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I was driving my 1997 Chevy Suburban the other day and when I pulled up to a stop sign all of the sudden my brakes felt super spongy, like the system totally lost pressure. Before that they had worked totally fine. I checked the fluid and the level was fine, and I couldn't spot any leaks. We did hit a large bump when I was pulling into a parking lot, and I thought maybe something would have dislodged one of the brake lines or something but everything seems fine. When I pump the brakes a bunch, they will kind of hold for a few seconds, but then it slips again. The e-brake works fine to stop the car, but that's not exactly a long term situation.

What's going on and what do I need to do?

  • A common cause of this is a faulty ABS unit on those year models. – Moab Jun 18 '17 at 4:15
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Another possibility is that you broke a seal in your master cylinder. The symptom you're describing of being able to build up pressure but then lose it after a few seconds very much sounds like that.

Basically what happens is there's a seal between the lines and the reservoir, and if that seal breaks then fluid can push past it back into the reservoir, thus reducing the pressure in the lines and the pressure you feel at the pedal.

To fix this, you'd need to rebuild or more likely replace your master cylinder.

  • That wouldn't change after a few cycles of the ABS though, right? Seems like it would actually be worse by triggering the ABS. – Wayne Werner Jun 7 '17 at 21:16
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    I'm not sure it'd get worse, but it definitely wouldn't be solved by triggering the ABS. If that does/did fix it then your master cylinder is likely fine, but it is also good info for other people who are looking for possible causes for this issue in the future – Ceshion Jun 8 '17 at 12:33
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I actually found the problem myself, surprisingly my first Google search turned up the answer.

Basically what happens is that you were probably pressing the brakes when you hit that pothole, and with an impact that severe, your ABS/pressure assist system gets confused and thinks that you need way less braking pressure.

The way to solve the problem is to kind of "reset" the system. Find a dirt/gravel road/parking lot somewhere, pick up some speed and then slam your foot down on the brakes. This will engage your ABS system (if you've never felt it before, the brake pedal will vibrate and the brakes may sound like they're shuddering/grinding as they rapidly engage and release to keep your wheels from locking up - this is normal!). You should notice the brakes start to stiffen up after a couple of non-slides. Depending on a variety of circumstances, after anywhere from 2-10 times of engaging the ABS and the system will figure out how much pressure it really should be applying to the brakes.

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    Have you tried this yet? Did it work? I would think disconnecting the battery for 30 min would reset any sort of memory like this. I've also heard of a common issue with the ABS engaging right before a stop <5mph. Can't remember what the fix was (wheel sensors?), but the workaround was to pull the ABS fuse. The method you described is typically used to bleed the ABS module if you don't have a Tech II scan tool. – rpmerf Jun 8 '17 at 14:05
  • Yeah, that's what I used. I was actually on my way to pick up a trailer, which I picked up, then dropped off at my house before finding a dirt road to try it. Thankfully, it worked (which is why I posted here :) - it was going to be a terrible day if it hadn't. – Wayne Werner Jun 8 '17 at 14:56
  • Glad to hear it worked. I have a 97 suburban also. I feel like the brakes haven't been the same since I blew a line a couple years ago. Maybe I will give this a shot. – rpmerf Jun 8 '17 at 15:51

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