Front brake disc conversion

Discussion in 'The whoa and the sway.' started by Droff, Dec 12, 2018.

  1. Droff

    Droff Well-Known Member

    Not to beat a dead horse on a brake conversion but I’d like some input if you all have any.

    I’ve got a ’67 GS with drum/drum and want to convert the front only to disc. I’ve got 14” wheels and from what I’ve found in some other threads, the 14” wheels could either be for drum or for disc, and there is a difference – caliper/rotor fit seems to be the problem. At some point I’ll be going to either a 15” or 16” wheel but right now I’m okay with 14”. I’ve got the wheels and a new set of tires.

    My unknowns are with the conversion kits. I’ve got 2 or 3 options lined up from suggestions in other threads but the 14” drum wheels I have are making me wonder about choosing. I don’t want to end up limiting myself down the road or end up buying another brake setup.

    I can get a kit for 14” wheels;

    This will work with bigger wheels, but would I have anything I’d need to be concerned with down the road if I go this route?

    This kit says it’s for a 14” wheel and larger, at least on the Right Stuff site;

    The same kit on the SS396 site says 15” wheel or larger;

    So, more gray area stuff…

    I don’t want to ‘make something work’ but a little bit of fiddling around to get things working doesn’t bother me. I don’t want to piece things together, so I prefer going with a kit.

    Appreciate any input you all may have.

  2. Gulfgears

    Gulfgears Gulfgears

    I did my 66 Skylark using a 72 Skylark disc brake setup. OEM type stuff, and 14" wheels I had fit fine. Got calipers, rotors and pads from Autozone. I know with all the parts hoarders there are on this site, someone has a complete 72 change over gathering dust. You already have the dual master cylinder, so you will only need to buy a proportioning valve to make it work.
    Easy weekend job, and I'm no spring chicken.
    68ElectraCustom likes this.
  3. pbr400

    pbr400 68GS400

    If you have ‘drum’ wheels now, you probably will need to find a pair or set of disc wheels. If you have steelies or rallies it should be pretty cheap to source a 14” disc compatible replacement (you almost have to give 14s away; you can buy a set of 14” rallies ffom G body Regals for example). The 14” compatible disc conversion gets you the stopping power that was considered adequate for cars that size well into the ‘80s. Many are fine with that (sone are ok with drums still, just makes you plan ahead!). . If you want more stopping power, stick with drums until you can buy brakes, wheels, and tires in one shot. (I’m guessing the kit that’s 15”&up would work with disc 14s but they say 15s to be safe-I think all Abody 15s are disc safe. You may want to ask...)
    bostoncat68 and Gulfgears like this.
  4. telriv

    telriv Founders Club Member

    YOU NEED A DISC BRAKE MASTER CYLINDER!!!! A drum brake master doesn't have enough capacity to supply the nec. fluid for disc brakes. Not saying a drum master won't work, as it will, but the brakes will not be as good.
    cjeboyle and Donuts & Peelouts like this.
  5. Droff

    Droff Well-Known Member

    I know there has to be some parts out there available, just don't feel like messing with running them down and making sure condition is good and buying new parts to work with the old. Did that not too long ago with a '68 GMC truck. By the time I got it on the road, a kit would have been much better time spent - at least for me.
    Was trying to avoid that big of a nut all at one time but it may be my best option from the way things sound.
  6. Droff

    Droff Well-Known Member

    How about a Booster size recommendation, 9" or 11"? Is bigger better or is this more of which one fits under the hood better?
  7. BrianTrick

    BrianTrick Brian Trick

    There are some 14” wheels that do and do NOT fit the factory style disc brakes. However,I have also found that the 14” rims that fit the factory GM disc brakes do NOT always fit the aftermarket kits. I did a customer’s car before,and he got a kit that looked 100% identical to one of my originals setups,BUT his wheels would not fit his kit. The wheels rubbed on the caliper brackets,but they fit my car. I figured that either the caliper brackets were bent or shaped slightly different,or the dimension of the rotor was somehow different,and it possibly moved the wheel in closer to the bracket.
    Yes,you need a master cylinder with a smaller bore. Drum/drum is 1 1/4” bore. Disc/drum is 1 1/8” bore. Less volume,more pressure.
  8. Droff

    Droff Well-Known Member

    I’m leaning toward either an Inline Tube or Right Stuff disc brake kit for the front end, it’ll most likely require 15” wheels but I’ll call whoever before ordering to get that lined out. I also plan on getting ahold of Hector about another steering gear just to update that. The gear in the car has a nice coat of grime on it, not positive where the moisture (oil, grease, whatever) originated but it came from somewhere.

    I’ve had the car for about a year, with little to no road time so while I have things apart in the front, I figured on replacing some suspension parts, as needed. I added some pics of the ball joints, pitman arm, idler, etc. When checking the ball joints the wheel is pretty solid, no wiggle and the top ball joints look like they’ve been replaced. The rubber boots, under the grease/grim, looks new. I haven’t figured out where it all came from, the engine has been cleaned up and looks pretty decent but everything in the front is nice and nasty. I’m just a bit surprised the ball joints look ‘new’ but are covered with crap like they are. Someone would just clean up the motor and do nothing with the front end otherwise?
    It looks like I’ll be replacing the control arm bushings but that seems to be the worst looking rubber under there.
    A question about the PS Pump hose. Is that supposed to be the length of that thing? Looks to be about 7" too long but I don't know what 'original' is supposed to be.

