Converting to disc brakes: has anyone used the stock 11" E-body rotors?

[MaximRecoil]

I got a pair of steering knuckle / spindle assemblies today from a '74 Barracuda in order to convert my '69 Charger's front drum brakes to disc brakes. They came with the rotors and caliper adapters (pin type) still attached, and the rotors are in good shape.

The conventional wisdom, as per Richard Ehrenberg's Disc-O-Tech article, is that after you get the steering knuckle / spindle assembly from an E-body or A-body:

"You'll also need a pair of rotors and caliper adapters (a.k.a. brackets) from most any '76-'79 B-body or 79-up R-body (St. Regis, etc.)"

This of course allows you to use the big 11.75" rotors. It would be a lot easier (and cheaper) for me to just use the caliper adapters and 11" (10.98") rotors that I already have, but is there much of a difference in braking performance?

Also, there is the sway bar interference issue on pre-1970 B-bodies when using the 11.75" rotor setup, which requires a workaround of some sort (e.g., replacing your original sway bar with an aftermarket one, or swapping the steering knuckle / spindle assemblies around so that the calipers are in the rear, with possible brake line / hose issues to deal with). Does this same sway bar interference issue exist when using the 11" rotor setup?

And where can I get a rear brake proportioning valve? I'd like to just use a stock one; can you still buy them new? If so, what are some cars that they came on?

[terrible one]

I can't really talk about the difference in braking power, since I haven't been able to compare, but I will say that I did a manual disc conversion on my '68 using exactly what you describe; the 10.87" rotors with pin type calipers. In my opinion the stopping power is really good. It pretty easy to apply enough force to lock the wheels up. That said, I am running 15" wheels with 235/60s in front.

You mention '74 Barracuda spindles, as far as I know the B&E body spindles are the same. I am using the spindles, etc. from a '73 Charger. As far as the sway bar goes, I kept the stock sway bar setup so I swapped the spindles side to side so that the calipers faced the rear.

The ticket for me was to use E body calipers. I used '73 Challenger calipers, not sure which ones are the same. With the B body calipers, the brake hose mounts on the very bottom and would hit on the lower ball joint nut if I'm remembering correctly . . . anyways it would make contact and interfere with turning. The E body calipers mount the hose up higher on the caliper itself so it clears everything by far.  

[MaximRecoil]

You mention '74 Barracuda spindles, as far as I know the B&E body spindles are the same. I am using the spindles, etc. from a '73 Charger. As far as the sway bar goes, I kept the stock sway bar setup so I swapped the spindles side to side so that the calipers faced the rear.

So the calipers will interfere with the stock sway bar even with the ~11" rotor setup?

The B and E body spindles aren't the same. From the Disc-O-Tech article:

Do not succumb to the temptation to use "lookalike" knuckles from later Mopars, such as 73-up B/R-bodies, F/J/M bodies, etc. These parts, while visually very similar, are taller, altering suspension geometry (camber change, bump steer, etc.), and possibly forcing the ball joints beyond their designed range, a/k/a "over angling".

While they are not the same, Ehrenberg's position that they should not be used is controversial. Somewhere online (Moparts, I think) there is a long argument involving Ehrenberg and others about whether or not you should use the "lookalike" spindles.

The ticket for me was to use E body calipers. I used '73 Challenger calipers, not sure which ones are the same. With the B body calipers, the brake hose mounts on the very bottom and would hit on the lower ball joint nut if I'm remembering correctly . . . anyways it would make contact and interfere with turning. The E body calipers mount the hose up higher on the caliper itself so it clears everything by far.  

That's good to know. What flex hoses did you use? And with the calipers facing the rear, did you have to do anything else with regard to brake line and/or hose routing other than simply installing the hoses?

The dilemma for me is that E-body calipers have a hefty core charge (doubling or more than doubling the initial price), and I have no cores. On the other hand, later calipers that would fit the bigger caliper adapters and 11.75" rotors have a small core charge or no core charge at all, but to use them I'd have to find some of the bigger caliper adapters and buy new rotors.

[terrible one]

You mention '74 Barracuda spindles, as far as I know the B&E body spindles are the same. I am using the spindles, etc. from a '73 Charger. As far as the sway bar goes, I kept the stock sway bar setup so I swapped the spindles side to side so that the calipers faced the rear.

So the calipers will interfere with the stock sway bar even with the ~11" rotor setup?

