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.

[vtblazer]

Nice post bro.

Thanks.

[1972CST]

Have you been sneaking around in my garage? This is exactly what I am getting ready to do once I get my firewall grommet for the brake rod. Great post, let us know how much difference you notice in stopping.

[jamie72]

thanks for the write up, i got one in the garage i`ll be installing when i do my motor swap.
jamie

[71jimmy]

Excelllent!!!!!!

Thank You

Needs to got into the FAQ!!!!!!!!!!!!!!!!!!!!!!!!!

[Willys47]

Thank you! I was going to up grade my trucks brakes and you have saved a bunch of work trying to making parts work together when they were never ment to.

[Big J]

I second it for the faq section. Thanks for takin' the time. I'll be doing this one.

[Gary 70 Jimmy]

That makes it look simple nice job.

[LUV2XCLR8]

Nice work

[big dump]

Was just reading this because I'm thinking it's time to upgrade my stopping power as well. What application of proportioning valve are you guys using with the 1 ton setup? Stock? I notice the one pictured is brass, is there a place to find these reasonably priced, and what's the application?

[72truckman]

What is the diameter of the 1972 1 ton in comparison to the regular 1/2 ton brake booster? I ask because i converted mine to hydraulic clutch and need to know if one of these will fit thanks!

[big dump]

Well Napa has the above mentioned booster and master cylinder as a unit. It lists the Booster Diaphram Diameter as 10 3/4". I'm not sure if that includes the thickness of the sheetmetal that encapsulates the Diaphram. Probably call it 12" in diameter to be safe for a little extra room. Anyone know of a good prop valve to use or the application to look for?

[AJs72K5]

Inlinetube makes direct replacement prop valves for 4 wheel disc, or disc-drum.

[Burt4x4]

AJ ~ Did you use the Inline P-valve?
Do you have 4w disk? can't remember..
if yes & yes what is the part number?

[AJs72K5]

Originally Posted by Burt4x4

AJ ~ Did you use the Inline P-valve?
Do you have 4w disk? can't remember..
if yes & yes what is the part number?

I am running 4 wheel disc. Part# PR102b

BUT, I'm also gonna put in a Wilwood adjustable prop valve on the rear brake line to reduce the pressure. The rears are locking up too early...even with the Inlinetube prop valve.

If I had to do it all over again, I woulda gutted the factory prop valve, and put the Wilwood valve on the rear line.

[Burt4x4]

If I had to do it all over again, I woulda gutted the factory prop valve, and put the Wilwood valve on the rear line.

Ya I have read about that, do you remember if you canjust "gut' the rear or when you "gut" the p-valve does it affect both and the inline on the rear is your only p-valve?
Sounds cheeper to gut it!

[big dump]

Does anyone know if you can rebuild the stock prop valve since nobody seems to know if there's a good application for a replacement that works with the 1 ton setup? Do any of the aftermarket adjustable valves have provisions for the brake light sending unit?

[tawd77]

Just to clarify for everyone, If upgrading to the 1 ton booster, you are not required to get the 1 ton master cylinder. You just have to retain the longer pushrod from the 1/2 ton booster, and slide it in the 1 ton booster, and the 1/2 ton master cylinder works great with it!!

[Burt4x4]

The mount too the boster is the same but would I do that...no, mainly cuz I wouldn't want an old master on my new booster. Remember too the 1Ton master is plumbed opposite of the 1/2 ton. Read that paragraph under the last pic in AJ's post^^^^
You can get a new master for like 30bucks at Autozone. Worth the peace of mind too me

Oh and you can buy replacement brake lines that go Master too Pvalve from inlinetube.com for like 25bucks and they fit perfectly.

[tawd77]

Originally Posted by Burt4x4

The mount too the boster is the same but would I do that...no, mainly cuz I wouldn't want an old master on my new booster. Remember too the 1Ton master is plumbed opposite of the 1/2 ton. Read that paragraph under the last pic in AJ's post^^^^
You can get a new master for like 30bucks at Autozone. Worth the peace of mind too me

Oh and you can buy replacement brake lines that go Master too Pvalve from inlinetube.com for like 25bucks and they fit perfectly.

So, your telling me I should replace my brake master cylinder, that was replaced less than a year a go, and works perfectly, because I put a new booster on? That makes no sense. If its isnt broke, Im not going to fix it. If the master cylinder does go out, I will be replacing it with a 1/2 ton master cylinder. The brakes work twice as good as they did before, so there is no need for the 1 ton master cylinder. It just makes it a pain, to have to switch brake lines around....

[swyfor5]

Or-- you could just buy the whole setup from one of our fine boardmembers here like I did. 1 Ton booster, 1 Ton master cylinder, prop valve for 4 wheel disc brakes, brackets, rod, boot, etc. Yet to be installed, but one sweet looking setup! Tried to post some pic's, but computer is not cooperating right now, need some help, will post up asap.

[swyfor5]

Here's some pics!

[trukman1]

Originally Posted by tawd77

So, your telling me I should replace my brake master cylinder, that was replaced less than a year a go, and works perfectly, because I put a new booster on? That makes no sense. If its isnt broke, Im not going to fix it. If the master cylinder does go out, I will be replacing it with a 1/2 ton master cylinder. The brakes work twice as good as they did before, so there is no need for the 1 ton master cylinder. It just makes it a pain, to have to switch brake lines around....

If you have a M/C that works great then, well, great. I would like to caution members about buying the rebuilt units. I bought a rebuilt unit and was driving down the road with working brakes most of the time but sometimes I'd go to stop and no brakes! I replaced that M/C two more times, (warrantied for life deal) same thing. At this point I'm thinking it has to be something else. Local mechanic asked if I was buying rebuilt units...yup! He said to buy a new unit and, walla, brakes worked fine. He said as the units get old the bore wears. When the units are rebuilt they are not re-bored and fitted with a larger piston, just the O-rings and seals are replaced. He said that it can cause the piston to hang-up in the bore and the fluid to pass around it giving you...no braking power. Bought a new unit for only $10 more than the rebuilt and no more problems. Just thought I'd let people know so they can avoid the problem I had. YMMV.

[BLUE THUNDER]

So, I can use my existing master cylinder and just swap out the booster. Sweet. I need to do this. I've noticed that sometimes I don't have enough braking power even with 33's I'm anxious to try this swap.

[tawd77]

Originally Posted by BLUE THUNDER

So, I can use my existing master cylinder and just swap out the booster. Sweet. I need to do this. I've noticed that sometimes I don't have enough braking power even with 33's I'm anxious to try this swap.

Yep, the little rod between your booster and master cylinder will have to be reused with the 1 ton booster. The 1 ton booster comes with a rod that is much shorter.