Brake Pressure Woes

[Paul in N FL]

My dads got a 98 Nissan Pathfinder that I changed the front pads in. After replacing the pads I figured I'd change his brake fluid as it hasn't been done in a couple years and was super black. So I changed the fluid per the Nissan Haynes Manual. After bleeding the brakes though, the pedal would drop to the floor. At this point I figured there was still some air in the system so we rebled them. (We're using the two-man pedal pump method). After a second bleed its still dropping to the floor, but if you pump the pedal fast it'll build up some pressure but then go to the floor. I just finished a gravity bleed and a bunch of air came out of the LR drum, but not much from anywhere else.

Is this a MC or just bad bleeding?

[Pathy415]

Don't know what MC means but here's what I learned in the past:

It's not recommended to do the 2 man pump bleed thing because if you don't initially prime the fluid drain tubing going into your waste container properly, you can easily get air pockets trapped inside the brake lines. The haynes manual is overall pretty good but it sometimes misses a few things( I have one and should know ). So the way I was trained if you're going to do it this way is to:

-get a large waste container2 liter soda bottle is great!
-Punch a hole with a screwdriver on the cap for your tubing.
-fill the container enough of brake fluid to where the tubing is submerged
-start with the bleeding process at the furthest wheel from the master cylinder (so passenger side rear)
- with one end of the tubing on the bleed nipple and the other submerged in the brake waste container have your helper pump the brakes until they are stiff
-with the helper still pressing down on the brake pedal crack open the bleed screw until you see a solid stream of fluid and no bubbling in the waste container (This step is very important otherwise this may be an area where you can get air into the system.) Before the pedal bottoms out close the bleed screw and make sure the tubing is till submerged in the fluid. If done properly you should have no bubbles.

The problem people have is when your helper releases the pedal before you close the bleed screw and the tubing happens to NOT be submerged in the fluid you will draw in air as master cylinder attempts to return to it's idle state.

After this, follow the haynes manual and you should be good to go.

Another problem is when doing the 2 man method you are forcing dirty fluid through the piston seals inside the master cylinder which are like minute particles of dirty that can damage the seals. I've seen this and it happens quite a bit.

The better methods are vacuum bleeding and pressure bleeding. I have a Vacula bleeder similar to this one http://usa.vacula.com/newsite/produkter ... oduct_id=6. You will need a compressor but it is so worth it!!!!

The pressure bleeding method is probably the best as it constantly supplies fluid during the bleed process but the equipment is a bit more expensive.

[Towncivilian]

MC stands for master cylinder.

And I your bleeding order is incorrect. Per the FSM, it is:

1. LSV air bleeder (4WD models)
2. Left rear brake
3. Right rear brake
4. Left front brake
5. Right front brake

[Pathy415]

MC stands for master cylinder.

And I your bleeding order is incorrect. Per the FSM, it is:

1. LSV air bleeder (4WD models)
2. Left rear brake
3. Right rear brake
4. Left front brake
5. Right front brake

Oh opps I have a 2wd. My Bad.

I thought the rear passenger side wheel was the Left rear brake? (if you are facing the front of the car it's rear wheel on the left, that's what I meant)

[Towncivilian]

Oh opps I have a 2wd. My Bad.

I thought the rear passenger side wheel was the Left rear brake? (if you are facing the front of the car it's rear wheel on the left, that's what I meant)

Uh, I think in the FSM, left = driver side. It's left/right in relation to the driver's seat I believe. The "General Information" section doesn't specify after a quick skim, so maybe I'm wrong. Anybody know for sure? And the bleeding order is the same for both 2WD/4WD, just that whatever the "LSV air bleeder" is must be bled because that's only found on 4WD models.

[Pathy415]

I traced the brake line and the longest one runs to the wheel I mentioned, although I could have taken a wrong turn =)

[sicwitit]

dude, quit messing around and just go pick up a Mighty Vac, or if you have an air compressor, they make brake bleeding tools that will cut bleeding brakes down to a 30 min job! its easier with 2 people, but it can be done with one.

check the service manual on the order your suppose to bleed them in, but if all else fails, start with the farthest brake away from the MC, and go to town. I've used both the mighty vac, and the air tool technique, both work like a charm, and I've never had brake or clutch bleeding issues on any of the systems I've flushed.

