power DRUM brake conversion (with a dual master cylinder)

[jocko]

Ok,
Have some dumb questions because I'm a brake idiot.
I have a 75 Imp Booster, 67 C10 Dual Res Master Cyl, and a headache.

Couple questions - if I were to go from my current stock single reservoir master cylinder (non-power) to the dual res 67 C10 master cylinder (non-power), I'd need NO adjustment to the pushrod - did all the measure ments, it'd be good to go.

But, If I wanted to add in the power booster, using Captain Fab's slick booster bracket, I have a few dumb questions...

There are 2 pushrods - the normal pushrod from the brake pedal that would normally go into the back of the master cylinder on a non-power setup, and then there's the little interim pushrod between the booster and the master.

So, 2 problems.
1) between booster and master, how much slop should there be between the interim pushrod and seating in the master cylinder pushrod? (Right now, I have TONS - look at the pics, the interim pushrod barely peeks out of the booster, yet it should insert almost 1+7/8" into the master cyl.)

2) in a "normal" setup - does the eyelet on the pushrod that goes into the back of the booster connect directly to the brake pedal? (in other words, the current brake pushrod is simply a rounded off straight rod that is currently hangin in through my firewall, but unless the answer is to simply cut the eyelet pushrod off and weld it to the brake pushrod, with an adjustable mechanism on it, then ok, I can do that. But the eyelet"ed" rod hangin out the back of the booster is not removeable.... So, is it a cut and paste (weld) sorta thing? Or could I just thread it if it's the right size and screw it into a junction on my prake pedal.

Bottom line, trying to figure out if I have a workable combo - it appears I need to lengthen my intermediate push rod (front of booster to master cylinder) about 1+7/8" and it also appears I need to cut and weld or cut and thread, etc the rod hanging out the back of the booster to make it compatible with the current brake pedal pushrod.

Not real familiar with the "power" part of power brakes. I THINK I know what I have to do, but the mismatch between booster output toward the firewall and brake pedal pushrod has me scratchin my head. If it were just too short or too long, then it'd make sense, but it's not even the same sorto thing. Not sure how I could even connect it since it isn't removeable from the booster....

Maybe I'll just put in the dual MC, plumb the lines, and call it a day.
Thanks for your help.

[Rich 5150 69]

Jocko, I want to say I read some where on the web that there should be only 1/16 to 1/32 of an inch of play in the rod between master and booster, but I need to find it....

i did look here http://www.mpbrakes.com/index.cfm, some hepful info on their tech pages, I do know that too long a pin will cause brake lockup before you even get started...

[RUSHNBOBO]

Originally Posted by jocko

Ok,

2) in a "normal" setup - does the eyelet on the pushrod that goes into the back of the booster connect directly to the brake pedal? (in other words, the current brake pushrod is simply a rounded off straight rod that is currently hangin in through my firewall, but unless the answer is to simply cut the eyelet pushrod off and weld it to the brake pushrod, with an adjustable mechanism on it, then ok, I can do that. But the eyelet"ed" rod hangin out the back of the booster is not removeable.... So, is it a cut and paste (weld) sorta thing? Or could I just thread it if it's the right size and screw it into a junction on my prake pedal.

Bottom line, trying to figure out if I have a workable combo - it appears I need to lengthen my intermediate push rod (front of booster to master cylinder) about 1+7/8" and it also appears I need to cut and weld or cut and thread, etc the rod hanging out the back of the booster to make it compatible with the current brake pedal pushrod.

Not real familiar with the "power" part of power brakes. I THINK I know what I have to do, but the mismatch between booster output toward the firewall and brake pedal pushrod has me scratchin my head. If it were just too short or too long, then it'd make sense, but it's not even the same sorto thing. Not sure how I could even connect it since it isn't removeable from the booster....

Jocko, you have the booster for this setup ...see pics...the eyelet is for a pin which connects to a pivoting link ...all supported by the interim bracket ..seen in black (sorry for the poor quality and non cropped pics just shot them in the dark 10 mins. ago) This one's off a '72 4x4 which I adapted to power drum/drum

looks like the parts you have are the right ones , you just need that center interim bracket w/the link and pins.

