power brake ?

[sumtercleaner]

I have a 72 non power brakes, found a 70 that everything is powered (old wrecker ) can i switch everything out from the pedal to the proportioning valve to my truckwith no problems? Both v8. Is there anything else i need off the donor? Thanks also getting a much nicer door from it too.
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[Lattimer]

You need all of the brackets on the firewall and the linkage all the way to where it attaches to the pedal.

I know on C/10 trucks the proportioning valve is different after 1970, and the master might be too. 1970 had front drums, later trucks have front discs.

On my 70, I kept my old master and proportioning valve and just pulled it forward and installed the booster/brackets/linkage behind it. Took some adjusting of the pedal rod and the brake light switch, but it works great now.

[sumtercleaner]

Yeah. Im gonna get the pedal to the proportioning valve and bracket. I didnt think to see if it was disc, assumed so since it was power. Was powered drum an option?
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[Lattimer]

Originally Posted by sumtercleaner

Yeah. Im gonna get the pedal to the proportioning valve and bracket. I didnt think to see if it was disc, assumed so since it was power. Was powered drum an option?
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Yes, it was. If its a 1970 donor, its got drums.

[sumtercleaner]

So i should keep looking?
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[Tx Firefighter]

Just unbolt your current master cylinder and prop valve off the firewall and pull it forward. Leave all the lines connected and untouched. Then install the booster assembly to the firewall and bolt the master cylinder onto it. No need to swap master cylinders, prop valves, or even bleed the brakes.
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[PanelDeland]

There's a good chance that the 70 is a one ton.IIRC everything still works but most wreckers were the heavier truck.You may need to check MC and Booster brand to make sure they are compatable.I think the 3/4 and 1/2 are slightly different but not sure on this one.Hopefully someone with more experience will chime in on compatability.

[Lattimer]

Originally Posted by Tx Firefighter

Just unbolt your current master cylinder and prop valve off the firewall and pull it forward. Leave all the lines connected and untouched. Then install the booster assembly to the firewall and bolt the master cylinder onto it. No need to swap master cylinders, prop valves, or even bleed the brakes.
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Thats what I did with mine.

[Lattimer]

Originally Posted by sumtercleaner

So i should keep looking?
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You can probably use your existing master and prop valve, just add in the power parts behind it.

[sapper4]

I just did this this weekend. As long as the proportioning valve is what you need (drum/drum or disc/drum) it will work.

[jocko]

The mc's are different. So, a drum/drum mc is not ok for the 72's disk/drum arrangement, as stated above. Disks not standard til 71. Will it "work" - yes, but not correctly. A pre-71 prop valve is mostly just a pressure loss switch that will light up on your dash if you lose a circuit - the proportioning takes place inside a drum/drum mc by the order in which the ports are uncovered when you hit the pedal. A true disk/drum prop valve actually proportions as the name implies - but, the MCs are different and it's not really ok to use a 70 drum/drum mc with a 72 prop valve, because your mc AND your prop valve will both be "proportioning" simultaneously.

However, just leaving your current master cyl in the mix between your proposed 70 booster and 72 prop valve will potentially not be a direct bolt onto the 70's booster if you add it in. i.e. be aware that, in most cases, the depth of bore in the master cylinder piston is deep in a manual master cyl while it is shallow (and perfectly opposite the booster intermediate pushrod) in a power setup. This could be an issue if you put your current non-power mc onto the 70's booster. If you have this mismatch, you'll need to cobble together about a 1" or more longer intermediate pushrod between the 70 booster and original 72 non-power master cyl. Not ideal and not worth the effort in my book of having to worry about it being the correct length. Screwing it up means no engagement with initial pedal push - or - draggy brakes because it's too long.

Personally, I'd buy a new 72 POWER master cylinder and just insert that in your swap and dump the 70 drum/drum master cyl and the original 72 non-power master cyl (i.e. use your current prop valve and all the 70 stuff behind the newly purchased master cylinder). What you really need is a correct 72 disk/drum, power master cylinder.

[Lattimer]

Originally Posted by jocko

The mc's are different. So, a drum/drum mc is not ok for the 72's disk/drum arrangement, as stated above. Disks not standard til 71. Will it "work" - yes, but not correctly. A pre-71 prop valve is mostly just a pressure loss switch that will light up on your dash if you lose a circuit - the proportioning takes place inside a drum/drum mc by the order in which the ports are uncovered when you hit the pedal.

However, just leaving your current master cyl in the mix between your proposed 70 booster and 72 prop valve will potentially not be a direct bolt onto the 70's booster if you add it in. i.e. be aware that, in most cases, the depth of bore in the master cylinder piston is deep in a manual master cyl while it is shallow (and perfectly opposite the booster intermediate pushrod) in a power setup. This could be an issue if you put your current non-power mc onto the 70's booster. If you have this mismatch, you'll need to cobble together about a 1" or more longer intermediate pushrod between the 70 booster and original 72 non-power master cyl.

Personally, I'd buy a new 72 POWER master cylinder and just insert that in your swap and dump the 70 drum/drum master cyl and the original 72 non-power master cyl. What you really need is a correct 72 disk/drum AND power master cylinder.

