burnfingers

Just picked this BSO* up on Craigslist because of the really obscure 70's Shimano disk brake on the rear hub, somehow it made it through the last 40+ years in really nice condition. The story as I know it is that these were produced by Shimano from ~'74 to '77 before being discontinued officially, and as in this case were typically installed on sh*tty Dept store frames here in the US. And I mean sh*ty, we're talking a gas pipe lug-less frame with a nasty single-piece crankset, brake-plate in place of a proper hanger, open-ended seat stays, seat and chain stays that 'clamp' onto the dropouts, plastic shift levers... this is a typical "Shimano equipped" 70's bike boom 10-speed courtesy of JC Penny, the kind of thing I usually avoid like the plague. But, all that aside, the disk is dam cool imo; I'm hopeful that I'll be able to swap it over to a proper frame. Just thought I'd post this as a rider interest item, I had no idea disk brakes were being experimented with back in the 70's until I saw this one.

Thoughts having tuned and ridden it:
-serious stopping power. I read somewhere that they were fairly weak, with this one at least that's absolutely not the case. much more grip than my dia compe dual pivot calipers
-heavy with a capital H, the disk is stainless and the caliper looks like cast steel, steel hub too. probably adds 6lbs or more to the bike
-tricky to adjust the caliper, it has a very crude tilt adjustment bolt and outside-pad adjustment but no lateral adjustment was provided for
-the chain torques the hub in one direction when pedaling and the disk in the other when braking, seems to be really good at loosening spokes
-gets the POS Dept store bike way more attention than is fair

*Bike Shaped Object

Shimagnolo

I'm impressed by that disk. It looks like there is enough mass there, and swept area, to actually handle the heat generated by repeated hard braking on a mountain descent.

Metacortex

I believe JC Penny was one of the first to offer a bike (made by Huffman) with the Shimano disc brake in the '70s. You can see the disc brake bikes in the 1975 "Great America Bicycle Tour": https://www.youtube.com/watch?v=k10233DdFi0

Here is another video showing one of these bikes: https://www.youtube.com/watch?v=Eqqa0sg9HNo

A close-up of the Shimano disc brake can be seen here: 2002 Disc Brake Up Close | The Sprocket Podcast

Lascauxcaveman 

Both ahead of it's time (because of the technology) and yet really dumb (because of the added weight). Automotive marketing in that era, at least in the US, made a very big deal of advertising disc brakes (or more often POWER disc brakes) as a significant performance upgrade. The JCPs of the world would be happy to piggyback on this to sell BSOs to teenagers who were also thinking of cars, even when they were still on bikes.

What a neat time capsule you have there.

Mos6502

It's pretty neat, and in all honesty would be out of place on any better bike. Plus Murrays aren't that bad compared to AMFs and Huffys. I've always found them to ride and handle better than their bottom of the barrel brothers (probably because they used a better frame geometry and brazed joints instead of welding).

burnfingers

I disagree, something as unusual as this would add a lot of intrigue to a nice commuter that would otherwise blend in. Or at least I think so, I'll be sure to add a thread when I start the project and see what ppl on here think.

For the sake of completness, here it is without the dust cover. The lower of the 3 bolts and the random one above the cover adjust the camber of the caliper, and the more I look at it the more I wonder if that big central nut is the lateral adjustment I was looking for earlier. I'll tinker with it. The caliper is rubber mounted btw, not sure if that was clear in in other pics.

Reynolds 

I think I saw that brake on 20"-wheeled, stick-shift, banana-seat bikes from the '70s.