Plymouth72
New Member
Hey guys I was was wondering what you think of using 9in drum brakes on all four corners pro/con?
9in drum brakes
- Thread starter Plymouth72
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matthew robertson
Active Member
probably cost effective but speaking from experience, do disk up front. drums on all four corners may feel sloppy. plus its easier to do burnouts with front disks;)
They are good if don’t need to stop.
On what car with what engine, transmission and rear axle combination? 9" drums can stop GOOD in light cars like A bodies with slant 6 or stock 318 power. Beyond that, you may find yourself needing to plan stops with some extra room. I have 9" drums all around on my slant 6 64 2 door Valiant. Even though the engine is a pretty hot slant 6, it still stops very well. I rebuilt the brakes system from the ground up with all new hardware, shoes and rebuilt factory wheel cylinders. It stops VERY well given what it has. I also have a set of Kelsey Hayes front disc brakes waiting to be swapped on.
That's just so untrue you should be hearing thunder. It all depends on the vehicle.
The small bolt pattern, A-body only drum brake parts are not always easy to find, and are not always inexpensive either. I’m not sure what the current status is for availability but the drums and other parts have dropped out of production more than once in the past.
The 9” and 10” drum brake hubs are not reproduced at all, so you must remove the hubs from the drums to replace the drums. If you need hubs, you have to source good used originals.
The wheel bearings on the pre ‘73 drum hubs were small, so overheating and galling can occur is they’re not maintained really well. All the ‘73+ stuff used larger wheel bearings, including the ‘73+ drums. The earlier drum spindles also use 1/2” bolts to hold the lower ball joint on, so, the entire weight of the front of the car is suspended by 4, 1/2” bolts in shear. The KH disks used 9/16” bolts for that purpose, the later 73+ disk and drum spindles used 5/8” diameter bolts for the same job.
I had 10” drums on my ‘71 GT, I replaced them with disks. The disks are far superior. I wouldn’t use 9” drums on anything that was going to see more than infrequent street use.
The 9” and 10” drum brake hubs are not reproduced at all, so you must remove the hubs from the drums to replace the drums. If you need hubs, you have to source good used originals.
The wheel bearings on the pre ‘73 drum hubs were small, so overheating and galling can occur is they’re not maintained really well. All the ‘73+ stuff used larger wheel bearings, including the ‘73+ drums. The earlier drum spindles also use 1/2” bolts to hold the lower ball joint on, so, the entire weight of the front of the car is suspended by 4, 1/2” bolts in shear. The KH disks used 9/16” bolts for that purpose, the later 73+ disk and drum spindles used 5/8” diameter bolts for the same job.
I had 10” drums on my ‘71 GT, I replaced them with disks. The disks are far superior. I wouldn’t use 9” drums on anything that was going to see more than infrequent street use.
if a newer car with 4 wheel disc brakes not to mention anti lock brake setups panic stops in front of you, will you be able to stop with any 4 wheel drum setup?
there is your thunder and lightning as well.
and with my luck it would be a high dollar new BMW, Ferrari or Mercedes.
I can, because I'm not stupid enough to tailgate. How bout you?
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I'm not stupid enough to know **** DOES HAPPEN.
Absolutely it does. Even with disc brakes.
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.
Here's a road test on a '71 Demon. 10" power drum brakes, and bias ply tires. Well, they had an absolute best stop of 169 feet. That's as equipped for '71, and not even the piss poor 9" drums. 169 feet!!! 9" drums would be worse.
Vintage Road Test: 1971 Dodge Demon 340 – Road Test Magazine Takes A Real Devil For A Spin
Mopar Muscle did some testing on a rear disk conversion on a '73 Dart Sport (a heavier car than a '71 Demon, BTW, but otherwise the same chassis) and checked the stopping distances between the rear drums and rear disks from 60-0.
Their first result , testing just the factory '73+ disk brakes and 10x2.5" BBP rear drums was that from 60-0 the car took 133 feet, 6 inches to stop. Now, this is a radial tire equipped car as well, with bigger tires than a stock Demon, so some of that improvement is definitely tires. But that's already a 36 foot improvement over the lighter 10" drum equipped Demon.
