soft brake pedal

[NEp8ntballer]

So saturday night with some help I finally finished the 96 brake upgrade on my 93 SHO. We replaced all four brake lines with SS lines, all new calipers front(duh) and rear, new pads and rotors all around and now my brake pedal is soft. before with the car off I could get a litle bit of pedal travel and enough pressure to keep the car from rolling backwards since the e brake was disconnected. now with the car off and bleeding about a quart of brake fluid total doing a full flush of the entire system I can now push the pedal almost entirely to the floor.

I had my nearly worthless sister in the car pumping the brake pedal while I listened for the weezing sound that is coming from somewhere under the hood. It makes the sound when you push the pedal down and on the way up you can watch bubbles come up in the brake reservior.

so anybody know what gives? The pedal was hard before with the motor off. I remember it being slightly challenging to push the clutch in to allow the motor to turn over with my left leg, holding the brake pedal far enough to keep me from rolling with my right toes, and also having my right heel on the gas with it all the way on the floor to cut the injectors to build oil pressure before I start it since it doesn't run very often at the moment.

 

[SHO Continental]

Leak!

 

[Kens1992mtxSHO]

Any puddles under the car? Maybe a bad brake master cylinder??

 

[hawkeye18]

sounds like you let the brake fluid reservoir get empty... and now your MC has air in it. You will now have to somehow park the car on a 20 degree incline and bleed the MC, or remove the MC from the vehicle and bench bleed it. That's the only way you're gonna get the air out of it...

of course, if you didn't let the reservoir go dry, then it's something else and that doesn't apply...

 

[NEp8ntballer]

sounds like you let the brake fluid reservoir get empty... and now your MC has air in it. You will now have to somehow park the car on a 20 degree incline and bleed the MC, or remove the MC from the vehicle and bench bleed it. That's the only way you're gonna get the air out of it...

of course, if you didn't let the reservoir go dry, then it's something else and that doesn't apply...

I doubt we let it get empty. we checked the fluid constantly when we were bleeding. and I'm not talking small bubbles but big massive ones that go glug instead of being quiet.

 

[Roady94]

-" . . . my nearly worthless sister . . ."

Sounds like some of the info you gathered could not have been acquired without her very worthwhile assistance. If you are an honorable man, or if she gets wise to your opinion of her, you will be performing the balance of the diagnosis alone, so let's start with that premise.

The below assumes you have done a thorough, proper bleed. (many instructional resources available on the web), and that brake hoses are sound.

Are you certain there are no leaks? No assumptions allowed here. You must make a complete visual inspection of the entire system. However, with the kind of pedal travel you are experiencing I would expect a visible level change in the MC reservoir if you had a leak as the cause. Is there a level change in the reservoir? If so, you have a leak - no other options - you must find it, fix it, re-bleed.

No level change? Again, assuming a proper bleed, check for an internal MC leak. This would be caused by faulty seals on the plunger. Not uncommon with greater than normal pedal travel during bleeding of an older system. The plunger travels into a little-used portion of the cylinder and scuffs the seals on the rougher sidewalls there. To check, disconnect the brakelines from the MC. Plug the holes. Pedal should be rock-hard with engine running and without. If there is still full pedal travel, MC plunger seals are shot. If there is sponginess, then firm pedal, you have air in MC and must bleed it as suggested in an earlier post.

If you have no plugs, buy a short length of brakeline (with fittings) and cut the last 1.5" off of each end. Pound the portion of the tubing flat after it extends beyond the fitting. If you do this with care, there will be no leaking of any consequence.

If pedal is rock-hard with engine running, MC is good, but you still have air in the system beyond the MC, regardless of your previous statements to the contrary. No exception. Reconnect the lines and bleed thoroughly.

Since you will now be bleeding alone, you will need to purchase a mechanical assistant. I have better results with, and more faith in pressure bleeders than with vacuum bleeders.

Don't forget to report back.

