Air in Lines While Bleeding Brakes

[NSXE]

I ran into an issue following the standard procedure for bleeding brakes on my '92 NSX and need help.

I sucked as much old brake fluid out of the brake reservoir as possible and filled it with new brake fluid. Starting at the passenger rear wheel I had my wife pump the brake pedal slowly while I opened and closed the bleeder valve. I used a clear tube on the bleeder valve and put the end of it in brake fluid so air wouldn't get sucked back into the caliper. I noticed that the brake fluid reservoir wasn't dropping at all.

I decided to move to the drivers rear wheel. Then after a few pumps of the pedal, the pedal became soft and would not get hard with the bleed valve closed. The brake fluid reservoir still had not dropped at all.

I moved to the front passenger wheel and started bleeding and eventually air came out. That's when I quit.

So there is clearly air getting in the system and the fluid is not being sucked out of the reservoir. Any ideas what's going on? Is the line plugged somewhere near the reservoir?

Thanks in advance for your help.

Jay

 

[pgilliam1]

You are doing it all wrong. Close the bleed screw, pump and hold the brake pedal, open the bleed screw until the brake pedal hits the floor and keep the pedal down. Close the bleed screw and then pump the brake pedal until it holds pressure - repeat until no air comes out. If you are letting off the brake pedal with the bleed screw open you're sucking air back into the system. No need to hold the tube from the bleed screw in fluid because nothing should go back into the caliper from there. Happy Motoring!

 

[NSXE]

That's exactly how we were doing it - closing the valve prior to lifting back off the brake pedal. I've done this before with other cars with favorable results - this is the first car where something like this has happened. I have no idea why the reservoir isn't going down at all because brake fluid was coming out initially, but now it's only air coming out at the front passenger wheel... I checked the service manual and it is conveniently missing that page.

Is it possible to overfill the reservoir? At first I had it all the way to the top which was over the max line - now I removed some so that the new brake fluid is right at the max line, but it's still not dropping at all after proper bleeding technique.

Any other ideas?

 

[pgilliam1]

Overfilling the reservior will not cause any problems while bleeding. You may have an issue with the master cylinder. If you are holding the pedal down when the bleeder is open, and until it is closed, no air will be sucked back into the system from there. If there is fluid coming out of the bleeder an the reservior is not going down - well that just defies physics, because it cannot come from anywhere else . Try opening the bleeder with the system relaxed (no parking brake or anyone holding the pedal) and watch the tube attached to the bleeder. It should slowly leak out and the reservior should go down (it is slow - so give it 30 minutes and you should have about a 1/2 cup of fluid). Good Luck and Happy Motoring!

 

[mrbythatmuch]

Hopefully a silly question but are you sure you are looking at the right reservoir.

Also submerging the end of the tube in fluid doesn't ensure air does not enter through the bleed screw, what about the air in the tube. Just have the tube go vertical for a inch or two. That way when you open the screw and fluid comes out and fillsthe tube if you happen to release the pedal you'll just pull the fluid back in.

 

[davidf]

I gravity bled mine {all 4}. Worked beautifully. Cracked each bleeder one at a time and let it drip in a pan until new clear fluid was dripping. In the end I never once pumped the brakes, of course I was by myself so I had to do it that way. Could'nt be happier.:wink:

 

[NSXE]

Hopefully a silly question but are you sure you are looking at the right reservoir.

Not a silly question at all...seeing as I was looking at the CLUTCH RESERVOIR. F-me.

Bleeding your brakes while actually using the BRAKE FLUID RESERVOIR makes this whole thing a LOT easier. Problem solved...sucks I have to buy another $20 bottle of brake fluid to get all the air out of the lines now. F-me x 2.

THANKS A TON everyone...I appreciate the help. :smile:

 

[davidf]

Not a silly question at all...seeing as I was looking at the CLUTCH RESERVOIR. F-me.

Bleeding your brakes while actually using the BRAKE FLUID RESERVOIR makes this whole thing a LOT easier. Problem solved...sucks I have to buy another $20 bottle of brake fluid to get all the air out of the lines now. F-me x 2.

THANKS A TON everyone...I appreciate the help. :smile:

Try my method.:wink:

 

[mrbythatmuch]

In an earlier post it was mentioned
"until the brake pedal hits the floor and keep the pedal down"
DON'T do this. Without the fluid pressure pushing the brake pedal to the floor will cause the piston to travel further than normal/intended and can damage the seals. If your afraid of pushing to far by accident put a piece of wood behind the pedal.

