For reference this is the thread I started the other day.

http://forums.corvetteforum.com/show....php?t=1408332

I'm trying to bleed the brakes out on my car. It has sat for quite a while and the brake system was open/taken apart while sitting. I've got no pedal when depressing the brakes after numerous attempts to manually bleed the system per the Helms manuals. The left front caliper, which is a C5 caliper I bought used, seems to not want to release when the pedal is not depressed and when the pedal is pressed I can, with some force, still turn the passenger side front roter. On the left side rotor I unhooked the brake hose from the caliper and from the line and can blow through it each way. I then attached it back to the hard line and got someone to depress the pedal and then let off while I held my fingers over the hose end and I felt it sucking back. Then I attached it to the caliper and bled the caliper out once again and loosened the bleeder valve while someone had the pedal depressed and put my finger over the bleeder hole and told them to let off and felt suction on my finger covering the bleeder hole. I then bled all four wheels again and tried the brake pedal, with the car on for the vacuum assist, and the pedal went to the floor. Any suggestions from you guys before I tear the front calipers apart tomorrow? BTW its a new master cylinder.

Also according to the local parts stores a caliper rebuild kit is not available for the C5 Calipers, does someone know where I can get one?



Does anyone think one of those vacuum pumps to bleed the brake system would be any help here?

 

My mity vac vacumn pump is what I use to bleed the brakes. Works like a champ every time. Crack the line, attach the hose, and pump. Pay close attention to the MC and fill as needed. I go through a pint or 2 and then I'm done. As far as your sticking caliper you must have some gunk in there so rebuilding will need to be done. As far as finding a kit I'm not sure but I have to believe a kit is available for that caliper. Good luck!

 

When you said the system was completely drained, what does that mean? Did you somehow remove all the fluid or just left the system open.

When you say you have bleed the brakes, do you get a hard pedal before you start the engine? After you start the engine and the vacuum assist is working, how easily does it go to the floor. Easy push, with moderate force or real hard push?

Got to ask the obvious. Did you bench bleed the master well, before the install. Then after you tightened the lines did you crack them open and do a bleed at that point.

As far as vacuum pumps go I have recently read on an ABS system a mity vac vacuum pump is not recommended because you are pulling a negative pressure in the system and it is designed for a positive pressure. I don’t know if this is BS. I’m sure many people use these vacuum pumps.

Another thing you might consider is to do a back bleed with the master out on front and rear. This would move up any air in the lines from the ABS and would insure that fluid is at the fittings at the master before installation. I use a dedicated oil can and a rubber hose. Got to make sure no air is in hose before attachment to bleeder, don’t want to make things worse. After your done under the hood, the last thing I do the re-bleed calipers.

On you release problem, once you press the pedal, and the wheel locks up, have you opened the bleeder to release the pressure and see if the wheel frees up. If it does not, it’s probably the caliper.

 

All good points. Some of which I've addressed. BTW its a '90 model

The system was left with no master cylinder or brake calipers for atleast 8 months. I did not suck the remaining fluid out but would assume alot drained out on its own over time due to gravity.

The pedal is moderately soft when the car is off and will go almost all the way to the floor, just short of tripping the Brake warning light. As soon as the car is turned on and pedal is applied it goes to the floor with little effort

I bench bleed it on the car with rubber hosed attached to the front and rear holes and pushing the pedal before hooking up the hard lines. I was under the impression that you didn't have to bench bleed it though, it would just take longer to bleed out the calipers if you didn't, am I wrong?

Never heard that


I am not familiar with this procedure, can you explain?

I did undo the bleeder valve and tried to turn the rotor and after a little working it back and forth it got a "LITTLE" easier.

BTW if I pump the pedal I can get it to firm up a little, like when the master cylinder is going out and you have to pump the pedal, but the Master cylinder is new. I changed it when I first noticed the problem thinking that was the problem. So I've had this problem with two MC's now.

Is there anyway the brake booster could be causing this, I would think the problem would be the opposite of a soft pedal if the booster were bad no?

 

You probably have air in the system because firstly when you bolted up the master, the fluid was probably not up to the fittings. You bleed the master so you don’t add to your problems by adding more air to the system. Also having it bled with fluid in it, it will pump better.

Back bleeding is forcing fluid into the caliper bleed screws or lines by an oil can or pressure bleeder so that the fluid comes out at the master fittings. The master can be on or off depending on what you trying to accomplish. I guess in your case I would back bleed and get the fluid up to the fittings and then connect master after is well bleed. In my view, I would try to get as much fluid into the system as I could before I connected the master. Then crack each fitting and press pedal (same procedure a bleeding a caliper) to get air out of the connections.
Then start to bleed the calipers normally lots of times.

