My 65 brakes are mushy again after they were bled and the master cylinder changed. There doesn't seem to be an obvious leak anywhere. Is this a problem with the older Sting Rays?
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Re: frequent mushy brakes
If they are mushy then there is air in the system. How is air getting into the system ? Seals in calipers generally. Due to: Old age of seals, pitted bores due to oxidation over time , improper run out of rear wheel bearing assembly causing a high speed pumping action of rear disc, failure to adequately expel all trapped air during bleeding process (gravity bleed with all ports opened seems to be the slow but better method with vacuum bleeding seeming to cause more difficulty, esp. with silicone fluid). Are all connections tight? There are a lot of them considering the bleeder valves and hydraulic lines. Was Master cylinder bench bled before being placed on car? I have done it both ways with fine results but some folks think this step is very important. Any signs of leakage out the back of the MC ? Hard to see after installation. Are we talking power brakes or the regular system? Silicone fluid or regular hydraulic fluid? -
Re: frequent mushy brakes
If they are mushy then there is air in the system. How is air getting into the system ? Seals in calipers generally. Due to: Old age of seals, pitted bores due to oxidation over time , improper run out of rear wheel bearing assembly causing a high speed pumping action of rear disc, failure to adequately expel all trapped air during bleeding process (gravity bleed with all ports opened seems to be the slow but better method with vacuum bleeding seeming to cause more difficulty, esp. with silicone fluid). Are all connections tight? There are a lot of them considering the bleeder valves and hydraulic lines. Was Master cylinder bench bled before being placed on car? I have done it both ways with fine results but some folks think this step is very important. Any signs of leakage out the back of the MC ? Hard to see after installation. Are we talking power brakes or the regular system? Silicone fluid or regular hydraulic fluid?Comment
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Re: frequent mushy brakes
Henry and Jack-----
I agree. Spongy brakes are virtually always caused by air in the hydraulic system. If the brakes can be firmed up after bleeding but then quicky degrade after driving, the problem is usually always related to "air pumping" caused by excessive rotor total indicated runout (TIR), front or rear. .005" TIR is the absolute maximum that can be tolerated on any 65-82 Corvette rotor without getting into the "air pumping" phenomenon IF stock-type brake pistons and seals are used. Going to the o-ring seal type pistons and seals will enable toleration of higher TIR, but there are other reasons that the TIR should be kept below .005".In Appreciation of John HinckleyComment
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Re: frequent mushy brakes
Henry and Jack-----
I agree. Spongy brakes are virtually always caused by air in the hydraulic system. If the brakes can be firmed up after bleeding but then quicky degrade after driving, the problem is usually always related to "air pumping" caused by excessive rotor total indicated runout (TIR), front or rear. .005" TIR is the absolute maximum that can be tolerated on any 65-82 Corvette rotor without getting into the "air pumping" phenomenon IF stock-type brake pistons and seals are used. Going to the o-ring seal type pistons and seals will enable toleration of higher TIR, but there are other reasons that the TIR should be kept below .005".In Appreciation of John HinckleyComment
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Re: frequent mushy brakes
I have experienced what your problem is with your 65. To make a long story short the only thing that solved my problem was having the rear discs rivetted to the rear spindles and trued as an assembly by Bairs. If I had done this after having warranty work on my rear bearings on my 70 I would of saved a lot of work and driven a safer car. It is so nice to cruise all day on the interstate and have the same excellent brakes I left home with. If your rear discs are not rivetted as they were originally, you have runnout, and its not going away. My 68 has never had the rivets removed from the rear discs and it has never had air in the calipers like my 70 did.Comment
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Re: frequent mushy brakes
I have experienced what your problem is with your 65. To make a long story short the only thing that solved my problem was having the rear discs rivetted to the rear spindles and trued as an assembly by Bairs. If I had done this after having warranty work on my rear bearings on my 70 I would of saved a lot of work and driven a safer car. It is so nice to cruise all day on the interstate and have the same excellent brakes I left home with. If your rear discs are not rivetted as they were originally, you have runnout, and its not going away. My 68 has never had the rivets removed from the rear discs and it has never had air in the calipers like my 70 did.Comment
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