Problem with FIL '78 Vette Pacecar brake caliper
 

I am working on my FIL '78 Vette which has not been on the road for the past 12 years. I have the engine running and replaced 1 leaking caliper (front passenger side), master cylinder and bled the brakes. The brakes have alway been squishy and not firm. After a test drive the brakes were still squishy so I checked all the brakes once again. I now have another leaking caliper on the rear passenger and the on the drivers front side the pistons visually retract about 1/4" away from the rotor when the brake pedal is released. I think retracting pistons are the root cause to the soft pedal all along. I am leaning towards installing new calipers on the remaining 3 wheels and being done with any further leaks.

What would cause the brake pistons to retract 1/4" away from the rotors?

Speedy:)

Not sure Speedy, but considering how long that thing has been sitting I would believe that the rubber brake lines have swelled and probably need to be replaced. I would also suspect that the diaphragm in the brake booster is probably shot as well (if it is utilizing one).

It would be a lot easier to just replace the calipers. Lots of cars from that era have over boosted power brakes. Sometimes a pad like axxis metalmaster will give a firmer feel, and these pads are period to the car, and so were designed for them.

I'm with Future on brake lines and booster. Those parts should be cheap to replace. Your much better off replacing than breaking down the caliper, honing, rebuilding. Accumulation of rust is more than likely the culprit on the piston issue. Sounds like the entire system needs to be replaced.

Those Delco-Moraine calipers should have little coil spring in each of the piston bores to keep the piston retraction under control. When they break, or are removed, the pistons will retract too far once you're off the brake pedal, and then there will be a long pedal stroke required to make piston-to-pad-to-rotor contact again.

The bores should have stainless steel sleeves in them, and stainless pistons, so corrosion may not be a factor. However, the springs inside are of ferrous metal, and WILL corrode.

Replace the rubber lines, completely flush the fluid, and replace the calipers. I have heard that really tight, new caliper piston dust boots can cause the pistons to pull back a bit, but wow, 1/4"?!

My dad had an '82 Vette. It had good brakes at one time. Then it sat for several years when he was overseas. He came back and had some work done including having the dealer fix a bunch of leaky calipers. He drove it for several more years, had a crate motor dropped into it, had the tranny rebuilt and different gears put in the rear. He even had the thing painted and had some of the interior replaced. After he died I drove it a bit and was horrified by the brakes. They worked, but were very squishy and wouldn't lock the tires. When my mom sold it I told her to tell the buyer that the brakes needed some work.

There are 3 kinds of brake calipers on early corvettes. Leaking ones, ones about to leak, and stainless ones.

The original calipers have a built in leak design. It is a result of the location of the sealing ring. Every caliper I have ever seen EXCEPT the Corvette calipers (used from 1965 to 1982) have the seal in the bore. This wasn,t one of GMs best designs and was probably done to avoid using someone elses caliper design patents
The Delco calipers have the seal attached to the bottom of the piston. What happens is the bore above the piston rusts and cuts the seal (which moves with the piston). The GM seal moves in the bore instead of the piston moving past the seal. The pistons are aluminum and don,t corrode too badly but the iron caliper bores rust quickly. This is agravated by long periods of storage.
The best fix is to replace all the calipers with stainless sleeved rebuilt units. The stainless ones are likely the same price or cheaper than typical aftermarket rebuilt units too. This eliminates the rusty bores and reduces the cutting of seals . The Corvette community also were some of the first to use silicone brake fluid (which also seems to reduce caliper sticking during prolonged storage.
My mother used to have a Corvette (many years ago)and I have rebuilt myriad calipers for her before the stainless sleeved ones were readily available.

Vette calipers that are origInal need to be replaced with stainless steel ones, period. Just did my bro-in-laws 82 collectors edition with 18k miles. 200 miles were put on in the last 6 years!!!

I am pleased to report i replace the remaining 3 callers. They are all now stainless steel leaves and bores. i test drove it down the driveway about 10 times and the pedal is nice and firm. i am guessing the front drivers side caliber had the springs broken and were causing the calper to retract.