JT

[Towncivilian]

I traced the brake line and the longest one runs to the wheel I mentioned, although I could have taken a wrong turn =)

Okay. I'm probably just misinterpreting the FSM, then.

[ARKQX33V6]

To assist with brake pedal stroke place a block or 2x4 so the pedal hits that before end of stroke. The ABS valve should be done and the farthest wheel from the M/C is done first because of length, but if done with care and a good team mate a simple coke bottle and tubing at the right size works. Before starting suck out the M/c and replenish with new fluid then start bleeding.

Do not be in a rush.

Older vehicles will need their bleeder valves tested with care or you will break them off.

[Paul in N FL]

Wheres the ABS valve? Haynes only mentions crakcing the input and output lines on the ABS.

[Pathy415]

This is the tool I was referring to, made by Vacula. Been using it for years and is superb!!! I think it was around $140 but has more than paid for itself over the years.

[Paul in N FL]

I got a MightyVac from Harbor Freight, and put teflon tape on the bleeder screws and bled each wheel per the manual. Got all of the air out of the system and the pedal still sinks to the ground after pumping it, which makes me more certain its the MC. I had a similar issue on my 86 BMW clutch master where it would sink to the ground.

I overnighted a MC from RockAuto last night so it'll be here tomorrow.
Does anyone have an estimate on how long R&R on the master SHOULD take?

[Pathy415]

Not sure how long it will take but make sure you bench bleed the MC real good and get all the air out of it then re-bleed all the lines one more time. There are videos on youtube for bench bleeding MC's.

[Paul in N FL]

Not sure how long it will take but make sure you bench bleed the MC real good and get all the air out of it then re-bleed all the lines one more time. There are videos on youtube for bench bleeding MC's.

The MityVac has instructions in the manual. You hook up the MityVac using one of the ten gazillion included adapters to one port of the MC while the other is plugged and you fill the reservoir up and pump until you see no more air. Then switch outlets and repeat. Then tilt the MC the other way and repeat both. Then move the piston while vacuum is applied, etc.

[Chuck Tribolet]

This started when you changed the brake fluid, right? The odds the master cylinder went bad at that instant are
ZERO. You have air in the system somewhere, not a bad master cylinder.

You can bleed the master cylinder on the truck, at least with my 2001. Put a flare nut wrench on the line coming
out of the master cylinder. Wrap with a zillion paper towels, and have a hose handy to rinse down when done.
Crack the flare nut open about a half turn, buddy pushes pedal down, close flare nut, pedal up. It should take
no more than two cycles on each flare nut. Remember that brake fluid removes paint, so flush immediately
with the hose. It's messy, but it works. You are basically using the leakage around the flare nut as a bleeder.

My '72 240Z had a bleeder on the master cylinder. I guess the bean counters killed that.

[Paul in N FL]

This started when you changed the brake fluid, right? The odds the master cylinder went bad at that instant are
ZERO. .

That's not always true. When you bleed the brakes the two man method and push the pedal all the way to the floor it can introduce movement into the seals of the MC that it isn't used to under normal operation and after a few years when you press the pedal down it can cause those seals to tear.

[Paul in N FL]

Well I think I've bled the brakes at least 10 times now. Replaced the MC and bench bled till it was only fluid and followed the instructions in the Haynes verbatim.

I now give up... Taking it in tomorrow for the brake bleed.

[Pathy415]

I totally forgot about the method Chuck was referring to. You should give that a shot before you bring it in. It's worth a shot. I've done it that way in the past and it has worked.

[Paul in N FL]

Yup, I did that already and did it until there were no more air bubbles.

[Chuck Tribolet]

Nobody ever answered your question about the ABS valve. It's in the back. Just trace a rear brake line forward and you
will run into it. If haven't bled it, that could very well be your problem.

[Paul in N FL]

Well I took it in and it turns out the RF brake caliper had seized up. Would've never thought of that :/.
Anyway, thanks for the help y'all.

[Chuck Tribolet]

Seized caliper won't cause a really soft pedal. You didn't hear the whole story.

[Pathy415]

Seized caliper won't cause a really soft pedal. You didn't hear the whole story.

I would think it would cause a stiffer pedal.

[Chuck Tribolet]

Seized caliper won't cause a really soft pedal. You didn't hear the whole story.

I would think it would cause a stiffer pedal.

I think it would be about the same. Certainly not softer.