The B and E body spindles aren't the same. From the Disc-O-Tech article:

Do not succumb to the temptation to use "lookalike" knuckles from later Mopars, such as 73-up B/R-bodies, F/J/M bodies, etc. These parts, while visually very similar, are taller, altering suspension geometry (camber change, bump steer, etc.), and possibly forcing the ball joints beyond their designed range, a/k/a "over angling".

While they are not the same, Ehrenberg's position that they should not be used is controversial. Somewhere online (Moparts, I think) there is a long argument involving Ehrenberg and others about whether or not you should use the "lookalike" spindles.

The ticket for me was to use E body calipers. I used '73 Challenger calipers, not sure which ones are the same. With the B body calipers, the brake hose mounts on the very bottom and would hit on the lower ball joint nut if I'm remembering correctly . . . anyways it would make contact and interfere with turning. The E body calipers mount the hose up higher on the caliper itself so it clears everything by far.  

That's good to know. What flex hoses did you use? And with the calipers facing the rear, did you have to do anything else with regard to brake line and/or hose routing other than simply installing the hoses?

The dilemma for me is that E-body calipers have a hefty core charge (doubling or more than doubling the initial price), and I have no cores. On the other hand, later calipers that would fit the bigger caliper adapters and 11.75" rotors have a small core charge or no core charge at all, but to use them I'd have to find some of the bigger caliper adapters and buy new rotors.

I honestly can't remember if the calipers interfered with the sway bar when mounted forward or not. I'm thinking it might have been that the bleeders weren't facing up when I mocked up that way.

Thanks for clearing up the info on the B/E spindles. I remembered that the B's were taller (and controversial) but for some reason I had it in my head that E's were the same. I have read both sides of the argument and it wasn't enough to keep me from using them. I only have a couple thousand miles on this setup so time will tell, but so far I haven't noticed any ill effects.

The flex hoses I used were for a '73 Charger as well and with this setup they really did just bolt on, no modifications to the stock brake line routing or making funky brackets to hold the hose out of the way, etc. These pictures show it pretty well: http://www.dodgecharger.com/forum/index.php/topic,39838.msg1364758.html#msg1364758

Wow, I just looked at the prices/ core charge on the E body calipers, that definitely does make a difference. I didn't remember them being steep but it's been a few years since I put this hodgepodge together!

[MaximRecoil]

The flex hoses I used were for a '73 Charger as well and with this setup they really did just bolt on, no modifications to the stock brake line routing or making funky brackets to hold the hose out of the way, etc. These pictures show it pretty well: http://www.dodgecharger.com/forum/index.php/topic,39838.msg1364758.html#msg1364758

So lock-to-lock, and through full suspension travel, no issues with those '73 Charger hoses? If so, that's awesome; one less thing I have to worry about.

Did you use a rear brake proportioning valve? If so, what kind was it?

[terrible one]

The flex hoses I used were for a '73 Charger as well and with this setup they really did just bolt on, no modifications to the stock brake line routing or making funky brackets to hold the hose out of the way, etc. These pictures show it pretty well: http://www.dodgecharger.com/forum/index.php/topic,39838.msg1364758.html#msg1364758

So lock-to-lock, and through full suspension travel, no issues with those '73 Charger hoses? If so, that's awesome; one less thing I have to worry about.

Did you use a rear brake proportioning valve? If so, what kind was it?

10-4! One of the few things I didn't have to worry about 

Right now I don't have a rear brake proportioning valve, the only valve in the whole system is an OEM disc brake combination valve from an A body. I think that if you used your stock (drum brake) distribution block you would need to add the proportioning valve, because the drum block would feed the same pressure front and back, but the OEM disc valves from like 73-76 are a combination valve that takes care of the proportioning as well. 

[MaximRecoil]

Right now I don't have a rear brake proportioning valve, the only valve in the whole system is an OEM disc brake combination valve from an A body.

Is that a direct replacement for the original drum brakes distribution block?

[terrible one]

Right now I don't have a rear brake proportioning valve, the only valve in the whole system is an OEM disc brake combination valve from an A body.

Is that a direct replacement for the original drum brakes distribution block?

What I can say for sure is that it bolts up in the same location with no modification, including the wire/ connector for the warning lamp. What I'm not sure on is the brake line fittings. I don't have original hard lines but when I ordered reproductions from Fine Lines I ordered them for a '68 Charger, and the description said 68-70 manual disc or drum, so I think they are the same.

