Will Rear Disc's Stop Better Than Rear Drums?? - Page 4 - Hot Rod Forum : Hotrodders Bulletin Board
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  #46 (permalink)  
Old 01-18-2006, 01:50 PM
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Hey Dan... guess which way my proportioning valve is turned. Bingo, all the way out. I was an industrial plumber before I retired and used to work with flow controls once in awhile. When those valves are turned all the way out your at full flow. I ASSUMED the prop valve was the same. Don't think I read the instructions either. I sure would be interested to see an internal flow diagram for one of these valves. Sometimes I have a hard time pictureing something until I see the print. I'll try cranking the valve all the way in and see what happens. Nice catch Dan, thanks.

Moon

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  #47 (permalink)  
Old 01-18-2006, 02:54 PM
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http://www.babcox.com/editorial/bf/bf50014.htm
Has a good explanation and decent, if hard to see, diagrams of the rear proportioning valve operation. The adjustable would be the same, except the screw increases or decreases the spring pressure.

I had a link to a better diagram somewhere. If I find it, I'll post again.
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  #48 (permalink)  
Old 01-19-2006, 06:40 AM
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Back to the topic...

The Question was " will discs stop better thabn Drums".In my experience.Yes!,I have a several old mercedes here,the newest car i drive is a 1974 280,with 4 wheel discs,Stopping is so easy in traffic you'd think it had ABS ,which was an option on the '78 and later big mercedes models.One of my other projects has vented rear rotors( a '69 300SEL 6.3) ,somethinmg you DO NOT get today,and does it stop?,does a fish swim?,
Mercedes started using 4 wheel discs in 1959 on the 300SE cars,after they got their *** kicked at Lemans by Jaguar,which had discs and mercedes still persisted with drums.
And why is this????
When you apply the brakes,you are creating heat energy...with drums they hold all heat in the drum,the heat doesn't dissipate very quickly and you get overheating and in the old days you lost your brakes.
Discs on the other hand are right out in the breeze,so the heat energy being generated by the braking action is being dissipated into the air and the more you apply the brakes ,the more energy is being absorbed and lost in the air...Better brakes.!!!!Thats why disc pads are so small,they don't need that big area that brake shoes require to lose that heat energy.
As for Drums being better in a damp climate,that sounds a bit strange to me,I spent years clearing mud out of Drum brakes on landrovers etc because once it's in there,it cannot escape,unlike the self cleaning action of the discs.

It's the 21 st century now,get with the program and STOP!
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  #49 (permalink)  
Old 01-27-2006, 06:11 PM
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I havent read all four pages but why bother, i'm sure they all say DO IT! after having a buick regal with 4WDB i just had to have them on my 55 truck and it stops on a dime, for a ton of bricks like it to stop that fast is absolutely amazing.

here is a link to a guy i just found out is near me, that is WAY LESS than anybody i've heard of: www.scarebird.com i plan on putting 4WDB on my Tempest before i drop the 455 into it. cheap cheap cheap! (i have not used any of these products... yet) but rear brackets for under a Buck is way better than paying $500 like i did for brackets and factory calipers. and btw! at the Truck dealer they have all these Firestone airbags and compressors out there, the counterman says if you want to do all the cutting on the control arms or wherever, and he says he has scores of kids coming in there to buy these things for their cars, (honda's i would assume) you can get a complete airbag suspension for half of what you would pay AirRide Technologies. the airbags should be online somewhere as they are made by firestone, and the truck dealer has all the hoses and fittings as well
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  #50 (permalink)  
Old 01-27-2006, 09:41 PM
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rear disc brakes

