Brake question
11-08-2012, 03:20 PM
#16
Rennlist Member
Thread Starter
I will be using a vacuum style bleeder tool today to get the brakes bled. I will have my woman help my keep the reservoir full while I am doing it. I have been lucky so far as to get the motor running with only relay work. maybe I will escape the replacement of the MC... I doubt it though, but one can dream lol.
11-08-2012, 08:01 PM
#17
Rennlist Member
Thread Starter
Brake update: I used a brake bleeder (vacuum style) tonight. I started to bleed out left front, fluid with bubbles came out, then there was almost a gulping sound and about 3 ounces of fluid came rushing into the bleeder. After that point, it wouldnt suck any more fluid out. It also wouldnt hold a vacuum. when I would pump the bleeder trigger, vacuum would build up, and then bleed off. the reservoir was still almost full too. I went to top it off after this happened, and it only took a small amount. I then went back to rebleed, and nothing would come out.
I decided to pump the pedal with the screw open to see what would happen. no matter how much I pumped the pedal, no fluid would come out. I did see little bit of fluid spray out with air while I was pumping it. very weird.
does this mean the MC is fried? Could it be anything else?
I also noticed that my brakes have had some work done to them. Stainless braided lines for starters. here is a pic of the left front:
I decided to pump the pedal with the screw open to see what would happen. no matter how much I pumped the pedal, no fluid would come out. I did see little bit of fluid spray out with air while I was pumping it. very weird.
does this mean the MC is fried? Could it be anything else?
I also noticed that my brakes have had some work done to them. Stainless braided lines for starters. here is a pic of the left front:
11-08-2012, 10:33 PM
#18
Nordschleife Master
I'd start by checking that there's no preload on the master cylinder from the pedal. The fact that its not taking fluid to the circuit you're checking could indicate the master cylinder piston isn't sliding back in the bore far enough to open the port.
Have you checked to see if one of the rear calipers lets you bleed fluid out?
Not sure on the early cars, but the ones where ABS was an option have 3 separate brake circuits (one for each front, and then both rears combined).
Have you checked to see if one of the rear calipers lets you bleed fluid out?
Not sure on the early cars, but the ones where ABS was an option have 3 separate brake circuits (one for each front, and then both rears combined).
11-09-2012, 10:45 AM
#20
Rennlist Member
Thread Starter
My apologies - I simply overlooked the actual loss of pressure, and was just thinking about the warning.
Yes, it seems that you have no pressure on one side of the brake system. The brake systems are split diagonally - one piston in the master cylinder applies left front and right rear, while the other piston applies right front and left rear.
If the brake fluid reservoir is full, and you can find no brake fluid leaks, but still have a very low pedal, the possibilities include:
- Air in the system. Carefully bleed all four wheels (and the clutch if a five-speed). You can use the two-man method, with a reliable helper on the brake pedal and you on the bleed wrench. Use a wrench that fits the bleed screw perfectly, so as to avoid rounding the bleed screw. Start by opening a caliper bleed screw. Tell the helper to slowly press the pedal to the floor and hold it. Use your finger to block the bleed screw, and tell the helper to let the pedal all the way up. Remove the finger, tell the helper to press the pedal down. (The usual commands are "down" and "up", with the helper understanding that the pedal remains as commanded until they are told otherwise.) Repeat until you get fluid with no visible bubbles. When this happens, close the bleed screw with the pedal down. Repeat on the other three wheels and the clutch slave cylinder.
You should now have a reasonably firm pedal. If so, have the helper stand hard on the brakes, and inspect the entire brake system for leaking fluid. If you find no leaks, drive the car for a few days, remaining very sensitive to any changes in pedal height or operation.
- Ballooning brake hose. If, after bleeding, you still do not have a firm pedal, have the helper hold the brake pedal down and check all of the brake hoses for any swelling or ballooning. Replace any that swell at all.
- If, after bleeding, you still have a very soft pedal, the chances are good that the master cylinder has failed. Replace the master cylinder. After removing the master cylinder (search on here for directions on replacing the cylinder), use a piece of cloth on a wire to check for fluid in the bottom of the brake booster.
