'73 Power brake upgrade-booster?

[MARKDTN]

I inherited a '73 LWB plain truck. (originally thought it was a '74 but it's a '73) It's been sitting for roughly 15 years and the master cylinder is bad. I want to upgrade to power brakes. What booster can I use? Any square body? 73-74 only? I can deal with lines and vacuum and all that, just curious what booster I can use.

[ltdmstr]

I'm a big fan of hydroboost. I have a '68 that was manual steering and manual brakes. Added ps, front discs and hydroboost and it's like a completely different truck Brakes are outstanding.

[Corts60]

Hey if you don’t feel like worrying about all that brake stuff, I’m happy to come down there and take the truck off your hands. Haha.

But, x2, hydro boost is awesome. You can find them in any factory Chevy/GMC diesel truck from 78-87 and of course the 88-91 burbs/blazers.

[MARKDTN]

Appreciate the advice, but I am not a Hydroboost fan. Actually the same company that originally owned this truck before my uncle had an early 80s C30 with Hydroboost and it spit fluid all over the interior more than once. I think I will stick with vacuum. So can I use any square body booster or is it 73-74 only?

[ltdmstr]

Originally Posted by MARKDTN

Appreciate the advice, but I am not a Hydroboost fan. Actually the same company that originally owned this truck before my uncle had an early 80s C30 with Hydroboost and it spit fluid all over the interior more than once. I think I will stick with vacuum. So can I use any square body booster or is it 73-74 only?

That's pretty strange. If a line broke I could see how it would make a mess of the engine compartment. But I have no idea how the fluid could get to the interior. The only thing on the inside is the rod going through the firewall

[MARKDTN]

Very common issue back in the day. The seals on the rod leak and there were no rebuild kits available. I'm sure they are better than they used to be but this truck is going to be very stock. I don't want to have to source new lines etc. I just want to put a booster and new master cylinder. I just don't know what fits. If you look at applications on '73 boosters, many show '73-'74 but I don't see why it wouldn't work on '73-'87? Surely somebody has added a power vacuum booster on a manual brake '73-74 before.

[69Tom]

In case you want to double check what you're buying, there were 2 boosters used in 73-74. Moraine, PN 2620594, and Bendix, PN 6259004. Maybe just check out the rebuilt boosters? RockAuto has one for $95 and that's with the core charge.

Also, I assumed that's a C10, but if it's a C20, there was one booster: Moraine 2620595.

[HOTFUN]

Originally Posted by 69Tom

In case you want to double check what you're buying, there were 2 boosters used in 73-74. Moraine, PN 2620594, and Bendix, PN 6259004. Maybe just check out the rebuilt boosters? RockAuto has one for $95 and that's with the core charge.

Also, I assumed that's a C10, but if it's a C20, there was one booster: Moraine 2620595.

69Tom
I can't find reference to the Bendix PN 6259004 in the GM book as it does show for 73-74 CK-1 cab, Blazer use Bendix PN 346401. May be my GM book is printed later than yours as mine is 2/85?
Do you see an application reference for the 6259004 for 73-74 CK1 cabs?
Thanks, Mark

[69Tom]

Originally Posted by HOTFUN

69Tom
I can't find reference to the Bendix PN 6259004 in the GM book as it does show for 73-74 CK-1 cab, Blazer use Bendix PN 346401. May be my GM book is printed later than yours as mine is 2/85?
Do you see an application reference for the 6259004 for 73-74 CK1 cabs?
Thanks, Mark

Hey Mark. Those numbers are from an actual 73-74 parts book. So if I had to guess, the number you are seeing supersedes the numbers I posted.

[Dead Parrot]

Might want to double check if the brake pedal needs replaced/modified. Some vehicles had the manual brake post for the MC push rod in a different spot then the post for a power brake setup.

[Factory Guy]

I am with you on the vacuum Brake booster. Mine stops great, its a 1973 C2500 GMC 3/4 ton Camper Special. Since this was a little heavier duty set up, my vacuum booster may to be the same. But it will put you through the windshield if you stand on the brakes and this truck is NOT light. Mine is all original right at 100,000 miles on the odo.

Sorry it keeps rotating the picture 90 degrees.

[MARKDTN]

There are a whole lot more 75-87 trucks out there than 73-74-most with power brakes. I was hoping to find somebody to say, "yes, any square body booster will work on a 73-74 if you do XYZ". Or maybe "yes, 73-82 all bolt up to the firewall but the master cylinder is different". Or something like that. Maybe I have to have a power brake pedal? I know that I can buy a 73-74 booster from Ebay or Rock Auto, but I think I can find used for much less. I'm not worried about the fittings on the master cylinder; I have a Mastercool tool and can make new lines if necessary. I'm just trying to find out what vacuum booster will physically bolt on to a '73 without cutting new holes in the firewall or pedal support bracket. Then I can hit up friends and junkyards and find one. I will buy a new master cylinder, but I can't do that until I get a booster just in case they have a different bolt pattern. Thanks!