Chevrolet Repair: 1999 Chevy Astro brakes, chevy astro, antilock brakes

Question
The brakes on my astro are very sensitive-they grab.After looking in a repair book, I blead the brakes and they worked better for about a month. Then back to the same old thing. The van has antilock brakes.  Could the master clinder need to be replaced or worse?
Thanks

Answer
Hello Dave,
I doubt the master cylinder needs replaced. I would bleed them again and see if you are getting air out during the bleeding.
You could have moisture in the fluid. Brake fluid absorbs moisture, so don't open the master cylinder on rainy days.
If moisture is in the fluid, it can evaporate when the brakes heat up, and become steam, or air.
The cure is thoroughly bleed the system to the point of flushing and replacing the fluid.
And don't let the master cylinder run low on fluid as you bleed them, or you can suck air into the system.
A shop with a pressure bleeder might be worth the cost. Say Midas?
Good luck,
Van