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1998 Cadillac STS
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65 Posts
Discussion Starter #1
I have brake issue that just occured out of the blue. I have a 1998 Cadillac STS.

When I press the brake pedal gradually there is no response until it reaches the floor and there is only minor braking action. For example, if I see traffic ahead and I want to slow down (not stop), the brake pedal travels to the floor because I am not mashing the brake.

When I slam on the brakes or press the brakes suddenly (to come to a quick stop - someone turns without turning on a blinker :annoyed: ), there is instant response and it stays firm until I let up.

I plan on bleeding the entire system, but I have a feeling that is not the issue. I do not have any codes reporting on this issue and the brake light is not on.

Has anyone experienced this issue or know what it is attributable to?

Thanks,

John.
 

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2001 DTS(140K), 2000 ETC(284K), 1990 allante( 80K)
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1,915 Posts
i am having the same problem with my 1994.
i was told it could be the seals on the master cylinder. because the fluid is going around the seals causing no pressure. but no loss of oil.
they are around 150-160 bucks and they look to be a simple install.
 

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1993 ETC, in Windsor, Ont.
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301 Posts
Poor fluid (old/air saturated) will cause exactly the opposite reaction.... it will stop well if the brake is applied gradually, but you will feel like you're stepping on a peice of concrete if you mash the pedal.
It's still a good place to start if you haven't bled the brake fluid in a few years.

It very well could be the master cyl. like eyekandy said
 

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93 Seville, 93 Fleetwood and a 96 Eldorado
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132 Posts
Check th fluid level, if it is low it can draw air into the line . Then bleed the brakes. Just to start from simple and cheap and work my way up to expensive and difficult. Just a little air in the line will give you a mushy pedel.
 

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2000 STS RHD 194,150 miles. what's a speed limiter???
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219 Posts
the abs pump may be failing, my '00 had a similar problem, a sticking valve in the pump allows fluid to pass into an internal reservoir allowing the pedal to hit the floor. because it is a mechanical fault and not electrical, no codes are shown. the symptoms are very similar to a faulty master cylinder.
take the car and have the abs pump checked out with the aid of tech 2, using tech 2 to check the pump will pinpoint a faulty valve and it is the recommended method of bleeding the brakes. a faulty valve may make one of the wheels difficult to turn with the car raised and in neutral.
the brake fluid should be changed every couple of years as water can accumulate inside the abs pump and cause the internal pistons to stick.
you should also be carefull when changing brake pads, you should clamp the flexi hose and open the bleeder, forcing the old fluid out into a container. pushing back the pistons and letting the fluid from the caliper back into the system can push dirt and water into the abs pump.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,990 Posts
If the pedal sinks slowly to the floor and there are no external leaks, I'd suspect the master cylinder seals are leaking internally. The pedal should slowly sink if you hit it hard and hold it long enough.
 

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Premium Member
2006 STS V8 AWD, '95 Ford Ranger
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28,974 Posts
Warped brake discs and/or loose and rattling calipers can tap the brake pistons back giving a long travel to the first application of the brake pedal. The master cylinder has to pump a lot of fluid just to get all the slack out of the system. The longer the interval between applications the worse it gets.
 

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37,297 Posts
+1 on the master cylinder, i had the same exact problem you describe on an Olds years ago, had to replace the master cylinder and it was fine
 
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