Disc brake conversion (70 Dart)

Discussion in 'Brakes for your Classic Mopar' started by StPaulSwinger, Jun 30, 2018.

  1. StPaulSwinger

    StPaulSwinger FABO Gold Member FABO Gold Member

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    So it sounds like the basic paths are:

    1) Rebuild with the parts I have (namely the spindles, using the rest as cores or throwaways) and then ordering new rotors/pads/bearings/tapered ball joint adapaters to match. Possible downside being using old tech for braking.

    2) Ditch everything and order a kit from Wilwood (or similar manufacturer). Theoretical upside being everything is new and made with new tech. Downside is cost, debate over performance improvement, and may require getting new wheels/tires because the ones I have (both on the car now and the wider rims I have as well) won't fit.
     
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    • oi81b4uu812b4

      oi81b4uu812b4 Well-Known Member

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      I'm short on data? Oh, you mean your made up data. Nice try though.
      I am and actual Mechanical Engineer in automotive.
      You wouldn't understand the data anyway. You're not a real Mechanical Engineer. You just play one on this site.

      I have tested every GM, Ford , Chrysler brake package available since 1996 and a lot of foreign OEM's. And a lot of brake packages suppliers try to pitch to OEM's. The Willwood's will work better reliably than the 40 year old tech. You seem to think the only thing that makes a brake package good is the size of the caliper piston... I doubt you could understand much else. You surely don't understand why even clamping force is a benefit.

      Where's your data, saying they are junk? Oh, it's just your opinion.

      The OP can choose to use the old brake system and most likely it will work fine for tooling around. It's his budget. He should plan on spending $500-700 when it's all said and done keeping the old design brakes if he wants to replace everything with new and rebuilds.
       
      Last edited: Jul 3, 2018
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      • inertia

        inertia Well-Known Member

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        Don't forget the Decal ! !
         
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        • StPaulSwinger

          StPaulSwinger FABO Gold Member FABO Gold Member

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          Oh trust me, I NEVER forget the decal! I might even ask for two, to double the gains!
           
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          • 72bluNblu

            72bluNblu FABO Gold Member FABO Gold Member

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            Yup, you've got it. DoctorDiff will have all the parts you need to refurb/replace everything for the 73+ mopar brakes.

            Also keep in mind your tire choice. If you're planning on running 15" wheels and BFG T/A's, you can put the biggest, most expensive brakes you can afford on there and it won't make a lick of difference, because you'll be traction limited before you're braking force limited. Doesn't matter how much clamp force you generate at the rotor if you can't put it to the ground.

            And, the "new tech" thing isn't really accurate. The old Kelsey Hayes calipers that were used on the A-bodies from '70-'72 are actually 4 piston fixed calipers, just like the Wilwoods are. The biggest drawback to them isn't their braking performance, it's the scarcity of reproduction parts available to rebuild them.

            I'm not sure what your problem is. I don't "play" a Mechanical Engineer, and I wouldn't claim to be an ME anyway because it would be selling my education short. I hold an Aerospace Engineering degree from UCLA, which required me to take every class a ME would take and then Fluid Dynamics on top of that. I participated in Formula SAE for two years while I was in school, and then a couple of Aerospace competitions after that. I left the industry after college, but let's face it, brake calipers are not rocket science and I'm more than qualified to weigh in.

            I would have no problem understanding any data you posted. Of course, you haven't posted any, not in any of your threads here. I know if I worked at a "suspension R&D shop" and had access to that kind of equipment I would be testing the crap out of all the stuff I was installing on my car, but I guess you don't bother.

            And I certainly didn't "make up" any data. I used the specifications right off of Wilwood's site, as well as the dimensions I pulled off of an extra set of the Mopar 73+ calipers that I have. Hell I even linked to the specs.