The large holes you see in the bracket are access holes to R&R the pins.

[Rich 5150 69]

Pin adjustment found here..http://www.autoshop101.com/forms/brake05.pdf
you`ll have to scroll down.

[jocko]

Rich - GREAT reference, thanks very much.

Rushnbobo - thanks, you may be onto something there. Interesting idea. This was the booster that CaptainFab listed as one that would work with his bracket - and it doesn't allow for the bell crank mechanism, so I'm a little stumped. I'm assuming that I could just chop the eyelet off and then connect it (carefully) to the brake pushrod - BUT, I'm concerned that if I eliminate the bell crank mechanism - I may goon up the lever ratios that have been set up by the factory. Thanks very much for going out and takin the pics, I really appreciate it. (I notice even an original 66 booster has the same eyelet setup - but it was a bell crank setup also, so that makes sense). Do you have any way to tell how much mech advantage the lever/bell crank provides?

Captain, you got any ideas on this?

Anyone know if a booster designed for a bell crank can be modified to work with just a plain ol brake pushrod?

If I need to go down the road of adding a different booster mount, bell crank, etc etc, then I may just be skipping the power setup altogether.

[Woogeroo]

brake rod pics

'65 c10 brake booster with '69 dual pot master cylinder

also check the rest of the site for my truck for other brake related pics.

different brake related links and images

-W

[jocko]

Maybe I should just sell my pc'ed 15x6 original steelies and throw on my rally wheels - THEN I could fit a 4-wheel disk setup.... Hmmm. But I LIKE my steelies!

I live in the CA desert and have had ZERO luck finding original 6 lug disk brake wheels off a mid-70's to 80's K10. Frustrating. That's what I really need - then I could skip my hodge podge approach. Piecing together bits and pieces of different factory brake systems isn't always a real smart thing - unless you take a FULL system off an old truck like some of you all have.

[jocko]

Thanks Woogeroo! If I had an original 66 booster, this would be easy. But don't, trying to make it work using CaptFab's bracket (so, no bellcrank/pivot, etc). Looks like the brake rod you modified was one that was for a power set-up to begin with? In my case, the booster has the eyelet for the pivot installed at mfgr - it's not removeable. And my pedal-side of the equation just has a blunt pushrod - like what used to go in the non-power master cylinder.

[Rich 5150 69]

Jocko I don`t believe the bell crank will change the pedal ratios, the only way to change pedal ratio is where the rod is attached to your pedal/arm the higher it is the lesser the pedal ratio, 6 to 1 for nonpower, 4 to 1 for power brakes...

[jocko]

Hmm.

Does the bell crank simply re-locate where the pushrod pushes (without changing ratio)?

If the bell crank has equal length actuation distance on either side of ITS pivot - then you are absolutely correct - and I could probably make this work (i.e. without any bell crank mech at all). But if it's not 1:1 ratio on the bell crank, then it would add to or subtract from (some amount) the overall effective pedal ratio I believe. I'm just not that familiar with brake systems with a bell crank - don't know if the pivot is centered or if it has unequal lengths on either side. Good point Rich - this is worth me chasing down.

[jocko]

Aha!!! I found an old link I saved that had a mod Bugeye made to his booster - here it is. I've pm'ed him for some follow-up. http://67-72chevytrucks.com/vboard/s...=377839&page=3 (see post #72 in page 3 of the thread - it should go directly to page 3, I think)

[jocko]

Hey, and while I'm at it - here's some more dumb questions....

One of Capt's recommended combos was a 75 Impala booster (which I have) and a 67 C10 drum/drum master cylinder (if one wants to stay drum/drum).

So - since by '75, the Impala was a Disk/Drum setup - is there an inherent problem using a drum/drum master bolted to a disk/drum booster??? Or can it work as long as the push rods are all mod'ed to the correct length, connected appropriately, etc etc...?

I'm becoming concerned my hodge-podge approach may backfire and I'm not sure I like the idea of dorking around with an "experimental" brake system.... But it's just hydraulics 101, so either it'll work or it won't - and if it doesn't then I can start all over from scratch and get a disk setup! (and sell my pc'ed steelies on ebay, oh, the humanity!)

