Hello. Thinking of swapping 11" rear drum brakes onto my 72 skylark. I have found a post on chevelle tech ( also an abody car) on swapping 11' drums. Certainly a lot less expensive than a rear disc conversion , by a longshot !! Should be relatively inexpensive , provided I can find the backing plates in a salvage yard, rotors are brand new for $30-$40 each , pads for $20 , and new hardware for $10-$12. I think the wheel cylinders are larger ( probably get those new as well ) Since my master cylinder is set up for 4 drums, there shouldn't be any necessity to change this.. I wonder if another proportioning valve will be necessary ? I'll have my parking brake and better stopping power, since logically there's more surface area for stopping. Since the police interceptors used the 11' drums, it should make a big difference in stopping. Anyone out there ever done a 11" rear rotor conversion ? Another bonus is of course is that it should be a bolt-on proposition , with the 5 x 4 3/4" bolt pattern. Any thoughts ? I plan to do this soon , since the brakes need some work anyway.. I'll post some information, and let everyone know how it turned out. Maybe a little mini writeup with some pics.
The 11" drums provide slightly greater swept area - versus the standard 9 1/2 " rear drums. Believe Master Power Brakes sells the entire setup new, as well as possibly others. The 73 - 77 A cars with the 11" drums are the setup you need to use. Don't believe 11" rear drums with 5 x 4 3/4 bolt pattern was used anywhere else - 65 - 67 Chevelle and a few 65 - 70 full size Chevies possibly. Could source you a good clean used setup from a desert southwestern donor - with clean backing plates, hardware, and drums.
73-77 a cars would include the Malibu , correct ? Looks like the el camino has the 11" drum as well . Maybe some of the full size gm cars , caprice, impala, etc .. ? Have to take my tape measure out to the junkyard . How much are you asking for the setup for the rear pair ? And the shipping ? i am in colorado . I am sure with new hardware and shoes it'll make a difference in stopping power..
Based on a little research I have done, rear brakes do not really make a big difference in braking power. I don't know how accurate this is, but I read that rear brakes only account for around 30% of braking. Depending on your car's front brake setup, perhaps, working on those would be a better option, and should not be much more expensive. If you do decide on the rear brakes though, and are having a hard time finding parts, maybe, (big emphasis on maybe :laugh early 90s b body drum brakes can be swapped in. They are 5x5, but if you were to go that route, maybe you could re-drill the drums or use adapters.
Very interesting, I need to build a rear set up and have 73/7 backing plates of a 76 Century. Are these the same as wagon? Are there any difference in regular 73/7 A body rear brakes and Wagon?
My '65 2 door Impala has 11" rear drum brakes with 4 3/4" bolt pattern rims. I think the '65 to '70 cars are similar but not sure of the bolt patterns on the later cars. Has 11" front drum brakes as well, combined stops that car good enough from just over 100 mph to make the first turnaround at Milan Dragway! The car is NOT light either, around 4,400 lbs with my fat but in it! Derek
I do not believe that the '73-'77 bolts are on the 4-3/4" bolt circle, but the larger bolt circle like the big cars. If you want more stopping power you can switch to station wagon rear brakes, with are 2-1/2" wide. But since you don't have the same weight distribution as a station wagon, it won't help all that much, as oldsbuickhybrid pointed out,as well.
Thanks everyone the input and advice.. I appreciate it !! The impala with 11" front drums is very interesting ... Hmm Your impala has 14" or 15" wheels ? I bet those backing plates, hardware. etc are a lot cheaper than a disc brake conversion. I could get a complete front end from a 1970 gto, with the spindles etc.. for $400, then I'll still need the master cylinder, lines, prop valve, etc. This doesn't seem cost effective though, since my front end is in decent shape, I just need new bushings, tie rod ends and sway bar links.. ( and shocks ) I think I'll scour the area for some more alternatives, I can get new hardware , shoes, and adjusters from NAPA, Advance. car quest , and tons of other places . So if I can just find backing plates I need with 5 x 4 3/4" pattern somewhere, I'll be in business.. I think my back wheels have a universal bolt pattern ( provided I keep the old centerlines on the back ) , and I am sure I could run adapters on the rally wheels , just push the wheel track out a smidge.. Now my brain is full of possibilities ! I don't think the skylark weighs anywhere near 4400 pounds, unless I put the extra transmission, alternator, carb, ac compressor, and five rally wheels back in the trunk..p
Don't change the shocks, unless you are going to some high performance ones. The same front shock fits everything from a Chevy Vega to a Skylark GS. The active valving takes care of the different car weights. '71 Chevy Vega- CEE-2600 from Summit '71 Skylark GS- CEE-2600 from Summit Crazy but true! I learned this over 30 years ago when working as a mechanic.
73 - 77 GM "A" cars have a 4 3/4" wheel bolt circle. 71 - 76 GM "B" cars have a 5" wheel bolt circle. 77 - 90 GM "B" cars had either a 4 3/4" or a 5" bolt circle. 91 - 96 GM "B" cars again had a 5" bolt circle exclusively. Some of the 73 - 77 A cars had the "standard" 9 1/2" drums, and many, but not all had 11" drums. A previous poster mentioned wagons. Wagons may very well have had wider shoes in the rear, and thus wider drums.
Here is some info on aluminum 11" drums (8 lbs lighter per drum) from certain GM A or G bodies which will work (conversion) for '68-'72 A body conversions to 11" rear drum brakes: http://www.buickperformanceclub.com/aldrum.htm. If you can identify the part number for the larger 11" diameter brake shoes (for rear drum brakes), you could do a reverse compatibility search for the years/models which had these brakes standard and then search for those models in the junk yards. The G bodies ('79-'87) had 5 x 4.75 in bolt patterns (Monte Carlo, Malibu, Cutlass, Grand Prix, Grand LeMans/(small)Bonneville & Regal).
Years ago Charlie Evans had mounted a set of the ''69-'70 front aluminum drums on the rear of his car. Didn't stop the car that much better, but did provide extra holding power on launch. Similar to what the Turbo guys do with the S-10 brake cylinders. Something else to think about.
