Drum vs Disc, Power vs non Power

[72Dodge]

Well, I'll tell you, I originally thought your way. Thought it would be cheaper, easier, and quicker to just retain and rebuild the front drums along with the back. Now that I know more, I wish I'd done a little more research upfront and just done the front conversion from the start. You will be money and safety ahead. Just do the Scarebird conversion and be done with it. The only good that came out of the way I did things to begin with is that now I know drum brakes like the back of my hand, but I'm not sure that's a good thing either!

 

[72Dodge]

Another note, you keep talking about price. First do the research on the Scarebird conversion, then check rockauto.com for prices on the calipers, rotors, hoses you need for it. You may be very surprised to find that it's not much more expensive than redoing your front drums. Maybe a little more, but not much. Don't make assumptions. You should be replacing it all either way, so the cost is pretty much a wash (other than the Scarebird brackets themselves) and you're better off down the road when you need to replace parts, because you'll likely have a much easier time finding them.

Also I think someone made the comment about wanting it to be all Mopar. What difference does it make, it's not like Chrysler made any of the parts you would be using either way. They're going to be Raybestos or Centric or whatever no matter what you do, it's just the application that differs. It's just as non-Mopar no matter which way you do it as far as the actual brake parts are concerned.

 

[Papaduster]

Ok after wanting to just reuild the 4 wheel drum brakes on my 71 Duster I read what other members are saying about converting to front Disc. Thanks for all the advice and turning me on to Rock Auto Parts. Although it'll cost me a little more to do a Scarebird Disc conversion it'll be better stopping and a much nicer project when completed Thanks to all who commented

 

[72Dodge]

Great! And no problem. I've found rockauto.com to be amazing. So quick, amazing prices, one of my fave sites hands down. Probably put in 10 orders with them total. You can get a lot of "wholesaler closeout" parts really cheap sometimes too.

 

[Mattax]

Maybe too late for you, but there is fundemental point in mechanics that ought to be addressed.

... Or even if an A Body car needs a power brake set up. On one thread one guy wanted to do power drums, He got a reply as its not needed due to the A Body cars weight. If thats so then Disc brakes arn't needed either.

It is not due to the weight. All the drum brakes on the a-bodies (and probably every production car of that era and newer) self assist. These are mechanical arrangements of the shoes to the drum known as servo or duo servo. All other things being equal, a drum brake car will require less force on the brake pedal to stop. This is why cars with front disks more frequently were (and are) equiped with power assist than cars with front drums.

This also leads to another point which is worth mentioning in relation to another question in the opening post.

As a good 4 wheel drum manual brake set up and new formula brake shoes are just fine, So why go to the added expense of swapping from SBP drums to LBP disc then and the added expense of new wheels if you already own SBP Rallys?

It is very important that the coefficient of friction is very consistant throughout the operating temperature range. If the friction goes down as the brakes get hotter, then the self assisting action becomes less. When this happens the driver has to harder and harder as the brakes work less well.

I don't know what new formulation people were mentioning, but a many brake linings sold aren't that good. On the lining's edge, or on the back of the shoe or pad is almost always stamped an 'Edge Code'. Within the ede code are two letters that very roughly represent friction. If the letters go down, this represents a lining that has less friction as it gets hotter. Do not use this for a drum if you can help it. Examples will FE or ED. You want EE, or better FF, GG, or HH.

So, yes you can have a very good drum brake system but it needs to be adjusted right, has decent linings, and it helps to have the shoes arced if the drums were ever cut. Because the reduced swept area of the smaller drums that came on some of the a-bodies makes it harder to keep them from getting too hot on repeated high speed stops, they're not a good starting point. Agreed that for the same swept area, a disk brake will be better in getting rid of heat. High speed stopping and weight are the main factors in generating heat.

 

[jerry6]

Looks like most guys are in favor of converting to Disc front brakes and so am I, its just Im on the tightest of tight budgets of all, so to get my Duster drivable and on the road I'll opt out for a $230 plus drum to drum brake rebuild, I'll keep my SBP Rallys and use BFG 215/70/14 front and 225/70/14 rear With the brake rebuild and tires plus a few cans of rattle can paint I'll hvave a decent looking daily drivable Duster and all for $800 plus Which is a lot less expensive than converting to Disc minus tires at over $1,500 plus. My main point is build what you have get your car on the road and save some money, not everything has to be high tech to drive Some things are just Old School and thats OK

You can get 15x7 and 15x6 SBP rallye wheels for about 100.00 each new . I picked up the wheels last year now running 225 60 15 up front and 245 60 15 out back , car stops and handles a touch better . I use the stock disk/drum factory 340 Swinger brakes with kevlar or ceramic pads . Car stops as well or better than my new cars . Car has new shocks poly bushings sway bar and is maintained on a monthly basis . It all adds up
If your just driving around town within speed limits , well maintained drums will be fine . Friend with a factory 440 six pac Challenger runs 4 wheel drums no problem . Also runs a stock hemi challenger in the low 10.2 range with stock disk drum setup .

 

[jerry6]

Maybe too late for you, but there is fundemental point in mechanics that ought to be addressed.

