9in drum brakes

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Usually the caliper will prevent the hub and rotor from completely coming off the spindle. If you've ever tried to pull the hub and rotor off without removing the caliper, you'll know what I'm talking about. Some disc brake setups are better than others in preventing that. The disc brake spindles are usually bigger and have bigger bearings, so, they're less likely to have a complete bearing or spindle failure. I've seen many 9" drum brake outer wheel bearings fail. Hubs too. I've only seen one of those spindles shear off the threaded end, but, many that were on the verge of doing so. The most common problem is the outer race spinning in the hub. This can cause the bearing to overheat and fail which can also overheat the spindle. If it's a severe overheat the metal in the spindle will turn purple changing the temper of the metal. It can melt and bend at that point too.
 
The switch from 9 to 10 inch drums is so easy and then parts are easier to get. 10 inch drums have bigger spindles and bearings and I have never seen a failure with proper maintenance in 50 years. There are even whole performance brake rebuild kits for the 10 inch drum brakes which are a significant improvement. So many people here are switching to factory or aftermarket discs you can probably get the whole set up cheap in one piece!

Even if you decide to go to discs later there are aftermarket kits that use the 10 inch drum spindle.
 
Bewy said:
Some common sense please. How many people are breaking 9" spindles? AJ has. Anybody else?
Breaking 9" [ or any other size spindle ] is uncommon. It is not a design fault. There would be other reason: spindle bent, fractured from previous collision damage, loose wh brgs, lack of lube to wh brgs or misadjusted, etc.
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Bewy said:
str12,
You get the gold star. 100% correct. I am seeing some nonsense in this thread from people who are usually more switched on.
There is a reason heavy vehicles use DRUM brakes.....
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You missed it, I already posted the reasons why the drum brake spindles fail. Usually it's not the spindle, but the lower ball joint bolts that fail. The drum spindles used 1/2" bolts there. The KH disks used 9/16", and the later 73+ 10" drums and 73+ disk spindles used 5/8" bolts. The original drum spindle to lower ball joint bolts were undersized and corrected with later designs. The 9" spindles are also smaller in diameter and use a smaller outer bearing. The smaller outer bearing has less surface area, so, they're more likely to overheat and seize on the spindle, which hastens spindle failure as well. And yeah, if the spindle fails at the outer bearing the whole assembly goes away. The later spindles are thicker and use larger bearings so they're less likely to fail anyway, but if they did the rotor will still be captured by the caliper as already mentioned.

As for the "heavy vehicle" thing, there are more considerations than just braking performance. Semi tractors in the EU are mandated to have disk brakes. In the US most are still drums, BUT, that's because the drum brakes are cheaper to produce. The trucking industry lobbies the crap out of the government to keep the drums standard and not introduce a disk mandate (like was done for passenger vehicles in 1976!). And those are all air brake systems as well, which does change things a bit because the drums are a bit easier to set up to compensate for an air loss failure. And then there's the fact that most "heavy vehicles" are also limited to slower speeds.

Disks win every time when it comes to heat dissipation, remaining correctly adjusted at all times because it happens automatically and not with some clunky adjuster, and typically stopping distance but that is specific to the system if you assume the adjustment is correct at that given braking moment. Regardless, this isn't just an "disks vs drums" from a design or theory standpoint. This is the 9" mopar drums vs disk options for these cars, and 9" drums lose that all day long. Can you make a drum brake system that will outstop a particular disk brake system? Sure. But the 9" drums for these cars don't beat the disks available for these cars. Not even close. And that's what we're talking about.
 
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ultimatejay said:
I guess since you think drums are better than discs maybe you should call all the professional race car teams and tell them to throw their discs setups out the window and get some old drum brakes.
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I never typed it or said it. Not once. Stop bein stupid and stop trying to cause an argument.
 
ultimatejay said:
You called 72blunblu and "idiot" because he gave true data so who's trying to cause and argument??????
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No. That's not why I called him that. I agree with all he said. Except the idiot part.
 
ultimatejay said:
You called 72blunblu and "idiot" because he gave true data so who's trying to cause and argument??????
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You're the one who came back on here and picked the scab, not me.
 
