I am only referring to the front i am leaving drums in the rear

 

-Do they need to be? I'm pretty sure the factory already did that for me. They evaluated the performance of drum vs. disc some sixty years ago, and determined, pretty much industry-wide, that discs were better than drums in virtually all situations. I can't imagine a situation, panic or otherwise, regardless of the car's weight bias, where a drum setup would be in any way superior to a disc/drum, let alone a disc-disc.

-So? That basically suggests I'd have been better off leaving the drums in place, and I find it odd that you'd even suggest such a thing. Again, there's a reason the factory- actually, ALL factories- switched to discs more than fifty years ago. And that you can buy dozens of different disc-conversion kits, but nobody sells a drum conversion kit.

I absolutely don't need to know the exact improvement in stopping power. I don't care if the modified car can stop 103.8 feet shorter or "only" 85.74 feet shorter. All of that is utterly irrelevant. What matters is simply that shopping distances ARE considerably shorter and fade is greatly reduced.

-There's a bunch we could argue about there, but generally speaking, that's correct. That's why rear discs use smaller pistons and pads- that reduces the grip of the caliper without having to muck about with limiting or proportioning valves.

And again, you're arguing against badly designed setups, but offering little help or recommendations towards good setups, giving the impression the user "shouldn't bother." Sure there's bad kits out there, but something set up by a name-brand shop, presumably like Behr or Wilwood, have a good chance of being much more properly designed and applied.

-Nothing about caliper volumes or pad sizes? Tht has more to do with rear braking than the P-valve.

-Again, your tone tends to strongly imply "don't bother". It's kind of like your tirades against frame reinforcing- X kit isn't, in your opinion, as good as the factory convertible boxing, so, as you end up implying, said kit isn't worth the cost and effort.

And that is, of course, horses**t, and always has been.

Is Brand X reinforcing kit as strong as a stock convertible frame? Who cares? Maybe it is and maybe it isn't, but wither way It's unquestionably stronger than the unreinforced frame. That's the important part.

Here, yes, one need to properly pick a proportioning valve. They also need to properly pick a master cylinder, properly size the calipers, properly size the pads, properly finish the rotor surfaces, pick quality fasteners, flare the tubes properly, ad infinitum, ad nauseum.

You'd be better off suggesting options and alternatives, or at least listing aspects that need to be carefully chosen, than just giving a blanket "if it's not utterly 100% perfect and fully factory tested, don't bother".

Doc.

 

I bet drum brakes are more expensive than disc brakes. That's the real reason drum brakes were abandoned.

 

Unless you're driving very hard-and-fast all the time going 0 to 90 repeated times which I don't think anybody is then drum brakes would work just fine Also drum brakes have more breaking surface than the disk conversions to stop a big car nobody's arguing that this aren't better but factory engineering like Joe said everything worked pretty well for the time and it still does

 

Lots of word soup to say the disc brakes need to be compatible to the car. I don't think anyone would dispute that.

 

-Certainly. My Toronado survived forty years and some 90K miles on the original drums and single-pot master.

But still, there is no question at all that the discs are better than the drums, and a dual master cylinder setup is considerably safer than a single.

-Easily done; use factory components. For almost all of this discussion, I've been referring to essentially stock-vs.-stock, assuming the OP was asking about installing '69 Cutlass discs to his "numbers matching" restoration. Rather than attempting to put 13" rotors and six-puck Corvette calipers on it.

Joe is exactly right that custom aftermarket setups like that need more careful consideration in designing the whole setup, but again, converting a factory drum setup to a factory disc setup is easy and straightforward- and similarly an indisputable improvement.

Doc.

 

Factory components are increasingly difficult to find which is why there exists a thriving aftermarket. Which brings us full circle to the question of adequate design and engineering for aftermarket disc conversion kits.

 

If you had two identical cars back in day in every way including price, except one is Drum the other Disc,
which would you choose?
That is your answer.

 

-Granted, though last I checked, I could still get rebuilt calipers and master cylinders, though I was forced to get Chinese rotors.

Doc.

 

Drum require occasional maintenance. They need to be cleaned and adjusted correctly to stop predictably.