            I DO understand why clamping force is a benefit. And I said in post #12 of this thread that multi-piston, fixed calipers are more efficient at transferring force at the piston into actual clamping force. They lose less of the generated force at the piston to flex and have more even pressures across the pads, both of which improve the clamping force. But, the Wilwood calipers in questions have a significant disadvantage because of their smaller pad and piston area. They generate less force at the piston than the Mopar calipers, that's just the reality of their piston area. I have NEVER argued that single piston sliding calipers are better than fixed multi-piston calipers in general. But that's not what we're talking about, we're talking about two specific calipers, and while the Mopar calipers do have a simple, less efficient design they also have a lot more piston area.

            Now, neither one of us knows for sure if the actual clamping force is better for the 73+ Mopar brakes or the Wilwoods. That number can't be calculated like the force generated at the pistons, it has to be measured because you have to know how much force is being lost to flex and uneven pad pressures. No caliper will transmit 100% of the force at the pistons to the rotors. The 73+ mopar calipers would need to lose an extra 24% of the generated force at the piston though, which is a lot, to end up having less clamp force than the Wilwoods we're talking about, because that's what the Wilwoods are giving up for piston area. Is it possible the Mopar calipers are losing that much force? Sure, it's possible. But again, someone would actually have to test it in order to know that for sure.

            Now, if you've tested every OEM brake system available since 1996 why don't you actually test a set of 73+ Mopar calipers against the Wilwood Dynalite's and post up the actual clamp forces? You can easily do that if you have the equipment and experience you claim to have, and personally I'd LOVE to see the testing results. Even if they prove me wrong. At least then people can make an educated choice between the 73+ mopar calipers and the Wilwoods, weighing the cost of the Wilwoods against their actual performance.
             
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            • dartfreak75

              dartfreak75 Well-Known Member

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              It nice to see I'm not the only one that believes more is not necessarily better things can be done on a budget and still be done right! All this aftermarket stuff like wilwood breaks and tubular suspensions and all that stuff yes its nice and I'm sure it works great but not everyone wants or needs 5k in suspension and breaks! If it where me if find you a 73-76 donar car and steal the front end get the control arms spindles calipers etc like said before you already have the spindles so that will save some money
               
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              • stroked340

                stroked340 Well-Known Member

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                Hmm.from what I've been told the guy your agreeing with has just about all that fancy stuff on his STREET never sees the track duster,talk about a overkill:rolleyes::rolleyes::rolleyes:
                 
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                • inertia

                  inertia Well-Known Member

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                  I think he was agreeing with me ! !
                   
                • 72bluNblu

                  72bluNblu FABO Gold Member FABO Gold Member

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                  Ok, since I've been called out for lack of "Data", here's all the calculations for braking force. This uses a 15/16" master cylinder for both system, the stock pedal ratio of 6.5, a modest foot input of 70 lbs, the same brake pad coefficient and the same wheel diameter. The effective diameter for the rotor is slightly different because of the 10.95 vs 11" rotors, but I did include it. You can clearly see which system generates more clamping force, and which has more total force at the wheels.
                  moparVSwilwood.png


                  Now, this calculator assumes 100% of the force generated at the pistons is transferred to the rotor. That never happens, and as I have said previously the Wilwood multi-piston, fixed caliper will be more efficient- it will not lose as much force to flex in the caliper, pads, etc as the Mopar single piston sliding design.

                  The question is, how much less efficient is the Mopar caliper? Do you think it loses 744 pounds of clamping force in flex? I don't. Now, that last part is my opinion, and you'd need a brake dyno to figure out how much force is actually being applied to the rotor by each caliper. But quite frankly, there's no way it's losing that much force to flex.

                  Here's the source of my calculator, all I did was input the Wilwood and Mopar numbers for the calculations. The spreadsheet is set up to calculate front and rear, I changed the header titles to match the brake systems I was comparing, and added the "bold" to the clamping force calculation results.
                  http://norcal-cobras.com/misc/brake-formula-mod.xls

                  For those of you curious about the equations used in the spreadsheet, there's a really awesome article by StopTech that includes all of the equations, as well as a pretty good amount of brake theory. It should be attached at the bottom.