Yes, it seems that you have no pressure on one side of the brake system. The brake systems are split diagonally - one piston in the master cylinder applies left front and right rear, while the other piston applies right front and left rear.
If the brake fluid reservoir is full, and you can find no brake fluid leaks, but still have a very low pedal, the possibilities include:
- Air in the system. Carefully bleed all four wheels (and the clutch if a five-speed). You can use the two-man method, with a reliable helper on the brake pedal and you on the bleed wrench. Use a wrench that fits the bleed screw perfectly, so as to avoid rounding the bleed screw. Start by opening a caliper bleed screw. Tell the helper to slowly press the pedal to the floor and hold it. Use your finger to block the bleed screw, and tell the helper to let the pedal all the way up. Remove the finger, tell the helper to press the pedal down. (The usual commands are "down" and "up", with the helper understanding that the pedal remains as commanded until they are told otherwise.) Repeat until you get fluid with no visible bubbles. When this happens, close the bleed screw with the pedal down. Repeat on the other three wheels and the clutch slave cylinder.
You should now have a reasonably firm pedal. If so, have the helper stand hard on the brakes, and inspect the entire brake system for leaking fluid. If you find no leaks, drive the car for a few days, remaining very sensitive to any changes in pedal height or operation.
- Ballooning brake hose. If, after bleeding, you still do not have a firm pedal, have the helper hold the brake pedal down and check all of the brake hoses for any swelling or ballooning. Replace any that swell at all.
- If, after bleeding, you still have a very soft pedal, the chances are good that the master cylinder has failed. Replace the master cylinder. After removing the master cylinder (search on here for directions on replacing the cylinder), use a piece of cloth on a wire to check for fluid in the bottom of the brake booster.
since I have stainless lines, I am assuming I can rule out hose balooning.
I am going to have to try to bleed one of the rears today to see if fluid comes out. Like I said, it was weird yesterday, front left was bleeding fine, and then it made like a gulping sound and pulled a few ounces of fluid into the bleeder, and then the bleeder wouldnt pull anymore. I took the bleeder off and put my finger over the hole to see if it would hold vacuum.. it did.
another thing I noticed, is that with the car running, when I press the brake pedal down I hear a hissing sound. it does not do it when the car is not running.
any idea what that might be?
11-09-2012, 12:10 PM
#21
Rennlist Member
Rennlist Site Sponsor
Hilton made a good suggestion - check the brake pedal adjustment to make sure that the pistons are not pushed in far enough to block the port between the reservoir and the master cylinder bore. That would explain most of your problems.
Adjust the pedal so that there is a slight amount of free play before the pistons start to move. Rebleed, keeping a very careful eye on the fluid level.
The noise may be normal, or may indicate a failed brake booster. It is not unusual for there to be a hissing or swooshing noise while you are moving the pedal - there should not be any noise with the pedal not moving.
To test the booster after you get the fluid problem solved.
With the engine off, press the brake pedal several times. You should now have a high, hard pedal. Push the pedal down and hold it with moderate pressure while you start the engine. As the engine starts, the pedal should move down slightly and get softer. Release the pedal and then press the pedal down with moderate pressure and hold it. There should be no hissing. Turn the engine off, and press the pedal with moderate pressure and release, then repeat. You should be able to get three application before the pedal again gets high and hard. If not, the vacuum is leaking at the check valve, or the booster is faulty.
Adjust the pedal so that there is a slight amount of free play before the pistons start to move. Rebleed, keeping a very careful eye on the fluid level.
The noise may be normal, or may indicate a failed brake booster. It is not unusual for there to be a hissing or swooshing noise while you are moving the pedal - there should not be any noise with the pedal not moving.
To test the booster after you get the fluid problem solved.
With the engine off, press the brake pedal several times. You should now have a high, hard pedal. Push the pedal down and hold it with moderate pressure while you start the engine. As the engine starts, the pedal should move down slightly and get softer. Release the pedal and then press the pedal down with moderate pressure and hold it. There should be no hissing. Turn the engine off, and press the pedal with moderate pressure and release, then repeat. You should be able to get three application before the pedal again gets high and hard. If not, the vacuum is leaking at the check valve, or the booster is faulty.
