Bleeding Brakes - Pedal Goes Mushy After Crank

[ThisIsSparTTa]

Hey guys, I did a rebuild on my calipers, and am having issues getting the brake system bled. I also replaced pads with brand new Hawk HP+. Yes, I have read the FSM. Yes, I have done a lot of searching. The problem is there seems to be a LOT of inconsistent information floating around.

Here's what I'm doing:
Made sure all bleeders are located at top. Initially my rear calipers were swapped.
Ignition OFF
Using 2nd person, pump brake until pedal gets stiff at top. Hold down pedal.
Open bleeder, close once fluid stops coming out. Repeat pumping/opening if any air bubbles were present. Move to next caliper
Per the FSM for a LHD, the order should be: Drivers Rear, Passenger Rear, Driver Front, Passenger Front, Front ABS Bleeder, Rear ABS Bleeder (Yes, I have a 1991, so the ABS does have the bleeders)

I don't know how many times we've done each bleed point, and we've probably been at it for close to 3 hours now with the problems below.

One point I'm not clear on is which ABS bleeder is which, although I don't think its the whole problem. Based on the shoddy diagram in the FSM, I've been bleeding the bleeder on the left when looking towards the rear of the car first, then the one on the right.

At this point, at best I'm getting a couple of tiny tiny bubbles here and there, otherwise, clear liquid, no bubbles, from every point. Initially too, there was kind of a whiny noise when the brakes were being pumped, but that's gone now, I think that was the air in the system.

With the ignition OFF, or even ON before cranking, the pedal is very stiff and firm at the top. Once cranked, it feels like it travels about halfway with minimal resistance, and then has an okay amount of resistance towards the bottom, not "hitting the floor". I drove like this around the neighborhood at low speeds, and it didn't feel right. I'm pretty burned on ideas now...and am also through my 3 $17 bottles of MOTUL RBF600, and I'd like to stop throwing money away. Thoughts? Just keep doing this indefinitely and hope it works itself out?

Edit, did some digging during lunch and found this anyone-know-their-brakes-inside-and-out ... 74221.html, and the suggestion to try checking the check valve. (To me) this would explain why its good until the car starts up. Would still appreciate other ideas, will check this when I get home.

[ThisIsSparTTa]

Brake booster check valve worked properly. Did the other diagnostics in the FSM for the brake booster, which is basically turning the car off with the pedal depressed, etc and that all checked out. Also, wasn't exactly clear on this from the manual, but disconnected the top 2 connectors to the ABS actuator and cranked up, and still had the same issue. Any ideas?

[Slizz]

Im having the same problem, I beleive, my pedals a little mushy after rebuilding the calipers i also put speed bleeders in and ran 64 fl oz of brake fluid through them in order and its still a little mushy i also have master cyl. brace but, i haven't driven my car in so long i can't remember if it was mushy or not before... hopefully you figure it out if you do post up so I can try mine still brakes fine just doesn't feel as stiff as it should.

[solaire]

Usually bleeding brakes that's a sign there's still air in the system. The booster applies greater pressure allowing this to happen only when the engine is running. My advice would be try the vacuum bleed method and see if that helps. The Mitsubishi lancer evolution requires this bleeding procedure. You can't get air out any other way. It pulls bubbles through the ABS system that pumping the brakes just doesnt. It uses the same calipers as our 300s. I would give that a try. I use this procedure on almost everything since I started realizing how well it worked on the evo's and it's been foolproof since on almost anything and makes the job easy for 1 person. You just need a good vacuum source. I've got a resevoir pump that hooks to air and pulls constant vacuum and drains it into a resevoir container.

[Metacom]

I'd go back to the calipers, and double check everything was installed correctly and right side up.

A friend rebuilt some calipers on a Jeep, had same problem. Turns out the calipers on the front somehow got put on upside down.

[ThisIsSparTTa]

Thanks guys, the calipers are definitely right side up now with bleeders on top. Initially the rears were swapped. One suggestion I found was to try disconnecting the battery as the ABS pump constantly gets +12V. I've see a bunch of other people with similar problems, but no one ever posted a real solution. I think I'm going to try another round or 2 with battery disconnected, then may have to try vacuum bleeding instead if there are still issues.

[nexus08]

This is kind of obvious, so probably not the problem, but you are making sure you keep the reserve filled so that no air can make it into the system. I've heard that if you get air into the master cylinder it is real hard to get out.

[schwar74]

My .02 . . .

This may not be an issue, but I did the actual bleeding a little differently and my brakes are fine after a recent master cylinder replacement and SS brake line swap. What we did was to have one guy on the pedal, and one on the bleeder. We'd open the bleed valve first, THEN depress the the pedal. This would blow air/fluid out of the bleed point. Then, with the pedal depressed, we'd close the bleed valve, and then get off the pedal. This pulls fluid from the reservoir into the system. We repeated this until there were no air bubbles present. I'm not sure whether pumping the pedal to build pressure before opening the bleed valve might be a problem, but it'd be simple to try.

