55.2-59 Frame mounted Dual chamber Master cylinder for Drum/Drum..who's done it? Who likes it

[daveshilling]

So I have a new 56 Chevy daily driver that I'm working on getting road-worthy. Nothing worth a build thread, it just needs brakes and fussing with a few bits here and there so I can get groceries/2x4's/fart around town.

I read somewhere to use a late 60's Impala drum/drum MC to update the old single pot MC in these trucks to dual, but I haven't seen this done on the frame.

I read somewhere else to get a disc/drum setup and then run a 10# pressure doodad inline if you have drum/drum, which is appealing if I ever decided to go disc.

My efforts to search the forum for this have been less than fruitful.

Has anyone replaced their frame-mounted MC with drum/drum to a more modern mc, kept manual brakes, and kept everything on the frame?


Additionally, if the frame mount drum/drum MC proves too costly/irritating, I've also been tossing around a DIY front disc setup after watching a guy on YouTube add disc to his 6 lug for under $200 including new calipers and rotors using late 70's blazer 4x4 parts. Then snag a junkyard booster for the firewall, but which one.... and has anyone done the 6 lug Blaze discs here? I don't want to throw too much $ at a straight axle.

[Johns327]

Take a look.

https://www.brotherstrucks.com/47-87.../MSTR900/DRUM/

it may get you close to the drum/drum option you want.

If you put disc on you will need some form of power assist. Also consider a adjustable proportioning valve. The residual check valves are also a great add on.

There are other vendors out there as well that have upgrade kits.

[daveshilling]

Originally Posted by Johns327

Take a look.

https://www.brotherstrucks.com/47-87.../MSTR900/DRUM/

it may get you close to the drum/drum option you want.

If you put disc on you will need some form of power assist. Also consider a adjustable proportioning valve. The residual check valves are also a great add on.

There are other vendors out there as well that have upgrade kits.

Thanks for your reply. Have you purchased/installed this setup?

It lists a 1 bail MC for drum/drum.. I assume its a 1 1/8" bore, and I can get one on ebay for $45 shipped instead of nearly $100 shipped on Brothers, and there is an ebay vendor selling a bracket that is simple and does not require that the pin be reused for about $65. So, maybe $110 and then bend up some brake lines. Or get the more substantial bracket that reuses the pedal hinge pin thing for an extra $20.

[Johns327]

No.
I have 4 wheel disk setup. The MC, power assist, bracket, and pedal came with my TCI front end kit. But it all looks sourced from CPP.

If your 56 is like my 55 it had a round connection from the pedal to the swing arm under the cab (one nut removal). It made it easy to pull the pedal out by its self and then cast bracket under the cab. My beef with my CPP was it is one LONG solid pedal arm from the pivot to the pedal. Pain in the backside working on it with the engine in and cab on. I ended up cutting the pedal pad mount off, trimming down the arm and re-attaching the pedal pad to the arm.

I have the residual check valves and adjustable proportioning valve. I'm really happy I have the adjustable proportioning valve. The first time I hit the brakes my truck stood on its nose and put me under the dash. I made some adjustments to add more rear braking and now it very smooth, even in a heavy braking situation.

[nvrdone]

ive got a '49 3100 and i changed to an under floor m/c & booster on a drum / drum setup. used a kit from Performance on line & the quality is great. kit with bracket, linkage, booster & m/c was about $300.00. its a corvette dual chamber m/c with a 1" bore. got the prop valve with it so i can convert front end to discs. parts are all new. the only problem is the pedal drops too far to the floor for my liking. still trying to figure that out.

[daveshilling]

Originally Posted by nvrdone

ive got a '49 3100 and i changed to an under floor m/c & booster on a drum / drum setup. used a kit from Performance on line & the quality is great. kit with bracket, linkage, booster & m/c was about $300.00. its a corvette dual chamber m/c with a 1" bore. got the prop valve with it so i can convert front end to discs. parts are all new. the only problem is the pedal drops too far to the floor for my liking. still trying to figure that out.

