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+power disk brake conversion

6K views 27 replies 7 participants last post by  wk2hons 
#1 ·
I bought a power front disc brake conversion kit from Summit Racing. Started with drivers side. took brake drums shoes, and backing plate and hardware off, only to find that the main bracket for the calipers wouldn't match no way no how. Put my drum brakes back together. I'm sick of these companies saying that a certain conversion will fit. They are refunding my money. Does anyone know of a power brake unit with master cylinder and proportioning valve that I could install and keep my drum brakes?
 
#2 ·
If you retain your drum brakes you don't need a proportioning valve. A proportioning valve is used on a drum disc system because disc brakes require a lot more line pressure to work. Drum brakes are self acting and require a big honking spring to retract the shoes once applied, not a lot of line pressure. This is why most disc brakes are power assist to keep Granny Goodwrech from getting a run in her stockings from standing on a non-power assist with both feet on the pedal..

There are many brake kits for your car. Price affects quality and safety of the parts.

The cheaper kits use parts from the bad part of Asia, Pakistan and India. They are to quote a phrase unsafe at any speed, but they are cheap.

Medium priced kits use brakes off of a G-body from the mid 80's. Those kits don't tell you that you can find these parts at many auto stores as they want you to buy their expensive kit. Look on line for a complete parts list. Once again the cheaper the part the more dangerous it is.

Finally there are the premium part kits made out of billet material by NASCAR racers turned auto parts resellers (Baer and Wilwood). They all offer from stock to huge rotors and caliper designs. From nine inch rotors to over fourteen inches in diameter, with one piston floating calipers, up to six piston bridging calipers.

As to a power assist master cylinder Rock Auto dot com has all of the replacement stock parts that Chevy used (eleven inch vacuum diaphragm, activating rod to fit your master cylinder (there are four different types) and of course the master cylinder sized for drum brakes.

Big Dave
 
#5 ·
I didn't see the model year of your car...

Try giving Tobin at KORE3 a call. He mostly makes big GM brake kits for older cars and often covers applications not listed on his web site.

I have his C6 Z51 kit on my fronts and rears. The kit is not listed on his web catalog and I had to wait about 6 weeks for him to make the front hubs. Well worth it. Fit was perfect and he was always available to answer questions.
 
#9 ·
What made you want to keep your drums if Summit can sent you the right parts? Mainly asking because I’m trying to decide if I want to convert my drums to disk also and I’m curious to see what your take is. Just don’t want to deal with the hassle of it all?


Sent from my iPhone using Tapatalk
 
#13 ·
If Summit indeed sold you a kit entirely from "The Right Stuff", that companies' kits have worked well for many members on this forum.

Either the wrong kit was sent, or maybe it got packaged wrong. Either way, both companies are solid and work to make us DIY'ers satisfied.
 
#14 ·
I've previously installed a CPP rear disk kit. Initially it did not fit and there were some issues that CPP worked to resolve fairly quickly. I got everything installed and working but it was marginally satisfying.

The KORE3 kits kits are a giant step up in quality and function.
 
#26 ·
Difference between drum and disc is the disc requires higher line pressure to work. Drums are self activating and requires a big strong spring to pull the shoes off of the drum as opposed to a disc requiring lots of effort to keep the pad in contact with the rotor to prevent creep at a stop light.

A motor with a big cam and a power booster could have your car creeping up on the bumper in front of you regardless of how hard you stand on the brake pedal. It is rarely a question of stopping the car, but in keeping it held in place. The vacuum level, diameter of the diaphragm, and piston diameter in the bore that allows your car to have power assist.

A Power Assist Disc Brake master cylinder will have a bore of at least an inch, or larger. A Power Assist Drum Brake system rarely exceads 7/8th of an inch; full manual (no Power Assist) has an even smaller diameter closer to 3/4 inch. Master cylinders differ by 1/64 of an inch so "About" has a lot of 64ths of an inch in it: different cars with different engine displacements, and different curb weights all use different sized parts.

Disc brake kits are put together by business men trying to make money, not engineers concerned about your safety or the safety of the car in front of you. The lawyers are not going to sue CPP, MPB, or any other reseller of factory brake parts, when you are the one who installed them.

There are so many variables such as brake rod end, length or location that most don't even think about. Does your new and improved disc brake system still have the residual valve that retained brake pressure to the wheels to prevent sucking in air on drum brake wheel cylinders? Did you install the proper proportioning valve to match the length of brake line from the MC to the rear axle? Have you sized the diameter of the master cylinder to match your caliper piston size? Have to remember a factory correct Power Assist master cylinder for a 1969-'76 full size car is sized for "big" wheel caliper piston bores on the optional disc brake package. The "Metric" G-body brakes frequently sold in aftermarket disc kits or the even smaller bore twin piston calipers 3rd gen F-body calipers are not going to behave with a mismatched master cylinder.

Just ask the man on the phone that you are buying these kits from to see if he even knows what you are talking about, or was he selling shoes the day before? Brakes are not a fashion statement! They are important and thought needs to be put into modifying the system or replacing parts that are mixed and matched by price point.

Big Dave
 
#27 ·
Dave, this is exactly why I'm careful about referrals for brake kits. Over in the pro touring forums there are literally dozens of people pulling their hair out about crappy disk brake conversions that don't stop their cars. A few knowledgeable guys usually step in with the usual questions about MC bore diameter, residual valves, brake pedal leverage, etc. People are actually getting into the weeds about needing larger diameter brake lines because they don't understand simple hydraulic circuits. All of this to save $150 by cobbling together parts. I ordered all of my parts from one guy who only does brakes. Aside from knowing what he is doing, he basically just copies the OE brake circuit over complete and if you don't try to make any changes, it just works. He'll even give away the advice for free and let you go off and fabricate your own stuff. Why people don't plan out something as important as brakes is beyond me.
Yes, getting my parking brake working was a bitch. It was actually the most challenging part of the whole thing. On the flip side, I absolutely hate working on drum brakes because of the added complexity. No disagreement that they work though.
 
#28 ·
The power booster with the master cylinder that I got from Roc auto.com, meant for power drum brakes, the master cylinder looked about the same as the manual master cylinder. I bench bled the master cylinder, and then each wheel cylinder starting from the one farthest away from the master cylinder. and the rod does go to the lower hole in the brake pedal. It stops a whole lot better.
 
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