rear disc are hard to get to work right and they are expensive. got to be just right. take it from one who knows. disc/drum are the simplist and best.
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  #51 (permalink)  
Old 01-28-2006, 04:56 AM
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Quote:
Originally Posted by black1970
rear disc are hard to get to work right and they are expensive. got to be just right. take it from one who knows. disc/drum are the simplist and best.
I have to disagree,I may also venture an opinion here,you may think drums are simpler because they are already on the diffs you are using.
Have you seriously considered the benefits of NOT having to adjust brakes shoes all the time?
Or how about "brake FADE"?
If your brakes have self adjustors ,do they still work after 20 or so years?
What is simple about Ford or Bendix brake systems,?
Can you really say that Mopar rear drum brtakes are simple?
Can you change both sets of rear shoes in under 1/2 an hour ?
and honestly say you enjoy removing stuck drums full of deadly asbestos then have to fight with at least 4 springs ,retainers,leaky wheel cylinders,hard to find bonded or riveted linings,scored drums .....
How about rusted or seized ajustors or seized articulating pins?
You see discs don't have ANY of these problems because the bits aint there.
...But have you ever considered why Disc brakes were utilised on cars in the first place?.
It was to get better brakes with the utmost simplicity and effectiveness...if drums were so good they would still be used on PERFORMANCE cars..I admit that even Toyota use rear drums on the Cheapo hacks still.
And HEY! we're Building High Performance vehicles here!, It's not good enough to build Big power and then use 19th Century technology to try and stop the thing ,Is It?
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  #52 (permalink)  
Old 01-28-2006, 01:17 PM
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discs require high pressure

The reason disc brakes are an "advantage" is thay they are designed NOT TO LOCK, Drum brakes have a self-energizing movement against the anchor pin to wedge thenselves in the drum. In the 40's, 50's, and 60's most cars did not have power brakes, and the self-energizing feature was needed. The problem was that they would lock, especially on icy roads. TROUBLE. You may notice that air brake trucks still use drums because of their massive size for the absorption of heat. Disc brakes on a truck would melt in no time coming down a mountain. As you may have seen, drum brakes can lock up with a 1" diameter wheel cyl. but disc brakes use a 3" piston, and high pressure from a power assist. Manual disc brakes will not stop a car, unless you have a manual trans, and disconnect the engine from the brakes. With an auto trans, you have to pull down the engine with the brakes. G.M. dropped the option of manual discs in 1973, as more auto trans came in. Everyone seems to be entranced in the miracle of 4 wheel disc brakes, but in actuality, 4 discs use 4 large caliper pistons, on a slippery rotor. When you increase the volume of 4 wheel cyls. into 4 3" caliper pistons, the master cyl volume must be increased. When you increase the piston size of the master, the line pressure goes down. So, the booster power must be increased to push the larger piston. The factories left the rear drums on for a long time, A. because they worked well, B. the parking brake would hold. They can't get enough cable leverage against the caliper to lock the disc. Mnay hot rodders love the Versailles rear axle because of the 3 pinion bearings, and the factory discs. Guess what? Versailles came with a large master, and a HYDROBOOST. The hydroboost can deliver up to 2000psi with a large master, and NO VACUUM IS REQUIRED. On Feb 21st. Overhaulin' will have a segment on the hydroboost install on a 67 Hemi Charger. It had the Baer PBR calipers on it. The point is, if you are in love with 4 disc, remember what the factories have to do to make them work.
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  #53 (permalink)  
Old 01-28-2006, 01:56 PM
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.."The reason disc brakes are an "advantage" is they they are designed NOT TO LOCK, Drum brakes have a self-energizing movement against the anchor pin.""
EH? ,designed not to lock ...? I have lost you from this point.
Disc brakes ,as I said are far more efficient that any drum set up will ever be,I won't go on any more about this because far GREATER ENGINEERING MINDS THAN ME OR YOU ,FOR THAT MATTER, have realized that the thermal efficiency and simple design are a Not a Compromise ,as the self energising feature was ,and that efficiency and simplicity are the marks of good engineering.
SAFETY is the reason we should ALWAYS consider rear disc brakes and I will repeat what I said before,We are Building HIGH PERFORMCE CARS here,Not restoring grandmas '60 plymouth grocery getter with it's dangerous drum brakes and no power boost.
And Trucks ,today ,If you would care to ask ANY long hual trucker have had ABS for at least 10 years,Lock ups are caused by bad maintenance and air line failure.The mecedes (who also build /built Sterling,Western Star etc ) Vectros Truck has all wheel discs, as has the Volvo Globe trotter,both are the most efficient heavy trucks in USE right across the world today.
They will have drum brakes on the trailers but then there are three axles with ABS to stop them too!
Most cities in the World who have rail transport have Canadian Bombardier designed or built rail suburban carsl ,all have Disc brakes.....need I go on?
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  #54 (permalink)  
Old 01-28-2006, 06:46 PM
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thermal efficiency