    Anyway, check out the pics and let me know your thoughts on the suspension parts – clean up and go or figure on replacing by the look of them? Replacement will be OEM type by the way.
    DSide1.jpg DSide2.jpg Pax1.jpg Pax2.jpg DSide3.jpg DSide4.jpg DSideControlArm.jpg DSideControlArm1.jpg

    Attached Files:


    STEPHAN LEENSTRA Well-Known Member

    Not sure any of this is true. The reasons for differences in master cylinders of disc vs drum brake are not because of fluid supply amounts necessary to operate the brakes. The reason some (not all) MCs made for disc brakes had bigger reservoirs was to have enough brake fluid in there to remove the possibility of running dry as the pads wear down - there's more travel as they wear vs drum brakes, the piston takes up the gap. Another potential difference is earlier drum brake MCs had residual valves in them to prevent the shoes from backing off too far to fast when letting off the brake pedal - they kept some pressure on them. They stopped using these at some point on drum brakes. Rebuilt units often don't have them.

    If you have a drum brake master cylinder that doesn't have the residual valves (they can usually be pretty easily removed anyway) and you make sure you keep up on the brake fluid - you should be good with a master cylinder for either. They should use the same piston bore as well, but if you go to power brakes, then you will definitely want to make sure you have the right bore master cylinder.

    And make sure if using manual brakes you don't use a power brake MC since you might not be able to provide enough pedal pressure when using the wrong bore size.

    Also you should make sure to use a dual reservoir master cylinder as well regardless of disc or drum brakes.
    Last edited: Dec 16, 2018
  10. BrianTrick

    BrianTrick Brian Trick

    If you are looking to rebuild the entire front end,with the disc brakes,center link link,tie rods,etc.,I might have all the parts. The suspension parts were for a 1970,but should be the same for 67.
  11. Droff

    Droff Well-Known Member

    Whichever disc kit I go with, it will have a new MC and prop valve.
  12. Bens99gtp

    Bens99gtp Well-Known Member

    I dont think there is a difference between power or non power matter cylinders. it's all in the pedal ratio from what I understood.

    there is a difference in the pressures disc systems need or drums. drums work around 700psi, disc works with pressures closer to 1000, so if you use a drum master on disc you will always has a soft pedal
  13. BrianTrick

    BrianTrick Brian Trick

    Correct. The drum/drum brake masters were 1 1/4” bore,and the masters for disc/drum were 1 1/8” bore. They were used for both power and manual brakes.
  14. Darron72Skylark

    Darron72Skylark Well-Known Member

    Looking at your photos, I'd plan on replacing all the steering linkage parts in the front end. Center links and tie rod ends can seem fine and solid until you unbolt them. That was the case for me. Once they were out, it was appalling how worn and sloppy they were. New Moog parts are a great investment.
    On the control arm bushings, those definitely look shot. I'd replace with Energy Suspension polyurethane bushings myself. Or upgrade to tubular control arms. Saves you a lot of time, and are already powdercoated and loaded with the nice bushings.
    I went with new tubular upper control arms and reconditioned the stock lower control arms myself. In retrospect, cheaping out on the lower control arms added a lot of time and effort to the project, and I probably wouldn't make that choice a second time.
  15. Droff

    Droff Well-Known Member

    Back to my disc upgrade questions.
    Not to ask a bonehead question but I can get conversion kits that use the stock drum spindle and keep the 14" wheels if I want. I would figure I could also run 15-17" wheels with this setup, not just the 14" wheels.
    Why would this be a bad idea, the size of the rotors maybe?
  16. Gulfgears

    Gulfgears Gulfgears

    I believe there is an article showing how you can turn down your existing spindles to accept the bearings for the disc brake rotors. Seeing as how you are going to have to replace the upper and lower ball joints, turning down the spindles is not a big, nor expensive deal. Then off to AutoZone or where ever and source rotors/calipers/pads/misc nuts and bolts.
    Then you can use 14" wheels.
    I went all OEM of a parted out 72 skylark and used 14" wheels.
  17. Droff

    Droff Well-Known Member

    So if I'm planning on going to a larger wheel down the road, would buying a kit for a 14" wheel now cause me any concern later?
  18. BrianTrick

    BrianTrick Brian Trick

    I worked on a customer’s car that had some type of disc conversion,using the original drum spindles. I was not impressed with it at all. The way the caliper bracket was fastened,required one of the bolts to have a very thin head,and the backside of the rotor needed to be machined to clear the bolt,which left a lot less surface for the pad to bite on. I don’t know what company made that,but I would not get that.
  19. 12lives

    12lives If it runs, it's done!

    Center link on a 67 is different than a 70. I found mine at Speedway Motors.
  20. pbr400

    pbr400 68GS400

    Rotors that fit under a 14 are the stock size for the A and G body cars. These were considered adequate by 1969-1987 standards. Those of us who are used to drums, small rotors, vague steering, tires with sidewalls, sealed beam headlights, etc. consider them fine. Some people (especially magazine writers who idolized european cars) found them lacking in the ‘80s and are appalled by them now. Do you personally think a GN or Monte SS stops ok? If so, you’ll be happy.

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