65-66 Six Cyl Mustang 'Vert Rear Drum Brake Confusion - And Conversion


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I've owned my first car, a 1966 Mustang Convertible, for almost fifty years now. For that entire time, parts stores and catalogs have claimed my six cylinder convertible should have the same size brakes on the back as the front, and with a 29/32" wheel cylinder instead of the base 27/32". Kind of like the early Falcon sedan/station wagon difference. Yet mine had the narrower 1 1/2" shoes and the 27/32" cylinders since new. Look around various forums and you'll see many similar reports. I asked over at the Vintage Mustang Forums, and was told that no early convertibles ever had the bigger back brakes actually installed. If you look in the Ford shop manuals, no difference in the coupe and convertible brakes is mentioned in the specs. So what happened here? How have parts vendors perpetuated this error for so long? Where do they get their info? It's not just a few vendors, it's all of them. It boggles my mind that so big a mistake has gone on for so many decades.

Anyway, I did notice that my Mustang's brakes never lasted long. After all, a six cylinder convertible is heavier that an eight cylinder coupe, yet gets smaller brakes. So a couple years ago I decided to go ahead and put the wider brakes on in the back. Pretty straightforward once you get the backing plates. I already had lots of 9 x 2.25 parts laying around from my front brakes. About the only issue was the wheel cylinder. While you still see a lot of the wider 9" front drums advertised for the convertible back brakes, the advertisements for the 29/32" cylinders died out a while ago. I just left the standard 27/32" cylinders in for now. The early 6s have a universal fit rear cylinder, left or right, as the brake line comes straight in the back. I'm not sure if there ever was a straight in 29/32" cylinder, but there are angled inlet L/R V8 29/32" cylinders readily available. I saw in a thread here that's what the Falcon wagons used. There's also a 7/8" bore straight in inlet version.

So here's my question, finally. Was the wider convertible rear brakes something Ford intended to do, but somehow never got around to actually doing, and forgot to tell the parts vendors never mind too? Was there any real engineering behind the choice of the 29/32" wheel cylinder, or is it all just a typo? I haven't noticed any issues with my brakes since I put the wider shoes and drums on in the back, but I haven't done any emergency stops in the rain yet either. I can fit some bigger bore rear wheel cylinders in my car, I see a few different ways. I could bore out some old 27/32" center inlet cylinders and put in a 29/32" rebuild kit. But then if a one goes bad you can't order another, you have to custom build again. I could go up halfway and install some 7/8" bore center inlet cylinders without much trouble. But if 29/32" is ideal, I'm better, but still a little short. And then I could use a pair of the 29/32" V8 cylinders with the angled inlets. I'm not sure if the six cylinder lines can be bent a bit to match, or if the V8 rear brake lines will fit on my six cylinder axle. A little bit more work, but probably doable. But I don't want to if I shouldn't. Any thoughts?
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An update to my previous post - After a lot of ebay searching, I found some NOS 60s Ford wheel cylinders that have the 29/32" bore and straight in inlet, no left or right. The few current examples aren't in very good shape. They don't seem to be available new. But now I know what to search for. Once I pick up a couple, next time I crack open my brake system I'll give them a try, since they're a relatively easy bolt-in replacement. I still wouldn't mind some advice from the more technically educated experts around here though.


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I don't kno why your Convertable has the smaller wheel cylinders maybe someone changed tgem be fore you got it. All tge Ranchero.'s, Wagon's, Sedan Delivery's, and Convertibles, were suppose to have the largest brakes installed. August 18, 1964 to 1970 had one style wheels cylinders, the earlier wheel cylinders August 17 1964 and back to 1960 models are harder yet to get. Most of the time with the wheel cylinders can get by with a light hone and a cheap rebuild kit. If the cylinders are really bad they can be sent in to have them machined for a Stainless Steel Sleeve to be installed to bring them back to as good of better than a new one. Best of luck