Well, I'm not here to argue, but I have been in the brake business for 40 years. If you notice the black dust on the front wheels of every car, that is the binders (resins) that hold the friction material together. At a certain temperature, they evaporate. The dust blows out all over the wheel, and the environment. If you remember, drum brake cars had hub caps and non vented wheels. The Rally wheel was invented to circulate some air around the rotor. All of these new custom cutout wheels out are to "cool" the rotor. Actually, rotors suck in air from the inside of the rotor, and fling it out, centrifugally, hence, the dust on the wheels. Like a hair dryer, or turbo. The number one complaint with f250 and Suburban owners is "warped" rotors. Cast iron only warps when it is overheated. If you know what a proportioning valve does, it is there to reduce the drum brake pressure to under 600psi. or else they will lock. Lock up at 600psi...Disc brakes need 1600psi or more to lock up, depending on the tire and the weight. My point again, is that disc brakes require higher pressure to work, or you wouldn't need a proportioning valve at all. 1200 to 1400psi is hard to build up with your leg and hold it a stop light. as far as air brakes, I'm not sure how many you have replaced, but the early air discs were all taken off of Fire Trucks, and City busses. They would not hold. Going down a mountain with air disc brakes? It won't make it. It's already been tried. They work great on the front axle only, to prevent lock up on icy roads.

Last edited by Deuce; 01-29-2006 at 09:17 AM.
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  #55 (permalink)  
Old 01-28-2006, 11:58 PM
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Does powerbrakebob sound a little bit too enthusiastic about his company,
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  #56 (permalink)  
Old 01-29-2006, 09:20 AM
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OK..........now guys........no bashing .....
We can all agree to disagree.......


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  #57 (permalink)  
Old 02-17-2006, 08:42 AM
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Quote:
Originally Posted by Deuce
As a general rule YES......

That's why Ford and GM have went to 4 wheel disc brakes on most of the newer vehicles.

The lighter the vehicle....the less difference you will see between disc rears and drum rears. You will also need a different master cylinder for a 4 wheel disc brake setup.

It is generally accepted that the front brakes does 60 % of the braking and the rear does the rest ( 40 % ) .....on most vehicles.



Actually this comment isn't true. GM went to disc brakes on certain vehicles and is now switching back to disc/drum. Trucks and small cars are disc/drum. Only the midsize cars are left.
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  #58 (permalink)  
Old 02-17-2006, 12:08 PM
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Quote:
Originally Posted by 88montecarlols


Actually this comment isn't true. GM went to disc brakes on certain vehicles and is now switching back to disc/drum. Trucks and small cars are disc/drum. Only the midsize cars are left.
...but the reason they went back to drums was $$$ just like always. I bet if it wasn't a federal law some cars would still come with drums in the front. Drums are cheaper...not better. That has never been in question.
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  #59 (permalink)  
Old 02-17-2006, 12:12 PM
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Quote:
Originally Posted by Triaged
...but the reason they went back to drums was $$$ just like always. I bet if it wasn't a federal law some cars would still come with drums in the front. Drums are cheaper...not better. That has never been in question.

how do you figure drums are cheaper, disks seem so much easier..

Anyway, those knocking it probably aren't running it. I have converted 3 different vehicles to full disk and I hope to never run drums again!

Bleh!
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  #60 (permalink)  
Old 02-17-2006, 12:21 PM
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Quote:
Originally Posted by BrandonMiller
how do you figure drums are cheaper, disks seem so much easier..

Anyway, those knocking it probably aren't running it. I have converted 3 different vehicles to full disk and I hope to never run drums again!

Bleh!
The major cost difference is in calipers vs wheel cylinders.

There is also:
caliper mount (often cast steel) vs backing plate (stamped steel)
modern disc brakes use a drum for the e-brake

Rotor vs Drum is about the same money.
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