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Brake question

jimbo

Bronze Member
GOLD Site Supporter
Yesterday my 2000 GMC experienced a rather odd brake failure situation. Brakes became soft, nearly, but not quite a to the floor situation. Since the brakes were operating marginally, I elected to nurse the vehicle home. Figuring I was going to need to do some repair work, stopped at the Auto Parts store for fluid.

When I restarted the truck, the brakes operated normally, and have continued to do so till now. No signs of fluid leak, master is full. Hoses appear in good condition. Brakes work fine. Any suggestions? As you know, the worst problem on a vehicle is one where you don't know where to start. OTOH, I'm a little anal about potential brake failure.

Not sure if it makes any difference, but the truck was serviced at a Jiffy Lube
within the past week.
 

muleman

Gone But Not Forgotten
GOLD Site Supporter
Power booster is acting up and makes it feel like almost no brakes. It wasn't humming like the ABS sensor was locking out the braking was it? To see if it was the power booster find a safe grade and coast in neutral then turn the engine off and see how the brakes feel.
 

jimbo

Bronze Member
GOLD Site Supporter
What am I supposed to be looking for when coasting? Also, should I turn the engine off while moving? Seems a little dangerous to lock down the steering with a dead engine and defective brakes.
 

muleman

Gone But Not Forgotten
GOLD Site Supporter
You just turn the key off long enough to kill the engine. Then turn it to on so you can steer. Just see if the pedal feels the same as you felt the other day.
 

waybomb

Well-known member
GOLD Site Supporter
Yesterday my 2000 GMC experienced a rather odd brake failure situation. Brakes became soft, nearly, but not quite a to the floor situation. Since the brakes were operating marginally, I elected to nurse the vehicle home. Figuring I was going to need to do some repair work, stopped at the Auto Parts store for fluid.

When I restarted the truck, the brakes operated normally, and have continued to do so till now. No signs of fluid leak, master is full. Hoses appear in good condition. Brakes work fine. Any suggestions? As you know, the worst problem on a vehicle is one where you don't know where to start. OTOH, I'm a little anal about potential brake failure.

Not sure if it makes any difference, but the truck was serviced at a Jiffy Lube
within the past week.

SOFT - meaning what? Pedal traveled farther than normal with weak braking, or, was harder to depress but seemingly no reaction? Did you try pumping the pedal?
 

jimbo

Bronze Member
GOLD Site Supporter
Soft like the system was going low on fluid, like a leak. I could at one point push the pedal to the floor, but the truck would stop. It did not feel more difficult to apply brakes,. The strange part is that now the brakes are behaving normally. I did try the coasting, turn the engine off and the brakes are now operating both in neutral and with the engine off.
 

jimbo

Bronze Member
GOLD Site Supporter
Fred, I could pump the pedal and gain some stopping power, but not a return to normal feel. It felt like a cylinder gone bad except that usually results in no brakes at all.
 

waybomb

Well-known member
GOLD Site Supporter
I would be looking at a rebuilt master cylinder.

If the booster was going bad, the pedal feel would be very hard pedal with little braking. If it were a wheel cylinder / caliper cylinder, you'd be low on fluid. The master would show no visible leak, and would give you a light pedal with little braking if it were leaking inetrnally.
 
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