did all SS in 66 have prower drum brakes? If not I well do they stop a big blocks. I am going to put on dual master cyindler on my car for saftey reasones, and thinking of puting disk up front and not have power brakes. is that a good idiea.

Keith,

My 66 Chevelle originally had non power 4 wheel drums with a single type master cylinder. During its rebuild I changed over to 70-72 spindles and rotors with a dual Master and an adjustable valve. They work great.

Power brakes were an option, disk brakes were not available until 67 and became standard with the SS package in 69. If you're planning to drive the car regularly a disc brake conversion is a good idea. You can buy kits from a lot of different suppliers or look for any 69-72 GM A-body (67/68 setups are harder to find) for a complete bolt on conversion. make sure to get all lines, brackets, spindles, and prop valve from the donor car. search this site for a lot of info on disc brake swaps.

In the beginning all Chevelles had the same brakes as standard equipment, namely 9.5” manual 4-wheel drums. Power assist was an option, but with the self-energizing drums it just made them too touchy in my opinion. It really didn’t address the issue of brake fade that is inherent to drum brakes with asbestos linings.

In 1965 the limited production Z-16 (Malibu SS 396) used larger 11” drums from the full size Chevy and did improve things some. Power assist was standard on the Z-16 as well.

I’m not sure when metallic brake shoes (RPO J65, Sinistered Metallic Brakes) became optional on Chevelles (1966?) but they improved things significantly. They were optional on all U.S. Chevelles but in Canada they were only offered if you had a 396 under the hood. This situation repeated in 1967.

For 1967 a new and welcome option appeared, (J50/J52) Power Front Disk Brakes. They were a 4-piston fixed caliper design and included the 5-slot wheels that would soon be known as Rally Wheels. Disk brakes were offered on any and all Chevelles. They weren’t that popular in ’67 though. With each passing year they would gain in popularity.

For 1968 manual 4-wheel drums were standard on the SS for the last time, but the SS and a limited number of other applications (327 4-speeds, cars with a/c) got finned front drums to help with heat dissipation. The metallic brake shoes were discontinued however. It is a moot point since the power front disk brakes were optional. I believe that the Rally Wheels were initially standard with disks but during the run were dropped from being standard.

For 1969 the Power Front Disk Brakes became standard on all SS396s, COPO 427s, and Police cars with 350s upward. They were redesigned into a simpler, cheaper, more forgiving single piston floating caliper design. The pistons were not prone to jamming in the bores or leaking like the 4-piston design, and the floating calipers were more tolerant of runout (slight lateral warpage) of the rotors. These are the brakes that are desirable for swapping onto the earlier cars due to less expensive and easier to find parts, plus they were far more common to find on donor cars. I think the finned drums became standard on all drum-brake cars.

Self-energizing drums were named as such because the leading shoe ‘grabbed’ the drum when you hit the binders and thus helped to reduce the effort in applying the brakes. The trouble with drums is that as the shoes heat up (and they do because of the enclosed design) the shoes go out of round, as do the drums on their own time as they heat up. This reduces the brake contact area. Also the asbestos loses some of it’s friction properties as it heats up. This manifests itself in dramatic brake fade. You get one panic stop at high speed with the standard drums, then your brakes ‘go away’ and make lots of smell. The J65 Sinistered-Metallic brakes helps in a number of ways. Firstly the iron did not lose it’s friction properties as they got hot. Secondly, the iron was welded onto the shoes in patches. As they heated up, the gap between the patches closed up some rather than distort the shoes and reduce contact area as with the regular asbestos linings. The iron shoes wore like granite (a little hard on the drums though). Since the friction material was hard and actually needed to heat up a bit for an initial brake use, Chevy suggested the optional J50 Power Brakes as a good pairing with the metallics. Not necessary if you posses good legs muscles though.

Today it is most popular to swap front disk brakes onto cars not already equipped. Disk brakes don’t lose contact area as they heat up, and since the rotors are exposed they cool down more effectively anyway. One reason that power assist was deemed necessary for the masses is because of the higher line pressure needed to squeeze tightly on the calipers, plus there are no self-energizing properties as on drums. The disparity in line pressure requirements are partially why a proportioning valve is necessary.

Another excellent and viable alternative to tossing the drums in the trash is to upgrade them with modern Kevlar linings. I believe Praise Dyno makes them. They dramatically improve drum brake performance. Just make sure that your wheel hub seals, axle seals and your wheel cylinders are not leaking,.


There’s my short answer :D

Cam, that was great. I learned a lot. No question, drum brakes just don't stop as well as disk, and now I know a bunch more of the why's.