Also if you are doing a fluid exchange I believe there is a check valve in the line going to the rear brakes. So even without speedbleeders you can open the bleeds and just pump. Note when doing so use a tube connected to the bleedscrew and keep a few inches of fluid above the bleedscrew so there is no chance air can enter.

Not sure how long a gravity bleed takes I'll take a look at that next time, if I continue to procrastinate and not by speed bleeders.

For bleeding, alternately what you can also do is take a piece of pcv tubing/pipe and use the power seat to apply pressure to the brake pedal. I don't recommend it for exchanging the fluid but to just bleed off the fluid in the caliper its a snap. Hence why I continue to procrastinate on getting speed bleeders.

 

[ChopsJazz]

In an earlier post it was mentioned
"until the brake pedal hits the floor and keep the pedal down"
DON'T do this. Without the fluid pressure pushing the brake pedal to the floor will cause the piston to travel further than normal/intended and can damage the seals.

Good advice. Also, there is an order that you should use when bleeding. Larry B posted it some this summer, and I was was surprised to learn that my old method (from the 70's) was not correct for the NSX. I'll try to do a search to find it.

Here it is:

for the NSX, and most modern cars, especially Honda's. It is: RR, LF, LR, RF

The brake lines are cross plumbed for safety reasons, and this is the specified bleeding sequence.

 

[pgilliam1]

In an earlier post it was mentioned
"until the brake pedal hits the floor and keep the pedal down"
DON'T do this. Without the fluid pressure pushing the brake pedal to the floor will cause the piston to travel further than normal/intended and can damage the seals.

Can anyone verify this? I have done this on every car I've owned and never had an issue. I'm not saying he's wrong - I'm just concerned that I am doing it wrong .

 

[CL65 Captain]

Can anyone verify this? I have done this on every car I've owned and never had an issue. I'm not saying he's wrong - I'm just concerned that I am doing it wrong .

It's possible if the MC is old and the seals are weak. As well, if there is dirt or debris in it then you are pushing it past the "normal operating" range. For a new MC or one in good condition you probably won't do any damage.

 

[NSXclear]

I think the plastic circle floater is blocking the passage on the brake reservoir. When you sucked out the old fluid, the plastic floater dropped to the very bottom. You then filled up the reservoir and the plastic floater did not float to the top like it was suppose to. Instead you create a vacuum and sucked the plastic floater to the bottom.

Remove some of the brake fluid from the reservoir before you try to get the plastic circle floater to back up top. Your going to get an air pouch when you try to pry it up and will get brake fluid everywhere. Use a flat head screw driver to get it to float back up. You should be able to just tap it on one side to dislodge it.

 

[Larry Bastanza]

In an earlier post it was mentioned
"until the brake pedal hits the floor and keep the pedal down"
DON'T do this. Without the fluid pressure pushing the brake pedal to the floor will cause the piston to travel further than normal/intended and can damage the seals.

Can anyone verify this? I have done this on every car I've owned and never had an issue. I'm not saying he's wrong - I'm just concerned that I am doing it wrong .

That is absolutely true, I have seen many a bad brake master cylinder after this type of operation. NEVER have the brake pedal(on a used brake master cylinder) travel more then it would if the system is fully pressurized.

On a new brake master cylinder it does not matter.

 

[R13]

In an earlier post it was mentioned
"until the brake pedal hits the floor and keep the pedal down"
DON'T do this. Without the fluid pressure pushing the brake pedal to the floor will cause the piston to travel further than normal/intended and can damage the seals.

That is absolutely true, I have seen many a bad brake master cylinder after this type of operation. NEVER have the brake pedal(on a used brake master cylinder) travel more then it would if the system is fully pressurized.

On a new brake master cylinder it does not matter.

Indeed (as if any seconding of Larry's opinion is needed ). I made the mistake of putting pedal to floor while flushing the brakes on my MR2 a week prior to a track day. Fortunately, only one of the two plungers in the MC failed so I still sort-of had brakes on my shakedown drive. I've put a block behind the pedal ever since.

I have done this on every car I've owned and never had an issue.

Some people smoke for years and never develop cancer...doesn't mean it's safe