 

[yamahaSHO]

I am going to agree with the above as my thoughts are the master cylinder. I was the one helping (I'm not his sister) him do the brake install and bleeding and we flushed about 1 1/4 bottles of brake fluid through. About every 10 or so pumps, there would be almost solid air in the lines. Bleed some more, and it goes back to solid fluid and then the air comes back. It was dark when we finished up the other day, however, any of the lines we touched are NOT leaking.

The MC level does not go down. It actually went up after doing some driving, however some of that can be from things getting warm. When I was looking at the MC, I had the cap off and there were no bubbles coming up, but you could hear a bit of a gurggling(sp) sound. Chris mention when he did some further testing, that bubbles appear with the cap on, and the reservoir swells pretty good while depressing the pedal.

Because one of the reman rear calipers does not clamp the pad very well and the parking brake does not hold very well, I suggested that we have another sent to try out. I don't think it will solve the problem, but we're doing it anyway. The parking brake hadn't been connected on the old calipers for I don't know how long, but you can see physical operation and it's doing what it is supposed to.

 

[Roady94]

- Well, if you are finding air when you bleed, then we need to figure how it got in there. If it is being introduced as a part of the bleeding process (pedal return after pumping) that would mean an open in the system somewhere. A sizable one from your description.

Any open that large would absolutely leak fluid under pedal pressure. Since you are certain there is no leakage, we can only assume that the air you are seeing is finite, and must be bled out.

A visible rise in MC fluid level after driving could be expected with excessive air in the system. When hot, air will expand considerably more than fluid.

Side Note: If MC seals are shot, they alone have no means of introducing air into the system.

 

[NEp8ntballer]

oddly enough I just pulled the tires off and to check to make sure the rears would still come off I tried to spin them both and both of them are holding tight, so for some reason the caliper that wasn't working before is working now as far as the e brake is concerned.

-" . . . my nearly worthless sister . . ."

Sounds like some of the info you gathered could not have been acquired without her very worthwhile assistance. If you are an honorable man, or if she gets wise to your opinion of her, you will be performing the balance of the diagnosis alone, so let's start with that premise.

to borrow a line from a former football coach of mine I could train a monkey to do what I had her do... maybe I should invest in a trained monkey to help me out... Anybody here willing to work for bananas?

 

[yamahaSHO]

- Well, if you are finding air when you bleed, then we need to figure how it got in there. If it is being introduced as a part of the bleeding process (pedal return after pumping) that would mean an open in the system somewhere. A sizable one from your description.

Any open that large would absolutely leak fluid under pedal pressure. Since you are certain there is no leakage, we can only assume that the air you are seeing is finite, and must be bled out.

No leak and I bled for over an hour. I'm willing to bet the MC is introducing the air.

A visible rise in MC fluid level after driving could be expected with excessive air in the system. When hot, air will expand considerably more than fluid.

Generally it doesn't like to come back up through the ABS pump.

 

[Roady94]

- Agreed as far as the ABS goes . . . generally. How do you explain the mentioned increase in MC reservoir level then?

Also, can you describe a process by which the MC can continue to introduce air into the system without an open, and without running the reservoir out? I can't envision one.

On the bright side, brake systems are one of the simplest systems to diagnose on a car, even with power boost, even with ABS. When this cause is discovered, it will be something simple.

 

[NEp8ntballer]

- Agreed as far as the ABS goes . . . generally. How do you explain the mentioned increase in MC reservoir level then?

Also, can you describe a process by which the MC can continue to introduce air into the system without an open, and without running the reservoir out? I can't envision one.

On the bright side, brake systems are one of the simplest systems to diagnose on a car, even with power boost, even with ABS. When this cause is discovered, it will be something simple.

I got it back on jack stands, pulled the tires and pumped the brake a good 20 times and it isn't puddling, dripping, or obviously leaking where we worked. I'm not getting full pedal travel though. the first couple inches are very soft but it really firms up after that and I can't get it to go to the floor with the car off.

the MC had seals that were plenty good before because the pedal wwould hardly move with the motor off. the only thing that could possibly affect the seals that I can think of would be the introduction of brand new fluid washing some crap off of the sides of the cylinder and allowing a pressure leak.