                  So, there are the numbers. Make your choices, spend your money.
                   

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                  Last edited: Jul 8, 2018
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                  • stroked340

                    stroked340 Well-Known Member

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                    I wasn't referring to you..
                     
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                    • stroked340

                      stroked340 Well-Known Member

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                      Wilwood all the way:thumbsup::thumbsup:
                       
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                      • dartfreak75

                        dartfreak75 Well-Known Member

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                        I dont know who has what but I do know you dont have to spend 1000 dollars to stop a car! If you can afford it then great I bet they are super nice but not everyone my self included can afford it even if I could afford it I wouldnt id spend some of that 1000 and go ahead and convert my rears to disks get me some good rotors and pads for the 100$ k frame I got from the junk yard and spend the rest on my motor and tranny lol I'm not just saying that the best of everything isn't always in everyone's grasp. Not everyone wants to spend 20k on a dart they paid 300 bucks for. And its not necessary you can convert to disk breaks and have perfectly safe and functional breaks without the name brand for a fraction of the cost.
                         
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                        • cosgig

                          cosgig MoBro Inc. FABO Gold Member

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                          Any disc brake setup is an upgrade over drums. Still, 1000’s are still stopping on drums with much success, myself included! It’s worth doing the swap, and if you can afford it, and want to go that way, buy aftermarket. Me, I can do well with factory parts just fine, and would use the factory setup if I had it around and it was in decent shape. For 90% of the cars out there, it’s just fine!
                           
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                          • billccm

                            billccm Active Member

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                            I've been watching this thread and reluctant to get into the debate, but I wanted to share my own experience. Granted this was over 20 years ago, but I did the Wilwood conversion on a Charger back in the 1990s. Long story short is I was not impressed. It was expensive, and had numerous issues with brake squealing. Wilwood support was there with several types of replacement pads, but it took a friend who worked at Kragens back in the day to match me up with some cheapo bottom of the line Bendix pads that finally solved the issue. Braking was defiantly improved over the drums, but it was a expensive conversion with it's share of headaches.

                            When I decided to convert my Road Runner to front discs I went with Dr Diff as many FBBO and fellow Mopar guys highly recommended the kit. I am very happy with the braking, so far, and all of the painful headaches this time was due to In Line tube's quality control as I replaced all brake lines during the conversion.

                            I can't say which product brakes the best as I can't compare the cars (sold the Charger in 1997 which was a big mistake), but for street use only, my opinion is you can't beat the Dr Diff kit for price and fitment. It was pretty much plug and play, I kept my 14 inch magnum wheels, and saved lots of money over the Wilwood kit.

                            I do appreciate some of the science that has been presented here as I'm an engineer in my day job. Thanks for the debate!
                             
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                            • stroked340

                              stroked340 Well-Known Member

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                              Can't compare his stuff to Wilwood..no even close!!
                               
                            • StPaulSwinger

                              StPaulSwinger FABO Gold Member FABO Gold Member

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                              Thanks, I'm leaning toward Dr. Diff after looking at a number of different options and hoping to give them a call on Monday to do a sanity check to make sure I'm not forgetting anything obvious. At least for right now it feels like overkill to pay the money for Wilwood especially given both sets of my current rims/tires wouldn't work.
                               
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                              • BillGrissom

                                BillGrissom Well-Known Member

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                                Why stop at Wilwood?, since there are even more expensive kits out there, and all will give purty calipers to show off behind new expensive wheels, just need to be rolling in cash like stroked talks big. Much more important than brakes are the tires since tires are what stop the car and the choice can make a 50% difference. The fastest you can stop is to brake the tires to the point just before they start skidding. If you think your big brakes are better at that, then sleep well. I never owned a front drum car that couldn't skid the tires. You also want them even L&R and the rear circuit adjusted so the rears skid just after the fronts (prop valve). Brake fade is another issue and where drums show problems, but mainly from riding the brakes down mountains or braking constantly on twisty roads, or from very high speeds. For normal sane driving, occasionally braking from 70 mph, all brakes should perform equally, as least in theory. Most "bad brakes" people report here are from neglect.