It is not due to the weight. All the drum brakes on the a-bodies (and probably every production car of that era and newer) self assist. These are mechanical arrangements of the shoes to the drum known as servo or duo servo. All other things being equal, a drum brake car will require less force on the brake pedal to stop. This is why cars with front disks more frequently were (and are) equiped with power assist than cars with front drums.

This also leads to another point which is worth mentioning in relation to another question in the opening post.


It is very important that the coefficient of friction is very consistant throughout the operating temperature range. If the friction goes down as the brakes get hotter, then the self assisting action becomes less. When this happens the driver has to harder and harder as the brakes work less well.

I don't know what new formulation people were mentioning, but a many brake linings sold aren't that good. On the lining's edge, or on the back of the shoe or pad is almost always stamped an 'Edge Code'. Within the ede code are two letters that very roughly represent friction. If the letters go down, this represents a lining that has less friction as it gets hotter. Do not use this for a drum if you can help it. Examples will FE or ED. You want EE, or better FF, GG, or HH.

So, yes you can have a very good drum brake system but it needs to be adjusted right, has decent linings, and it helps to have the shoes arced if the drums were ever cut. Because the reduced swept area of the smaller drums that came on some of the a-bodies makes it harder to keep them from getting too hot on repeated high speed stops, they're not a good starting point. Agreed that for the same swept area, a disk brake will be better in getting rid of heat. High speed stopping and weight are the main factors in generating heat.

Wow , good info . Never knew of the edge code on brake linings , will look out for that next time I pick up brakes .
Thanks !

 

[Mattax]

Sure. Glad to share. I first came across the reference on a website dedicated to F*rd SHO, SHO times. Although equiped with front disks, brakes on the first generations had barely enough swept area for the heavy front weight of those cars. As a result, they often had issues with brakes getting hot, even in street use.

After some further digging, the Edge codes are a practice from the manufacturing trade group. In other words, they don't seem to be government mandated, but something the industry found helpful for themselves and maybe because the OEMs want it.

The Friction code is based on the SAE J661
The marking standard is SAE J866

First letter represents the test coefficient of friction from 0-200 F
Second letter represents test coefficient of friction from 200-600 F

To get an idea of what temperatures to expect during hard driving, the author of the SHOtimes article stated the following:
"...measured 385 F on my front rotors in rush hour traffic on a 45 mph street because of several sequential stoplights. (I have an 89 SHO with 10.1 in. rotors.)
...four back to back 60 mph stops generated 550 F."
In addition, on my Barracuda, the temperature marking paint indicates that neither the front disks (Kelsey Hayes) not the rear drums have exceded 485 degrees on the street or autocrossing. Granted the lining material and the metal that contacts it wil be a little hotter than the edges where I put the marking paint, but not a lot.

Looking through the 10x1.75" rear brake shoes I have here, the ones I can read are marked either FF or FE. Obviously FF is likely the better lined shoe if all else is equal. If someone has any OE shoes, it would be very interesting to see how they rated.
E = .25 to .35 coef. of friction
F = .35 to .45 coef of friction

As you can see there is quite a range within each letter rating. So edge codes are not the final word, but certainly useful for comparisons. It is also sometimes reveals if the lining will change grip is it gets hotter.

PS. Brake pads are marked the same way.

 

[67Dart273]

It is very important that the coefficient of friction is very consistant throughout the operating temperature range. If the friction goes down as the brakes get hotter, then the self assisting action becomes less. When this happens the driver has to harder and harder as the brakes work less well. .

The opposite effects of changes in friction characteristics was a big big problem for some of the early stuff such as Velvetouch which was incorrectly suggested to folks in the late 60's early 70's. A good friend got sucked into this stuff for his 70 Chev K20. You'd be on the highway/ freeway, thundering along, brakes cool, and need to stop for some jam-up ahead.

You'd mash on the pedal and LITTLE would happen, until the damn lining started to warm up, and suddenly you'd be trying to "back out" of the pedal as they warmed up and started to work. Severe drum wear was another factor with that stuff.

 

[BillGrissom]

You should be able to rebuild the drum brakes for way under $250 in parts. Wheel cylinders cost ~$6 ea so I didn't even bother rebuilding them. Hoses are ~$6 ea. Shoes are ~$15 per axle. If you need new drums, costs go up. $20 ea for 10" fronts and maybe $80 ea for used 10" rears if you can find them. Very few have rear disks, so most people here are in the same boat, unless you change to a BBP rear. 9" drum parts are much easier and cheaper.

I rebuilt the 9" and 10" drums in my early-A's. I might add front disks someday when I have time to play, but I don't want cast-iron single piston sliders (73+ or Scarebird), nor pay >$600 for Wilwood, etc. What limits braking initially is the tires. As long as the brakes can lock up the tires equally, you can't do any better (other than anti-lock). After repeated braking, continuous braking (down-hill), or from a very high speed (one guy said 150 mph!), drum brakes will fade much sooner, but I don't plan to drive that way. I did have the drums in my 69 Dart slip after driving thru a very deep puddle in FL, but that is a rare "act of God" occurrence when you need to be aware. Driving in heavy rain doesn't matter. Indeed, the inside of drums must stay drier than disks. My 65 Newport has massive 11"x3" front drums that have no trouble stopping it.