72bluNblu said:
If you think 9" drums will stop an A-body as fast as a set of disks you're simply ignorant to reality. Let's look at the reality, with sources included. ...
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I'm guessing those writers don't have an engineering degree, nor even took Physics I. Comparing skinny bias-ply tires with modern tires is silly. Tires stop the car, not the brakes. I read an article comparing modern Winter tires with All-Season. The Winter tires stopped in HALF the difference on ice, which demonstrates "tires matter". Sticky tires like come on current sports cars (Mustang, etc) can stop from 60 mph in 95 ft. Current sedans stop in ~125 ft. Current pickups in ~150 ft. If your brakes can stop the tires rotating, and do it evenly, how could any other brakes do any better?
 
BillGrissom said:
I'm guessing those writers don't have an engineering degree, nor even took Physics I. Comparing skinny bias-ply tires with modern tires is silly. Tires stop the car, not the brakes. I read an article comparing modern Winter tires with All-Season. The Winter tires stopped in HALF the difference on ice, which demonstrates "tires matter". Sticky tires like come on current sports cars (Mustang, etc) can stop from 60 mph in 95 ft. Current s
edans stop in ~125 ft. Current pickups in ~150 ft. If your brakes can stop the tires rotating, and do it evenly, how could any other brakes do any better?
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NO, brakes stop the car tires aid in stopping the car. Softer tires will allow shorter brake distance and so forth, but brakes are the force that stops the car. c'mon man
 
I had 9" drums on my 1969 Dart (stolen in 1994). The worst problem with them, in my opinion, is the tiny wheel bearings on the 9" spindles. I recall they were Timken SET1 and SET3. The outer bearing on both sides spun the race to ruin the hub and a new hub is a junkyard treasure hunt. In contrast, my 1984 M-B 300D uses SET3 and SET5 wheel bearings, the same as a 1980's Chevy pickup, and even those have required replacing. Perhaps the biggest advantage of the 1973+ setup is that the rotor and hub is integral, so buying a new rotor gets you a new hub. Downside might come when you can no longer source new rotors. I have 9" drums on my 1964 Valiant. No issue since not driving it. If I ever change to disks, I'll probably first swap to 10" spindles and hubs before buying a Scarebird or Wilwood kit because I have 10" parts on-hand.
 
It takes both tires and brakes working together to determine stopping distance (that and the weight of the vehicle). Assuming you can lock up the brakes both front and rear, they're working good enough and then it's up to the tires to grip the pavement. The problem with drum brakes is that under certain conditions, you can't lock the brakes. You overheat a drum system, you will have fade, where there's no way to lock up the brakes. You get a drum system wet, you'll have the same problem until they dry out, plus you may have wet brakes cause the car to pull severely to one side making you let up on the brake pedal to keep the car straight. With those two issues alone, disc brakes make much more sense safety-wise.
 
BillGrissom said:
Confessing you never took a Physics course? Arguing about Physics with someone who has an M.S. in Mechanical Engineering.
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I don't care what degree you have, its common sense. Both brakes and tires stop the car but brakes are the main force that stops the car. We can go on and on just stop it with your " I'm smart degree crap".
 
BillGrissom said:
I'm guessing those writers don't have an engineering degree, nor even took Physics I. Comparing skinny bias-ply tires with modern tires is silly. Tires stop the car, not the brakes. I read an article comparing modern Winter tires with All-Season. The Winter tires stopped in HALF the difference on ice, which demonstrates "tires matter". Sticky tires like come on current sports cars (Mustang, etc) can stop from 60 mph in 95 ft. Current sedans stop in ~125 ft. Current pickups in ~150 ft. If your brakes can stop the tires rotating, and do it evenly, how could any other brakes do any better?
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The articles didn’t compare bias ply tires to radials. I listed both articles. The Mopar mag article compared the same tires on the same car and only swapped out the rear drums for rear disks. That was the only change. And that was still an 11 foot improvement in stopping distance even though that was a REAR disk swap.

BillGrissom said:
Confessing you never took a Physics course? Arguing about Physics with someone who has an M.S. in Mechanical Engineering.
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And my degree is in aerospace engineering. You show me ANY article, ANY data that shows a 9” or 10” Mopar drum brake set up outstopping a KH disk or 73+ disk set up on the same car line. You can’t, because they don’t.

I’ve said this before, and you should know better. A quick stab of the brakes will lock up a wheel with less stopping power than a slow, steady application. You know that rolling friction and sliding friction are not the same, and you should realize that a short impulse can impart a high enough force to lock the wheels. Skidding the wheels is not an accurate way to evaluate stopping power. It never has been, that’s the physics.


ultimatejay said:
NO, brakes stop the car tires aid in stopping the car. Softer tires will allow shorter brake distance and so forth, but brakes are the force that stops the car. c'mon man
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You guys are arguing semantics. The best brakes won’t perform for crap with lousy tires, and the best tires won’t perform for crap if the brakes behind them can’t keep up.