                                Most new cars have ABS. That way you don't think about how hard to brake just before skidding, you just jam down the pedal and let ABS take over (pulses & skids). Interestingly, ABS apparently needs to be tuned to the tires and suspension. Tesla's Model 3 did miserably in Consumer Reports Mar 2018 tests, taking 150 ft to brake from 60 mph. They did an over-the-air computer update and it improved to a more normal 130 ft. Me-thinks that happened after they switched to a softer suspension and changed wheels ~Dec 2017 and didn't compensate in the ABS algorithm, but could also have to do w/ their initial regen braking. Many current sports cars brake in <100 ft, but their sticky tires wear fast. I just hope no manufacturer goes to brake-by-wire, since I prefer a mechanical/fluid connection between pedal and brakes, not dependent on electrons. And since some here are challenging credentials, I have an MS in Mech Engr. I even worked in a plant that designed brakes for large aircraft, but I only designed fuel controls. Most engineers in automotive design only work on specific areas, so true experts are probably very rare.
                                 
                                Last edited: Jul 8, 2018
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                                • volunteer

                                  volunteer Member

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                                  Also just picked up on this. Have to agree with #37 and #38 - very profound and sensible. Also, the 'tongue-in-cheek' reference to Willwood in #42.
                                  I also agree that most drum brakes (not 'breaks'!) are well capable of squealing the tires (f or r) - but, biggest factor here would be power assist. My Signet has the 9-inch drums. Stock 13 inch tires were quite easy to 'squeal', however, I find myself adding left foot to the right foot for quicker stops (poor man's power-assist).
                                  A booster has to make a difference, but I may not go that route. Perhaps too much 'playing around'?
                                  Since this car will stay with the small bolt pattern, likely the (four-piston) set-up (from '70 Swinger) will be utilized. That will also include the booster - and new rotors. The Dart will go with OEM setup as donated from '74 Duster, but with new rotors and calipers. Another benefit is the larger studs / bolt circle - which makes wheel selection much easier. However, aftermarket rear axles will be needed - at a significant cost. But, I do have access to 6 good spindles and 4 brackets and, upper control arms as well, because the ball-joint stud is bigger (same as B or E-bodies). The rest is little stuff and low in cost.
                                  To some people, installing 'aftermarket' brake system would be almost like putting Chevy small-block under the hood. (yikes!) Most of us would prefer to keep as original as possible (ie: numbers-matching) for any Mopar with 'H'-code engine (or higher). But there are always safety upgrades to consider - at a decent cost - and I for one don't need to brag about 'parts-unknown'.
                                   
                                • milty

                                  milty New Member

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                                  Hello all;
                                  This is the first time I've written anything on FABO, so bear with me and my ignorance.
                                  Regarding the 70 Dart disc break conversion.
                                  I'm sure this has crossed the forum before, but here it goes....
                                  I used 73-76 A body V8 disc break spindles with 78-80 Chrysler Cordoba adapter, calibers, and rotors on my 70 Dart, they work great.
                                  You do need to get larger wheels though.
                                  I'm sure you need to change the proportioning valve to something else, but I didn't and they seem to work.
                                  There over the counter parts and somewhat inexpensive.
                                  Please tell me if I'm full of it or if this modification works.
                                  Again, this is my first time submitting anything on FABO.
                                  Thanks for reading and any support is well appreciated.
                                   