Drum generally have more surface area, so potentially the can stop just as well as discs. If the brakes (regardless of type) can provide more stopping power that overcomes the tires grip to the road, then the tires become the limiting factor.

The biggest flaw with drums is brake fade. The drums don’t dissipate heat nearly as well, resulting in fade.

 

Thanks for clarifying that.

 

-This is a common misconception. The surface area works against braking power, not for it. It has to do with pressure applied per unit area, and applies to both sides of the pad.

In a caliper- assuming a GM midsize such as the OP was referring to- has a piston about what, 2-1/2" in diameter? The rear drum has a piston more like 1-1/4", which roughly equates to the caliper having four times the working surface for the brake fluid to push against. And that's standard hydraulic theory- a larger diameter piston can apply more force given the same fluid pressure, than a smaller one.

And generally, a proportioning valve doesn't limit or reduce the ultimate pressure of the brake fluid, at best they just limit the rate (speed, essentially) of pressure rise. Therefore front and rear pressures are generally about the same. (Point of note: That has to be the case, else a typical distribution block/proportioning valve would shift the inner spool, and activate the "BRAKE" light on the dash.)

So, given the same pressure (volume is a separate but related issue) the larger front caliper pistons can apply more force than the smaller rear drum cylinders.

Couple that with the pad swept area. The pads on a caliper aren't much larger than the area of the piston itself, while the pads on the drum are many times that of the area of the cylinder. Meaning the force applied by the caliper piston is, for want of a better phrase, more concentrated, while the force of the rear cylinder is spread over a wider area. Back in college, the example was a pair of snowshoes, or tank/bulldozer treads. In either case, the weight (force) of the object is spread over a larger area, reducing the contact pressure per unit of area.

There is, of course, far more to the whole system than that- people can and have written whole books on the subject. And often as not, even those books often leave many salient bits out.

But, the bottom line is no matter how well the drum is designed, it's almost never as good as even a mediocre disc setup. The old Studebaker Avanti came from the factory with Girling, I think, discs, same as Jaguar used back in the day. Today we see those as laughably primitive, worth little more than throwing far away. But the fact was, they were still [i]miles[i] better than the drums Studebaker used at the time. (Which were, point in fact, laughably primitive even when new. )

Doc.

 

You’re overlooking the self-energizing function of the drum brakes.

 

True, though i didn't have the time to write a whole book. I also left out the idea that the pads don't usually fully contact the drum- that is, they pivot at the bottom, and expand at the top, So there's minimal pressure at the bottoms of the pads, and maximum at the top- meaning that while the shoe has more area than the disc pad- as suggested above- not all of it is actually put to work.

The "self energizing aspect" is simply an assist- it was developed (or rather, discovered) prior to the advent of proper power assist for brakes, and long before the switchover to discs.

Doc.

 

The aftermarket kits are junk. Damn near all of them.

If you put factory disc parts on a car, and do it right, you may pick up some braking performance. Does it matter? I would posit that, with today's vehicles having much more stopping power, and much better crash protection, no, it really doesn't. The chances that you will be in a wreck where the disc brakes would have saved you and the drums did not, on a car on classic car duty, with classic car duty cycle, going to classic car places, driven by a guy who knows how to drive safely, are very, very low. The entire car is underperforming in safety, why don't you update springs, shocks, wheels, suspension components, tires? I mean, surely, good wide wheels and modern tires and better shocks and bushings and stuff would help. How about racing seats and safety belts? Roll cages?

As you can see, it gets dumb in a hurry. The disc brake upgrade adds as much stopping power as the OAI upgrade adds horsepower. Everyone still does it. I have one old car that can't have front discs. It's dangerous for a lot of reasons. So, I drive slower.

 

For me at least regarding DIY brake maintenance, I'd much rather service disc components than drum - not a fan of working on drum setups.

I will say though I recall being generally unimpressed with the A-body front disc brake kits I reviewed when I first got my ragtop in 2016 - supplied rotors, shoes, hardware all seeming to be crap with only the spindles themselves being worth a damn.

And I ultimately only used the spindles from the kit I did purchase, instead sourcing the other hard parts from individual higher quality brands.

