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Discussion Starter · #1 ·

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You should match the master cylinder bore size to your front calipers. Which ones do you have? Do you have a power booster?
 

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Discussion Starter · #4 · (Edited)
Rick, I have the small metric calipers and NO booster. I've got a complete booster master kit here, but it sticks out too far and the lines are sticking out everywhere. I don't like the bulkiness so I decided to go with just a NON power setup.
 

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Discussion Starter · #5 ·
Also, Do I need to run 3/16 to the rear brakes since its disks?
 

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with the metric calipers I would run a 7/8" master cylinder. and I only use 3/16" lines for brakes, both front and rear. just my 2 cents.
 

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I contacted Wilwood before buying mine and they recommended 7/8" bore.I bought the master and same prop valve you pictured but have not installed it yet.I am curious how tuff its going to be to adjust the valve to the right pressure.
 

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Discussion Starter · #9 ·
They don't list a 250-9439. They list two 260-9439's. I called Wilwood yesterday and left a message but they never responded.
 

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7/8" is the way to go with manual brakes, unless your metric calipers are "low-drag". Low-drag calipers use a special piston seal that's designed to pull the piston back farther when the brake pedal is released, thus reducing pad-to-rotor drag. More fluid is required to move the pistons outwards in this type caliper. As I recall, GM used a special "fast take-up" master cylinder with these type calipers.

You may be able to Google "GM low drag metric calipers" to determine which years they were used.

Also, save some money. Don't buy a proportioning valve unless the rear brakes lock up prematurely. At least with an adjustable valve, you can crank it wide open, which is probably where it will end up on the majority of 55-57 cars.
 

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Discussion Starter · #11 ·
I ordered the master cylinder and adjustable prop valve today. I'm needing to lift off my body from the chassis but wanted all the brake lines bent and mocked up first. Thanks everyone. Its 4:15PM and Wilwood still has not returned my call. Not good customer service for sure.
 

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Call them again.

Also, they're very likely to tell you to buy the 7/8's M/C. Many of us on this forum have used a 1" M/C (including myself) with the metric brakes and it's not a good fit. Go with the 7/8's version.

Also, MikeB has a 7/8's Wilwood and manual brakes on his tri-5 so he knows what he's talking about. I have a 1" M/C on my '56 with Wilwood brakes and calipers...it stops well but I do have to apply a fair amount of pressure. When I get done with a few other things, I'll likely be going to a smaller bore M/C as I have manual brakes as well.

Last, on the prop valve I think MikeB is right...you'll likely have the rear wide open. I have discs out back as well and my prop valve (which is the same Wilwood as you want to get) is wide open and my rears do not lock before my fronts. You may very well not need it.
 

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The 7/8" master cylinder is probably a good match for Wilwood calipers, as they have a relatively small bore.

I'm not so sure about metric calipers. I think 15/16" may be more appropriate for some people. The 7/8" would be fine except that the pedal stroke is going to be very long for some guys, but the pedal force will be less. If you don't like the pedal stroke with 7/8", then the 15/16" might work for you but you'd have to push harder on the pedal to stop. Some might even like 1".

Here's some numbers, with 1" bore as the reference.

1-1/8" bore: 27% more force required at the pedal, 21% less stroke than the 1".
15/16" bore: 12% less force required at the pedal, 14% more stroke than the 1".
7/8" bore: 23% less force required at the pedal, 30% more stroke than the 1".
 

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Discussion Starter · #15 ·
Call them again.

Also, they're very likely to tell you to buy the 7/8's M/C. Many of us on this forum have used a 1" M/C (including myself) with the metric brakes and it's not a good fit. Go with the 7/8's version.

Also, MikeB has a 7/8's Wilwood and manual brakes on his tri-5 so he knows what he's talking about. I have a 1" M/C on my '56 with Wilwood brakes and calipers...it stops well but I do have to apply a fair amount of pressure. When I get done with a few other things, I'll likely be going to a smaller bore M/C as I have manual brakes as well.

Last, on the prop valve I think MikeB is right...you'll likely have the rear wide open. I have discs out back as well and my prop valve (which is the same Wilwood as you want to get) is wide open and my rears do not lock before my fronts. You may very well not need it.
I don't need to talk to them now since I already ordered the parts today. I wanted the adjustable prop valve to use at the drag strip to hold me on the line while I'm foot braking it. I got a line lock to do a burn out.
 

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Discussion Starter · #16 ·
After reading my last reply, I sound harsh but its NOT how I meant it. :shakehands: I got the 7/8 as was sugested by everyone.
 
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