I've read that about the rod before, but mine fit perfectly. I don't know if it varies year to year or truck to truck. The new booster I bought fit the non-power master cylinder that was already in my truck. I had the entire assembly from a donor, so I kept all the brackets, turned in the booster for a core, and junked the old master.

[jocko]

thanks Lattimer - good to know. Like I mentioned - could potentially be a problem.

However, the lingering concern I'd have is the fact that sumter's proposed swap also includes going from a 72 disk/drum non-power mc to a 70 drum/drum power mc (on a truck WITH disk brakes) while still retaining the 72 prop valve (i.e. pretty sure the drum/drum mc has internal proportioning and this could conflict with what the 72 prop valve is trying to accomplish).

Lattimer, can you elaborate on your swap? Was it 70 drum/drum non-power to power? Or were disks included in the overall swap? etc.

[Lattimer]

Originally Posted by jocko

thanks Lattimer - good to know. Like I mentioned - could potentially be a problem.

However, the lingering concern I'd have is the fact that sumter's proposed swap also includes going from a 72 disk/drum non-power mc to a 70 drum/drum power mc (on a truck WITH disk brakes) while still retaining the 72 prop valve (i.e. pretty sure the drum/drum mc has internal proportioning and this could conflict with what the 72 prop valve is trying to accomplish).

Lattimer, can you elaborate on your swap? Was it 70 drum/drum non-power to power? Or were disks included in the overall swap? etc.

Mine was a power setup from a drum/drum truck to my truck with manual drum/drum. Not sure of the year of the donor parts, they were thrown in when I bought the truck.

I agree, there are definitely different master's between the drum/drum and disk/drum trucks.

[jocko]

still - very interesting point about the fact that the depth of piston in your drum/drum manual mc was the same as what you needed for when you added the booster. Very good data point for me - thanks.

[Lattimer]

Originally Posted by jocko

still - very interesting point about the fact that the depth of piston in your drum/drum manual mc was the same as what you needed for when you added the booster. Very good data point for me - thanks.

No problem!

[Rudy-g]

I have a 69 gmc with power drum/drum and I have swapped a 72 disc/drum front suspension. I guess I need to replace my booster and mc, and prop valve, How about my metal brake lines? Are they the same size?
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[sumtercleaner]

Wow. Lots to digest. All that being said, let me re state my concern/?. All the parts on the 70 are available to me. I would more than likely use the or my master and the booster for cores as the donor has set for 18 years. So.... i guess now i need to know will donor pedal, rods brackets booster (new from core donor ) and a new power brake master for a 72 disc/drum and my current disc drum proportioning valve all work?
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[jocko]

sumter, got your pm, here's what I "think" I think

I'm not sure you need to swap the pedal itself, perhaps just the pushrod - but when you look at the 70, compare the pedals and if the same, I'd keep the 72 one in the 72 and re-use it. Here's what I'd look for/try to do:

Off the 70:
- grab the pushrod from the pedal to the back of the booster (and perhaps the pedal, just in case)
- grab the booster and its brackets that attach it to the firewall (and the vac line and check valve AND manifold vac fitting)
- grab the pushrod that comes out the front of the booster (it should be pretty short, just a nub stickin out).
- grab the mounting nuts and washers, etc.

From your 72:
- retain your prop valve and lines (to & from, hopefully the ones between prop valve and mc will fit)

THEN, check to see if the booster pushrod fits perfectly into the back of your master cylinder's piston hole (i.e. if you have a shallow hole in the back of your master cylinder to mate to the short nub intermediate pushrod coming out of the booster), then you can re-use the existing 72 master cylinder.

IF it doesn't mate up (i.e. short intermediate pushrod and deep hole in the master cylinder piston - or, vice versa for some reason), then, from the auto parts store:
- buy a new 72 disk/drum (implied in a 72) POWER brake master cylinder (look at it when you pick it up to make sure it is the correct depth master cylinder piston hole - the difference is very obvious to see when you see it).

Personally, I'd grab the mc from the store anyway, but if it was working, and it is from the 72, then it is already a disk/drum mc and should work in conjunction with the 72 prop valve you're already using - and then you're just adding a booster into the setup. If you're really not wanting to roll the dice on old parts, I'd buy a 72 booster and mc COMBO - that way you know they will mate up correctly and this little worry disappears. But, I understand you are wanting to save a few bucks and use the 70 stuff as much as possible. But, if it has been sitting for a long time and you're not sure if it works - I'd just nab the hard parts and buy new hydraulic stuff. But over to you on that. Completely understand wanting to save $ and the 70 booster and 72 mc may be just fine.

If you run into mounting problems, keep in mind CaptainFab makes a great booster bracket. Recommend pm him if interested and he can explain how to hook it up, etc.

Hope that helps.

[sumtercleaner]

Ok. I think for $125 for whatever i need for brakes and a good door, ill get it and take the chance on making it work with the help of new MC from parts store. Thanks for so much info.ill update yall in couple of weeks.
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[sumtercleaner]

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[sumtercleaner]

Ended up leaving thae brake stuff where it was. The wrecker was a one ton with drum/drum. Thanks again for the help.
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