 

-Define "junk". They don't fit right? They're not designed well? They don't stop as well as drums? They're the wrong color?

The Summit kit is junk? It appears to use factory components. Year One and RestoMod carry very similar kits. Can you specify how those are "junk"?

MasterPower Brakes has a 13" upgrade kit. I'd be very curious to know your opinion as to why that kit is "junk".

-Gonna stop you right there, if you'll pardon the pun. The "crash protection" you refer to essentially doesn't exist on anything prior to around 1973-'75. The OP's '69 is only a few years removed from cars having a solid rod straight from the steering box, and poised to spear you through the heart in a crash. That, point in fact, was one of the many things Ralph Nader had against the Corvair, among others.

If you're referring to modern safety systems, most of them, like airbags, energy-absorbing bumpers and crumple zones, are only there to help you, the occupant, survive the crash. The point of stronger, more reliable brakes is to prevent the crash in the first place.

In something like a '70-'72 Cutlass, there are no (intentional) crumple zones, the steering wheel isn't padded, there's no airbags, there's no side-impact protection, and the bumper is unyielding steel, bolted firmly to the frame. In a crash with any modern car, it's going to come out the loser, virtually every time.

-I think most of us here, who own enthusiast, if not collector, cars, very likely drive a little better and more defensively than most. Speaking personally, I'm not worried about ME, I'm worried about THEM. The other 900 cars on the road at the time. The guy with the tires so bald the cords are showing. The minivan with no license plate. The truck that's more rust than sheetmetal. The kid texting. The kid vaping THC oil. The drunks. The guy with the bald "space saver".

THOSE are the ones I worry about. Those are the ones you need to be prepared for.

-Hyperbole much? If you look, most of us already do that. Adding 3-point belts instead of just lap belts. Not driving on old, dry-rotted tires. Bumping up to wider tires. Installing coilover shocks.

Speaking personally, I completely rebuilt both the front and rear suspension on my car. Tubular upper A-arms, poly bushings, new shocks, new brakes, etc. I replaced the manual shoulder-strap belt with an aftermarket retractable. I replaced the broken bench seat with newer buckets with more support.

-Horsesh*t, pure and simple. Disc conversions- as I've said, I've done two, though I readily admit that hardly makes me an expert- are night-and-day difference. My Toronado suffered brake fade after ONE stop. Heck, Car & Driver, in 1965, rated then brand-new Toronado's brakes as "poor". Upgrading to '78 discs on mine was a huge improvement. I could drive it like a normal car, not like a barge needing a tug to moor.

Ditto the Cutlass.The drums it has when I first got the car worked fine- stopped nicely, pretty firm pedal. After rebuilding the rears and replacing the fronts, the difference was, as I said, night and day. It went from stopping reasonably well, to the proverbial stopping on a dime and giving nine cents change.

Yeah, my "butt dyno" may not be optimally calibrated, but it can still register a significant improvement.

Look, I'm not saying everyone needs to upgrade to four-wheel 13" discs and six-puck calipers with carbon-ceramic pads. What I am saying is that if you are contemplating swapping, then by all means, do it. The discs are better in virtually every way.

Doc.

 

Reading back over the thread, I'll say this: you certainly had me fooled.

 

As said, disc brakes are superior. I have seen drums on big trucks work but as said, massive and many of them. When the shoes freeze to the drum, you have never experienced joy. I was shocked to find 4 wheel drums on my 70 Cutlass. Crazy GM kept it as an option 56 years ago. Biggest thing with drum brakes is set up. I have seen my own vehicles, had a wheel cylinder blow on my Dakota due to not self adjusting. Of course Dodge couldn't get disc brakes right either, so many seized calipers on their 70's and early 80's vehicles. I had a Master cylinder fail, leaking past the rear seal. I should have done it with all 4 leaking wheel cylinders. I barely stopped in time on my 70, wasn't flying and almost no traffic. Replaced it, noticed the brakes still sucked, adjusted the drums, actually stops decently now, go figure. As said, these cars are mess compared to something like my Challenger GT handling wise and 4 wheel disc vs 4 wheel drum brakes. Honestly, I have considered this kit to keep my 14" wheels once the front shoes are toast.
https://www.summitracing.com/parts/rsd-afxdc14

 

That's what you got from my posts? Go back and read them again. Or not, since you've made up your mind and don't want to be bothered with facts. Good luck with your car.