[Troy]

I had a 73 Barracuda with factory discs and it stopped very well. I have no idea if going to a bigger rotor would have a big impact on braking performance (presumably it will have some sort of positive impact). Mine was also a small block with A/C so if you're putting the same setup in a Charger with a big block you'll have a few hundred extra pounds to slow down. I would certainly expect it to be better than 10" drums and, in my experience, better than 11" drums (I had my 68 R/T at the same time and there was a marked difference). For absolute best results I think I'd follow the recommendations in the article. It's a proven setup.

Troy

[MaximRecoil]

I had a 73 Barracuda with factory discs and it stopped very well. I have no idea if going to a bigger rotor would have a big impact on braking performance (presumably it will have some sort of positive impact). Mine was also a small block with A/C so if you're putting the same setup in a Charger with a big block you'll have a few hundred extra pounds to slow down. I would certainly expect it to be better than 10" drums and, in my experience, better than 11" drums (I had my 68 R/T at the same time and there was a marked difference). For absolute best results I think I'd follow the recommendations in the article. It's a proven setup.

My car has a 318 and 10" drums. The 10" drums work okay under normal conditions, but I'd hate to have to rely on them (or any front drum brakes, for that matter) in a panic stop situation.

[Troy]

My first 68 Charger was a 318 car with 10" drums. I rolled into the back of another car at a stop light once. After that I decided I wasn't going to run factory drums any more. It was only later that I learned the R/Ts had bigger 11" drums and I didn't want to mess with originality. They still didn't inspire lots of confidence if you had to slow down in a hurry. I have big discs for my next Charger and I'm on the fence about what to put on my 4-speed R/T. Everything else will be stock so it's a tough call (I probably won't put nearly the miles on it as my other cars).

Troy

[MaximRecoil]

For absolute best results I think I'd follow the recommendations in the article. It's a proven setup.

By the way, I was rereading the Disc-O-Tech article, and this 11" brake setup I'm planning to do is an optional recommendation:

If you can't bear to part with your mint 14" rallies, no sweat, we have the cure: Use the "optional" 10.87" HD rotors and adapters shown on the parts list.

And in the parts list, the calipers and caliper adapters for the 11" setup are from a '70-'74 E-body (along with some other cars that also used them), which is what I'm using.

I wonder why he refers to them as 10.87" (about 10-7/8") rotors. I measured mine and they are 10.98", i.e., 11" for all intents and purposes (about 10-63/64"). To get an accurate measurement, I measured the circumference, which eliminates the problem of finding the exact center of the circle if you are trying to measure diameter with a tape measure. The circumference was 34.5", which is 10.98" diameter. They are rotors from a '73 Barracuda that were put into storage along with the steering knuckle / spindle assembly at some point back in the '80s.

So I wondered: Why the .11" difference between the diameter of my rotors and the 10.87" diameter stated in the article? Then I looked online for rotors for a '73 Barracuda, and I saw this:



Those rotors are supposed to fit:

Code Select Expand

CHRYSLER    CORDOBA      (1975 - 1982)
CHRYSLER    FIFTH AVENUE      (1984 - 1989)
CHRYSLER    IMPERIAL      (1981 - 1983)
CHRYSLER    LEBARON      (1977 - 1981)
CHRYSLER    TOWN & COUNTRY    (1977 - 1979)
DODGE    ASPEN      (1976 - 1980)
DODGE    CHALLENGER      (1973 - 1974)
DODGE    CHARGER      (1974 - 1977)
DODGE    CORONET      (1974 - 1976)
DODGE    DART      (1973 - 1976)
DODGE    DIPLOMAT      (1977 - 1989)
DODGE    MIRADA      (1980 - 1982)
PLYMOUTH    BARRACUDA      (1973 - 1974)
PLYMOUTH    DUSTER      (1973 - 1976)
PLYMOUTH    FURY      (1975 - 1976)
PLYMOUTH    GRAN FURY      (1984 - 1989)
PLYMOUTH    ROADRUNNER      1975
PLYMOUTH    SATELLITE      1973
PLYMOUTH    SCAMP      (1973 - 1976)
PLYMOUTH    VALIANT      (1973 - 1976)
PLYMOUTH    VOLARE      (1976 - 1980)

Since those Centric 121.63010 rotors are also 10.98", it leads me to believe that the 10.87" in the article is either a typo, a mismeasurement on Ehrenberg's part, or some published source (such as Chrysler) originally misstated the diameter as 10.87" and Ehrenberg just went with it.

