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L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

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Old 03-05-2007, 10:24 AM   #1
corvettedan22
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Default How to check if brake booster is bad b4 replacing. (pressure) ?

How to check if brake booster is bad b4 replacing.

I belive I can do a pressure check ? How can I do this just hook up to the line and check the pressure when hitting the brakes ? What should normal be ?

The reason I want to check this is because I pretty much have no breaks. But my rear master cylinder bucket is lossing fluid. There is fluid all over the bottom as that is where its leaking from. Hopefully proving my booster to be A ok

Well im hoping that is the case and that i can just rebuild the master for $40 and not buy a new master for $200 and a new booster for $200

?

I know i never get much feed back with a brake question so Good luck to me.

Dan
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Old 03-05-2007, 11:08 AM   #2
VetNutJim
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I believe the majority of the brake boosters fail when the diaphram leaks.
If it's really bad you can hear the air hissing thru when you apply the brakes.
Some of them leak so badly it shows up as a large manifold pressure leak.
A vacumm 'leak down' would be a valid test for this.

Pressure testing would probably be testing in the wrong 'direction'.
Vacumm testing is the way to go.

A vacumm hand pump with a gauge on it can be bought at most any of
the chain part stores.
The booster has considerable volume so you'll be 'pumping' on it for awhile. But after you get it pumped down to around -10~-14 PSI it
should hold without leaking down.
If it doesn't hold ANY vacumm, it's definitely bad.
Don't apply the brakes while you're doing this test.

I usually replace MC's when they leak but you could take yours apart and replace the seals in it if you were inclined to do it.
I'm a little spooky about master cylinders (don't know why) so at the first sign of one giving trouble it's outta there and a new one goes in it's place. The master cylinder (or any other brake component) is a major safety item so I feel better with new ones but there's no reason you couldn't repair your old one.

To test the MC, apply constant, considerable pressure to the brake pedal. If it doesn't feel solid as a rock, the seals are leaking. If it slowly moves down under the pressure, it's bad. If fluid is getting out of it anywhere, it's bad.
Make sure there are no OTHER brake fluid leaks when you do the 'leg' test. A leak anywhere will allow the brake pedal to slowly move down.

Brakes aren't something to experiment around with. They are a 'do it 100% right' or take it to a shop kind of thing.
That doesn't mean you can't fix them. It just means to be honest with yourself about your capability to do so. Your life (and the lives of others) is truly in your hands when you work on brakes so there's NO 'almost right' acceptable when you're working on them.


Good luck with it and 'good testing'.

Last edited by VetNutJim; 03-05-2007 at 11:24 AM. Reason: Added Info
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Old 03-05-2007, 11:43 AM   #3
corvettedan22
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Thanks for that great info, ill let you know what i find.

I have no problem doing it right. I just dont have the $400.00 for a new master and booster ?

I guess well see what happens.

What do you think about a used guarenteed to work from vette2vette or something ?

Dan
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Old 03-05-2007, 01:10 PM   #4
Carl Johansson
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Quote:
Originally Posted by corvettedan22 View Post
Thanks for that great info, ill let you know what i find.

I have no problem doing it right. I just dont have the $400.00 for a new master and booster ?

I guess well see what happens.

What do you think about a used guarenteed to work from vette2vette or something ?

Dan
If it's the booster You can get a metal replacement from hotrodUSA - for 130 bucks -
Carl Johansson
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Old 03-05-2007, 01:11 PM   #5
Carl Johansson
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Quote:
Originally Posted by corvettedan22 View Post
Thanks for that great info, ill let you know what i find.

I have no problem doing it right. I just dont have the $400.00 for a new master and booster ?

I guess well see what happens.

What do you think about a used guarenteed to work from vette2vette or something ?

Dan
If it's the booster You can get a metal replacement from hotrodUSA - for 130 bucks -
Carl Johansson
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Old 03-05-2007, 02:46 PM   #6
firstvette2
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Default Brake Booster

Checking the Booster is relatively simple. Hold the peddle down with the engine off. Start the engine. If the peddle goes down a bit when the engine starts the booster is OK. Been there Done that.
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Old 03-05-2007, 09:21 PM   #7
Carl Johansson
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If it's the booster You can get a metal replacement from hotrodUSA - for 130 bucks -
Carl Johansson
How in tarnation did this get posted twice?
Carl Carl
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Old 03-05-2007, 09:21 PM   #8
Carl Johansson
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Quote:
Originally Posted by Carl Johansson View Post
If it's the booster You can get a metal replacement from hotrodUSA - for 130 bucks -
Carl Johansson
How in tarnation did this get posted twice?
Carl Carl
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Old 03-05-2007, 09:39 PM   #9
VetNutJim
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Carl is throwing snake eyes.

Personally. a good USED part is JUST as good as a good NEW part.

Soon as you get a NEW part installed it becomes USED in the first microsecond.

A good 'yellow tag' part is AOK with me and they usually 'fit my pocketbook' better than new parts.
That makes'em 'feel better' in my hands.

Used parts to me are simply 'Previously Tested' parts. Ya never can tell with new stuff... that's why they have to give you a guarantee with new parts.
A guarantee isn't worth a darn out in the middle of the boonnies.
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Old 03-05-2007, 11:10 PM   #10
jsinga
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You can replace the diaphram in a C4 booster. It was under $50 I don't have the place I got the part from with me.
Test it by shutting off the engine and pull the hose/valve some. If it doesn't hiss either the valve or diaphram is bad.

JS
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Old 03-05-2007, 11:10 PM
 
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