The disk set ups for these cars will stop the car significantly better with better tires. Even the drums that came on these cars benefit from better tires, although they run out of juice before the disks do.
 
Bewy said:
72,
For some reason most of my post [ #12 ] did not get printed. So I will try again.
For the same line pressure, a drum brake Chrys car will stop quicker than a disk brake car.
That is because C [ & many other brands ] use duo-servo [ DS ]drum brakes. This action links the two brake shoes & causes a wedging action of the shoe against the drum. In effect, the braking force gets multiplied with DS brakes & provides deadly stopping action. A highly efficient system.
In contrast, a disc brake is nothing more than a G clamp & has no multiplying effect. It also loses some clamping force because of it's open end which spreads open.

A disk brake requires faaaaaaaaaaar more line pressure than a DS drum brake to be effective. That is why proportioning valves are used with disc/drum brakes, to reduce pressure to the rear drums which would otherwise lock up from the high pressure the disks get.
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. Ill propose a few bits of information to this argument. To consider a cast iron caliper as an open ended C-clamp is a stretch. Iron don't bend, its too brittle. If a production caliper can pump itself apart, its trash and has no place on a car. Ill say the disc brake system has 8x multiplication built in. A 4 piston caliper has 4 (!) 1.63 bore pistons with a total piston area of 8.448 square inches. The MC bore is typically 1.125 (.992 in2) for a roughly 8:1 factor at the pedal. Disc brakes only need the very minimum of clearance so there is no wasted pedal travel and the pad backing plates dont deform under extreme load. 15/16 drum brake pistons (.694 in2 x2) is only >1.4in2 of piston area using the same pedal force. The multiplication factor is only ~1:1.4, then you have to factor in the brake shoe leverage and if the full brake shoe is contacting the drum....all in all the drum brakes will stop you but they suck when wet, suck when hot and generally suck over a disk option. My 4 9's on my 65 Barracuda were sub standard. the 10's on my "S" were much better but the 67 Disks I have now are even better. Disk brakes cool faster, offer less brake fade, are self cleaning, shed water faster, can shed their pad dust far easier than a semi closed drum, are always self adjusting, and are far easier to service. Only draw backs of front disks are more costly to build which is a non issue on today's classics. Rears require a seperate E brake drum.
 
Pishta,
A disk brake IS a G clamp. Very naieve to think that the open end of the clamp doesn't flex some, even if it is only 0.003-4", it becomes lost clamping force.
Obviously you can improve any braking system. With discs, use a bigger piston. Same with drums. The Bendix duo-servo drum brake is a very efficient braking system that creates a wedging action of the shoes, improving the braking action; something that disc brakes lack. Discs rely on more line pressure. This pressure discrepancy was why we got proportioning valves when discs first appeared on the front wheels. They need about 50% more line pressure to provide the same stopping power as drums, so the PV was added to reduce pressure to the rear drums & prevent lock up.
The Bendix system has been around for decades. My 1948 Olds had it.
 
ultimatejay said:
I don't care what degree you have, its common sense. Both brakes and tires stop the car but brakes are the main force that stops the car. We can go on and on just stop it with your " I'm smart degree crap".
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First you slap disagreed with him and said brakes stop the car. Now you say both. So which is it? Which would you rather have with drum brakes? Bald bias ply tires or good radials?
 
Surely how the driver applies the brakes matters. Perhaps 72bluNblu is arguing that one can apply more finesse with disk brakes than with drums to come closer to that "just before skid" point. Not sure what his "stab" refers to and sounds like a jiggy driver. I doubt a competent factory design would show fade (friction material melts) in drums when braking from 60 mph. The other issue is having all 4 brakes perfectly matched. Drums are touchier to slight friction changes, due to their self-amplifying effect (has to do with where the pivot point is and if fwd and rear shoes interact - "floating design"). In worst-case, gummy junk on drum shoes can make them self-lock. Perhaps trickier to insure L & R front drums are matched, but if all parts are clean and new they should. Caliper pistons can get sticky to vary L & R. Front to rear proportioning is also important, and varies when you mod the car's weight distribution. I wonder how close the factory gets it, and they likely err on the side of rears skidding quite a bit later than fronts, for safety.