[ws23rt]

Is this question you ask to find an error as to two different advertised diameters of 11 in. brakes?

The od of the discs is not an issue when one is talking about less than 1/16" on radius.

I expect the rotors are cast and the od is not a critical dimension.  It may not even be machined.

I admit that I don't know if more that one manufacture made these but from a fabrication view point the od dia. tolerance would be generous.

[MaximRecoil]

I'm just wondering where the 10.87" figure came from when the rotors are actually 10.98" (or 10.97" from some manufacturers, such as Raybestos, Pronto, and Wagner).

[ws23rt]

I cannot answer that but expect that many were made with that OD. It must be true due to the dimention advertised. A mistake in measuring does not fit with common sense.

I have a question---How far from the od of the rotor do the pads reach

[MaximRecoil]

I cannot answer that but expect that many were made with that OD. It must be true due to the dimention advertised. A mistake in measuring does not fit with common sense.

I have a question---How far from the od of the rotor do the pads reach

I don't know; the brake pads are on the way along with the other parts I need to do the conversion. Should be here Friday.

[MaximRecoil]

Are those anti-rattle clips/springs that came with the calipers supposed to be used? In the Disc-O-Tech article it says:

If you find any anti-rattle springs, clips, etc., packed with your calipers or pads, just toss 'em over your shoulder!

But why would they include them if they aren't supposed to be used?

[68charger440]

I did the conversion on my 68 charger many years ago using the spindles, calipers, rotors, etc. from a 72 or 73 dart (can not remember which right now but I could look it up probably).  All I had to do is reverse the calipers to the rear and everything else worked fine including the hoses. The stock sway bar didn' get in the way at all either.

[Cooter]

11" rotors with big C body drums work awesome.

[HPP]

E-burg has typically collected his dimensional data and specifications out of factory sources. As such, the factory most likely had these specified at 10.87 when they were first released back in the early 70s. What aftermarket vendors have done in the ensuing 4 decades since is allow the spec to creep into larger maximum sizes that maximize the use of the casting molds across multiple product lines. After all, why have a 10.87 Chrysler specific casting mold of you can use 11.125 and use it on AMC and Buick as well and simply machine it to final spec based on application.


E-burg has also admitted in ensuing years since the disc-o-tech article was written that the taller spindles may not be an issue. However, he has said he will not update the article to reflect this. At this point, there are builders who now specify use of the taller spindles instead of the shorter units because of their lighter weight, improved axis inclination, and positive geometry changes.

Moving from 11 to 11.75 is an 8% increase in diameter. That would presumably translate into a 8% improvement in braking torque. Can the average driver feel this, probably not. It also results in an 8% increase in surface area which provides a bigger heat sink and a longer time until fade is induced by heat.

[MaximRecoil]

What are you guys using for a master cylinder? My car is a '69 Charger, and I used one from a '76 Volaré, because it was cheap (~$12 new/rebuilt), and the article said:

Additionally, besides the obvious parts such as pads, wheel bearings and seals, splash shields, etc., you'll need, (only) if you now have drums, a master cylinder from virtually any '70-up disc car, even one from such common junkyard dogs as a 1976-78 F-body (Volaré/Aspen.)

With that master cylinder, the pedal would go to the floor even after the brakes were completely bled out, and my friend figured we needed to lengthen the rod that comes out of the power booster. Then I remembered something about that in the article:

Each body style requires a specific pushrod, which can be recycled from a drum setup, but be sure to pull the pushrod out of the old cylinder before removing it from the car - way easier that way. Alternately, you can use an new MP adjustable pushrod, p/n P5249316.

The pushrod that comes out of my power can be adjusted in length (I don't know by how much), so is that what I need to do? On the other hand, I was thinking that if I used a B-body master cylinder, like say from a '73 Charger, it would work as-is?

[terrible one]

I'm using what is probably the same master cylinder as your Volare unit, I ordered for a '76 Dart with manual discs.

[b5blue]

  The 8% gain in rotor diameter is a gain in mass that helps absorb heat then disperse it. The friction of the pads on the rotor convert motion into heat to transfer momentum then disperse it. So the gain is much greater in repeated or very large brake events. (Repeated stop and go or pull down rapidly from high speed.)
   The rod for manual brakes runs from the peddle leaver into the master, nothing from boosted brakes linkage is used. 