[Rich 5150 69]

should`nt make any differance, might have a larger hole in the booster than is larger than the master cylinders....on some master cylinders, don`t ask me how I know,,,LOL

[jocko]

hmmm. Appears I may have a non-power master (67 C10 drum/drum) that I am trying to mate to a 75 imp booster - thus the huge gap between my booster's pushrod and the bottom of the master's piston. Hmmm.

[Rich 5150 69]

LOLsorry I don`t mean to laugh

[Captainfab]

Once you get the correct master cylinder, you just need to cut he eyelet off of the booster pushrod. Then mount the booster and bracket to the firewall. Temporarily install your original master pushrod on the pedal. Then align the two pushrods, and make a mark on both, where you can cut them both and join them together. This can be done by welding them together, threading and using a coupling nut, or using a sleeve over both and bolting or pinning them together.

On my '66 Suburban, I retained the drum/drum brakes, installed a '72 Impala booster with a power brake '67-'70 master cylinder. This is when I designed my bracket in 1992. That setup has been on there for over 120,000 miles with no problems.

Also, there is absolutely no need for a bellcrank assembly to make this work.

[jocko]

Ha! That underline seems to be the key here...

Thanks Capt, appreciate the help and the pm's. You too Woogeroo.

Rich, sounds like you've been down this road before! Laughing not allowed

I guess if it was simple, it wouldn't be fun!

So, if OReily will take back the separate booster and master I bought and "kindly" sell me a matched 67, I'll be good to go. If they won't then I may get by with just buying a power master from a 67, although they didn't list power and non-power as a separate part - will have to look into it in the store I suppose.

I better look and see if I even have a place to hook up the vac hose to the engine for this whole mess! Last resort is to stick on the current dual res master (the manual one) and skip the booster altogether and call it a day. Always pays to have a back up plan! Thanks guys.

[RUSHNBOBO]

Jocko,
I had some time on my hands so I broke this down for you ...master cylinder 101. Some more semi--useful info, Here you go...................

DRUM/DRUM
Master is designed to deliver fluid pressure and volume to the front and the rear of a braking system in equal proportions. Drum brakes will require less fluid and pressure than disc brakes. Typically a drum brake master will be smaller than a disc master and the fluid reservoir chambers will be equal in size. Since drum brakes require the use of residual pressure valves the original drum master cylinders had residual valves built into the outlets. Later model aftermarket units do not have these valves and they must be installed in the lines externally. Failure to incorporate residual valves will cause spongy brakes.

Generally speaking it's not a good idea to use a drum brake master for disc brakes since the amount of fluid the cylinder pushes will not be sufficient.

DISC/DRUM
A disc / drum master is designed to push more fluid volume to the front disc brakes since disc brakes require more volume than drum brakes. Generally speaking a disc / drum master will have one fluid reservoir larger than the other.This is because the disc brake pads wear faster than the drum shoes and the fluid reservoir will drop faster. Original disc / drum masters had a built in residual pressure valve to the rear drum brakes only.

Never reverse the outlets on a disc / drum master. Doing this will cause the front disc brakes to drag excessively from the residual pressure valve.

[jocko]

Thanks Rushnbobo. Copy all on that, and that is something I did understand - although was not aware about the old drum masters having resid press valves built in. Never heard that one before. Hmmm, wonder if the 67 dual drum master I bought has that... For some reason I thought residual press valves were for when one had a master mounted below the lines, as in an older truck/car under the floor master. Learn something new every day.

I'm drum/drum only - I have a drum/drum master from a 67 - the real issue was that it was not a POWER drum/drum master as Captain Fab pointed out. This was and is the root of my problem and confusion. Need to buy a matched booster and master, that's all.

Thanks again.
jocko

[jocko]

BY THE WAY - for those that have done the power brake conversion (drum/drum or disk/drum), I only have the stock 4 bbl manifold - and the only fitting I can find that I could hook the booster to is the fitting with the single outlet that goes up to the base of the carb. No other plugged barbs to hook it to...

