Left side; front brake sticks, locks and drags?

HELLOHIWELCOME

MEMBER
1999 CHEVROLET SUBURBAN
V8
4WD
AUTOMATIC
238,700 MILES

After I drive around or step on the brake pedal a few times, the front brake on the left side sticks and the rotor gets hot and smokes but the other brakes works fine. When the vehicle rests for about 30 minutes or so it does not stick until I drive around or fiddle with it. I replaced both calipers seeing if that would fix the left side from sticking (locking, grabbing, dragging or whatever) but it still sticks, and I bled brake system as well. Even though I bled the brake system, the brake pedal still feels spongy or mushy. Like I'm stepping on a marshmallow. What are the causes of this problem? Thank you!

5 Replies

CARADIODOC

MECHANIC
33,916 POSTS

The combination of symptoms suggests the brake fluid is contaminated with a petroleum product such as power steering fluid, engine oil, transmission fluid, or wheel bearing grease. The next time the brake locks up, crack loose the steel line at the master cylinder to see if it releases. If it does, we'll have to discuss replacing a LOT of parts. If it does not release, open the bleeder screw on the caliper to see if it releases.

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Monday, March 15th, 2021 AT 11:34 AM

HELLOHIWELCOME

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I open the the steel line at the bleeder screw and the brake released. So, what is next?

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Monday, March 15th, 2021 AT 11:34 AM

CARADIODOC

MECHANIC
33,916 POSTS

Which one, the steel line at the master cylinder or the bleeder screw on the caliper?

What does the rubber bladder seal under the reservoir cap look like? Will it pop back into the cap or is it blown up, soft and mushy?

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Monday, March 15th, 2021 AT 11:34 AM

HELLOHIWELCOME

MEMBER
21 POSTS

I opened the bleeder screw and it released. I opened the steel line at master cylinder and it released. The rubber bladder is in great shape It pops right in with ease. Should the right caliper or rear drum brakes be blocked and locked from fluid contamination as well if it were fluid contamination. Could it be the hydraulic hydroboost?

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Monday, March 15th, 2021 AT 11:34 AM

CARADIODOC

MECHANIC
33,916 POSTS

You would expect both front calipers to lock if there was a problem related to the master cylinder but sometimes it takes less trapped fluid to keep one applied than the other one. That's why we don't want to overlook the easy stuff.

The next thing to try would be loosening the master cylinder's mounting nuts from the booster. If that lets the brake release, something has happened to the push rod adjustment, the brake light switch is holding the brake pedal down a little, or one of the seals in the master cylinder has grown or is coming apart from the piston and not fully retracting. That would be the last thing I would suspect because that seal sits quite a ways away from the port when it's released. You might also look into the hydroboost unit. Remove the master cylinder from it, then watch if the push rod extends when you start the engine. There shouldn't be any fluid there either. If power steering fluid is leaking from in front where the master cylinder attaches, you can expect there's more going on than just fluid leakage.