Is this factory master cylinder?

[Toro]

In changing my master cylinder on my 72 4wd Blazer, I'm not sure if what I removed was factory or not. After reading other posts across the board, it seems that shallow bore MCs are for power brakes, and the deeper bore MCs were for manual brakes. Mine has factory power brakes, but when I removed the MC, it has the deep bore, and the longer push rod coming out of the booster. Originally this was posted on the truck board regarding bleeding, but a few pointed out that my setup was not correct as it should have been from the factory. And the PO must have changed the MC. I guess it doesn't matter, but it made me wonder. So, do any of you know what the factory MC setup would have been, or did any of you run across this on your Blazers/Jimmys?

Please see the photos below of what I pulled off. Judging from the way it was and looked, if it wasn't from the factory, it had been on there a long, long time.

[hemi43]

That's a drum brake master cylinder, and 72 came with discs. So, no! it's not original, IMHO.
Most OEM disc master cylinders will have a larger resevoir for the front calipers.

This is how my all original K5 came with. It's a 1970, so it had drum brakes all around.

[Toro]

Thanks for the photo. I think anyone would agree, trying to figure out what PO did years ago is impossible. Just didn’t get why if MC was replaced, you wouldn’t just use correct one, and then go to the trouble to change booster rod just to use the wrong one. As I said, who knows, but thought on the odd chance Blazers came this way I would ask here.

[1970cstblazer]

Per the 1979 parts book, the correct 1971-72 Blazer master cylinder with power brakes is 5472650, which is described as Moraine oval with two wire bails for retention. The master cylinder on my 1972 Blazer parts donor is like the one in the first post. My 1970 Blazer with front drums has the smaller unit as posted above.



Another pic of an untouched original 1972 Blazer from this forum:



A beautifully restored Blazer from a member of this board

[Toro]

Originally Posted by 1970cstblazer

Per the 1979 parts book, the correct 1971-72 Blazer master cylinder with power brakes is 5472650, which is described as Moraine oval with two wire bails for retention. The master cylinder on my 1972 Blazer parts donor is like the one in the first post.

Thanks for sharing this here, that is good knowledge to have as I've seen lots of conflicting info about this, specifically that it was drum/drum MC and would not have been factory for a 72. Do you know if that part # was cast into the MC? I'll give it a look over and see if I can find it.