Most newish cars have ABS. My 1996 Plymouth does and it was the absolute base model (4 cyl minivan, newspaper ad), though rock lists non-ABS driveshafts so maybe even cheaper ones. My guess is that in braking tests, they just jam the brake pedal and let ABS take over. That should give the very consistent data. Theoretically, a very competent driver might brake faster than ABS, but hard to know where that skid point is. How ABS "chatters" probably has a big effect. I suspect that because early Tesla Model 3 showed poor ~150 ft stopping in Consumer Reports test, akin to a pickup. They did an over-air software update and it dropped to a normal sedan ~125 ft. My guess is they boogered with ABS settings, since they had softened the suspension design a few months prior so perhaps hadn't re-optimized ABS settings. But, also might have had to do how regenerative braking is set. BTW, tests have shown minimal benefit from ABS as many drivers are scared by the chattering pedal, thinking something broke so let up on the brakes. Need to practice it in a snowy or wet parking lot so you aren't surprised in the real world. Just keep the brake pedal jammed down.
 
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ultimatejay said:
I don't care what degree you have, its common sense. Both brakes and tires stop the car but brakes are the main force that stops the car. We can go on and on just stop it with your " I'm smart degree crap".
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Degrees don't matter, but knowledge does. Not sure what "smart" means. I just know some things, mostly leveraged from hundreds of years of other's research, and much to still learn. Read thru Ch. 5 on friction in any Physics book (even high-school) and report back to us. The force which stops a car comes from the road and only the tires touch the road.
 
BillGrissom said:
Degrees don't matter, but knowledge does. Not sure what "smart" means. I just know some things, mostly leveraged from hundreds of years of other's research, and much to still learn. Read thru Ch. 5 on friction in any Physics book (even high-school) and report back to us. The force which stops a car comes from the road and only the tires touch the road.
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Some of the smartest/dumbest people I have met are engineers and nerds like you. Smart in some areas but when it comes to common sense and dealing with people they are the dumbest of dumb. You don't need to bring up petty physics in a brake forum. You really think you're smart but you're not, its actually gravity that stops the car. Gravity, drag and friction. Seems like you need to go read some more books
 
BillGrissom said:
Surely how the driver applies the brakes matters. Perhaps 72bluNblu is arguing that one can apply more finesse with disk brakes than with drums to come closer to that "just before skid" point. Not sure what his "stab" refers to and sounds like a jiggy driver. I doubt a competent factory design would show fade (friction material melts) in drums when braking from 60 mph. The other issue is having all 4 brakes perfectly matched. Drums are touchier to slight friction changes, due to their self-amplifying effect (has to do with where the pivot point is and if fwd and rear shoes interact - "floating design"). In worst-case, gummy junk on drum shoes can make them self-lock. Perhaps trickier to insure L & R front drums are matched, but if all parts are clean and new they should. Caliper pistons can get sticky to vary L & R. Front to rear proportioning is also important, and varies when you mod the car's weight distribution. I wonder how close the factory gets it, and they likely err on the side of rears skidding quite a bit later than fronts, for safety.

Most newish cars have ABS. My 1996 Plymouth does and it was the absolute base model (4 cyl minivan, newspaper ad), though rock lists non-ABS driveshafts so maybe even cheaper ones. My guess is that in braking tests, they just jam the brake pedal and let ABS take over. That should give the very consistent data. Theoretically, a very competent driver might brake faster than ABS, but hard to know where that skid point is. How ABS "chatters" probably has a big effect. I suspect that because early Tesla Model 3 showed poor ~150 ft stopping in Consumer Reports test, akin to a pickup. They did an over-air software update and it dropped to a normal sedan ~125 ft. My guess is they boogered with ABS settings, since they had softened the suspension design a few months prior so perhaps hadn't re-optimized ABS settings. But, also might have had to do how regenerative braking is set. BTW, tests have shown minimal benefit from ABS as many drivers are scared by the chattering pedal, thinking something broke so let up on the brakes. Need to practice it in a snowy or wet parking lot so you aren't surprised in the real world. Just keep the brake pedal jammed down.
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We had a super cool WWII generation gentleman who was a retired Mercedes Benz mechanic as our auto shop instructor in high school. One thing he kept repeating all three years we took that class was "braking is least effective during a slide" and he was right. During a skid, the best brakes in the world won't do you a dime's bit of good.
 
Also, I have not seen ONE person disagree that disc brakes are better than drums. Not one.
 
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