So you changed a drum/drum MC to a power Disc/drum? Is that compatible if you just omit the prop valve? The drum mc would be 1.125 bore, but unassisted, so I suppose a power 1" bore would be less effort

[mr48chev]

I used a 68 Chevy C-10 master cylinder on my 48 on a bracket that my buddy and I fabbed that bolts to the bracket that the stock master cylinder did. Drum/drum no power.

The main issue I ran into was that the first extended push rod for it wasn't strong enough and I had to make one that was far stronger.

[nvrdone]

my m/c is a 1" bore out of a mid 80's (?) corvette. both chambers are the same size. kit comes wit a prop valve but is not used on a drum / drum system. check out there site. mucho info.

[geezer#99]

Originally Posted by nvrdone

ive got a '49 3100 the only problem is the pedal drops too far to the floor for my liking. still trying to figure that out.

Check your pedal ratio.
Booster likes 4.5 to 1.
Most stock pedals are 6 to 1.
Apologies for the thread jacking.

[geezer#99]

Originally Posted by daveshilling

So I have a new 56 Chevy daily driver that I'm working on getting road-worthy. Nothing worth a build thread, it just needs brakes and fussing with a few bits here and there so I can get groceries/2x4's/fart around town.

I read somewhere to use a late 60's Impala drum/drum MC to update the old single pot MC in these trucks to dual, but I haven't seen this done on the frame.

I read somewhere else to get a disc/drum setup and then run a 10# pressure doodad inline if you have drum/drum, which is appealing if I ever decided to go disc.

My efforts to search the forum for this have been less than fruitful.



Has anyone replaced their frame-mounted MC with drum/drum to a more modern

mc, kept manual brakes, and kept everything on the frame?



Additionally, if the frame mount drum/drum MC proves too costly/irritating, I've also been tossing around a DIY front disc setup after watching a guy on YouTube add disc to his 6 lug for under $200 including new calipers and rotors using late 70's blazer 4x4 parts. Then snag a junkyard booster for the firewall, but which
one.... and has anyone done the 6 lug Blaze discs here? I don't want to throw too much $ at a straight axle.

If you go firewall mounted booster you’ll need to watch for firewall flex. Extra bracing will need to be made. I made some brackets back to the bottom of the dash to stiffen mine.

[geezer#99]

You’ll also need 10# residual check valves for front and rear if you keep the m/c under the floor. Fluid tends to drain back otherwise.
Plus an adjustable prop valve for the back.

[nvrdone]

pedal ratio is 46 to 1. 10# valves in both lines. system pressure bled - no air in lines. new brake shoes. adjusted with in spec. all specs are as POL recomends. pedal goes to about 2" above floor before brakes will lock up. i think we have covered all the bases. this may be just the way this system works

[daveshilling]

Originally Posted by nvrdone

my m/c is a 1" bore out of a mid 80's (?) corvette. both chambers are the same size. kit comes wit a prop valve but is not used on a drum / drum system. check out there site. mucho info.

I looked and everything with a prop valve specifically says that is for a disc setup.

I did find this setup they offered for drum/drum, and they include a 1" bore and 10lb residual valves instead of the prop valve with lines yet the MC does look identical.

So it stands to reason, I could get this kit and run the 10# residual valves, then for a disc upgrade, add a booster and prop valve and not need to repurchase a MC? Also you mentioned you lock at 2" above the floor, is that with a factory pedal travel i.e. you haven't altered the pedal length? I see what you mean, that is quite a bit of travel for power assisted brakes.

[geezer#99]

Nice kit.
To swap to discs you’d need to change the front 10# to a 2# check valve.
I’ve used a prop valve like this in the rear line too.

https://www.speedwaymotors.com/Speed...0aAskGEALw_wcB

I ran disc/drum with booster in a 56 bel air and used a 2# front, 10# rear And the prop valve I linked.

