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1994 Cadillac Eldorado Touring Coupe & 2013 Cadillac ATS Bas
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19 Posts
Discussion Starter #1
Hi guys, so I did the front brakes and rotors on my 94 Eldorado and now the pedal goes straight to the floor when it's running, it also makes a hissing sound as I'm doing so as well. I did the advised checks from other threads, hold the brake then turn the car on (went to the floor easier as soon as it ran), ran the car for 2 minutes held the brake down and turned it off (it stayed down). I sprayed around the check valve and master cylinder with carb cleaner for leaks (also saw that on here as well) still no dice. Just wondering what else I can try before she goes into the shop. Any advice is appreciated.
 

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2004 Deville
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275 Posts
Brake fluid ok? Brakes going down to the floor would typically indicate a blown brake line or loss of pressure on the brake system. When my brake booster was had a vaccum leak, the car would stop and the pedal would not go to the floor. The vacuum leak was so bad that the car would stall when I would press the pedal, but it would still stop the vehicle.

Did you exercise the pedal after pushing in the calipers?
Any codes on the car?
Where is the hissing noise coming from?
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,605 Posts
If the pedal goes to the floor with no external leaks, the master cylinder is bad. It's leaking past the piston (internally). A vacuum leak will not cause the pedal to go to the floor.

As for the hissing (vacuum leak), have you checked the parking brake release diaphragm?
 

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1994 Cadillac Eldorado Touring Coupe & 2013 Cadillac ATS Bas
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19 Posts
Discussion Starter #4
I don't know how it worked but I bled the brakes several times and somehow that fixed the issue I was having. Everything has been all good the past 2 days. Weird but I'll take it.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,605 Posts
Pretty sure yours is vacuum operated. Either replace the diaphragm or, if you don't want to bother and can live with manually releasing it, pull the vacuum line and plug it.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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67,963 Posts
Yep - his 1995 parking brake release (and part of the HVAC door system) is vacuum operated off the same vacuum line that comes from the passenger end of the intake manifold.

You might find the diaphragm assembly in www.gmpartsgiant.com - or the vacuum line may be either broken or disconnected.
 

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1995 SLS
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52 Posts
Diaphragm????? I don't know where that is. Also how do I get the brake booster off I got the hissing brake pedal once it's in gear not on idle. I'm getting drilled and slotted rotors and ceramic pads delivered today and I want to make sure my braking system is safe again is there a special way I have to diagnose the hissing sound because I want to know what else needs to be replaced. Also pedal does sink and when I cut the car off pedal pushes against my foot . I read a couple of other posts saying that I could be getting a misfire from bad brake booster because in theory the vacuum hose coming from the booster is directly behind the throttle body and may be feeding unmetered air to cylinder 6 or 7 (cylinders that were misfiring). But just a theory. All I know is I got this car passed down to me from my grandfather who bought it new in 95 and I remember him saying that this Northstar runs on pressure so I guess what I'm asking is could this be where my intermittent misfire be coming from it's bugging the shit outta me that I've got used to clearing pcm codes to get it to run right mind you my dash lights such as fuel,climate,and warning display flicker to life when it wants to which is annoying
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,605 Posts
Diaphragm????? I don't know where that is.
#15

It has nothing to do with the braking system. Just he parking brake auto release. This statement (" I got the hissing brake pedal once it's in gear not on idle"). verifies that.

If the diaphragm is leaking, that is a vacuum leak and MAY be the cause of your misfire. Fix that first and see if it solves the misfire.

578006
 

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1995 SLS
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52 Posts
Ok cool. Sounds good but I don't know what it looks like or where this diaphragm is ...... You wouldn't be talking about the brake booster check valve because I changed that already. So what you are saying is fix the diaphragm or the hissing if it's the diaphragm I need to know where it is on my 95 sls also if it's the hissing sound that you are saying to fix first then is it the brake booster or master cylinder I just got my rotors and pads and I want this misfire and hissing gone ASAP. Ps your help is greatly appreciated
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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67,963 Posts
The parking brake release diaphragm is part of the parking brake mechanism and pedal assembly - your left foot operates the parking brake.

It appears that the diaphragm is not in stock, so it may be junkyard time.

Trace the vacuum line from the diaphragm and try to find the location of the leak (hissssss......).

Once again, you need either a real GM/Cadillac/Helm service manual set (ebay) or a subscription to www.alldatadiy.com.

 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,605 Posts
Brake booster - no. Even if it was, you'd never hear it in the cabin.

Parking brake vacuum diaphragm - very possibly. It's very simple to check. Just pull the vacuum line off of the parking brake release actuator (diaphragm) and put a piece of tape over the tip of the hose. If the hissing goes away, you've found the source.
 
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