If the system was holding pressure and you cracked the bleeder, the wheel should free right up. Sounds like the caliper is the problem.

At this point the booster is not a consideration in your current problems. Probably it is going to be fine, it sounds like its working OK. Did you adjust the adjustment screw on the booster, because it probably didn’t need it, and small adjustments make big effects.

This web page has some good information on brake bleeding and thought it was the one about ABS and vacuum bleed but check page 44. MIght have seen it some where else.
http://www.phxsyss.com/images/manuals/manual.pdf

 

Going to read the PDF link tonight. Just got through going through the system again. First I took the problemed caliper apart and cleaned and reinstalled. It will now release just fine. I started at the master cylinder and bench bled it by putting a fitting in the front bore and attaching a piece of hose to it and putting the other end in a jar of fluid. Then I pumped the pedal. Then refitted the brake line. I repeated for the rear line. I filled the reservoirs up with fluid and got a helper (read S.O.) to slowly depress the pedal and hold while I cracked each fitting at the MC several times. Then I moved to the calipers. Starting with right front, right rear, left rear, left front, which is the order the manual suggests. I did each caliper 8-10 times and had nothing but fluid come out each time. On the rear calipers my helper noticed that when I cracked the bleeder valves open the pedal went the rest of the way to the floor. It did not do this on the fronts she said. Also with the system tightened up I can turn the front rotors with force by hand even when the pedal is fully pressed.

Any other suggestions. I don't have the tools to do the back bleeding procedure.

 

[QUOTE=hz900]For reference this is the thread I started the other day.

http://forums.corvetteforum.com/show....php?t=1408332

On the left side rotor I unhooked the brake hose from the caliper and from the line and can blow through it each way. I then attached it back to the hard line and got someone to depress the pedal and then let off while I held my fingers over the hose end and I felt it sucking back. Then I attached it to the caliper and bled the caliper out once again and loosened the bleeder valve while someone had the pedal depressed and put my finger over the bleeder hole and told them to let off and felt suction on my finger covering the bleeder hole.
Also according to the local parts stores a caliper rebuild kit is not available for the C5 Calipers, does someone know where I can get one?

QUOTE]

Ok, two things:

First, I will tell you that I had put a rebuilt master on a car not too long ago and had a similar problem. The breaks suck before, and they got worse. It turn out I had to go through 3 master cylinders to get one that worked. The new one (from A-zone) worked, but both rebuilt ones leaked. I watch this and was amazed of the possibility of getting not one but two crap master cylinders.
My advice is to watch closely for bubbles when you are bleeding it.
Watch for leaks and hope you don’t have a broke line.

Second, I looked at your post and you stated your putting your finger over the bleeder bolt while the person in the car is letting off on the brake peddle. I would recommend tighten the bleeder screw back up in-between each up ward peddle movement. I would be concerned that the air can be pulled from either around your finger or the threads of the screw.

 

That was just that one time to see if fluid was being sucked back like it was supposed to be. Thanks though. The possibility of a bad MC has crossed my mind.

 

Seems like you are concentrating on just one caliper. Did you not bleed ALL the calipers???????? Or have I missed something??
You have to look at the whole system.

Larry
code5coupe

 

Yes I bled all the calipers, in order of the Helms manual as stated above, three times now. The one caliper was just sticking originally was why I was mentioning it more than the others.

 

Been working on the brakes this morning, thought I'd give an update in hopes that someone comes up with an answer.

Also I forgot to mention earlier that I have a DRM bias spring in the master cylinder that I put in and took care not to nick the o-rings when installing it.

I bought a Vacuum bleeder and against one previous suggestion tried bleeding the brakes with it (I was out of other options). It looked like I got alot of air out of the system so I thought great maybe this will help. I bled all four calipers in this order; front right, rear right, rear left, front left. I went around the car twice. Still have a soft pedal when the car is off and when I crank the car to get brake booster assist its even worse than before, the pedal goes to the floor and is SLOW to come back to the top. I'm about at my wits end and am about to go and buy a new not rebuilt master cylinder and see if that solves the problem. If that doesn't work I guess the only other thing is to find an abs pump and change that, then the system will be completely new/reconditioned except for the brake lines themselves. I just hate throwing parts at a problem and thats what I'm down to it looks like.