Soft pedal (suburban road trip content)

So this is fun. Headed to DC for the flyover tomorrow: 1999 Suburban with 228,000 miles on the clock. Me, my non mechanical brother and 4 kids.

All was fine and dandy for the first 3.5 hours (non-stop, occasional slow downs on the interstate but nothing extreme) when I stepped on the pedal for the last time to exit the truck slowed but the pedal was very soft and travelled to near the floor.

I looked under the truck at the gas station and there are no leaks. The reservoir is full and there are no weird hisses or other noises from the system.

What does the hive say? Master cylinder finally given up and stopping on bypass? Ok to continue traveling until I get home Sunday?

Will a couple of pumps get the pedal off the floor? If so, I'd probably drive it. If not, I'd want to bleed them at a minimum and see if that helps.

It never gets to the floor and it seems to stop ok. The pedal is just much lower than it was before. What might bleeding them help?

A master cylinder failure will generally start out a bit intermittent. If you hold your foot on the pedal, it will generally sink away slowly at first, and if you stab the pedal hard, it will generally not sink, because you have shocked the rubbers hard enough they seal.

A hose leak will be pretty obvious, but a corroded steel line may take a while to create any sort of a puddle, particularly because wherever it has rusted out (just above the front fuel tank mount) is generally packed full of the mud that caused the corrosion in the first place, and it will absorb the fluid for a while..

Does it have drums on the back? The wheel cylinders leak regularly on them, but it will make a mess on the backing plate. Mechanical failure in the adjuster or springs will allow the pedal to be very low as well.

Any wheel bearings packed up? If a front hub is moving around a bunch, it will push the pads back, and give you a low pedal. It should pump up, and stay up til you move again and push the pads.

Last summer I had the rear hard line fail and replaced it. That felt different as it never built pressure when I stepped on the brake fluid shot out dramatically. I had my brother pump the brakes repeatedly while we were stopped and saw no hint of a leak (and as I mentioned, brake reservoir is full).

It's soundung like a piece in the rear drums more and more then.

If it's rear drums, try depressing the e-brake a couple of clicks. If the adjusters have puked, that might give you some pedal back. Don't over do it or they will drag. If you run it too long like that, you stand a chance of popping the pistons out of the cylinders.

Bleeding will help if you have air or water in the lines. That will give you a soft/weird pedal as well.

Interesting, thanks.

My brother had something similar with his Astro van. Unplugged the ABS and everything's been fine since. (just no anti-lock feature)

I'd guess either a bad master or bad wheel cylinders (if rear drum). Keep an eye on fluid level. Keep driving but pick up a bottle of DOT 3 next stop, and some vise grips.

Feel the wheels. My 2001 did this and it was a caliper that hung and boiled fluid. The wheel was eleventy billion degrees hotter than the other three. Once I got through all of the travel the brakes acted normal for the last quarter inch of travel.

I had a 'Burb of that era and there was also an issue of the rear seals leaking axle grease onto the brakes and causing a loss of braking efficiency. The brakes were never very good on that model as I recall because the anti-lock feature just meant that no matter how hard you hit the brakes, they would push back and refuse to lock up even when locking up was the only way to deal with physics.

Made it home with wounded brakes. Tomorrow I'll tear into the rear end first and see what's going on. I'm hoping simple hardware failure and not bum hydraulic stuff.

I just did the rears on my truck. Similar symptoms but with noise. One of the rear adjusters had fallen appart and cooked one side. Good luck.

The ABS module on this era truck fails internally to where the pedal gets really crappy. I've repaired a couple by bypassing the ABS hydraulically.

This of course is assuming that everything else is okay - you didn't lose an adjuster or smoke a wheel bearing so the pads are getting pushed back or something else more likely.

The exact same thing started happening on my Volvo yesterday. It would occasionally go nearly to the floor but still stop. A couple pumps and it was fine. I have yet to look into it.

Adjuster failed. Braking for 800 miles had indeed pushed out the brake piston. At the auto part store now getting all new stuff.

Could have been worse I guess.

Sounds familiar. Glad it wasn't major.

Thanks.

And so far the parts store sold me the wrong wheel cylinder.....but since the brake line tore while taking it off I needed to go back anyway. Sigh

In reply to KyAllroad:

Yeah, pulling brake lines is always scary. It's amazing how fast a simple job can turn into a nightmare.

Not really, if you're prepared for it. Cut the line off at the wheel cylinder and the flex hose, hammer a socket onto the nut still in the flex hose so it can be removed easily, change wheel cylinder, make new line.

It takes less time to make a new axle line than you would spend trying to save an old one, even if you have an oxyacetylene rig at your disposal to try heating up the nut to break it free from the line.

In reply to Knurled:

98% of the time they come off clean down here, so I don't keep any brake line parts on the shelf. The other 2% is what sucks and is when the job goes to E36 M3.