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Discussion Starter · #1 · (Edited)
I just found my dream car and bought my second 55. i now have twins. The new one has Disc front and drum rear. The power brakes scare me. They are firm but just do not stop fast enough for me. I have a friend with a long hot rod back ground. He says they are fine to him. I know there is a proportion valve. But I see no adjutment to it. Now I may be about to solve the problem because it is also geared to low for me. I am about to replace the rear end with a an 8.8 F*&^ with disc.
 

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Since the car is new to you, I'd pull and inspect the brakes at each wheel.....Also, the rubber hoses in the system probably should be replaced, if its been a while.
 

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What size and type of power booster do you have? Does your engine make sufficient vacuum at idle? What is the master cylinder bore size? How is the booster mounted - flat or angled?

Have you checked the operation of your booster? There are good booster troubleshooting procedures at mpbrakes.com and on the CPP website.

You didn't give much information to be able to help you.
 

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A lot of these old beasts with either disc/drums or even disc/disc brakes just never feel like a modern car. Just the nature of hot rodding. I've only had two cars that really had a modern feel, my wifes '65 Mustang with disc/disc and my Cobra FIA built for racing and street.
My '55 has disc/drum, it brakes quite well but just doesn't have the modern car feel to the pedal.
 

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Did the car sit for a while, before you bought it?.....Since the car is new to you, I'd pull and inspect the brakes at each wheel.....Also, the rubber hoses in the system probably should be replaced, if its been a while.
David has a point. A car sitting for a long time can cause contamination or rusting within the brake system lines and wheel cylinders (if they used conventional brake fluid). A check to each outer end may show some sign of leakage or other issues. Silicone brake fluid is a much better choice. Especially on cars that are used infrequently. Bought a Vette stored for over 20 years and the fluid was still clean and contamination free because they changed to silicone type.

Metallic brake linnings can also give you the sensation of not stopping aggressively. Might want to check the linnings while you're at it.
 

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Discussion Starter · #6 ·
WoW you guys are fast. And very Thorouth. The answer to your questions Is I don't know YET.. Just got it home. But it scared me on the way home. The good thing is it stays stright. My other one (pictured below) is drum only and not power. Never know which way it will pull. Was about to do the switch to it. But now will sell it... And THANKS to ALL for trying to help me..
 

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Discussion Starter · #8 ·
Well it has been a while. A couple health issues and time spent getting the old 55 sold. But yesterday I decided to replace the old fluid and bleed the system. The right rear would not pass any fluid so I replaced the wheel cly..
Did not get the project completed but feel like I am on the right path. Another Doctor this am to have splints removed from nose. Hope to feel well enough after to finish. The power booster is smaller than I remember not sure what kind it is. And vacuum is a little low on ideal.
 

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Discussion Starter · #9 ·
New fluid one new wheel cylinder. It feels the same. Hard brake, weak stopping. No way will it slide a tire. I suspect the proportion valve. (disc front drum back) If not enough fluid is pushed to the rear that would explain the right rear being frozen up. Is there a test for the valve? or do you just replace it. Should it be adjustable? It is not..
This is a smaller power booster. I have a vacuum pump to test the booster today. Vacuum is a little low at idle, But good just above there.
 

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It sounds like you have a few typical problems,
1. low manifold vacuum
2. small inadequate booster
3. possibly to large diameter master cylinder
4. possibly metric small disc brake calipers.

Tune up engine and maybe even increase idle speed to improve vacuum

Look closely at the booster you should have at a minimum, an 8" dual diaphram booster. the 7" & 8" single ones are useless and inadequate. 9" single ar 11" work well

Check master cylinder size by unbolting from booster and measuring the piston diameter. 1" diameter piston M/C for 8 "dual booster or 9" booster, 1 1/16" or 1 1/8" M/C for 11" booster.

Check the caliper to see what you have. The smaller metric calipers that come in some kits are undersized and can't create enough clamping force for propper brakingon a heavy car like a tri5. You need the standard gm calipers like for a chevelle or monte carlo.

Good luck keep us posted
 

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What size brake booster does it have on it? I started with a 7" single booster on mine and the brakes took a lot of pressure to stop. Went to an 8" dual diphram booster and they were better. A month or so back bought a new chrome master cylinder and went with the 1" bore cylinder and now the brakes are real good.
Terry
 

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Do you know what master cylinder it has ?

If its too small compared to the calipers/wheel cylinders, the master cylinder can't displace enough fluid to push the pistons out to put the brakes on.

If you do a search you should find ratios of master cylinder size to the calipers/wheel cylinders to ensure good braking, might be worth a look.
 

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[QUOTEIf its too small compared to the calipers/wheel cylinders, the master cylinder can't displace enough fluid to push the pistons out to put the brakes on.
][/QUOTE]

Usually too big a master cylinder is the problem. Bigger bore = more flow but less pressure.

When you have a problem with a small master cylinder it's too much stroke, as you said.
 

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Discussion Starter · #16 ·
Rear wheel cylinder =7/8". not sure about front or MC. Will larger Booster interfere with LS2 install? Also expect to very soon change rear end to 8.8 Explorer with disc.. Would like to only buy new parts once.
 

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Hard pedal typically means not enough boost or a too-small master cylinder bore.

A one-size-fits-all "fixed" proportioning valve will also reduce pressure to the rear brakes. You need one of these only if the rears tend to lock up prematurely. And then you should use an adjustable valve.

Also, pull your rear drums and see how much of the shoe surface is actually contacting the drums.
 
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