11-09-2012, 12:55 PM
#22
Rennlist Member
Thread Starter
I'd start by checking that there's no preload on the master cylinder from the pedal. The fact that its not taking fluid to the circuit you're checking could indicate the master cylinder piston isn't sliding back in the bore far enough to open the port.
Have you checked to see if one of the rear calipers lets you bleed fluid out?
Not sure on the early cars, but the ones where ABS was an option have 3 separate brake circuits (one for each front, and then both rears combined).
Have you checked to see if one of the rear calipers lets you bleed fluid out?
Not sure on the early cars, but the ones where ABS was an option have 3 separate brake circuits (one for each front, and then both rears combined).
11-10-2012, 12:40 AM
#23
Rennlist Member
Rennlist Site Sponsor
Get down and check the movement of the push rod going into the master cylinder - it should be possible to move the brake pedal a little before the push rod moves. If not, loosen the lock nut and adjust the rod so there is a little free play.
11-13-2012, 08:07 PM
#24
Rennlist Member
Thread Starter
there appears to be a little bit of free play before the brake pedal engages the piston. so I can rule out free play issues. so does that only leave the master cylinder?
I want to be able to rule out anything else before I go ahead and purchase a new master.
I want to be able to rule out anything else before I go ahead and purchase a new master.
11-13-2012, 09:05 PM
#25
Rennlist Member
Rennlist Site Sponsor
First, I would try bleeding the brakes the old fashioned way as described earlier. You can develop 600psi with the pedal - that should push fluid down the line if there is any in the master cylinder.
I would also try bleeding the right front and see if the problem is the same on both sides. It does seem as if something is preventing the fluid from flowing from the reservoir to the caliper - could be in the master, could be a blocked brake line.
I would also try bleeding the right front and see if the problem is the same on both sides. It does seem as if something is preventing the fluid from flowing from the reservoir to the caliper - could be in the master, could be a blocked brake line.
11-14-2012, 11:16 AM
#26
Rennlist Member
Thread Starter
ok so I called the PO last night. He decides to finally let me in on the fact that he had to disconnect one of the front brakes from the "brake block" in order to tow the car, and that it had brakes up to that point.
WTF? like maybe that would have been useful to know. That would explain why I couldn't bleed any more fluid out of the front line. It because it isnt hooked up anymore. SO, where exactly is this brake block as he put it? I am sure I can find it if I look around, but a little help would be nice too.
WTF? like maybe that would have been useful to know. That would explain why I couldn't bleed any more fluid out of the front line. It because it isnt hooked up anymore. SO, where exactly is this brake block as he put it? I am sure I can find it if I look around, but a little help would be nice too.
11-14-2012, 01:28 PM
#28
Rennlist Member
Thread Starter
do the lines in the pic above look suspect? As far as I can tell, they look just like the stainless braided kit I have on my mustang.
I talked to him again today. he said he loosened one of the lines under the hood from what he keeps referring to as the brake block. He said it was to one of the two front lines. If the front line I tried to bled wasnt connected, it would have sucked the fluid out in the manner I experienced I think. It also would account for why no more fluid was taken out from the master... I am pretty sure it explains it.
so does the car have a brake block? I assume he is referring to a spot when all the lines connect. I have no idea what he is talking about to be honest with you.
11-14-2012, 01:41 PM
#29
Archive Gatekeeper
Rennlist Member
Rennlist Member
FWIW I don't know anything about the brake hardline routing on an '80, but the picture in PET looks like it has 4 individual hardlines routed to each wheel, so there are no distribution blocks, per se. But- there are a pair of brake pressure regulators, which (from other threads, like https://rennlist.com/forums/928-foru...-cylinder.html ) seem to be mounted just below the master cylinder. Maybe that's what the PO is talking about?
Pictures = 1000 words.
Pictures = 1000 words.