Front calipers extremely tight

[Vicinity]

I went to test out my car now that I finished the suspension, but the car required a bit of effort to move. I put it up on the lift and come to find out my brakes work, but the calipers are holding down tight on the wheels. It's the front wheels only, the rears are fine. I can turn the wheels by hand, but it's pretty hard, I almost have to put my weight on the wheel to get it to slip. I've bled the system 4-5 times since putting the brakes on, but I honestly never really paid attention. Once the bleeders are cracked and shoot some fluid out, the calipers release all tension.

I've come to 2 conclusions, the flex lines collapsed on the inside, or the pistons I bought (used) are worthless. Am I correct in this assumption?

I'm weighing out just buying a new set of C5 calipers and braided lines from Kore3.

[Apogee]

Dan, it sounds like you're maintaining some residual pressure in the front circuit only. If it were a hose issue, you would typically only expect it to be on one side since rarely would two hoses fail in the same way at the same time. I would suggest pumping the brakes and then loosing the nuts holding the master cylinder and checking the front brakes. If this fixes the issue, then your pushrod isn't allowing the MC piston to fully return against the internal snap ring.

If you were experiencing some sort of piston/seal issue, I wouldn't really expect it to get better when you released pressure from the caliper since it's a mechanical drag at that point, not hydraulic. That said, did you lube everything up when you assembled the calipers?

Tobin
KORE3

[Vicinity]

Dan, it sounds like you're maintaining some residual pressure in the front circuit only. If it were a hose issue, you would typically only expect it to be on one side since rarely would two hoses fail in the same way at the same time. I would suggest pumping the brakes and then loosing the nuts holding the master cylinder and checking the front brakes. If this fixes the issue, then your pushrod isn't allowing the MC piston to fully return against the internal snap ring.

If you were experiencing some sort of piston/seal issue, I wouldn't really expect it to get better when you released pressure from the caliper since it's a mechanical drag at that point, not hydraulic. That said, did you lube everything up when you assembled the calipers?

Tobin
KORE3

Loosen the nuts holding the MC to the brake booster?

I did that, didn't change anything. The pedal is just as tight as before, as are the wheels.

EDIT: I thought it was weird that both hoses would fail at the same time as well, but I did buy the calipers for pretty cheap off eBay, so anything's possible.

[SShep71]

What power system are you using vaccum or hydraboost? Does the caliper tightness return after you run the engine without pressing the pedal?

[Vicinity]

Vacuum, brakes do not change whether there is vacuum or not (engine on or off).

[SShep71]

What type of prop valve are you running?

[Vicinity]

CPP brass prop valve.

http://www.classicperform.com/Store/1947_59_Trucks/PV2.htm

That's basically it.

[Vicinity]

The master cylinder was also a used piece off eBay, if it's not the hoses on the front calipers, is it possible it's just the front most plunger in the master?

[David Pozzi]

Try cracking open the line at the master cyl. If that frees it up, your master cyl is causing residual pressure.

[Vicinity]

I took the master cylinder completely off the brake booster and then only put the nuts back on about half way on each side. The wheels freed up and I could push the car around, so I hopped in and scooted around the yard a bit, and the pedal wasn't anywhere near as hard as it was (didn't have full travel, turned into a rock about halfway), now I got about 3/4 travel and the wheels don't lock up completely until about then.

So I guess Tobin was right, I just didn't loosen it enough. Is it safe to shim the master off the booster? Right now the nuts are just loose and it drove pretty decently. If this means I'll just lose boost pressure I can live with it.

[dontlifttoshift]

Glad you pinpointed the source.

The pushrod coming out of the booster is adjustable on most aftermarket booster. If not you may have to get creative. You need .020" to .025" of clearance betweeen the pushrod and the piston in the master. Some aftermarket master cylinders are all machined with a deep, manual style, bore and a slug is used to make up the difference for a power assist unit. You may be able to grind the slug down if the pushrod is not adjustable.

First make sure the pushrod from the booster to master cylinder is adjusted properly.

[Vicinity]

Glad you pinpointed the source.

The pushrod coming out of the booster is adjustable on most aftermarket booster. If not you may have to get creative. You need .020" to .025" of clearance betweeen the pushrod and the piston in the master. Some aftermarket master cylinders are all machined with a deep, manual style, bore and a slug is used to make up the difference for a power assist unit. You may be able to grind the slug down if the pushrod is not adjustable.

First make sure the pushrod from the booster to master cylinder is adjusted properly.

Well, it's a Booster from an LS1 Camaro, theres not really any adjustment. I welded a threaded rod on the end of the booster's plunger, but I guess I welded it too far out.