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                                  • oi81b4uu812b4

                                    oi81b4uu812b4 Well-Known Member

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                                    That's a lot of write up for still not understanding even caliper clamping force on the rotor. I really don't care if a caliper clamps with 3000, 5000 or 10,000 pounds of force. If it ain't putting it down evenly, it's not efficient. And if it clamps the pads unevenly and can't do it repeatedly with consistency, it's inefficient. A smaller brake pad making parallel clamping contact with the rotor will always be more efficient than a large pad being clamped unevenly. I think you need to review the Statics, Dynamics and Materials classes you should have taken to earn your claimed Rocket Science degree.

                                    Once again, you really don't understand why a multi piston caliper would have sequential piston sizes either.

                                    And sorry a Aerospace Engineering degree from UCLA is about as good as a used piece of toilet paper. Probably why you're a firefighter instead.

                                    But,everyone else posting on here would probably be happy just swapping to an old single piston Mopar caliper and it will meet the needs of their application. Even drum brakes stop great just driving around with, if they are driving like a little old lady, which is what 72bluNblu says he does, they will be fine. They just don't work the greatest when hot.

                                    And yes, we have tested Willwood brakes here! They work great!
                                     
                                    Last edited: Jul 12, 2018 at 7:26 AM
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                                    • myduster360

                                      myduster360 FABO Gold Member FABO Gold Member

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                                      When upgrading my 10" Drums it was a short leap to Wilwood. Here's my thought process.

                                      For me, the deal braker going factory was:
                                      1. having to buy spindles. If you need disk spindles, even a GREAT price for used spindles is at least $125 shipped---New off shore copies are $200 shipped
                                      2. The TWENTY EXTRA POUNDS PER WHEEL OF UNSPRUNG WEIGHT.{I think its ridiculous to see guys spout off about how great their thousand dollar+ suspension mods are the bees knees in one post but also swear to their dying breath that the HEAVIEST disk brake setup available is pretty much always "the best"}

                                      FABO group think dogma says just go to get factory stuff from Dr.Diff,,ok well that's over $550. Not really a steller deal and that's for reman calipers and Chinese knuckles,,,,meh
                                      upload_2018-7-11_21-49-37.png

                                      Even if you RockAuto most of the parts and find knuckles, the core charges and shipping still winds up the same price

                                      Ok so over $550 for 38lb PER WHEEL worth of factory bits.
                                      I'm building my Swinger with a 3.6L pentastar for better weight distribution and 40lb hanging off each knuckle wasn't siting well, especially for $550. WFT! For $150 more I could just get 100% brand new Wilwood.

                                      upload_2018-7-11_21-48-59.png

                                      But is the $150 difference worth it?!?!

                                      Then I remembered an OLD Mopar Performance News(Dec 1993) article i read some 25years ago(found it tonight in the basement). The MP engineers were going on about their MP branded Wilwood disk kits--the SAME kits being discussed. The engineers claimed when a vehicle's UNSPRUNG weight is reduced, there's a 6:1 advantage per lb vs the same lb removed from SPRUNG weight.

                                      "A acceptable rule of thumb in racing is that every pound of sprung weight you can remove from a vehicle will give you the performance equivalent of 6lb of sprung weight"

                                      In the MPN article, they dropped 20lb PER WHEEL for the Wilwood vs 10.75" factory Disk. So the resultant drop in ET would be equivalent to reducing overall vehicle weight by 240lbs!(20+20 x 6)--a potential drop in 1/4 mile ET of .20s. Now isn't that about what ~10-15hp gets you? Not too shabby side benefit for Fen BRAKES!

                                      This would be ON TOP OF all the benefits of lighter wheel weight has on handling, which is 99% of the time why unsprung weight is reduced. So yeah WILWOOD!

                                      My Wilwoods are 24.4lb total with the lighter weight 10" drum knuckle + LBJ.
                                      The 10" Drums, Knuckle + LBJ weighed in at 35lb
                                      The Stock 10-3/4" disks are ~38lb WITHOUT the knuckle OR LBJ, so maybe 45-48lb? if included.


