The 67-72 One Ton Brake Booster Swap Guide ***PICS***

[AJs72K5]

On these old rigs we all could use some better brake power. It doesn't matter how much horsepower and torque you put to the ground if you can't stop the truck. To upgrade the brakes on one of these rigs you have a couple of options: hydroboost or a 1 ton vacuum booster. The one ton booster was supposed to be an easy swap, so that's the direction I took.

I picked up a 1 ton booster and master cylinder combo from the local auto parts store. The most cost effective (cheap) was a Cardone model 50-1007....basically a rebuilt Delco Moraine. I wanted to make the swap as painless as possible, so I went with the booster and master cylinder combo. If you choose to go with a different brand, you'll need to get one for a 1971 or 1972 Chevy K20 or K30...other models, including GMC, will work, but that's the easiest to remember.

Once you've got your new-to-you booster, the next order of business is to remove your the old booster. Here's my old one (left) next to the new 1 ton (right). The differences are pretty easy to spot.



It appeared that the previous owner of my rig put a pre-1971 (drum/drum) booster on my 1972 K5. It's no wonder my brakes were lousy after swapping in a 14FF rear with discs.

Here you can see the difference in the lengths of the input rods. The pre-1971 being about 3.25"


The length of the input rod on the 1972 1 ton booster is about 5.5"


If you have a 1971 or 1972 1/2 ton booster your input rod will be the same length as the 1 ton. Your swap will be easy as you already have the correct bracket mounted to the firewall. It'll look like this:



If you were fortunate enough to have a 1971-1972 bracket already bolted up to your firewall, you can skip to bolting up the new booster.

However, if you have pre-1971 booster with the short input rod, your firewall bracket will look very similar, but be about 1.75" shorter.


This picture has a better measurement on the pre-1971 as I wasn't flush to the firewall in the picture above.


The pre-1971 bracket will need to be removed. I took mine off and headed to the local salvage yard in search of a 1971-1972 bracket. The two side plates are the pieces you're really concerned with. The center brake pedal lever pieces with the pins can be reused. Here you can really see the difference in the size of the two (71-72 on the left and pre-71 on the right):


Once you find them, get 'em cleaned up and painted and start reassembling the brackets. Here's the 1971-1972 assembled reusing the pre-1971 center section:


BOLTING IT ALL UP. Slide the bracket onto the studs on the firewall and run the nuts on, but leave them out about 1/4". This will give you some play to hook up the brake pedal rod and later the booster itself. After attaching the pedal rod, push the bracket and lever up against the firewall check to make sure your brake pedal hasn't come forward and turned on your brake lights. You may have to adjust the throw so that your brake light relay isn't tripped (I got everything together before realizing this and had to tear it all back apart). Assuming your pedal throw is good, line up the studs on the booster with the bracket and slide it on. Run the nuts for the booster on and leave them out about 1/4" like the bracket nuts. This will give you a little play to hook up the booster rod to the brake pedal lever on the bracket. Once you've done that, tighten the nuts for the booster and then tighten the nuts holding the bracket to the firewall. Last step: hook up the vacuum hose...it's not much of a vacuum booster without one!

The money shot:


Keep in mind that if you do go with the 1 ton master cylinder as well, that the brake line outputs are backwards from a 1/2 ton. The rear brake resevoir is in the front of the master and the front brake resevoir is in the back of the master. You can see that the lines cross in the picture above. Bench bleed your new master cylinder, hook up your lines, bleed the whole system and you'll be ready to lock up some tires.

It should also be mentioned that there are two support braces that the 71-72 booster may have. They attach from the booster to the firewall for a bit of extra support. The donor truck I pulled the bracket from did not have them...someone else already took 'em.