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1968 Mustang Coupe-slightly built original block 289
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Discussion Starter · #1 ·
Ok brake experts, I’m stumped. I just replaced my factory front drums with wilwood 4 piston disc kit, staying manual. I also have a new dual bowl manual drum/drum master cylinder that I’ll be installing, replacing the identical factory dual bowl MC. Do I need to also add a proportioning valve or replace the stock distribution block? I purchased a standalone adjustable prop valve that apparently goes in line from MC to rear brakes? Do I need a MC for disc/drum, what in the world do I need? Any thoughts/ideas greatly appreciated! Pics below are new prop valve, factory dist block setup, new MC
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787534
 

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You need a manual disc/drum master cylinder. The common swap is the 15/16" bore Raybestos MC36440 used in mid-seventies Maverick's and Granola's. It has NO rear circuit residual valve so one needs to be added. I would do so immediately after the distribution block (yes, you can use your existing one) and before the adjustable proportioning valve.
 

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Like woodchuck said, you need to install that proportioning valve you have after your dist block rear brake line. So basically, it needs to go between your rear port on the dist valve and the rear brake line.
I just did this to mine, however mine is power, but the lines will run the same.
Troy
787564
 

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Discussion Starter · #4 ·
Like woodchuck said, you need to install that proportioning valve you have after your dist block rear brake line. So basically, it needs to go between your rear port on the dist valve and the rear brake line.
I just did this to mine, however mine is power, but the lines will run the same.
Troy
View attachment 787564
Thank you Troy. Still with the disc/drum
MC like Woodchuck said? The drum/drum I have now will not work?
 

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Thank you Troy. Still with the disc/drum
MC like Woodchuck said? The drum/drum I have now will not work?
Drum/drum is incorrect for disc/drum. Spend the $ and get the right one.

You need to get the right ratio of caliper piston area to MC piston area.
What model Wilwood caliper are you getting?
 
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Discussion Starter · #6 ·
Drum/drum is incorrect for disc/drum. Spend the $ and get the right one.

You need to get the right ratio of caliper piston area to MC piston area.
What model Wilwood caliper are you getting?
I actually just ordered the disc/drum MC last night from CJ Pony. I have the 4 piston option, part # 120-13551
 

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I was just trying to give some insite into the routing, I didn’t try to suggest woodchuck was incorrect. I would follow his advance for sure! But, sounds like ur on the right track with the mc now.
Troy
 

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Discussion Starter · #8 ·
I was just trying to give some insite into the routing, I didn’t try to suggest woodchuck was incorrect. I would follow his advance for sure! But, sounds like ur on the right track with the mc now.
Troy
No worries at all! Your pic helps a ton. I was a bit confused as to where the prop valve would go, your pic shows that clearly. I have a disc/drum with 1” bore on the way. Hoping that will do the trick. I’m still fairly new to this, so any advice is always welcome. Thanks again!
 

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I actually just ordered the disc/drum MC last night from CJ Pony. I have the 4 piston option, part # 120-13551
Okay, those calipers have 1.75" pistons vs 1.63" for Kelsey Hayes, thus 15% more surface area. For those calipers to work with a similar pedal travel and feel to KH w/15/16" MC you would need a 1" MC. I think CJ sells a lot of 1" so you should be good to go.
 
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Discussion Starter · #10 ·
Okay, those calipers have 1.75" pistons vs 1.63" for Kelsey Hayes, thus 15% more surface area. For those calipers to work with a similar pedal travel and feel to KH w/15/16" MC you would need a 1" MC. I think CJ sells a lot of 1" so you should be good to go.
Awesome! The one I ordered has the 1” bore. So I just connect that to my distribution block lines and I’m good to go, or do I still need the prop valve in line with the rear brakes? Thank you so much for your help, I really appreciate it.
 

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Awesome! The one I ordered has the 1” bore. So I just connect that to my distribution block lines and I’m good to go, or do I still need the prop valve in line with the rear brakes? Thank you so much for your help, I really appreciate it.
Yes, I would highly recommend a proportioning valve so that you can properly balance your brakes. If your new master cylinder does not have a residual pressure valve for the rear circuit you will want to add one of those too.
 
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Yes, you route your lines from your new MC to the distribution block. From there, the lines to the front brakes remain the same, BUT in the rear circuit (between distribution block and rear brakes) you must add a residual pressure valve, followed by the proportioning valve you bought.

The residual pressure valve keeps a very small amount of pressure on the brake fluid in the rear lines, which allows your drum brakes to actuate more quickly when needed by keeping fluid from flowing all the way back to the MC when the brake is off. Drum brakes use a lot of fluid and the rear lines are quite long (obviously), so keeping the brake fluid a little compressed in that line helps give you a head start on making those drums actually do something immediately when you press the pedal.

The proportioning valve controls the bias between your front and rear drum brakes, by reducing or increasing the TOTAL amount of pressure that can be applied to the rear brakes. If your rear brakes are too 'strong' (too much pressure allowed), they will grab, lock up, and spin you 180* when you slam on the brakes.
 
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Discussion Starter · #13 ·
Yes, you route your lines from your new MC to the distribution block. From there, the lines to the front brakes remain the same, BUT in the rear circuit (between distribution block and rear brakes) you must add a residual pressure valve, followed by the proportioning valve you bought.

The residual pressure valve keeps a very small amount of pressure on the brake fluid in the rear lines, which allows your drum brakes to actuate more quickly when needed by keeping fluid from flowing all the way back to the MC when the brake is off. Drum brakes use a lot of fluid and the rear lines are quite long (obviously), so keeping the brake fluid a little compressed in that line helps give you a head start on making those drums actually do something immediately when you press the pedal.

The proportioning valve controls the bias between your front and rear drum brakes, by reducing or increasing the TOTAL amount of pressure that can be applied to the rear brakes. If your rear brakes are too 'strong' (too much pressure allowed), they will grab, lock up, and spin you 180* when you slam on the brakes.
This is exactly what I needed. I really appreciate it!!
 
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