 

-I am having good luck with my car, thank you!

Handles like a dream, stops on a dime. What more could I want?

Doc.

 

-I realize the internet has made us all prefer the clickbait headline and soundbite. "A whole paragraph?!? I'm not reading that novel!"

But while it's easy to just blurt "all those kits suck!" with some imagined air of authority, it takes time to explain that no, that's not the case.

Doc.

 

Well, they mostly do suck. You've had a couple engineers explain to you why. You're too emotionally invested in the argument to listen.

 

Did Olds actually put drum brakes on the 69 W-30 because the cam wouldn't draw the requisite vacuum needed to run power brakes be they drum or disc? I owned one of these cars in the 90s and this was a story I heard. True?

 

-Er, no, they haven't. I even asked specifically why, in fact, they suck. Is it that they have poorly-fitting brackets, or is the swept volume of the piston wrong for the application? No one's said. It's just "they all suck", period, full stop.

AND, perhaps more to the point, no one has suggested a kit that doesn't, in their opinion, suck. That leaves the reader with the strong implication that there are no good kits, and that's absolutely, categorically untrue.

Offer Options. If you don't know an option- none of us know everything- then at least try not to sh*t on those offering one.

Doc.

 

Excuse me, bud. You don't get to say I am trying to **** on you after saying horseshit to my comments.

Like I said, emotionally invested.

 

All right then, let me ask you this directly: What kit, in your opinion, is not "junk"?

I mean, there must be at least one, since there's about 148,000 people out there driving around in vintage cars with aftermarket disc conversions. They can't all be so badly designed the owner would have been better off with drums.

Do you have any valid advice to offer, a positive rather than just negatives?

And yes, I'll gladly admit I'm emotionally engaged in this discussion. You say that as if you're not.

Doc.

 

I'm not. You're championing the disc brake upgrade as some sort of crusade and it seems very important to you that everyone agrees with you. It doesn't matter to me if you don't agree with me.

I'm not offering any more advice here. You called both my and Joe's information horseshit. You need a serious attitude correction.

 

-So correct it. Show me where I'm wrong. Show me one of these mythical "junk" disc conversion kits! (And one that isn't sourced from Temu or Alibaba or eBay. )

More importantly, tell us WHY it's "junk".

You- and Joe- essentially stated that "all" of them are junk, so it ought to be easy for you to point to a kit on Jegs or Summit or YearOne, and point out exactly what makes them "junk" and why.

I'll wait.

Doc.

 

It's probably a combination of having a huge friction surface and the self-energizing of drum brakes. You likely need much larger disk brakes to provide equivalent braking in such a heavy vehicle.

 

I don't want to disrupt any chick fights, but I thought of one other thing that I've noticed different between my OEM power front disc/rr drum, and my OEM manual 4 wheel drum A body cars - the discs seem to rust quickly and it makes the car hard to roll around easily. If I didn't turn the wheels for a couple of years, I suspect they'd be locked up because of the rust on the brake rotors. My drum brake car rolls easily no matter how long it sits. This might not matter to the OP, but it is something that made me happier with my drum brake car in the long run.

The older brake rotors seemed to take longer before they rusted, but todays steel brake rotors seem to rust quickly.

 

How do you come to the conclusion that "most of us" have these things? Aside from dry-rotted tires, I suspect you are overstating things.

 

Wouldn't the aftermarket drum brake parts be just as "Chinese" as disc parts? I gotta think there aren't many folks using parts from 1970 these days.

 

-"Us", in this case, doesn't necessarily mean "just this one small group of Oldsmobile enthusiasts". We don't have a particularly huge contingent of old-car nuts in the area, but there's a pretty good group. I've been one of them since I was a teenager.

And almost everyone, with the exception of a few restoration purists, adds upgrades like 3-point belts, better rims and tires, suspension/handling modifications, and most importantly, brakes. There are a few, as evidenced here, with "show cars"- maybe not Ridler type stuff, but cars that they made mostly just for cruisin' and showing. Several of those guys kept the old drums, and a few even kept the old single MC. And that's fine.