Scott

[nissanfreak12]

Are you sure the Master Cylinder is not bad? It is possible to have the seal go bad and it push past it.

[ThisIsSparTTa]

This is kind of obvious, so probably not the problem, but you are making sure you keep the reserve filled so that no air can make it into the system. I've heard that if you get air into the master cylinder it is real hard to get out.

At one point it did make a slight gurgle as fluid got low, but it wouldn't have been more than a pump or so. If so, hopefully I could get the BMC re-bled rather than have to do a rebuild or something.

[ThisIsSparTTa]

Are you sure the Master Cylinder is not bad? It is possible to have the seal go bad and it push past it.

What are the symptoms of a bad BMC? What tests can I do to it? I haven't found any real clear ones, except for leaks and generally brakes not working. The BMC was fine before the installation. The pedal was initially going to the floor, which I've been told could be bad, but its not like it was being forced to go further than it wanted.

[solaire]

Are you sure the Master Cylinder is not bad? It is possible to have the seal go bad and it push past it.

I wouldn't rule this out after you do the other 2 bleeding procedures. I've seen them bypass internally and no matter how much you bleed it the pedal will always be soft.

[ThisIsSparTTa]

Tonight I'm going to try another round of bleeding with the battery disconnected, and also holding pressure down on the pedal to make sure I'm not leaking anywhere. If that doesn't work I guess I'll have to start looking at the BMC

Quick question, since I did possibly introduce air into the BMC, is it worth my time to try and bench bleed my existing BMC?

Also, has anyone used the BMC rebuild kit? I've seen a couple of people say its easy, and a couple people say only a professional should do it.

[nissanfreak12]

One thing that will show a MC is bad, car off, press the brakes. Hold it down with the same pressure, if it slowly goes down, its a bad MC as long as there is no leaks in the system. There are a few other test, but that one is guarantee to be a bad MC.

MC rebuild is easy, they always say to get a professional to rebuild to cover their own a$$. I know I either need to rebuild mine or get a new one, I know mine is bad as well.

[ThisIsSparTTa]

Yea, with car off, the pedal is very firm and at the top. I held it down with a fair amount of pressure for about a minute, and it didn't feel like it moved at all. It only does this stuff once the car is cranked. I'm thinking most likely I'm going to need to bench bleed the BMC this weekend, and I'll also try to check out the seals when I do.

Tonight, I disconnected battery. Pumped brakes a BUNCH. First did a round of bleeding with my new Mityvac vacuum bleeder, same thing. Did another round of normal bleeding, got ZERO bubbles from any of the 6 points, same thing. Fingers crossed the MBC just sucked in a bunch of air. I'll give an update on Sunday. Thanks for all the thoughts so far.

[solaire]

I'd lean towards master cylinder then. We had master cylinder recalls at the dealer for the B16 sentra's and they'd do the same thing if you didn't bleed the master cylinder fully, Rock solid pedal but crank it and you got mush. Your BMC is old and actuating it so much could have just been too much for it. Better to find it now than when driving down the road

[ThisIsSparTTa]

Update: Bench Bled BMC.

After the bench bleed both outlets were slowly leaking fluid, and pushing out air bubbles (somehow). I figured this meant seals were shot, but I put it back on car, in case, and yea, problem seems even worse now, so I think BMC is the root. RockAuto thankfully has the Centric 17/16 size for only $75, so I jumped on that. Will try to update once BMC arrives, and hopefully this headache ends.

[ThisIsSparTTa]

Banging my head against the wall at this point. New BMC, bench bled, and on. 2 rounds of bleeding, basically no air coming out. Pedal still travels about halfway once car is cranked before I get resistance. I've done an insane amount of searching on this, and just am not sure. Only thing I've seen is some people claim it takes a couple hundred miles for their new stuff to break in. Doesn't really seem right to me, but I think I'm going to take it to some lots near the house in the morning and just work the brakes for a while, and see if anything changes. I would gladly welcome any more ideas.

[solaire]

it's a possibility it's getting trapped in the abs. i have yet to try this on a nissan but it works good on chryslers.
Find a good sized dirt/gravel lot. Get up to about 35mph and stand on the brakes. Make sure the ABS actuates. If there is air in the system it should make the pedal get more stiff. You can do this a few times then try bleeding again to make sure those air bubbles didn't get further into the system.

[ThisIsSparTTa]

Thanks, yea, that's kind of what I was thinking. Kind of wanted to ~autocross it in some nearby lots, but then we had to get rain today. Hoping it dries up a bit.

[ThisIsSparTTa]

Good news. Maybe I was being a little paranoid. Took it up to a local lot. Was able to go 70-0 pretty solidly, and tried a bunch of other scenarios. Took it up to get some gas after, even had it bite a little more than I thought it would a couple of times. Feeling much more confident now. Debating whether I want to try 1 more round of bleeding after using the ABS. So tired of putting the car up, wheels off, etc. Might save that for the next time the car is up. Thanks for the help.

[solaire]

Good to hear it's getting better.