Power Brake Upgrade...

[YourBuddy'sTruck]

I just finished installing a new 7" power brake booster and new Master Cylinder in my '70 C20.
I know that a 7" booster is not that big, but it fit in there easily, so that's what I went with.
Swap went very well and the only hard part was plumbing into my old lines
All done, and I don't really have more braking "power", per se, but it is easier to push on the pedal.
I was thinking it would grip the pavement off the road, but it's not really much better than my old manual master cylinder, just easier to push the pedal.

Am I expecting too much from my 7" booster?

Pretty sure I got the lines well bled.
And I stayed Drum/Drum.
Just used new longer lines to jump from new MC into the same block that was there before.
Should I have skipped the block?
Is there a way to adjust the feel?

I'm pretty happy, but if anyone knows a link here or elsewhere, I would appreciate any input.
Cheers!
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[68gmsee]

I have a single diaphragm on my 68 and it locks the drums. If all of the brake shoes are adjusted correctly where they're just barely rubbing on the drums it should lock them all up if you stomp on the brake pedal. Make sure the booster to master cylinder push rod is adjusted correctly and that you have the proper length rod for the master cylinder that you have.

Here's a post I did earlier on the same subject: http://67-72chevytrucks.com/vboard/s...50&postcount=2

[tmc1986]

You should get a decent amount of power out of the seven inch. More than likely its cause you are still drum/drum. I put a seven inch in my 67' but put discs up front and I can lock the tires on pavent no problem
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[Mister-B]

Originally Posted by 68gmsee

I have a single diaphragm on my 68 and it locks the drums. If all of the brake shoes are adjusted correctly where they're just barely rubbing on the drums it should lock them all up if you stomp on the brake pedal. Make sure the booster to master cylinder push rod is adjusted correctly and that you have the proper length rod for the master cylinder that you have.

Here's a post I did earlier on the same subject: http://67-72chevytrucks.com/vboard/s...50&postcount=2

He's got a '70, running drum/drum. My understanding, is that the instructions you posted are for disc brake booster/MC applications? I don't think there's a different MC push rod for drum/drum trucks, or an adjustment
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[YourBuddy'sTruck]

Good reading on those links.
Thanks...food for thought.
I have the truck in service for deliveries tomorrow and will play with it more tonight.
I never even looked at the linkage between the bracket rod and MC? Just assumed it was correct.
Seems to engage right off, so I don't think it's sloppy or gapped too far.
Hmmm....
With the engine off, a few pumps kills the vacuum in the booster and they then pump up like my old MC did, so I feel safe in using the truck.
My Vacuum source is a T off the line for the TH350, btw.

I have to throw in a thanks to all that post on this forum as I would not have been able to get this far without reading and reading and reading here.
Every week my truck is running better and better from it!
Cheers!
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Just checked and there is about 1/4" of play between bracket rod and MC before it engages.
That equals about 1" of play on the pedal.
I'm going to try to adjust that and see what happens.

[Mister-B]

Originally Posted by YourBuddy'sTruck

Good reading on those links.
Thanks...food for thought.
I have the truck in service for deliveries tomorrow and will play with it more tonight.
I never even looked at the linkage between the bracket rod and MC? Just assumed it was correct.
Seems to engage right off, so I don't think it's sloppy or gapped too far.
Hmmm....
With the engine off, a few pumps kills the vacuum in the booster and they then pump up like my old MC did, so I feel safe in using the truck.
My Vacuum source is a T off the line for the TH350, btw.

I have to throw in a thanks to all that post on this forum as I would not have been able to get this far without reading and reading and reading here.
Every week my truck is running better and better from it!
Cheers!
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Just checked and there is about 1/4" of play between bracket rod and MC before it engages.
That equals about 1" of play on the pedal.
I'm going to try to adjust that and see what happens.

If you have the correct non disc brake booster and master cylinder, I don't think there is even the ability to adjust the rod between the booster and the MC. What you CAN adjust, is the rod that goes from the brake pedal to the booster. That's why so many guys who have drum/drum set ups that add a booster, just keep their stock MC and install the booster to it without even needing to bleed.
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[YourBuddy'sTruck]

Ah!
Well...my original MC is in the trash as it was leaking out the back into the firewall and spilling onto my floorboard! =[\ Yikes!

I did adjust the rod you are talking about and it did give me more pedal/power.
I was actually able to apply the brake and give it some gas...and not move.
Before, I could not "power brake" even if I wanted.
I'm feeling a little better, but will still tweak on it as I go about my day tomorrow.
Thanks again...
Turn the engine off. It's time for cocktails!
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[Mister-B]

Originally Posted by YourBuddy'sTruck

Ah!
Well...my original MC is in the trash as it was leaking out the back into the firewall and spilling onto my floorboard! =[\ Yikes!

I did adjust the rod you are talking about and it did give me more pedal/power.
I was actually able to apply the brake and give it some gas...and not move.
Before, I could not "power brake" even if I wanted.
I'm feeling a little better, but will still tweak on it as I go about my day tomorrow.
Thanks again...
Turn the engine off. It's time for cocktails!
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Which rod did you adjust? The one that attaches to the pedal? If you're referring to the rod between the booster and the MC, I wonder if you've got a disc brake booster/MC setup. Can you post a pic?
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[WIDESIDE72]

Do you have the booster hooked to the intake or carb? It needs to tap into the vacuum port on the manifold between the carb and dist, I believe it's 3/8".

Other than that, you're it going to get better braking from the booster swap only, only Less effort to do what the brakes were already capable of.
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[Mister-B]

Originally Posted by WIDESIDE72

Do you have the booster hooked to the intake or carb? It needs to tap into the vacuum port on the manifold between the carb and dist, I believe it's 3/8".

