OK, I'm confused (it doesn't take much) but I bleed my rear brakes. They are the TSM's rear disk brake conversion calibers off of a 76-78 Eldorado with parking brakes. I needed new pads and wasn't planning on bleeding them. Not the case because you don't just push the piston in to make room for the new pads. You have to remove the bracket for the emergency brakes and adjust the rachet back as you push the piston in. Fluid escaped so I proceded to bleed. Used a mitivac but the brakes were not hard. I proceded to read on TSM's website that you should gravity bleed them because the bleed value is on the top and tap with a hammer to jar the air bubbles up and out. So, I gravity bleed the brakes today and have a strange sitution. With the engine off, the brakes are rock solid hard and do not sink down. With the engine running the brakes when pushed and held down will sink down. What the heck is that all about? Is my master cylinder going bad or is my vacuum assist going bad or am I not getting the air out of the brakes?? To me, if I still had air in there, then why with the engine off are the brakes solid?? Thanks, Glenn

 

With the engine on your brake booster is making the brakes soft. You need to keep bleeding.

 

I was afraid of that!

 

Its normal to have a rock hard pedal with the truck off. You don't have any power assit. Just wait till your vacuum pump goes out and you have to drive the truck. 2 feet on the brake pedal.

Now how fast does the pedal drop when running. Do you have a normal feel to the pedal then like it your sitting at a stop light the pedal very slowly sinks? If that is the case it "normal". The booster keeps getting more and more assist. Ford has made a revised booster to fix the issue but if you can live with the sink its not hurting anything. Rubberduck installed a booster like that after I told him about it and it works well.

 

what tj said... as long as its not spongy then you are fine......how did you lose fluid while changing pads? that part confused me????

 

Thanks Tim, Bleed them twice and think their bleed OK. Joe, on those type calipers with the emergency brake bracket on the caliper, its like a racket. The cables stay adjusted by using the emergency brake. To get the piston in for new pads, I had to remove the emergency brake bracket from the caliber and reverse the racket (bolt the bracket mounts on) as I applied pressure to the pistion. Fluid came out from around the bolt that is the 'racket'. When its together there is a rubber seal around the bolt but after removing the bracket the seal loses contact and leaks. Its not your normal caliber with the emergency brakes as part of it. I'm glad I ordered them that way from TSM, I use the emergency brakes alot. I hope I explained that OK, if not let me know.

 

so its normal to have them leak when compressing the piston? i dotn like that idea

 

I guess maybe there is one benefit of being a big, fat guy. I had the hose split and I lost vacuum. Yes, I had to push hard, but it was never scary and I drove one footed.

 

I don't think that is normal. Not on any I have ever done but I have never done a set of these particular calipers.

 

Agree. Could of blown the seal.
Most rear disk brakes with self adjusting park brake (caliper),
have rotational pistons. You have to turn the piston
to reseat it. They make a tool that grabs the inside of the piston.

Bill

 

Bill, I tried rotating the piston, it would not move. I didn't have the proper tool but had a nice big round pair of vice grips, would not move, either direction. Then I used the same pair of vice grips with one side on the back of the capiper and the other on the pistion, would not move. Only when I released the emergency brake bracket from the back of the caliper, thus releasing the racketing bolt, did the pistion start sinking. I didn't want to bleed the brakes so I never opened up the bleed value. Never had to before, pushing the pistion in would force the fluid back up into the master cylinder resorivor. I for sure blew the seal, its held tight by the nut on the rackenting bolt. Looking back, I should have tried opening up the bleed value and trying to push in the piston. I don't think that would have worked because of the rackenting effect in place to hold the pads tight against the rotors with the emergency brakes applied. Fluid or no fluid the emergency brakes should work. I don't know, maybe I should have titled this thread 'Hard & Sinking", that's something we can all understand, lol!!!!!

 

time to find an eldorado book and see how it is supposed to work. and in the mean time go get a new caliper

 

Well Joe, they were both the same procedure when I did them and they are on and working. Also not leaking, I would be curious of what the 'book' would say though!!

 

oldbird

Correct. You have to unbolt the lever before you can seat the piston.
IIRC the piston is turned clockwise to seat.

Bill

 

Doesn't using the parking brake re set the piston after it has been compressed ?...