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Post Info TOPIC: Who arcs brake shoes?


WATERFORD, ONT

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Who arcs brake shoes?
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Last year I had a run of wheel bearing and brake issues on my 58. I remedied the front wheel bearing issue by upgrading to a taper bearing hub kit. Done. The brakes were a whole new bag of tricks. I kept this car stock with 4-wheel non-power drums and the single suicide master cylinder. I ended up replacing a pile of stuff once I admitted to myself that my restored Chevy was restored 20 years ago and the time is coming around to replace all those parts that I still figured were new. (A lesson to a lot of guys I bet!) Anyhow, I stepped up and installed a dual non-power master. Now the car needs a cruise ship anchor thrown out the window to stop it. It seems most of my braking is on the rear.

(Sorry for the long-winded write-up.)

I installed two 10 lb residual valves just after the master. There is no propotioning valve. One of my Club brothers brought up the old practice of arcing the shoes to fit the drums. Could this be my problem?

Does anyone know of any one still doing this? Hoping someone has gone through this instead of a friend-of-friend-of-a-friend BS.

 

Thanks.



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ADMINISTRATOR

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If it stopped fine with the single MC and now it doesnt with the dual, I would suspect that more than the arc of the shoes. You may want to try a proportioning valve from a car with drum/drum brakes with am dual master.......What is your dual master from?

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ONTARIO

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As Harry said, if it stopped before the swap then shoe arcing isn't a problem. Did you change out the shoes and drums when you swapped out the MC? Sounds more like the wrong MC or it is not bled properly. Installing a proportioning valve will give a better braking bias. We can only guess at this point, untill you give us more info.biggrin



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WATERFORD, ONT

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The master is a "Corvette" style where the front pot is just slightly larger than the rear. I replaced all shoes and one front drum as well as both front flex hoses. I replaced a couple of hard brake lines too. Bled the master on the bench then bled the hell out of everything a few times.



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WOODLAWN, ONT

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If I may add a few things, comments. If you installed a non power dual master cyl find out if the master has the residual valve built in. Some are in the master and some in the proportioning valve. If not get a proportioning valve for the car you got the master for. eg: 71 nova/ chevelle with a manual master. Check on line or at the local parts store for what replacement brake items are available for the car that the master was used on. You did bench bleed the master first? On my 57 wagon I used 71 Chevelle brake parts, but I also have disc's on the front.

Here is a link to Bob's Impala brake items, worth a call to them.
http://www.impalas.com/brakes/

Here is a link to rock auto master cyl's
http://www.rockauto.com/catalog/raframecatalog.php

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WATERFORD, ONT

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Thanks. I really wish I knew what this master is from. I got it from Brian Hopkins from Chev Enthusiast. He sold the "kit" with a proportioning valve but a GM mechanic from our Club told me it was for a disc/drum set up so I returned it. Mistake?

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BLACKSTOCK, ONT

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No not a mistake, if it was for Disc/ Drum set up??? it won't work on all Drums. I did this conv. on my 64 Catalina, & used a 68/70 A body [chevelle, Cutlass, Skylark etc] Dual M/cyl. "drum brake" application & didn't put a porportioning valve in & it works "just fine"!!!!! But as stated you do have to "Bench" bleed the master b-4 you install it on car then bleed the system.

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TORONTO, ONT

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Also make sure you have the right ports going to the right brakes. If you have them reversed, the front brakes will be really week. Don't ask me how I know...



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BLACKSTOCK, ONT

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RacerRick wrote:

Also make sure you have the right ports going to the right brakes. If you have them reversed, the front brakes will be really week. Don't ask me how I know...


 OK I won't ask, BUT have a very good guess?????



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WATERFORD, ONT

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Thanks for all the tips. Everything is plumbed right and I did indeed bench-bleed the master. Next step?

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BLACKSTOCK, ONT

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I think "maybe'the M/cyl. you have may be TOO BIG in the bore dia??? Did you get "good" pressure when bleeding front bleeders? Also was there a rubber boot on the back of M/cyl.where push rod goes into cyl. ??? My replacement M/cyl. had one & it restricted the stroke, & I "binned" the boot & got more stroke.

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WATERFORD, ONT

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Will have to have a look at that. Hmmm.

