hey guys there r a lot of smart people here i hope someone can help me i just replaced brake booster and master cylinder on my 77 because they were hissing no brakes now i bleed brakes they work great for about 5 minutes going down highway then no brakes driver front always has air when i bleed them work fine 5 minutes more air in driver side bad hoses? now i have broken bleeder i have done it so much any help would save my life Ihave already done 1 360 when some idiot pulled in front of me thanks for your help

 

Hello
From the information you posted I would say you need to replace your front caliper, and possibly the rotor.

For a quick fix I would replace them both. For the most economical fix you can check the caliper if it is leaking or the brake rotor for runout, and replace the problem unit.

Here are some things to check.
1. Are you losing brake fluid in the front reservoir? If you are then you are leaking fluid which could also add air into your system.
2. The front caliper needs to be rebuilt. You can buy a seal kit at an auto store for around $15. If your calipers have stainless sleeves in them, then this may be a cheap fix instead of buying a new front driver caliper.
3. The rotor is warped, or you have a lot of rotor runout which is causing the pistons in the caliper to cavitate- suck in and out so much that it is allowing air into the system causing it fail. To check for runout you will need to have or buy a metering unit that checks for runout as you spin the front rotor around 360 degrees. This is not the same as the auto stores think it is and check for rotor thickness at several locations around the rotor, but is an indication of how true the rotor is.

There should be others that will chime in and help with some more suggestions.

kdf

 

thanks for answering so fast someone from napa said bad hose on front driver caliper sticking causing fluid to boil and causing air does that make sense just replaced rotor and caliper last year then blew engine and has been sitting for a year does that help

 

There are a couple of items that combined can be causing this problem, but I dont think the brake fluid boiling is one of them. Not unless you are racing your vette on a slalom course and really getting the brakes to heat up.

Now just because you replace the rotor, does not mean that the rotor runout is good. The rotor itself may be flat, but as it rotates on the front wheel spindle it may have a wobble. That wobble is what causes runout, which will cause the the brake pistons to oscillate in thier bores and draw air in and out. That is more the likely cause than brake fluid boiling.

And the brake hose can not stick. Its just a hose that transfers the fluid to the calipers. It can swell under pressure, and cause a soft brake pedal feel. Its easy to replace, and if you dont know the age of your brake hoses, it may be good to replace all of these. A better method would be to spend the extra money with braided steel hoses that will not expand under pressure.

Now back to your rotor and caliper. You said you replaced the rotor and the caliper, then blew the engine and the car sat for a year. That may mean the brake fluid can be bad, and should be replaced. That is not a difficult thing to do, but can be time consuming. The reason for this is the brake fluid can degrade over time by absorbing water, which will cause the brakes to feel soft. But for your problem, I would go with the rotor not being true on the spindle. Just because the rotor is new, does not mean it cannot have runout when it is installed on your front spindle, You really need to have a gauge that will measure the runout, and then put shims between the spindle and the rotor to minimize the runout, and the amount of wobble the rotor may have.

kdf

 

Check run out on the left front. Based on your post, it's out and allowing the rotor to pull air.

 

Thanks for all your help watch out for reman calipers that was my problem thanks again

 

with Easy Mike: Rotor run-out causes air to be sucked back into the system. Look into that and good luck