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Power Drums in 1970 or only disc? |
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1970GroceryGetter
AMC Apprentice Joined: Apr/05/2021 Location: Detroit Status: Offline Points: 44 |
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Posted: Sep/22/2021 at 6:06pm |
Does anybody know if Power drum brakes were an option for 1970? Or only Disc? I’ve been trying to locate a power brake booster for my 70 Rebel wagon w 304/shift-command auto. I spoke to one guy but he said I will basically need a whole pedal and push-rod setup, because the pedals and push-rod are different on my manual drum brake car.
Does anyone else know this to be true? I’m in a wheelchair and drive with hand controls, and though I get by just fine, it would sure be nicer to drive with power brakes with those hand controls! I don’t mind, but my mom would like to drive it too and she flat refuses with the manual brakes. She drove it home for me after I got the carb rebuilt, but before I had the hand controls on it, and I couldn’t figure out why she was going like 30 in a 50 mph zone, and staying so far back behind me, it was the damn manual brakes! If they didn’t do power drums, she just might have to get used to it! Thanks in advance-Rudy
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Sonic Silver
Supporter of TheAMCForum Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7950 |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6884 |
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The difference between power drum brakes and manual disk brakes - disk brakes win every time. 15% to 30%+ more stopping force depending on system used in ideal conditions. Even more if wet or hot.
Personal opinion would be to upgrade to front disk brakes first, before entertaining the idea of power brakes. It would be like driving a different car! |
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
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In 1970 the parts book seems to say the Rebels with auto used the same pedal, manual or power. Not the case in 71 according to the same parts book.
Sometimes the pedal is different, sometimes it is the same. I took the power brakes off my 69 Rambler cause I hated how much the booster was in the way, and the pedal was the same. Trader, one thing to be cautions of is drum brakes are self energizing so they take less pedal effort as long as everything is in good shape. Manual disks typically take more effort, so in this case where he is looking for less effort manual discs might be a problem. |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6884 |
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Ken, are you talking effort or pedal travel?
Yes, disk brakes will take more travel of the brake pedal. But effort in lbs force will be much lower. A master cylinder change "may" be required, but AMC typically used the same master cylinder piston size for manual and power brakes. If the poster goes to a Wilwood or Scarbird AMC front disk brake manual system, pricy, but sized correctly. I know of half a dozen Wilwood setups with the factory master cylinder that are quite a braking performance upgrade. Mind you, they need at least a 16" rim. Even a donor Spirit or Concord disk setup is a great upgrade with the factory manual master cylinder in my experience. Don't see a downside. Even IF you have to raise the brake pedal with an adjustable rod because you have short legs - it's worth it. My Dad fixed a 2x4 to the brake pedal of the Ambassador so my 5'-2" Mom could stop the car without "reaching" for the pedal. The rest of us hated this, but got used to it, maybe just to keep Mom happy!
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ccowx
AMC Addicted Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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Actually trader, I don't agree with some aspects of what you say about drums. In fact drums can have more braking force than discs. They have more swept area typially and better mechanical advantage. Where they do not shine is in multiple applications or long steady applications and since today's drivers know nothing about they car they are in they don't pump brakes or anything like that. Drums big disadvantage is that they are lousy at dissipating heat. That is the reason why disks are more consistent than drums and are used basically universally in modern cars, but it is NOT because they have superior braking force.
Chris PS: This assumes all else being equal and I am not comparing non power drums to power disks for example.
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7544 |
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Drum brakes in poor condition suck, and practical and economic reasons might make it that a Scarebird upgrade is the best choice. But ccowx is right. Drum brakes are very effective, have built-in servo (positive feedback) action.
I'm a huge fan of drum brakes but they have two sets of problems. Drums don't "scale", 9" x 2.5's are fine for little cars (like my Americans) but 10" are getting heavy, and they all suck at dissipating heat as ccowx points out, when they get wet they're scary. Drums in good working order work fine within their limits. But the backing plates get wear grooves, the shoes don't sit square to the drums, the drums get belled and grooved with wear. Springs wear out, and after 50 years it all needs teardown and work. If your Rebel wagon has 10 x 2.5" drums, those will stop the car fine *in good order*. But I bet the drums are scarce and expensive. It might be cheaper and easier to install a Scarebird setup. I use those, but I hate feather-touch power brakes, all mine are manual. YMMV, etc. For small AMCs, like the little AMericans, 9 x 2.5 drums are great. I'm making a set now for my 60 American, which has stock 9 x 2's now, I slapped together to get on the road. I'm doing the drum-drilling trick that pretty much solves the heat dissipation and water problems. RockAuto doesn't list drums for a '70 Rebel with V8, so I assume those are the 10". Parts availability might make the decision for you. The Scarebird stuff will be all available parts. |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
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The self energizing stuff is the direction of friction load actually adds to the shoe braking force. The brakes have to be designed correctly, and the Bendix and other drum brake designers back in the day were very good. Been 40 years since that machine design class, but IIRC it is the location point compared to the friction plane. It's a little tricky to get right, and why drum brakes can get "grabby" sometimes when everything is not right.
It's why those who think freely sometimes use drum brakes in a drag car. The self energizing aspect means they grip better in some cases, like on a starting line at high stage rpm. And in good shape they work fine - once. A drag car only has to stop once and then has cool down time. As stated by others the big (and I mean big) advantage of discs is cooling. I have vivid memories of being in a pretty hopped up Chevy II with original tiny drums as a passenger with a somewhat crazy driver, and the car stopped fine the first time. It would not stop the second time, smoke pouring out of the wheel wells as we sailed through the intersection with other cars taking evasive action. Everyone survived, but I will not forget that experience! I've also been 125 mph on the drag strip in a 64 Classic that had been changed to the smaller and lighter 9" drums (the original brakes off my 69 Rambler) and it stopped excellent. On discs the caliper load is normal to the disc there can be no self energizing at all, so all the force must come from your foot or the booster. Why the cylinders are so much larger to get more piston load.
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Bruce Clarkson
AMC Addicted Joined: Feb/09/2013 Location: New Bern, NC Status: Offline Points: 538 |
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Just as a footnote, I was able to get the big front drums as used on my 67 and 68 Ambassador from Kennedy. I think they're the same size drums.
And just q quick usage report: I don't drive either car in a performance scenario and, given that, the well maintained drum brakes will do the job. One set is power. One set is manual. Both have many highway miles on them. Both have had been asked to lock all four wheels in an emergency and have done so. But one would be ill advised to try such tricks twice in a row without time to let things cool down first. If I was to be driving either of these in a performance manner, the drum brakes would have to go. None of the above is to say anything bad about the disk brakes. Good luck, Bruce Clarkson |
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Bruce Clarkson
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1970GroceryGetter
AMC Apprentice Joined: Apr/05/2021 Location: Detroit Status: Offline Points: 44 |
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Thank you for the feedback guys! The drum brakes are in excellent condition, and were gone through (leaky wheel cylinders replaced, properly adjusted, etc) when I got the car this spring. All things considered, I think it stops just fine. I had manual brakes (front disk rear drums) on mustang I built, it went 8.97@152 with me driving it to and from the track that day. It took some serious effort and a prayer to get her reeled in with those hand controls, and I most certainly had to take the second turn-off at the end of the track. It’s really no worse than no that!
Thank you very much guys! -Rudy
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