Brake problems!

[kev75stingray]

I have a 75 Stingray and am having problems with the brakes. The left front caliper was leaking so I replaced it, and the proportioning valve was leaking too so it was also replaced. The brakes were bleeded but the pedal still faded. I took it to a shop and they replaced the master cylinder and it was fine for about 2 weeks then the pedal faded again. I took it back and they put another master cylinder in and this one lasted about 3 months and now the pedal is starting to fade again. Is there anything else this could be? Any input would be great! Thanks!

 

[rick7402]

You need to rebleed all brakes and see if any one corner improves the feel. If it does I would replace that caliper. A dry caliper may not be good, some will introduce air into the system. I would also verify all line connections are dry and leak free. This should be a good place to start.

 

[80convertible]

How do your rotors look? Do you feel any pulse from the brake pedal when applying the brakes? The reason I ask is I have read post from others that a warped rotor could allow air to work into the brake piston. This would happen slowly and cause brake fade over time versus a few days. Also have you inspected all the calipers. My brother had a leaking caliper although no fluid was visible until the caliper was actually removed. The caliper was noticed during his annual state inspection. Just a couple more suggestions.

Jim

 

[DDLS3]

kev75stingray,

Brake discussions come up often here as they are a recuring problem on C3's. On the main forum page click on search, then type brakes or bleeding brakes into the keyword search. There is a ton of information there.

 

[Nut]

Cavitation

Key,

If there are no disernable leaks anywhere let's try this. As Rick and Jim said rebleed the calipers again starting from the left front and work back. Which (if any caliper(s) are you getting air from?

Older Corvette calipers have a nasty habit of sucking air IN the system when the rotor is barely out of round. I've even seen as little as .020 inches out of round cause the pistons in the caliper to cavitate. The crappy lip-seals on the calipers keep the fluid from leaking out but don't do a real sporty job of keeping air from being sucked in. You may never even feel the pedal pulsate. It's been a nagging problem of mine over the years, especially the front rotors since they are not attached directly to the bearing assembly hub.

If you got air then I would look into having the suspect rotor returned on the bearing assembly, not loose. It needs to be trued to the assembly. That should hopefully cure your problem. You probably didn't need a master cyl. but at least it's a new one now.

Let us know what you find............... Nut

 

[kev75stingray]

Thanks for all the info. I am parking my car this weekend for the winter, it comes early here in Canada. I think i'll save up over the winter and come spring I might just do a entire brake job because they look pretty old and what you guys say makes sense. Thanks for the help!

 

[Nut]

Good luck Kev. It would kill me to have to put mine up for the winter this early. Fortunately the middle Atlantic states usually has moderate enough weather in the winter that I can keep my '81 running all year. Good luck. Have any more problems or questions don't hesitate to ask. We're all here to help.

.............. Nut

 

[cntrhub]

I think there might be a little contorversy here. You bleed the caliper that is, "farthest from the M/C." Therefore, bleed the R-Rear first. L-Rear second. R-Front third. L-Front last. In theory, air will be pushed farthest from the M/C.
If the rotor is warped from heat, the high spot of disc will retract the brake puck back into the caliper, so as you press on the pedal again, it will take more than one push to bring the pedal back to a hard feel. This may not be an "air" problem. If the rotors have been turned, make sure they are within thickness specs. Too thin a disc will surely warp (from heat) like an old 33 rpm vinyl record.
You can tell if there is air by removing the M/C filler cap, press very hard on the brake pedal and release. The fluid returning from the compensating port to the M/C reservoir will capture a few balls of air, and you will see them float to the top. For sure then, you have an "air" problem. Be careful not to press so fast as to create a geyser from the breather port hole, when you have the cap off.

 

[Nut]

Good catch ctrhub. I wasn't paying attention. Thanks...... Nut