Brake problems

[DieselDavy]

This isn't a diesel problem as it is happening to my gas 1/2 ton.
When I turn into a parking place or round a corner while braking, 4 times now, I have experienced the brake pedal going almostto the floor, antilocks chattering, and I roll to a stop slowly. I hit a stairway railing right in front of our own store Friday.
How embarrassing! Brakes are spongy immediately afterwards for a couple of stops and then all is fine until next occurrence.

Any ideas?

[DieselDavy]

I should have stated that my truck is an 2002 GMC 1/2 ton gas.

[DmaxMaverick]

I'd venture a guess the wheel bearing you were leaning on is failing/failed. It doesn't take much play in the bearing to foul the ABS signal, which can cause the effect you experienced. Couple this with the ABS reluctor/sensor corrosion issue (road salt), and you could be due for a hub replacement.

Jack the wheel off the ground and check the bearing. Push/pull the top of the wheel in/out. Any movement (at the hub) indicates a failure.

The brakes shouldn't be "spongy" afterward, so you may need a system service (flush the system with fresh fluid), to start with.

[DieselDavy]

Thanks DmaxMaverick,
I think you are right on. From my local research, (stopping by a couple of local garages) I get the same advice.
This all makes sense now. The only times now that it has happened is when turning (both directions) and once straight when on a very bumpy grass lot during a very big bump. That would mean that as weight was removed from the hubs during the apogee, one of the sensors lost communications with it's target and I got that sick feeling. (from the pedal going to the floor, not from that falling feeling!)

I'm lucky in that I have a vehicle lift in my own shop and it's time for an oil change. So I'll run it in and up on the lift and check the hubs. I expect the rust to be the main issue. At the last oil change, my hubs felt fairly snug with little play. From what I hear, it is easier to just change the hub rather than try to dig out the sensors.

Any advice there?

Thanks,
Dave

[DmaxMaverick]

If there's ANY play in the hubs, they are going/gone. Hub replacement is simple, especially if you have a lift. Fastener torques are critical, though. Get those ahead of time, so you don't have to slow down (I posted them recently in the 2500HD/3500 Trucks & Drivetrain forum for all modern chassis options, try a search). The axle nut is the only fastener recommended to be replaced with new (GM service manual), and the rest should get a fresh drop of Blue Loc-Tite. The brake caliper brackets are on very tight, so have your BIG wrench handy for those (breaking these loose should be part of the World's Strongest Man competitions).

The sensors/reluctors can be cleaned/lubed, but it's about a 50/50 shot at success. Odds are the hubs need replacing, anyway. The new hubs will have new sensors/harness included. Shop around for the hubs, the prices vary from $150-350. GM wholesale is about $175. Look them up at www.gmpartsdirect.com .