Now, I've heard people here say many times you don't need rear disks at all, drums are fine, and have just as much stopping power. Well, after the rear disk conversion the stoping distance improved to 122 feet 4 inches. More than 11 feet better.
Rear Disc Brakes - All Bound Up - Mopar Muscle Magazine
So no, your drum brakes are not as good, they don't have as much braking power, and they will not stop you just as fast. Even just changing the REAR drums for disks, when the rear brakes only account for 20-30% of the braking, improves the stopping distance significantly. And yes, 11 feet is significant, especially if that's 11 feet into the car in front of you.
And for reference, a boring old 2021 Honda Civic can stop from 60-0 in 112 feet. Which means even if you're NOT tailgating and you're running 9" drums you're gonna clobber that car if it decides to lock 'em up in front of you.
https://www.carindigo.com/honda/civic/performance
But you don't tailgate. So let's see. At 60 mph your perception/reaction distance is 88 feet. That's the distance you travel before you process seeing those brake lights and actually step on the brakes (and no, you aren't faster than that Rob, I promise). Then, if you're rocking bias plys and drums, well, it's another 169 feet. So that's 257 feet before you stop. How far back do you follow? Cause from the moment you see that Civic lock 'em up they're stopped in 112 feet. You're going another 257. So do you ALWAYS follow at 145 feet back when you're doing 60? I bet you don't. Now, if you're running 15" radials and 4 wheel disks you're only gonna go 210 feet. So that's a 98 ft difference with that Honda. I bet we're all a lot more likely to be 100 ft back from that Civic. Certainly more often then we'll all be at least 145 feet back.
Leave the 9" drums in the last century where they belong.
Here's a road test on a '71 Demon. 10" power drum brakes, and bias ply tires. Well, they had an absolute best stop of 169 feet. That's as equipped for '71, and not even the piss poor 9" drums. 169 feet!!! 9" drums would be worse.
Vintage Road Test: 1971 Dodge Demon 340 – Road Test Magazine Takes A Real Devil For A Spin
Mopar Muscle did some testing on a rear disk conversion on a '73 Dart Sport (a heavier car than a '71 Demon, BTW, but otherwise the same chassis) and checked the stopping distances between the rear drums and rear disks from 60-0.
Their first result , testing just the factory '73+ disk brakes and 10x2.5" BBP rear drums was that from 60-0 the car took 133 feet, 6 inches to stop. Now, this is a radial tire equipped car as well, with bigger tires than a stock Demon, so some of that improvement is definitely tires. But that's already a 36 foot improvement over the lighter 10" drum equipped Demon.
Now, I've heard people here say many times you don't need rear disks at all, drums are fine, and have just as much stopping power. Well, after the rear disk conversion the stoping distance improved to 122 feet 4 inches. More than 11 feet better.
Rear Disc Brakes - All Bound Up - Mopar Muscle Magazine
So no, your drum brakes are not as good, they don't have as much braking power, and they will not stop you just as fast. Even just changing the REAR drums for disks, when the rear brakes only account for 20-30% of the braking, improves the stopping distance significantly. And yes, 11 feet is significant, especially if that's 11 feet into the car in front of you.
And for reference, a boring old 2021 Honda Civic can stop from 60-0 in 112 feet. Which means even if you're NOT tailgating and you're running 9" drums you're gonna clobber that car if it decides to lock 'em up in front of you.
https://www.carindigo.com/honda/civic/performance
But you don't tailgate. So let's see. At 60 mph your perception/reaction distance is 88 feet. That's the distance you travel before you process seeing those brake lights and actually step on the brakes (and no, you aren't faster than that Rob, I promise). Then, if you're rocking bias plys and drums, well, it's another 169 feet. So that's 257 feet before you stop. How far back do you follow? Cause from the moment you see that Civic lock 'em up they're stopped in 112 feet. You're going another 257. So do you ALWAYS follow at 145 feet back when you're doing 60? I bet you don't. Now, if you're running 15" radials and 4 wheel disks you're only gonna go 210 feet. So that's a 98 ft difference with that Honda. I bet we're all a lot more likely to be 100 ft back from that Civic. Certainly more often then we'll all be at least 145 feet back.