But anyone that wants to actually drive drive their cars, virtually to a man will have a disc conversion if the car didn't originally come with them.

Yes, I could indeed be extrapolating from incomplete data, but it's worth noting that even the magazines- and I have an extensive collection- agree. 3-points, handling improvements and stopping upgrades are nearly as prevalent in the articles as carb tuning and head porting.

Doc.

 

-Clearly it does.

-So prove me wrong. Show me all the "junk" brake conversion kits out there. You and Joe both stated, rather unambiguously, they're essentially "all junk".

Please show us these junk kits, and not ones on Temu or Alibaba or eBay.

Let's see the kits that Summit or Jegs or Year One sell, and explain to us why, exactly, those kits are, in fact, junk.

Doc.

 

-How's the "rebuilt" market doing? That's a genuine question, by the way. When I did my conversions, I simply ordered new calipers and cylinders from the local NAPA. Pretty sure I got reman'ed pieces, and they looked and worked just fine. But the Toro was 20 years ago, and the Cutlass around 10, and I've heard the supply of rebuilt parts was having issues. Probably because all the wrecking/salvage yards are being crushed and turned into housing estates, and so the supply of cores is drying up.

Doc.

 

"And almost everyone, with the exception of a few restoration purists"
Again, you conclusion is not based on actual knowledge of cars out in the world, or at least not in my part of the world. One of the largest, longest running car shows in Phoenix is chock full of cars that do not fit your description

 

It matters to me that a low post count member is being rude on a forum I frequent. I don't care what you think of brakes personally.

Since you insist. My qualifications are a couple of engineering degrees and a career in automotive in the employ of a very large car company. Brakes are among the systems upon which I have worked professionally with design. The issue with most aftermarket kits is cheap steel, or not enough of it, along with poor reverse engineering. One I will speak of is Scarebird. Their kit is designed to mount on the drum's dust shield, which is a part never designed to take a caliper. However, if you were to use enough steel and of enough strength and the right hardness, along with replacing all the related parts in the system, you could probably replicate or exceed the factory systems. A person with a modicum of intellect could glean that, when I said "they mostly do suck" that I am not talking about $3000 or more Wilwood setups. I didn't need any engineering degree to tell you that, though. Most of the guys here understand metal and strength of materials pretty well. Joe touched on this, but a lot of people who are not technical will not work on the integration enough, and unbalance the system. Why is that the fault of the brake setup maker? Because they are only responsible for their product, and they leave the proper setup to the owner, who is often an overconfident idiot.

I wish to address a previous point where you blundered twice. Firstly, you mistook my listing of an increasingly ridiculous group of measures to take to bring these cars to modern safety standards as hyperbole, when, it reality it was an explanation of why adding disc brakes to a 60 year old car is not the panacea you claim. Secondly, you falsely claim to speak for everyone here when you said, twice, that people here add 3 point seatbelts, rims, and tires, suspension upgrades, and brakes. Very few do that. This website is classicoldsmobile.com. It is mostly for stock maintainers. Your need to modify and be combative is probably better suited to yellowbullet or ROP. So much of these old cars is a compromise already. Adding disc brakes is not a magic bullet to fix it all.

To conclude, please do what you like, but there is no need to farm validation here on swapping to discs. There are reasons to go either way. I hope that answers all your questions of me.

 

-Heh. I would counterargue that the majority of the cars in a show like that aren't driven much further than on and off a trailer.

I've already said if it's a show car or restoration, by all means keep the original brakes, be they disc, drum or a stick in the spokes. My point is and always has been cars that are actually driven regularly. You and the missus just cruise to the malt shop once a week? No sweat. Drive it daily? Yeah, you should probably think about upgrading.

Speaking personally- I do that a lot - our 'summer driving season' up here is about 37½ minutes long- I tend to want to drive mine as much as I can. I will readily admit not everyone does that, but for those that do- which includes the bulk of my local "car scene"- virtually everyone upgrades steering, suspension and brakes.

Doc.

 

Wrong again.