[MaximRecoil]

I'm using what is probably the same master cylinder as your Volare unit, I ordered for a '76 Dart with manual discs.

I got it sorted out. The master cylinder wasn't the problem (the depth of its plunger was exactly the same as my old '69 Charger drum brakes master cylinder; I checked with a depth gauge); apparently the problem was with the sides I mounted the calipers on. I chose the side based on what would allow the rubber hoses to bolt to them without any interference, but in doing so, it resulted in the bleeder screws not being as high up on the calipers as if they were switched around (and switching them around resulted in the hoses' brass banjo fittings coming very close to the shocks and the rubber touching the lower control arm at full lock).

So after telling some 30-year-old stories about the same problem he's encountered before when the calipers were mounted on the wrong side of the car, my mechanic friend had me remove the calipers from the caliper brackets, and he blocked them off with plates of steel and C-clamps, tilted them so the bleeder screws were at the highest point, and then bleeding was successful.

It seems like it's never easy. I got all the parts swapped over fairly quickly, and then the "fun" began when it came time to bleed them. First, the bleeder screw on the rear passenger wheel cylinder broke off the moment the slightest hint of torque was applied to it, and it was only 3 years old (it wasn't even rusty). Of course, it was Sunday afternoon and the parts store was closed.

The next day I took a look at the driver side rear brakes, and they were all wet with brake fluid, because that wheel cylinder (also 3 years old) had recently started leaking. So I had to tear those brakes all apart, soak all the parts in gasoline, and now I needed two new wheel cylinders. And of course, those crappy little 3/8" flare nuts which are made of the softest steel known to man wouldn't come off (the 3/8" flare wrench just rounded them off; even Vice-Grips wouldn't remove one of them, so I had to cut the line). Since those lines (which I made 3 years ago) were steel, and showing a bit of rust (and one was now cut anyway), I decided to make new lines for the rear, both of them, with copper/nickel line.

And so it went ...

In any event, the brakes are done and they're good; they feel about the same as the brakes on my 2001 Dakota. No more squirrelly, grabby brakes for me.

[MaximRecoil]

E-burg has also admitted in ensuing years since the disc-o-tech article was written that the taller spindles may not be an issue. However, he has said he will not update the article to reflect this. At this point, there are builders who now specify use of the taller spindles instead of the shorter units because of their lighter weight, improved axis inclination, and positive geometry changes.

When I read the long argument among Ehrenberg and others on, Moparts I think, I don't remember him conceding anything; his main issue was increased bump steer, but he eventually had enough of the argument and said he was done. Has he said anything new on the topic since then?

Moving from 11 to 11.75 is an 8% increase in diameter. That would presumably translate into a 8% improvement in braking torque.

About a 7% increase (6.8%), though I'm not sure there's a 1:1 relationship between diameter and braking torque, but regardless of that, the pads would have to also increase in size in order to increase braking torque, as braking torque is determined by the size of the pads-to-rotor contact area, clamping force and all else being equal.

Now, my brake pads and pin-type calipers are for a 1973 Barracuda, but those same pads fit some cars that had 11.75" rotors, such as a '77 Cordoba, and a '78 Monaco and Fury, and a bunch of others. In the part list section of the Disc-O-Tech article, the only pin-type calipers he lists are the ones I have, which are for:

'70-72 B- body; '70- 74 E-body

So as far as I can tell, those same calipers are used for both the 11" and the 11.75" rotor conversions, and that means they would take the same pads. In fact, for pads he says:

Any Mopar w/pin calipers

Since the 11.75" rotors are using the same calipers and pads as the 11" rotors (when using pin-type calipers), the braking torque should be identical in both cases.

It also results in an 8% increase in surface area which provides a bigger heat sink and a longer time until fade is induced by heat.

Absolutely true (though your math is a bit off; an 11" diameter circle has ~95 square inches of surface area, while an 11.75" circle has 108.4 square inches of surface area; a 14.1% increase in surface area), and as far as I can tell, this is the only actual advantage of the 11.75" conversion over the 11" conversion (with regard to the Disc-O-Tech conversion only; the 11.75" rotors have more potential braking torque, but the calipers and pads aren't taking advantage of the rotors' increased surface area). On the other hand, the 11" rotors have the advantage of being lighter (I assume), which would actually translate to effectively having slightly more braking power (emphasis on "slightly"), all else being equal, until heat saturation-induced brake fade enters the equation.