There is a plugged vac port at the base of the carb on the front, not sure if it is full time vac port.

Is it ok to tee into the vac line that currently runs between the carb and the block (i.e. the fitting just aft of the distributor)? Or is a new fitting of some sort required? Seems a tee would accomplish the same thing. But does that introduce crap into the booster somehow?

So many questions, so little time! Thanks guys.

[Rich 5150 69]

The tap just behind the carb in the back is the one GM used for all asscesories /Tans and power booster....http://www.google.com/imgres?q=GM+in...luImnCg&zoom=1

Fitting you can get them at napa I think or ny wrecking yard http://www.gmclassicparts.com/INTAKE...-_p_26937.html

[jocko]

thanks rich - therein lies my problem - my intake does not have that fitting because it does not even have that hole in the manifold. The pic you posted is a big block, but you're spot on - the small block boss is located in the exact same location, right over the #8 cyl intake runner. Mine is smooth as a baby's butt.

Since I have no intention of removing the intake to tap into it - AND - because my long term plan calls for swapping on and old offy dual wcfb intake ala early 60's vette-like, and IT has no provision for such a fitting, and if I were to tap the only available real estate on there (there is a small boss, undrilled under the rear carb) well.... this gameplan just made its own decision and left me out of the loop!

I COULD remove the current intake, drill/tap and so on and hope for the best - but the long term plan would leave me high and dry - because if I drill/tap the boss on the offy intake - it will undoubtedly interfere with the distrib.

Anyone in the market for one fo the good Captain's most excellent brackets? it is very nice and powder coated too!

I'll see if Oreily will take back my booster and I'll just keep the manual master I bought in the first place, mistakenly, but very appropriately correct now that I'm not gonna mount that goober of a booster.

Ironically - the whole reason I installed the T5 now was so that I could get the 3-on-tree shifter ears out of the way of the booster!

Ha - not perturbed at all, the non-power master should work just great too - my current single master cylinder was just fine (perf-wise) it seemed, that is until it seized up. Hmmm. A sign? Could be.

Thanks for all your help gents. I'm sure this isn't over yet!

[RUSHNBOBO]

Originally Posted by jocko

thanks rich - therein lies my problem - my intake does not have that fitting because it does not even have that hole in the manifold. The pic you posted is a big block, but you're spot on - the small block boss is located in the exact same location, right over the #8 cyl intake runner. Mine is smooth as a baby's butt.

I COULD remove the current intake, drill/tap and so on and hope for the best - but the long term plan would leave me high and dry - because if I drill/tap the boss on the offy intake - it will undoubtedly interfere with the distrib.

Jocko,

This is "ALMOST" getting entertaining,

--1. What carb are you running, most all have a full manifold vac port for pcv....at the baseplate ...even my speed demon does...this comes from the same place as the port at rear of a manifold, Just tee off of there , or plug directly in if you don't run pcv valve. that's how I run mine.

--2. And also before you abort the booster idea..I've got to ask the obvious question? ...why not run the factory bell-crank setup...no cutting...no welding ...parts a plenty ...parts a cheap...easy bolt in 1 hour or less. May not be "quite as pretty" as that bracket that you got but it's all factory engineered GM stuff and it works perfect. You've already got 75% of the sh** you need why go back to manual when your there. I had "leg-strong" brakes and "arm-strong" steering in my truck when I got it...took it out and i'll never go back.

Just a thought ...no matter how good they look if you want to drive them in some sort of comfort there's might be a slight trade-off.

[jocko]

Already had the bracket and already had the impala booster. Original 66 boosters i priced were pretty pricey, so elected to go with Capt's bracket and use a less expensive, plentiful booster.

Could tee into the base plate, but that won't solve the problem when I swap over to the old vette setup - no room there for the valve and/or baseplate. So, mission aborted. And that's ok - like I said, the manual brakes worked fun until the old single master cyl crapped itself, so will probably just go the manual route at this point, already have the master cylinder for it!

[Fleet '66]

Interesting circle we just went through there but was good information none the less. I may have a similar situation that you all just helped shed some light on. Thanks