 

[Roady94]

- The fact that the pedal is getting firmer is a good thing. Couple that with the absence of leaks, and it looks like no new air is being introduced into the system and the bleeding is helping.

Firm pedal with engine off is common even with some air in the system.

If there was "crap" on the sides of the cylinder within the normal stroke range of the plunger prior to the fluid change, the seals would have already been compromised by stroking across that "crap", causing pedal-to-floor before you began your brake upgrade.

If you want to end any question about the MC seals, disconnect the lines and plug the MC as I suggested earlier.

• Rock-hard pedal = Good to go = Air somewhere else in system.
• Soft, then firm pedal = Air in MC = Bench bleed.
• Pedal goes to floor = MC seals are shot = rebuild/replace.

There are no other options.

Next step will be determined by results of this test.

 

[hawkeye18]

Back when I replaced the front calipers and installed bias plugs and SS lines all round, I had to bleed the system at least three times at one month intervals before I got a firm pedal again, and that was with bleeding the ABS pump (I have an ABS pump thingy). It might seriously be that you just had that much air in the system...

 

[NEp8ntballer]

Back when I replaced the front calipers and installed bias plugs and SS lines all round, I had to bleed the system at least three times at one month intervals before I got a firm pedal again, and that was with bleeding the ABS pump (I have an ABS pump thingy). It might seriously be that you just had that much air in the system...

If I push the pedal as far as I can get it with the car off and move it back and forth an inch or so it won't bubble. but if I take it from all the way out to about two inches of travel down I can get it to bubble into the reservior every time on the up stroke.

 

[cfamilyfix]

Go over all the fittings again...they are very unforgiving. You may not be leaking fluid, but a fitting could still be taking in air. Anyone who has worked on a manual trans equipped honda accord will tell you. Changing a line and bleeding on those is always an act in frustration. (pedal justs rests on the floor) It may be relevent here as well. Put a wrench on all the fittings and even the slightest movement could be the difference. Hope this helps.

 

[yamahaSHO]

I think you're stretching now...

 

[NEp8ntballer]

Go over all the fittings again...they are very unforgiving. You may not be leaking fluid, but a fitting could still be taking in air. Anyone who has worked on a manual trans equipped honda accord will tell you. Changing a line and bleeding on those is always an act in frustration. (pedal justs rests on the floor) It may be relevent here as well. Put a wrench on all the fittings and even the slightest movement could be the difference. Hope this helps.

considering the amount of bubbles I'm getting into the reservior, for it to not make puddles would most likely qualify as a miracle.

 

[Roady94]

Back when I replaced the front calipers and installed bias plugs and SS lines all round, I had to bleed the system at least three times at one month intervals before I got a firm pedal again, and that was with bleeding the ABS pump (I have an ABS pump thingy). It might seriously be that you just had that much air in the system...

- This is excellent info, hawkeye18. Particularly since you have access to the ABS bleeding tool. I've had similar experiences on other cars, but none tested my patience as much as the SHO did. It's amazing how much fluid you can pass through the system and still have air hiding there.

Of course, all worth it when you finally do get that pedal to firm up.

NEp8ntballer, are you sure you are seeing bubbles, or are you seeing a visible turbulence as the fluid is forcefully returned to the reservoir on the up-stroke?

 

[NEp8ntballer]

- This is excellent info, hawkeye18. Particularly since you have access to the ABS bleeding tool. I've had similar experiences on other cars, but none tested my patience as much as the SHO did. It's amazing how much fluid you can pass through the system and still have air hiding there.

Of course, all worth it when you finally do get that pedal to firm up.

NEp8ntballer, are you sure you are seeing bubbles, or are you seeing a visible turbulence as the fluid is forcefully returned to the reservoir on the up-stroke?

I'm almost 100% sure it's bubbles. i can feel the pedal catch and release coinciding with the gurgling sound and it only does it for less than the first inch of pedal travel. I can hold it close to the floor and bouce it back and forth all day without it making noise but if I move it almost all the way out it'll gurgle every time.