Caliper Piston Retracting

[1bad68cat]

Hi everyone,

Need some insight/recommendations. My setup: 66 c10 with 2012 CTS-V brakes front and rear, hydroboost from an Astro Van, and Corvette 1-1/8" bore master. I was doing some maintenance/suspension work and noticed that the caliper pistons/pads have retracted from the rotor approximately 1/8" on each side of each rotor. I pump the brakes to reseat, but later in the evening I saw that the pistons/pads had retracted again. This may explain the not so great pedal first thing in the morning when leaving the house for work. This has been going on for some time but didn't think much of it because brakes always felt good after pumping them in the morning. Does anyone know if the cast iron corvette masters come with residual valves? Would it be a good idea to install 2lb residual valves to prevent the pistons from retracting? What other parts should I look at to prevent this? Appreciate any help I could get.

[Hotwire]

Only reason for a residual valve is if the master is lower than the calipers causing drain back.

Are both/all pistons pulling back?

Are any brake lines running close to exhaust causing the fluid to heat up?

[1bad68cat]

Only reason for a residual valve is if the master is lower than the calipers causing drain back.

Are both/all pistons pulling back?

Are any brake lines running close to exhaust causing the fluid to heat up?

That's what I thought too Jeff.

As for the pistons, all are pulling back and none of my brake lines are running near exhaust. I should mention, I noticed this when the truck was cold. It had been on front jack stands for a couple days already.

[oleyeller]

Are the rotors from the CTS-V? Are they the correct thickness? Seems to me the rotors may be to skinny for the calipers you're using... If they all came from the CTS-V, then something really weird is causing the contraction of the pucks. Can you shim the pads to gain space... Is the master cylinder properly vented? Let us know what you find.

[1bad68cat]

Are the rotors from the CTS-V? Are they the correct thickness? Seems to me the rotors may be to skinny for the calipers you're using... If they all came from the CTS-V, then something really weird is causing the contraction of the pucks. Can you shim the pads to gain space... Is the master cylinder properly vented? Let us know what you find.

Oleyeller, the calipers, rotors, and pads are all off a Gen II CTS-V (2009-2012). The reason the gap is possible is that it is getting close to maintenance time. I plan on changing the rotors and pads soon. As for the master, I am not sure. Never thought to look at that, but at the same time, not sure how that is accomplished. Any suggestions on how to verify the master is venting properly?

[Hotwire]

Master cylinders need to be sealed, otherwise the brake fluid would pull water out of the air.

You should have a stepped seal that loosely pulls away from the lid so that the brake system can "breath"without creating vacuum. I'm running an 80's corvette master, the seal has partitions for front and rear reservoirs.