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LONDON, ONT

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Chris,
The size of the lines don't hamper the pressure at all. Pressure in a closed hydraulic system is equal in all directions. They will have an impact on the volume of fluid delivered. I tend to agree with Dualquadpete that the master may in fact be too big. This is from Dean Oshiro a definite guru and all round good guy hotrodder. Take particular notice of the section regarding master cylinder piston size and pressure diferential. If you want to learn more about brakes go here and be overwhelmed

http://www.deanoshiro.com/brakes/master_cylinder_test.html


Formula for Master Cylinder Pressure

I have been asked hundreds of times how do you determine the pressures output of the master cylinder. The following information will help you determine the proper size master cylinder:

To figure how much pressure your master cylinder is putting out:
C = pedal ratio
D = pounds of pressure apply by your foot
E = area of you master cylinder
F = pounds of pressure out of the master cylinder
C X D /(divided by) E = F

Example: If you have a 1" master cylinder the area equals 1/2" x 1/2" x 3.14 = 0.785 Square Inches. So, 100 pounds (of applied foot pressure) X 6 (pedal ratio) divided by 0.785 = 764 pounds of pressure.
If you have a 1-1/8" master cylinder, 100 psi X 6 (pedal ratio) divided by 0.9935 = 604 pounds of pressure.

Here is some info on master cylinder with "constant" of 6 to 1 pedal ratio and 100 psi being applied.
3/4" master cylinder = 1359 psi
13/16" master cylinder = 1158 psi
7/8" master cylinder = 998 psi
15/16" master cylinder = 870 psi
1" master cylinder = 764 psi
1-1/8" master cylinder = 603 psi

DO NOT Try to use a OEM master cylinder smaller than 1" without calculating the volume requirement. It is like choosing between jump off a cliff or a plane, how do you want to die? Remember you can not do anything after you run out of brake fluid, but you can still press on the brake pedal harder.



-- Edited by Rochie on Tuesday 24th of April 2012 09:42:38 AM

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WATERFORD, ONT

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Just to update the guys who supplied some tidbits of info. I purchased an adjustable proportioning valve but haven't had a chance to put it in (busy replacing the fuel tank on my Chevelle).
I thought I knew the answer to this...but now I'm not sure...do the SIZE of the brake lines play a part in my problem? In the next few days I will make note of what I've got for line sizing and relay it to you guys here to see what y'all got to say.
Thanks again for all your advice.

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WATERFORD, ONT

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Whew! Math this early? I'm at work right now so have to concentrate on making a living. I will try to digest all this later. Thanks man. Tell the boys at the ELTA howdy if you venture by there!

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BRADFORD, ONT

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Try DORMAN Part # M71277 Master cylinder. Fits '67-72 442 with 4 drums, power or manual. has 1" bore. (see Rock auto catalogue, great reference info). This will give good brake pressure (psi) and is dual chamber. If you clink the part number on Rock Auto catalogue it will show you what else this unit fits. Newest seems to be 1976 Jeep cj-5 or cj-7. Happy stopping!

 

 



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WATERFORD, ONT

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thanks l will check it out!



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COBOURG, ONT

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larger bore masters tend to be for non power systems, more surface area equates more leverage, a power system uses more power on a smaller bore.  from my experience, a four wheel drum system doesnt require a proportioning valve since it works on a equal pressure system stopping with all four wheels, even if you go to a separate system using a dual chamber master cylinder, you should simply be able to plumb the front and the back to the corrosponding chamber. your reduced braking sounds like a defect of some kind



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NORTH BAY, ONT

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Chris...i went through the same thing on my 63 Nova and my 55 chevy..everything was new for the front braking system.listened to a half dozen mechanics and it kept costing me money by replacing lines, shoes etc.., yet nothing worked.....finally ordered a 68 camaro non power master cylinder put it on,threw the proportioning valve away ,"t"d of the front lines and bang, i had excellent brakes in both cars.....if by chance you doubt what dualquad and i are saying, just ask anyone who was at the arm drop drags how my car stopped after making a pass.... one thing i have learned over the years , when playing with these old cars, it's trial and error on most modifications..

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WATERFORD, ONT

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Hey fastchevy, was it a dual chamber master?



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NORTH BAY, ONT

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yes it was Chris,,,wish i had the box with the part number for you but its long gone,,,

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WATERFORD, ONT

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No problem. Thanks for the input.



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WATERFORD, ONT

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Here's the follow up to my issue...

I bought a dual reservoir master cylinder for a 68 Chevelle with NON-POWER 4 wheel DRUM brakes from Carquest. Bench bled it. Slapped it on. Bled the brakes. Done.

Now I stop like I should.

Thanks to all who gave their 2 cents and especially to Rochie to provided his wealth of experience while sittin in a lawn chair at the Plunkett Show earlier this month.

I think the master I was originally sold was either defective or for a disc/drum set-up.

Chris



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LONDON, ONT

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I'm glasd it turned out good for you Chris.....

Now buy me a beer at ELTA next time OK?



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WATERFORD, ONT

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My pleasure. Maybe 2?

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