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76 master Cylinder port sizes

 
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BroncoJim
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Joined: 16 Dec 2006
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Location: Atlanta, GA

PostPosted: Mon Dec 24, 2012 11:31 am    Post subject: 76 master Cylinder port sizes Reply with quote

Another day another hassle...
I bought a new stock MC for my Bronco. I cleaned it and cleacoated it, bench bled it and when I went to bolt it on I found the port sizes were incorrect. The new ones are too big. I recall this happening before the last time I swapped out the master cylinder (10+ years ago) but I can't recall how. I think I ended up ordering a new one from JBG and it was fine. What a PITA!

Has this happened to anyone else? If it matters I am using Wild Horses stainless brake lines from the master cylinder to the proportioning valve.

TIA,
Jim

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Jim
1976 Bronco, 351W, C4, 4.11s, 2 1/2 BC Broncos lift, 33's, 3G. 24 years and it's almost done.
1965 Mustang 5.0 SEFI, T5 lotsa fun...
"If you didn't build it, it's not really yours"
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Stan
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PostPosted: Mon Dec 24, 2012 4:19 pm    Post subject: Reply with quote

I think the last MC i bought came with a couple of adapters/bushings.
Any decent auto parts store should have them in the brake line/parts section.
Stan

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BroncoJim
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PostPosted: Tue Dec 25, 2012 7:20 am    Post subject: Reply with quote

Thanks Stan, I know I can get an adapter but I shouldn't have to.
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Jim
1976 Bronco, 351W, C4, 4.11s, 2 1/2 BC Broncos lift, 33's, 3G. 24 years and it's almost done.
1965 Mustang 5.0 SEFI, T5 lotsa fun...
"If you didn't build it, it's not really yours"
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Stan
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PostPosted: Tue Dec 25, 2012 9:35 am    Post subject: Reply with quote

Ya - i agree - you pay good money for something you should at least get all the parts.
Stan

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carrier6
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Joined: 04 Apr 2007
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Location: Damascus, Oregon

PostPosted: Fri Dec 28, 2012 12:56 am    Post subject: Reply with quote

I had the ports on my backwards, after looking at a bunch of them what I found out is it all depends on the manufacturer. Raybestos made the one I needed with the little port in the front and large port on the rear. If that's your set up, I got mine at O'Rielys for $38 brand new. Their part number is MC 83072
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BroncoJim
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PostPosted: Fri Dec 28, 2012 5:12 am    Post subject: Reply with quote

The one I bought from autozone had the big hole and the little hole where they needed to be but they were too large. When I went and talked to AutoZone about it they told me that sometimes when they rebuild them they will take the port sizes one size over. I responded that this is supposed to be new, not rebuilt. The guy just shrugged...and offered to pay for adapters if I could find some.
It's going back.
I'll try the O'Reillys one Thanks Carrier6

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Jim
1976 Bronco, 351W, C4, 4.11s, 2 1/2 BC Broncos lift, 33's, 3G. 24 years and it's almost done.
1965 Mustang 5.0 SEFI, T5 lotsa fun...
"If you didn't build it, it's not really yours"
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mhowsmon
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Joined: 02 Jun 2015
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Location: Amarillo, TX

PostPosted: Tue Jun 02, 2015 6:55 pm    Post subject: 1976 Bronco Brakes Reply with quote

Hey all, been having some trouble with my 76 brakes. Any answers to the following questions greatly appreciated.

Setup - Front Disc / Rear Drum

1) Is there any difference in size of brakes lines from front than rear for?
2) MC - should front brakes hook up to front valve or rear?
3) Bore size, what is the recommended size? I have heard smaller is better braking?
4) Power brakes, assume the vacuum of off of booster provides this? How far should tube from brake peddle push in the MC?

My symptoms are that after bleeding brakes, I can get the drums working pretty well but I am not getting enough brake line pressure the ever engage the disc brakes (brand new calipers). I have bench bled MC, checked and re-checked for leaks. Any advice for good known setup would be greatly appreciated.

Mike

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DirtDonk
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PostPosted: Tue Jun 02, 2015 11:17 pm    Post subject: Re: 1976 Bronco Brakes Reply with quote

mhowsmon wrote:
1) Is there any difference in size of brakes lines from front than rear for?


Usually on the fitting sizes are different. For all intents and purposes, the line sizes are the same.


mhowsmon wrote:
2) MC - should front brakes hook up to front valve or rear?


At least for our Fords, the front brake lines are ALWAYS to the rear port.
As are most vehicles.


mhowsmon wrote:
3) Bore size, what is the recommended size? I have heard smaller is better braking?


Almost no such thing as a consistent "is better" as it depends on the circumstances and what you're trying to achieve.
A larger bore will move more fluid, and is appropriate for power assist and larger brakes (i.e. large calipers and such) but a smaller bore will allow your foot to impart more "power" through the pedal because it has to move less fluid. But that fluid has to do some work, so there is a compromise. Too small and you don't move enough fluid. Too large and you have to push down too hard to get it to do anything.
I think all EB's were something like 7/8" maybe? Dont' trust my memory though on that. Wait for someone to confirm.


mhowsmon wrote:
4) Power brakes, assume the vacuum of off of booster provides this? How far should tube from brake peddle push in the MC?


Correct as far as the engine vacuum goes. Not sure what your other question is though. What tube, and are you talking about with, or without power assist?
Assuming your '76 had the factory power brakes (most did, but manual was still available I believe) the pedal rod does not directly contact the master cylinder.
The pedal rod connects to the cantilever mechanism in the angle bracket, which pushes the booster diaphragm, which in turn pushes the booster rod into the back of the master cylinder's piston.

What are you referring to when you say "how far"?


mhowsmon wrote:
My symptoms are that after bleeding brakes, I can get the drums working pretty well but I am not getting enough brake line pressure the ever engage the disc brakes (brand new calipers). I have bench bled MC, checked and re-checked for leaks. Any advice for good known setup would be greatly appreciated.


Your proportioning valve could be bad. Or a hose collapsed maybe?
Are you pulling out on the little nipple thingy (delay valve) on the prop valve when you're bleeding the front?
The prop valve is the little distribution block thingy mounted to a bracket on the frame just below the master cylinder. It's what the soft lines from the master plumb into first.
Pulling the delay valve while bleeding is not always needed, but if you're having trouble you should do it just to rule it out.
Besides, if it's sticking it could block fluid flow to the front brakes.

Good luck.

paul

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mhowsmon
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Joined: 02 Jun 2015
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Location: Amarillo, TX

PostPosted: Wed Jun 03, 2015 2:28 am    Post subject: RE: Reply with quote

2) Rear port is closest to firewall correct?
3) The bore size comes out of what exactly? The bore size to the lines coming out of MC?
4) I am referring to the end result, how far booster rod gets pushed back into the cylinder piston (thanks for help with terminology). The rod seems sort of short to engage MC fully but I'm sure if you go to far you will blow ring or something.
5) I did get a new prop valve so I think it is good. Pulling out on the nipple is something I have not tried but will.

Thanks for help!

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Mike H
1976 Bronco
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