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Topic: Brake Problem

in Forum: C4 Handling Components

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Brake Problem (1/6)
4/14/14 2:10pm

tbirdsps
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Ridgecrest, CA - USA

Vette(s):
1990 Coupe

Joined: 2/19/2013
Posts: 117

I'm having brake problems.

Driving around town all feels well. Trying to whoa things down from highway speeds requires a whole lot of brake pressure.

I'm thinking one of three things:

1. The rear brakes are doing nothing.

2. The booster is bad.

3. Bad Master Cylinder

One thing I do know is that the booster is not leaking. I would think if it was the engine would idle fast or idle roughly of which neither is the case. I checked the hose with the engine idling. However when I shut the engine off there was no "whoosh" when I pulled the hose off. I would think the booster would hold the vacuum for a few seconds....or minutes. Maybe the check valve is open?

If the rear brakes are indeed doing nothing maybe the master cylinder is bad. I've had that happen on two Fords before resulting in high pedal pressure to whoa things down.

I've not been able to get the ABS to pulse the brakes under any conditions. The ABS light comes on when the key is turned on but does not light at any other time. I think that indicates things test good. The red brake light also tests good but does not come on at any time other than when the key is turned to the on position. Also zero leaks. The pedal is not soft at all nor is it stiff. Feels normal to me.

The car stops straight under all conditions with no pulling to the right or left.

|UPDATED|4/14/2014 11:10:29 AM (AZT)|/UPDATED|

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If it isn't broke, I haven't fixed it yet....

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Re: Brake Problem (2/6)
4/14/14 3:54pm

laurieb
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Sacramento, CA - USA

Vette(s):
1995 Coupe, Automatic, Dark Red Metallic, 1G1YY22P6S5100376 1985 Coupe, Automatic, Gold Metallic, 1G1YY0783F5114974

Joined: 4/11/2013
Posts: 109

I would think that the master cylinder may be okay. Although I had to apply a lot more pressure when my master cylinder went bad, the pedal felt spongy and would sink at stoplights. It sounds as if your pedal is feeling normal, though. The fact that you hear no whooshing sound when you remove the hose makes me wonder if it is the valve or the booster. I would expect to hear sound if there were adequate vacuum. Have you checked the valve?

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~Laurie~

1985 and 1995 coupes:

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Re: Brake Problem (3/6)
4/15/14 1:19am

davep85c4
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Joined: 4/4/2009
Posts: 254

Try bleeding the brakes. Just a few pumps per wheel. Not so much that bleeding will improve things, but to demonstrate that fluid is indeed reaching all four calipers.

The brake lines and hose ends are made of steel. Brake fluid absorbs moisture with time. The steel parts rust internally, and scale build-up can block the small passages at the hose ends, banjo bolts, and sometimes the lines themselves. So check that you have fluid flow at all four wheels.

I just went through this on a 1967 Porsche I'm restoring. The metal lines were completely blocked internally. I rteplaced about 50% of the metal in the car. I also had a hose on the LF of my 85 get plugged with sediment while bleeding after replacing the master cyl. So lines and hoses CAN plug up, or become blocked. Something to check.

If you have pressure at all calipers, contemplate changing the pads with new ones with an edge code of FF. Old pads get hard, and become inefficient. Slap some ceramic FF's in it, and you'll be amazed at the improvement.

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Re: Brake Problem (4/6)
4/15/14 9:12am

tbirdsps
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Ridgecrest, CA - USA

Vette(s):
1990 Coupe

Joined: 2/19/2013
Posts: 117

I may have accidentally fixed it.

After work I went home and tried some old fashioned "Ford" troubleshooting.

I pumped the brake pedal with the engine off and while holding the pedal started the engine. The pedal dropped about 1.5". That's a good thing.

I opened the hood and disconnected the hose to the booster. I blew in the hose as hard as I could and could not blow air in to the booster. Again a good thing. It indicates the check valve is good.

When reading the shop manual it said that the system self tests when the engine is started and the car is accelerated up to 7mph. It said you can hear the anti-lock modulator work and if applying light pressure to the pedal one can feel the system self test. I did this and it worked.

I took it on a drive and for the first time could feel the anit-lock system modulate the brakes during a "panic" stop. I did that 4 times and when back home. each of the rotors were hot which indicates to me that all four brakes are working.

The brakes felt a whole lot like normal after. I'm not sure what happened or what I did but the brakes feel quite normal now and will really stop the car well.

I did back up the car pretty quickly and slammed the brakes first. Maybe it was forcing the anti-lock system to work had some effect both in reverse and forward.

I do need new pads soon and maybe they are a little glazed. The rotors look like new. Could it have been cleaning solution I used on the wheels? Or spray tire shine stuff? I'll avoid that in the future. May be getting the brakes pretty hot cleaned that stuff off. May be excersizing the anti-lock did something but all is well now.

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If it isn't broke, I haven't fixed it yet....

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Re: Brake Problem (5/6)
4/15/14 10:29pm

Adams' Apple
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Duncanville, TX - USA

Vette(s):
1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.

Joined: 3/18/2009
Posts: 2230

tbirdsps said: Could it have been cleaning solution I used on the wheels? Or spray tire shine stuff?

Possibly...if you get enough on the rotors, it could cause them to be too "slick"....kinda like driving thru water and trying to brake hard. If the pads get wet enough, they don't grab onto the rotors very well until they get hot enough to burn the moisture off.

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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

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Re: Brake Problem (6/6)
3/19/17 10:46am

Alfred
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, - Ecuador

Vette(s):
1996 corvette lt1, coupe

Joined: 3/18/2017
Posts: 2

Same thing happened with my 96 c4 vette, my abs light was on for about a year, the code H23 indicated the FR speed sensor damage, I changed it and nothing, later I found th real cause, a hidden wiring damage, I fixed it and the light went off, the brake was working just fine without the abs, no fading at all, but when the abs system engaged instantly I felt the brake pedal fading problem, the car brakes fine in the first instance, but you can feel the pedal fading, obviously the abs where creating the feeling in the brake pedal, after a route test the abs light went on again, I pulled out the codes and then the code h76 appeared, the lateral accelerometer was indicating a 6 g's acceleration for a long time!, that's why the brake act strange, it sent erroneous information to the abs module, the car responses like the car is turning at night speed, so this sensor is very important!!

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