[nvrdone]

ok, POL's kit is BB2-T4755 7" dual diaphram, disk / disk kit
Quote" Our 1947-55 Chevy and GMC Truck frame mount power brake booster kits will help your truck stop better than ever. These bolt on kits mount to the original master cylinder frame bracket and use the factory pedal assembly. Improves performance and driver comfort. Available in 2 or 4 wheel disc applications and drum brake applications."
the m/c is the same for all applications. the difference is which prop valve is added for disc / drum or disc / disc.
My pedal ratio is 4.5:1. this was acheived by lengthing the lower arm. I did try with the connecting rod in the original 6:1 ratio hole and the pedal went right to the floor.
For reference, my Grand cherokee, acura TL and nissan versa all have power brakes. On all of them, the pedal goes down about 4" and the brakes fully lock. On the pickup, the pedal goes down about 7" ( 2" above the floor) before the brakes will lock.
The brake shoes were professionally replaced along with turning the drums. The shop also pressure bled the brake lines to make sure there is no air in the system.

[geezer#99]

I’m amused at the statement ‘it improves driver comfort’.
Not much comfort when the pedal travels that far without any action.
That would induce a bunch of panic for me.
Seems you might need a bit more pedal ratio. Maybe a new hole drilled if you can.
It’s a pain having to re-engineer bolt on systems.

[nvrdone]

so maybe go to an 8:1 ratio? im also looking at putting some kind of vacuum restrictor in the system

[geezer#99]

Stock is usually 6 to 1.
You’re at 4.5 to 1.
Try a new hole 1 inch lower in the arm.

Vacuum resistor!
What? Why?

[nvrdone]

stock is 6:1 for manual brakes. if my research is correct power brakes are 4:1 which is a longer arm.
im thinking lengthening the arm to about 3:1 may improve pedal response

[mr48chev]

True drum brake master cylinders have residual or check valves in them.

On single piston cylinders it is at the end of the master cylinder and you know it as the check valve if you have rebuilt any. That holds a minimum pressure in the line.

Dual cylinders have them behind the seat for the brake line fitting. The springs in those aren't strong enough to maintain pressure in the lines to keep the wheel cylinder cups tight in the bores though. I figured that on my 48 years after I stuck it in the shed. The brakes were good as long as I was driving it every day but if I let it set for a couple of weeks I had to bleed the brakes. Those were in the very rare times that it wasn't my daily driver in a fifteen year stretch. It will work with out the 10 lb valves but will work a lot better with them. I don't think they were even available in 1989 when I put it back together and put the MC back under the floor.

[nvrdone]

agreed, but the m/c in POL's kit is a disc / disc m/c. thats why there are 10# valves in the brake lines. the nice thing is I have the prop valve to convert to a disc / drum set up in the future.

[jwhotrod]

The master cylinder does not know what it is attached to, with a drum/drum system the 1" bore system should be acceptable the drum wheel cylinders do not require as much fluid volume as the discs. but your master cylinder will be mounted below the wheel cylinders and as such requires 10# residual valves in both the front and rear lines to keep the wheel cylinders from retracting or leaking air past the seals. a dual master cylinder will work in either disc/drum or drum/drum systems it doesnt care.

[daveshilling]

Okay, I went shopping on eBay today:

7" zinc booster
Frame mount booster bracket that reuses the stock pedal (my preference)
2 10lb residual valves
pack of 4 3/8" plugs for one side of the MC

Total (after 5% off through Target.com ebay gift card purchase..ur welcome): $116

I already have a new 1" bore corvette-style MC with 3/8" outlets I got at a local auction for $1.75, but if I had to buy one it would be another $50, so by buying the bits separately, you are saving a few bucks over these kits online.


And if/when I swap to disc, I only need to swap the front residual valve and add a prop valve for the rear.

Wish me luck!

[geezer#99]

Mights well add the prop valve now.
Gonna have the line apart for the rear check valve anyways.

[G&R's57GMC]

Dave on a chassis mount power booster/master cylinder do yourself a favor and run the vacuum line from the engine to a high point on the firewall and install a vapor separator from a 70s 80s Chevy caprice or Malibu then run the line down to the booster .

Phil my friend with a Cameo didn’t and had to replace the booster later because the fuel vapor wreaked the rubber in the booster.