72 or 73 and up 3/4 ton master cylinder???

[70rs/ss]

Like the title says, are you guys upgrading your 1/2 ton Blazers with the 3/4 ton master cylinder and booster from the 67-72 vintage or are you using the 73 and up 3/4 ton stuff?? I looked at NAPA yesterday and the mounting flanges are different, but I am sure they both could be made to fit?? Let me know as the price is the same for both, so if one fits better or they both work the same let me know and I'll use that one!?

Thanks for the help!,
70rs/ss

[Burt4x4]

What I did to my 72 was bought a 72 K30 1ton Booster & Master (pic above).

I don't know exactly when the change occured but there is a short style pushrod & a long. What I mean is the rod that pushes into the master from the booster can be a long style or short. So I would buy a matching set and then you should be fine.
Oh one ohter thing that is different is the brake lines that go to the Master are opposite on a 1ton than on a 1/2 ton. If you look at the pic again you can see my new lines I got from In-Line Tube http://www.inlinetube.com/
The back now goes to the front and visa-versa. I tried to rebend my onld line but wasn't working very well and the 20bucks or so I spent ont he two lines was way worth it...
Good luck hope this helps
Burt

[orange72blazer]

I just did this this summer, I used the stock 1/2 ton master cylinder and a 72 3/4 ton booster everything bolted right up and was real simple, I just couldn't use the bracket that goes down at an angle from the booster to the firewall. It stops way better than with the 1/2 ton booster.

[70rs/ss]

Has anyone done the swap with the master and booster? I can get the 1/2 ton or 3/4 ton master booster combo from Autozone Napa etc for $100 so if I can use them both from the 3/4 ton I'd like to. Is there any difference in the performance from the 72 3/4 ton and the 73 and up 3/4 ton? I want to do this this weekend, so any input would be greatly appreciated!!

[orange72blazer]

I think if you use the 3/4 ton master cylinder you have to change the lines around, I'm not exactly sure what all is involved but this is the reason I used the stock 1/2 ton master cylinder with the 3/4 ton booster.

[krue]

Originally Posted by orange72blazer

I think if you use the 3/4 ton master cylinder you have to change the lines around, I'm not exactly sure what all is involved but this is the reason I used the stock 1/2 ton master cylinder with the 3/4 ton booster.

I just put a 3/4 ton booster on mine with the same lines, no problems. I used the same m/c even.

[Burt4x4]

Originally Posted by 70rs/ss

Has anyone done the swap with the master and booster? I can get the 1/2 ton or 3/4 ton master booster combo from Autozone Napa etc for $100 so if I can use them both from the 3/4 ton I'd like to. Is there any difference in the performance from the 72 3/4 ton and the 73 and up 3/4 ton? I want to do this this weekend, so any input would be greatly appreciated!!

Is there a performance difference between 72 & 73 parts = No

The performance gain comes from changing the Booster from a single diaphram to a double.
When I was doing this swap I new for sure the 1Ton setup had the double diaphram booster I was after (the main reason I asked for 72 K30 1ton parts). My 1/2 ton master would not work with the 1ton booster I bought as my 1/2 ton master had a long push rod and the new booster had a short one...so I went back to Autozone and got the matching Master...everything bolted right up. I bent/modified the support rod that goes to the firewall so I could still have that inplace(double booster is much fatter). Now I can lock up my 35" swampers instead of praying for my rig to stop like before
Burt

PS ~ you do need to switch the lines to the P-valve if you get the double diaphram booster....simply swaping the master doesn't give you all that much...
.02c

[70rs/ss]

Originally Posted by krue

I just put a 3/4 ton booster on mine with the same lines, no problems. I used the same m/c even.

Just to be sure what I buy is correct and will fit/work properly.

You used the 72 3/4 ton master and booster (the $100 one I was talking about from NAPA or Autozone?) I am going to town tomorrow to get it!! Is it normal to be excited about having brakes that work?! Right now unless I jab at them hard and fast I have no pedel at all, now that is good for a butt pleat in the seat. If I keep it up I'll have a complete set of butt pleated seats for both sides (the guests in the Blazer are doing the passengers side for me!)

[krue]

Yeah, I got them used from Palf70step. The only thing is mine is a 70, so I could be bum doping you. Easiest thing to do is have them show you both 1/2 and 3/4 master cylinders side by side and make sure they're the same (I'm pretty sure the m/c's are the same regardless of truck rating.)

[JMac11]

Just curious

[low'n slow]

I'm intersted too. My new Jimmy has no power brakes. It's all over the road before I can get it stopped.

[1976K5CHALET]

Allthough i do not have an instant answer to your question i have a source who can answer your question. Over at coloradok5.com is a fellow who goes by mosesburb...a long time dear friend of mine who by the way is a walking breathing book of knowledge when it comes to gm part numbers...

Remember that last little bit of trivia and get a hold of him...he'll most likely blow your mind...i walk around with a notebook and a pen when i visit him to take notes...lol.

Anyways...i moved to colorado and decided to sell our (my wifes) project 72 Burb which i was unable to advertise because nick snapped it up post hast. Anyways besides the 90 Burb harness and various other improvements like my donated 31 g 79 K5 fuel tank....he has installed a late model P (?) series master and booster set-up...some fab work required...but if you pm him over there i'm sure he'd be glad to share his knowledge...

DW