Getting Disc Brakes to Retract

[Joe Flanagan]

I'm bleeding my brakes (AAJ disc setup in the front) and the calipers in the front will not retract. I installed them many years ago, a job I think I should have waited to do till now. I always wondered whether they'd be operative when I finally filled the master cylinder and now I guess I have my answer. I'm assuming if I open the bleeder valves on the calipers they will release, but I'm also assuming these calipers have sat unused for too long. Am I correct in my thinking? They are for a 1971 El Camino and were new when I got them. Is there any other reason they would not retract besides being old and having sat for 12 years? The piston in the master cylinder seems to want to take its time returning to position after the pedal is depressed, but gets better the more you pump it. Just mentioning that in case there might be something else going on. Thanks for any suggestions.

 

Joe

[Don Coatney]

Make sure the fluid return hole in your master cylinder is not obstructed. The one with the prick punch pictured below

 

[Joe Flanagan]

Thanks, Don. Will check that right now.

[Joe Flanagan]

That hole appears to be clear. A geyser of brake fluid shoots out of it when the pedal is depressed. The pedal comes back to its normal position now, but the front brakes still won't retract.

[casper50]

Pistons could be stuck after 12 years.  You might have to remove them and use a clamp to compress

[_shel_ny]

Are you saying that the wheel stays locked, or you just don't see back movement of the piston and pads?? No springs on the disk set up to retract things like on drums and shoes. My understanding of disc is that when the pedal pressure is released the pads are still very very close , or even in light contact with the rotors, but not restricting movement. Not a mechanic, just throwing that out there.

[Plymouthy Adams]

shel..actually the rotating of the square cut oil ring under pressure as the piston moves out is the same force that pull the piston that ever so slight a distance back from the rotor..

[Joe Flanagan]

The wheel stays locked and you can't rotate it with any amount of force. I opened the bleeder valves on both sides and they released. But if you operate the brake pedal, they seize up again. At one point, they wouldn't release even after I opened the bleeder valve but I was able to force the pistons back with a pry bar. I installed these brakes in 2002 and they've just sat there since. What rubber you can see around the pistons looks dried out. It wouldn't surprise me if they can no longer move in their bores. 

[Plymouthy Adams]

Joe..disassemble the caliper,remove the piston and clean well..carefully remove the o-ring and clean inside with solvent and 0000 steel woolor quick hone or wet and dry 500, clean unit good with lint free cloth, re-wet with clean brake fluid and reassemble..odds are your problem will go away..also..clean the slide of the caliper good at the same time..do not wet lube these slide..that leads to rust and gathering of dust dirt and other foreign matter...

[Joe Flanagan]

OK, I'll do that, Tim. That's a good project for tomorrow morning. 

[JerseyHarold]

Check the rubber brake hoses going to the calipers.  They may have swelled internally over time and are acting like a one-way valve that prevents the brake fluid from leaving the caliper.

[Plymouthy Adams]

JerseyHarold, on 01 Jun 2014 - 3:23 PM, said:

Check the rubber brake hoses going to the calipers.  They may have swelled internally over time and are acting like a one-way valve that prevents the brake fluid from leaving the caliper.

another excellent possibility...

[falconvan]

I'd go with the hoses, I've had that happen a few times on old cars.

[nonstop]

Just throwing it out there too, although it sounds like issues with the calipers, but did you remove the residual pressure valve?

[Don Coatney]

Just throwing it out there too, although it sounds like issues with the calipers, but did you remove the residual pressure valve?

One more good thought.

[Joe Flanagan]

I don't recall removing the pressure valve. I'm using the original master cylinder (rebuilt). I also have residual pressure valves installed, same as Don's setup, I believe. I got them from Jegs. I think they keep 2 lbs. of pressure on the front brakes and 10 lbs. on the rear. As far as the hoses go, they were new when I installed them back in '02. Could they have swelled in that amount of time? 

Edited June 2, 2014 by Joe Flanagan

[nonstop]

Your residual valve is in your master. From the sounds of it, it is probably not the main culprit, but there was definitely a much more noticeable drag before I removed it and went with an inline 2 pound valve.

[Dave72dt]

You can easily test them by  applying the brakes and then cracking the lines at each connection, working your way back toward the master

[Joe Flanagan]

The setup I have is exactly like Don's as shown in this thread:

 

http://p15-d24.com/topic/33551-not-understanding-brakes/?hl=residual#entry337148

 

Also, I think the residual valves are 2 lbs. for the front and 10 lbs. for the rear. As far as I know, the original residual valve is still intact. 

[Jeff Balazs]

I ran into this problem when I added discs to my truck. Get rid of those 2# valves and things will work just fine.

 

Jeff

[Joe Flanagan]

So you got rid of the 2# valve and kept the 10# for the rears?

[Jeff Balazs]

Joe;

I did not install residuals on the rears. I put a Grand Cherokee rear axle that has 12" discs with a M/C from the same model Jeep.

I added a Wilwood proportioning valve and a pair of their 2# residual valves for the front end. The residual valves gave me problems from the get go. When I spoke with friends who build cars all the time they told me to remove the residuals as they were totally unnecessary and would cause the brakes to drag and wear prematurely. Just as soon as I removed them the brakes started working as I expected. The proportioning valve works fine and is a good idea. It is adjustable and is used to balance the braking between front and rear. Before I began making adjustments the rears would lock up well before the fronts.

 

Jeff

[DJ194950]

Still have the built in factory MC residual valve? Remove it. It will hold 10 lb. to front and back I believe, causing the front to hold too much residual pressure. No effect to rears as both hold 10 lb. to rears.

Probably need to remove and clean up the front calipers as Tim said also.

 

Just one more thought!

 

DJ

[1941Rick]

Sounds like you have to remove the residual vale from the master cylinder...

Question.....why not a dual master cylinder?

[Joe Flanagan]

I figured that using the original MC was simpler and I'd heard of other guys who'd done it. It sounds like there are two schools of thought about this: 1-Remove the residual valve in the MC, and 2-Remove the after market 2# valve I installed.