Other than that, you're it going to get better braking from the booster swap only, only Less effort to do what the brakes were already capable of.
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That depends on what carb he has, no? I asked this question in another thread before installing my booster, and got mixed responses, but the bulk who knew I had a Quadrajet said to install it to the back port of the quadrajet
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[YourBuddy'sTruck]

Pulled vacuum off the manifold...T at Tranny connection.
I'll have to learn how to post a pic to do so?
File size? Attach? I have iStuff? Not really adept with it either??

My pedal goes to a rod that connects to a linkage through the firewall.
Then the linkage goes up and connects to another linkage that then goes through the booster.
So the booster is offset from the original MC mounting on the firewall.
Maybe its a Disk/Drum one...i have no clue...obviously.

My booster does NOT mount directly onto the firewall like the old MC did.

Anyway...I'll figure out the pic thing and ask more then.
Thanks.
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[YourBuddy'sTruck]

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Photo of my new booster/MC
I'm still Drum/Drum and not really getting the power I thought I would.
Did I get the wrong set up for Drum/Drum?
Am I missing something?
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[Mister-B]

Originally Posted by YourBuddy'sTruck

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Photo of my new booster/MC
I'm still Drum/Drum and not really getting the power I thought I would.
Did I get the wrong set up for Drum/Drum?
Am I missing something?
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That master cylinder looks like the kind intended for trucks with front disc brakes. It probably also has a proportioning valve, which drum/drum trucks don't use.

Unfortunately, I think you got the wrong thing....but the masters on here may have ideas to get it to work with your application
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[YourBuddy'sTruck]

Oops. That doesn't sound good for me.
No funds to go disk now or in the future.
Seems to me there would be a way?
I have no proportioning valve on this set up.
Just plumbed into existing block to old lines.
Perhaps I found a new way to look like a moron?


Help?
Any ideas?
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[68gmsee]

I used a disc brake master cylinder on my 69 with drum/drum with no issues. Just make sure all adjustments are correct. I adjust new brake shoes until they lock the drum and back off until barely touching. On used shoes, I do the same but back off slightly more -maybe a click or two.

If your truck is still not braking like it should the shoes themselves may be the problem. Some manufacturers use different materials that won't have the friction needed for good braking. Also, drum brakes have a "self assist" pivot braking action that increases the braking power when shoes are tight against the drum. So, the harder you push the more pivot and more braking action.

[YourBuddy'sTruck]

Yeah...
Something is not right with them.
I need new rear anyway, so may as well get to it this weekend.
We have great weather for it and instead of complaining, I'll think of it as an adventure.

Next time I want an old pickup, I'm just going to start with the lug nuts and go from there. ; )
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[68gmsee]

Forgot to ask: What manufacturer and where did you get the booster and mounting bracket? Doesn't look like the stock ones.

[YourBuddy'sTruck]

GPS Automotive...ebay store.
Cheap!
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[jocko]

Cheapest solution for you right now is to buy a parts store drum/drum POWER master cylinder. Probably less than $20 at OReilly or equivalent. Must specify a power mc or the intermediate rod between mc and booster will not be correct (it would be obvious if you tried to install it). The drum/drum mc will have the correct mc-built-in factory proportioning/sequencing, no prop valve required (but, a pre-71 brake pressure switch is required if you want to be able to get the brake light switch in the dash to work - and properly sense a failed front or rear brake circuit), and you should maintain factory size 1/4" brake lines front and rear as long as you remain drum-drum.
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[YourBuddy'sTruck]

Thanks again to all of you for the advice/help with my braking.
It's been a week now and I actually have stopping power that does not require massive effort from my right foot.
Below is a photo of my "weekly burdon" and the reason I opted for the C20.
Just thought to share why I refer to my truck as my Rum Runner.

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[WIDESIDE72]

As i stated above, the power brake booster upgrade alon will not make your truck stop any better than it did with the manual brakes. It will only require less pedal effort. It has been my experience that disc brakees do not stop any better than properly maintained drum brakes in good working order. The only benefit is the disc brakes will dissipate heat better and not fade like front drums. Long downhill grades where you are riding the brakes or multiple high speed stop and starts will quickly overheat the drums up front. Many drag racers still swear by front drums as they are lighter and create less drag. They only need to stop the car once at the end of a 1/4 mile and usually have plenty of time to cool between passes.
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[YourBuddy'sTruck]

I totally agree. And learned a lot doing all the brake work on my truck.
I'm going to run'em like they are for a couple of weeks and then re-adjust the adjuster screw once then break in a bit.
And my backing plates do not have the access hole for doing the job with a screwdriver.
So, while in there, I'll be making the hole too for future work.
There's a great hardware store here with a good assortment of rubber auto plugs and such where I'll get the plug first and make the hole to match.
I'm actually looking forward to doing it too!
In all of this, I think that I may have caught the bug for these old trucks.
Gotta save up a couple'a bucks to go legit with my membership here.
Thanks again.
Cheers!
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[Mister-B]

Originally Posted by WIDESIDE72

As i stated above, the power brake booster upgrade alon will not make your truck stop any better than it did with the manual brakes. It will only require less pedal effort. It has been my experience that disc brakees do not stop any better than properly maintained drum brakes in good working order. The only benefit is the disc brakes will dissipate heat better and not fade like front drums. Long downhill grades where you are riding the brakes or multiple high speed stop and starts will quickly overheat the drums up front. Many drag racers still swear by front drums as they are lighter and create less drag. They only need to stop the car once at the end of a 1/4 mile and usually have plenty of time to cool between passes.
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I agree about your disc brake comment, but to say all a brake booster does is make it less effort to press the pedal is off the mark IMHO. I could never stop as well prior to installing a booster, even if I slammed on the pedal with all I could. Power brakes are amazing
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