Leave the 9" drums in the last century where they belong.
Idiot.
all my originally 318 70 darts came with 10 inch drums all the way around. Never heard of an A-body with V8 and 9 inch drums - always thought they were a /6 only thing...
These days with the car in front of you sporting 4 wheel discs, you better be real conservative about how you drive in traffic, or upgrade the brakes. If the car in front of you locks 'em up you better be able to stop as fast as they can or have lots of room between you...
These days with the car in front of you sporting 4 wheel discs, you better be real conservative about how you drive in traffic, or upgrade the brakes. If the car in front of you locks 'em up you better be able to stop as fast as they can or have lots of room between you...
Ok Rob, let's see the actual stopping distances with sources that back up your name calling.
Or you can save your time, because you're not going to find anything, anywhere, that shows that a 9" drum will outstop the later disk brakes for these cars. Will they stop the car? Sure. They just take a lot longer to do it.
Whether you like it or not, those are the facts. Jump up and down, call me names, stomp your feet, whatever, not gonna make your car stop any faster.
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.
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.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Since 1969, I have had 9inchers on only three of my modest number of A-bodies, and
on two of them I broke a spindle off, just motoring around a corner; and one was an inside turn with some weight transferred to the other side. So that was just bazarre; watching my wheel in the oncoming lane, with cars going this way and that, dodging that MIA wheel, eventually doing the dance of death. Bam! down went my car, now skidding along on the backing plate.
And yes, one of those also spun a wheel bearing, wrecking the spindle.(or maybe there were two....... that was a long time ago)
I was cured; never again did I run 9inchers. Those spindles are barely strong enough to keep the car off the pavement........ IMO.
on two of them I broke a spindle off, just motoring around a corner; and one was an inside turn with some weight transferred to the other side. So that was just bazarre; watching my wheel in the oncoming lane, with cars going this way and that, dodging that MIA wheel, eventually doing the dance of death. Bam! down went my car, now skidding along on the backing plate.
And yes, one of those also spun a wheel bearing, wrecking the spindle.(or maybe there were two....... that was a long time ago)
I was cured; never again did I run 9inchers. Those spindles are barely strong enough to keep the car off the pavement........ IMO.
make mine disc brakes please, wishing safe motoring to all you's with drum brakes and God's good grace be with you. may Saint Christopher protect you.
cudamark
Well-Known Member
'64 A-body V8 cars came with 9" brakes.
cudamark
Well-Known Member
I have 9" drum brakes on my drag car. Mainly because that's what it came with when I bought it. The good is that it's a nice light setup and there's no problem with fade on just one stop at the end of the strip. They actually have pretty good swept area, but, no way I would use them on the street for a number of reasons, some already mentioned. The clamping action of disc brakes over the expanding shoes design is just far superior. Cooling to prevent fade is also far superior with disc brakes. As AJ mentioned, you lose an outer wheel bearing (those crappy set# 1's), break a spindle, or have the nut come off, and the tire/wheel/hub/drum is going to fly right off and probably pass you by. Disc brakes for the most part won't allow that to happen. As for the argument that 9" brakes will work just as good, is just not valid. If that were true, the B,C,E, etc bodies would be using them too. The same lame argument is sometimes made with the single system master cylinders. Sure, when they work, under normal conditions, there's no problem. They're just not the safe ticket when sh*t happens.
I agree with almost all of this but I am curious as to how a disc brake set up would do anything different than a drum system if you broke a spindle, seized a bearing or something, the whole assembly would come loose and head down the road with the addition of the whole caliper set up. I don't think the brake hose would hold it all in place !
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.
Breaking 9" [ or any other size spindle ] is uncommon. It is not a design fault. There would be other reason
Daves69
Well-Known Member
FWIW, it was a 383 4 spd car. BH29H9B
What came off it......
I still have this old MC laying around here somewhere.....
Sway bar was already gone when I traded my '71 Challenger Rt 340 4 spd for it and a '66 Satellite back in '80. The HD leafs are still on it.
Never broke a spindle but the Cragar 7/16" lugs had to be checked constantly.
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