So I just got my 99 Jimmy about 3 months ago after having a 95 blazer. Right after I got the Jimmy, I had to replace all the brake lines. After that, it was fine for about 2 months. Now, I'm having very little brake pedal pressure, as in I have to press it down almost to the floor to stop the truck. 9/10 times under heavy braking, the emergency brake light will come on, then go off when I let off the pedal. It did this when the brake lines went when the truck was running out of fluifd. I had it checked out at Midas today, they said everything looks good with the brakes, but they bled the system because the fluid looked pretty dirty, and told me I needed a new front wheel bearing. Any ideas on what could be cuasing this VERY ANNOYING brake problem?

 

Stopped, push the brake pedal firmly for a minute and test if it goes down slowly. If do that is the time fror the brake pump. It MUST stay at the same level. Thje light being on/off maybe is related with low fluid level.

 

I can't imagine why you had to replace the brake lines - but given that you have, the only things left that can cause a brake problem like this are a faulty master cylinder, a bad power brake booster (possibly an MC leaking into the booster) or a bad/leaky caliper or brake cylinder. A leaky caliper or brake cylinder would be easy to spot, but master cylinders can be tricky.

There is no "brake pump". No such part exists.

It sounds like you're getting air in the brake lines. I'd go back and do a long, careful brake bleeding. If you keep having problems after that, unless you're mechanically adept I'd take it to a shop and have them diagnose it. This is a safety issue and could bite you hard.

 

Brake pump = master cyl. Sorry.

 

I replaced the rear brake lines because they were leaking when I got the truck. As for air in the brake lines, the tech specifically said he didn't get any air out of the lines when he bled them. As far as leaky caliper or master cyl, I am losing no brake fluid at all since the brake lines were done. Which is why its strange that the e-brake light comes on uner heavy braking, as the fluid is full right to the top at all times. Also, I've found if I pump the pedal once about half way down(not enough to engage the brakes) and then brake fully, the pedal has normal pressure to it and doesnt go down to the floor nor does the e-brake light come on. What could this mean? Also, could you give me more info on the power brake booster? Does this sound like a symptom of that? I had a similair type problem on the 95 blazer I had before this 99 and I replaced the master cyl. and it did not fix the problem.

 

Bleed the front brakes, too, just to be on the safe side...

If the fluid was dirty, like the guy said, it should have been drained as much as possible and replaced.

 

Naaaaaaaa. Master cyl or whatever the name is. When you push half the pedal you are pumping and you get better pedal. The fluid is probably passing to the rear of the pump: no looses of fluid but internal leaking. Do my one cent test. THE PEDAL MUST NOT MOVE WHENIS PUSHED DURING A LONG TIME. Air is different as well as spongy hoses. And if you pass the test, well ....I'm wrong and you'll have brakes when you need them.

 

The whole brake system was completely bled and fluid replaced. did not help at all.

 

My 99 blazer, after changing the brake fluid did the same thing, I kept bleeding the brakes and after disconecting and reconnecting the battery, I went for a drive in a empty parkinglot, and hit the brakes a few times very hard, seems this all has to do somehow with the anti-lock-brake system, my issue was corrected, hope this helps you out as well.

 

Still having the problem. Brakes still work, but I have the jam the pedal down to the floor almost and the brake light still comes on. But if I pump the brake pedal once and then brake it seems normal. what gives?