                                      upload_2018-7-11_22-46-57.png


                                      Oh one more thing,,,that super scary 500lbf deficit the Wilwoods have compared to the "stock" disks,,it only takes an extra 15lb of foot pressure to make up the difference--about 2 toes worth lol
                                       
                                      Last edited: Jul 12, 2018 at 12:43 PM
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                                      • myduster360

                                        myduster360 FABO Gold Member FABO Gold Member

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                                        2nd source on the 6:1 performance advantage comes from Olaf Manthey, Porsche race team owner/driver.

                                        Olaf Manthey: “Removing 33 pounds of unsprung weight at the wheels is equivalent to losing 198 pounds from the body of the car, as a 1:6 factor has to be applied when the car is moving and that weight becomes mass. In fact, we are conservative with the 1:6 ratio, as Porsche considers it to be 1:7"
                                         
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                                        • StPaulSwinger

                                          StPaulSwinger FABO Gold Member FABO Gold Member

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                                          The Wilwood kits I'm seeing are definitely more expensive than what you're showing (in the 900 range), not sure if it was a short duration sale or something but I thought I checked their site around the 4th to see if they were running any specials.

                                           
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                                          • 72bluNblu

                                            72bluNblu FABO Gold Member FABO Gold Member

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                                            More name calling, still no facts. If you've tested them, post the data.

                                            Yes, for the 10th time, calculated clamping force assumes 100% transmission to the rotor, which is not achieved by ANY caliper. But the Wilwoods are at a 24% total force disadvantage. That's not a small difference, and would mean the Mopar disk would need less than 80% efficient to match the Wilwoods for stopping power. Is that possible? Sure. I seriously doubt they're that bad though. Even if they really are that inefficient, it means they provide similar stopping power for significantly less money. Which makes them a perfectly valid choice in a comparison against the Wilwoods.

                                            Again, post your data showing how much more efficient the Wilwoods are at putting clamp force to the rotor and prove your case. Or just keep calling me names, but I couldn't care less. Resorting to calling me names just shows you don't have any real data to support your case.

                                            - You quoted a sale price on the Wilwoods. Nice if you can get it, but you're not comparing straight across

                                            - The original poster of this thread doesn't need spindles, he already has them for the '73+ disks.

                                            - Sure, you can arbitrarily add more brake line pressure to just the Wilwoods. But if you compare apples to apples using the same brake line pressure, the 73+ Mopar calipers still have more clamp force. If you're willing to increase the line pressure, you can do it for the Mopar calipers too. On that note, the 70 lb applied pedal force I used is already kinda high. Most newer cars with boosted systems use a pedal input of about 45 lbs. Maximum pedal pressure is usually assumed to be around 85 lbs, but that's not a sustainable force for most people. 70 lbs is typical for performance type vehicles, where it's assumed the driver is in decent physical shape. You can assume an 85 lb input force, but you may not be able to generate that all the time, which means you're not putting that force to the rotors all the time either.

                                            - Yes, removing unsprung weight is always an advantage in performance. But, you're talking about racing and ET's, not brake force. If you want to spend cubic dollars to save a few tenths at the track, awesome, buy Wilwoods. But not everyone here is talking about racing, they're talking about having reliable brakes on the street.
                                             
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                                            • 72bluNblu

                                              72bluNblu FABO Gold Member FABO Gold Member

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                                              Yup, that modification works great. Those are 11.75" rotors with the same 2.75" piston diameter Mopar calipers. They'll outperform the 10.95" rotors for braking force because of the larger diameter rotor, and they make for a great braking system.

                                              They do require 15" rims though, and like the 10.95", 73+ rotors they're the large bolt pattern.

                                              If you have the 73+ spindles, all you need to use the 11.75" rotors is the rotors themselves and a new set of caliper brackets. DoctorDiff sells them new if you can't find them locally.
                                               
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