of disk brakes would be an advantage if you were racing, lived in the mountains, or pull a trailer, but otherwise the factory drum brakes are plenty sufficient. IMHO

I suspect that the reason people experience brake failures/problems has nothing to do with the design of the system, and everything to do with the age of the system. Corroded steel lines, dry cracked hoses, or improperly adjusted brakes are probably some of the biggest culprits. A properly functioning hand brake is probably a good idea as well.

John, the above all give good advice. Make sure your brakes are "factory standard," in good shape. Good drum brakes will stop you as quickly as disc, but not repeatedly in the mountains or racing, which is why Jaguar beat Ferrari and Mercedes at Le Mans in the '50s.

If you want a Packard, or any such period car, have one. Don't reinvent the wheel. The only exception in my car is a bolt-in, no butchering, positive-ground 55-amp, 6-volt alternator, for brighter lights at low speed or stop lights at dusk or evening, faster battery recovery, and the Optima Red Top 800 cold cranking amp six-volt battery is vastly better than a traditional, leaky, off-gassing, heavy wet cell battery. Packard made neither generators nor batteries, so you're hardly altering the essence of the car, no more than using modern lubricants and oils, or radial tires. Because i'm at heart a sport car guy who fell for 1939-47 overdrive Packard 8s and Super-8s, seeing these machines as "road cars," luxe or not, am a believer in weight is the enemy. These two improvements reduce weight in nose heavy cars that plowed off the showroom floor.

Don't try to re-engineer a Packard. Pay attention to your linkages, all the details. Few do, which is another reason for all the modern cowboy crapola.

Again, Jeff Adkins, Moose Motors, Penngrove (Petaluma), CA in the North Bay, not only has all mechanical and electrical parts for 1935-56 Packards, but drum brakes parts for everything from Auburn through Zephyr, even supplies such to area NAPA and other retailers. Jeff has every quality new brake item for your car (707) 792-9985, packardguy54@sbcglobal.net Please tell him that Mike, 1947 Super Clipper, Walnut Creek referred you. I've known and dealt with Jeff for 40 years.

Another source is the equally knowledgeable Mike Grimes, at Merritt (317) 736-6233 ext. 103
mike@packardparts.com
www.packardparts.com
Mike is a gentleman. Please tell him i referred you. He and Jeff always get it right, know every nut and lock washer on your car.

Drum brakes will stop a car just as effectively as disc brakes -- often even more so. Why more so? Because the braking surface area of drum brakes is much higher and drum brakes are self-energizing, meaning the rotational force on the leading shoe applies pressure to the trailing shoe, providing a mechanical power braking increasing the braking force with less pedal pressure (and why the trailing shoe is bigger than the leading, to equalize the shoe to drum pressure). Disc brakes are not self-energizing and rely on booster systems (vacuum, electric) to increase pressure. Lose that booster system which often relies on the engine running and you've lost your ability to brake. The advantages of disc brakes is they tend to cool faster and more critically don't heat up the brake fluid as much because there's no hydraulic cylinder inside the drum but is instead external in the open air. Secondarily, they inherently self-adjust without the need of mechanical adjusters so generally require less maintenance between replacements (though do wear out faster requiring more frequent replacement).

So the bottom line is that drum brakes have some significant advantages over disc brakes but the one issue of greatest concern regarding drum brakes is that of the boiling point of the hydraulic fluid. Once liquid turns to vapor in a hydraulic system you've lost the incompressibility of that fluid, meaning the pedal goes to the floor with virtually no actual braking. DOT3/4 boils at 401F/450F when dry, but it does absorb moisture. Wet, you'll get boiling at 284F/311F. The very incompatible DOT5 does not absorb moisture and boils at 500F, but is prone to entraining air so is difficult to bleed and thereby tends to have a spongy feel. The newest, and compatible with DOT 3/4, DOT 5.1 does again absorb moisture but boils at 500F dry and 356F wet.

So you can see with the wide swing between dry/wet boiling points that the problem with drum brakes is mostly due to neglect, i.e., lack of proper maintenance. With all these facts, my general recommendation for an otherwise sound system is to flush the brake fluid out of the system with fresh DOT5.1 (or at least fresh DOT4). It's an inexpensive yet huge upgrade. For a daily driver whenever shoes are replaced (at a minimum) replace all the fluid -- more frequently the less the car is driven. With this one simple change the boiling point can go from 284F to 500F! With the danger of fade thus mitigated, with no sponginess, you get all the advantages of drum brakes and no huge expense of a disc brake conversion. Another useful upgrade is a larger fluid reservoir ideally with a bladder to isolate it from the air which will help a great deal with keeping that moisture out. I installed a remote reservoir on my '55. They were sold back then as an aftermarket accessory so are actually period correct.

Drum brakes need to be adjusted properly which requires some expertise, with the pivot pin centering the shoes and the adjusters taking up the slack. Adjusters require periodic readjustment until shoes are worn out and replaced unless self-adjusters are present (they adjust when braking in reverse). Disc brakes are for dummies, as the expression goes. There's not much to them other than to properly lubricate the pins they float on.

Keep in mind also that a conversion requires a lot of engineering expertise to get the front/rear braking forces balanced properly. Front discs paired with the original rear drums has challenging compromises to deal with and you may find stopping distances (and safety) actually worse than with the original brakes.

With the original drum brakes the braking force can be easily proportioned front to rear by varying the wheel cylinder piston size to a small degree (generally about an eighth of an inch), which is what exists originally. When you mix a disc front with an existing drum rear those ratios are way off as they can't control the existing rear and the front calipers are off the shelf for a range of vehicles. The typically applied solution is a proportioning valve to try to compensate for the mismatch. Those valves complicate bleeding and are another source of failure, and again are off the shelf items that often don't get the proportioning quite right between front and rear resulting in less effective braking.

Fun fact: You don't often see disc brakes on semi-tractor rigs, which have much higher braking requirements due to their loads, but they avoid the boiling hydraulic fluid issue by using compressed air. Otherwise they retain the advantages of drum brakes. (My prediction is that when the big rigs go electric with regenerative braking you'll then see them finally move to disc brakes and abandon the whole air compressor thing for simplicity and compactness.)