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Brakes go to floor - WHY?

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Old 08-20-2010, 04:19 PM   #1
Steve.in.Roanoke
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Default Brakes go to floor - WHY?

Seems I'm not asking the right question or the right person hasn't read my post.

New pads & rotors & all was fine.

A month later pedal kept going further down to apply brakes.

New master cylinder installed, brakes bled very carefully.

Pedal goes almost to floor before brakes engage. What is going on?

Please, somebody help me on this...
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Old 08-20-2010, 04:51 PM   #2
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Maybe your brake calibers are locking up on the slides and as the brakes wear the pads have to keep extending out farther and farther to actually apply the brakes. I cannot remember how the corvette calipers are designed, but if the pistons are on one side only, then it is possible that the calipers are locking up and not allowing movement for brake wear which will cause the problem you are describing. What happens is the rotor and mounting hardware deflect under brake application and eventually the deflection is so high that the brakes will no longer come on with one stroke of the pedal. This is probably the case if the breakes work OK with more than one pump of the pedal.
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Old 08-20-2010, 05:05 PM   #3
0Paul Ruggeri
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If you're not losing fluid, then the master cylinder is probably defective.
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Old 08-20-2010, 06:38 PM   #4
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Questions:

Can you get braking by pumping the pedal?

If so, is the pedal firm or soft?

Are you losing juice?
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Old 08-20-2010, 06:54 PM   #5
Hokies83
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That would not be Roanoke Virginia would it?
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Old 08-20-2010, 09:06 PM   #6
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Is the level of fluid in the MC reservoir dropping? Is there any indiciation of moisture around any part of the brake lines where there is a connection of any sort?

You didn't specify what year the car is but if it has ABS, check the compartment behind the driver' seat for fluid. If the ABS pump is leaking, that could be part of the problem.

When you installed the new master cylinder, did you bench bleed it before installing it?
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Old 08-23-2010, 02:19 PM   #7
Steve.in.Roanoke
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C4cruiser: No, No, Not yet, yes. 1992

Thanks for the check points. I'll go in search of the ABS part tonight. Some kind of reservoir?

Roanoke as in VIRGINIA, Hokies83. Work down on Crystal Spring Ave. across from First Presbyterian.
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Old 08-24-2010, 11:04 AM   #8
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when the pedal goes to the floor, there are a few things that can cause it.
1. an internal leak in the master cylinder.
2. not enough fluid in the system
because of:
A. improper assembly
B. pistons all the way out in calipers when assembled, and not topping off the reservoirs.
C. cracked or leaking reservoirs
D. loose or bad brake hoses
E. chafed metal lines under the car somewhere.

Most likely is the master cyl is defective.
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Old 08-24-2010, 12:18 PM   #9
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Quote:
Originally Posted by coupeguy2001 View Post

Most likely is the master cyl is defective.
That's a good point. Did you buy a new M/C or a reman one? Sometimes the reman units are not assembled properly, a rubber o-ring seal didn't fit properly or is missing, or the cylinder housing has corrosion in the bore and allows fluid to pass thru as the brake pedal is pushed.

If you have the store receipt, take it back for an exchange and see if there is a difference after it's installed.

It's also possible that there is air in the ABS unit. On the C4's, the ABS is bled by using a GM Tech 1 scan tool with the insertable brake module. What the Tech 1 does is to run the ABS pump as fluid is bled out of the bleeder valve. The valve is on the side of the pump and it is a messy job as the fluid drains out into the bottom of the compartment.

Even though teh ABS pump runs a self-test briefly every time the engine is started and the car moves thru 2-4 MPH, that's not enough to bleed the ABS pump. The ABS unit is self-contained and it's very pricey. No reservoir or anything to look at.
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Old 08-25-2010, 06:32 PM   #10
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Don't think it's the MC just because symptoms were there before & after replacement with NEW MC.

Brakes are @ 1" from floorboard & do not pump up.

ABS is functional as tested on gravel surface.

ABS compartment clean & dry.

No fluid leaks as MC is retaining level.
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Old 08-26-2010, 08:08 AM   #11
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having almost the same prob. Out of town now but I am going to change the flex hoses at the wheels. A friend had a problem with his colapsing on the inside. Either way mine are 21 years old. I'll check back after.
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Old 08-26-2010, 03:40 PM   #12
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if brakes are almost to the floor, it is the positioning of the pedal in relation to the master cylinder.
In order for the master to absorb the proper stroke to port fluid to the lines, the piston has to move a certain amount.
If the pedal pivot, or the linkage rod and pivot are not in the proper relation to the master, the booster in the middle between the pedal and the master may be the problem. There is a spring inside the booster to return the pedal to it's resting place. There is also a spring inside the master. If the master is not returning for some reason,there is no piston travel.
If the spring is broken in the booster, or the diaphragm is not in the right position, you can have a master in the end of the stroke, and the pedal up where it needs to rest, and the pedal will go the length it needs to, and the master isn't actually moving much.
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Old 09-19-2010, 03:12 PM   #13
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Any updates on this ? im having the same problem but i think it happens when it gets hot
I Got a new MC , ready to go in !

What gets me curious and want to learn is a possible leak in the ABS circuit ....
Any of you have experienced that ?

http://forums.corvetteforum.com/c4-t...-a-second.html
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Old 09-20-2010, 07:37 PM   #14
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Two questions for you. In your original post I wasn't clear whether the brakes worked ok for a while and the problem started after a month or the problem was always there. Also, by any chance did you replace the calipers?
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