Brakes occasionally lock up at parking lot speeds

ROBERK26

MEMBER
1994 CHEVROLET S-10
4.3L
V6
4WD
AUTOMATIC
108,000 MILES

I tend to do a lot of driving on slippery and/or icy roads, and as such my braking habits are always to start applying brakes early and slowly increase pressure on the pedal as I slow down to prevent locking and skidding. I try to keep ahead of the ABS if I can help it, mostly because I drive older vehicles where the ABS system no longer works as well as it should.

That being said, occasionally as I leave the parking lot and come to a stop before entering the road, I begin applying brake pressure and it feels like the brake system just dumps full pressure into the lines as soon as I move the brake pedal. This will also happen as I slow to a stop at the intersection just down the street. Braking action will be fine down to roughly 5 mph, then it feels like it just dumps full pressure to the brakes. I can hear the ABS trying to unlock the wheels, and I feel movement in the pedal, but the 26 year old system just doesn't work right anymore. I manually pump the brakes when this happens, but it is like I am operating a switch instead of a pump--either full brake pressure, or nothing, instead of being able to increase or decrease pressure.

Like I said, this only happens occasionally. When I do have this issue, 90% of the time it goes away after 10-15 minutes of driving around.

3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

The ABS applies the brakes. What do you mean you hear it releasing?

Did you have the codes checked for any faults in the ABS system?

https://www.2carpros.com/articles/abs-warning-light-on-easy-repair-guide

When was the last time you changed the brake fluid? Dirty brake fluid will cause all kinds of application issues.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Roy

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Saturday, March 14th, 2020 AT 3:41 PM

ROBERK26

MEMBER
5 POSTS

Thanks for the reply, Roy

This truck hasn't given me any warning lights so far. I did want to run a scan to see if there were any hidden codes (or a burnt out warning light), but the GM OBD1 scanner has been on back order from my local parts store.

Sorry, I didn't describe that very well. When the ABS system engages and operates normally, I can hear some noise up front, which I assumed was just normal from the ABS module in a situation where it senses a lock-up situation. The same sound occurs when I have the issue where the brakes lock up, but the ABS system can't seem to unlock the brakes until I pull my foot off the pedal. I manually pump the brakes out of instinct, and like I said it feels like I either have max pressure, or no pressure when this issue arises.

As for changing the brake fluid, I have not done that since I purchased the vehicle 6 months ago. All the fluids appeared to be topped off and fresh when I bought the truck. I know the radiator/cooling system got flushed, and the oil changed just before I bought the truck. The brake fluid in the reservoir looks fresh, but that doesn't mean it got flushed. I can tell the brake system is bled. I will try flushing the brake system a little later this spring when it warms up a little and the road back to the hangar where I keep my tools is a little more passable. I wasn't thinking far enough ahead and I only grabbed my aircraft repair tools, and left pretty much all of my metric stuff back in the hangar.

Bob

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Saturday, March 14th, 2020 AT 4:30 PM

ASEMASTER6371