Actionclaw

This is actually a general brake question but I'm already a member here and the brakes happen to be on a '93 Nissan 240SX so..

This relatively simple job has turned into a several MONTH long nightmare plagued along the way by one thing after the other from flat tires, dead batteries to suddenly failing jacks, etc. If my frustration seems BIG, that's why. I'm at "wits end", I've tried all I know, I'm out of ideas, there's now snow on the ground and I still don't have a car! I can really use some help!!

Heres the story:
Brakes were fine - not "ideal" but OK. Brake fluid level would drop over a week or two and turn on the idiot light.
I found a corroded, ruptured brakeline (to rear about at middle of car). I wanted to replace the entire line from Master Cylinder to the "splitter" (terminology?) in the back but fittings too corroded. Not easily accessible and I couldn't remove. Didn't want to replace all the way to calipers so decided to patch instead.

Bought factory flared (20") section and flared the mates myself.
This MAY be significant: This was my first attempt at double flares and I honestly don't know if I know what I'm doing. I practiced some on scrap brakeline. Some turned out crap, some OK. They didn't look like the diagram - all doubled over - but looked OK. Similar to the factory's. I guess I don't know exactly what the perfect double flare is supposed to look like. The replacement section looks pretty good. Have not found any brake fluid on lines at unions.

After repairs done, proceeded to bleed lines.

Tried usual pump and hold.
Didn't seem to be working well.
Badly vice-grip chewed-up Bleeder screws at a wheel or two made this difficult (especially with tube attached).
Hard to tell if fully opening/closing properly. (Eventually replaced all four bleeder screws.)

(A bit of advice. If you don't have a flare nut wrench, buy one! Don't even try to use a regular wrench, pliers or anything else. And if you already did and you've begun to round the edges, replace those bleeder screws right away! They're only a little over a buck each and it's still a simple job at this point!

For those that might come across this in the future searching for the right size bleeder screws, all 4 are:
M10 x 1 x 33 (30mm-35mm). )

I noticed that, while pumping, there'd sometimes be a bubble in the master cylinder.
I figured I introduced air into system by pumping with bad (not completely closed bleeder screws) I disconnected and "bench bled" master cylinder (while left mounted in car.) Bench bleeding seemed to be successful.

After master cylinder reconnected, "gravity bled" system.
First with calipers mounted, then unmounted hung by wire. Tapped with a hammer to dislodge bubbles.
Seemed to be working. Got a decent flow but at only 3 wheels (perhaps due to car not being level?)

Bought MityVac and tried vacuum bleeding.
Seemed to work. Gauge showed vacuum. Lot of bubbles then more fluid than bubbles. Kept master cylinder level up throughout.

We then did the pump and hold again with not much improvement.

Replaced all four bleeder screws. At this time it was more-or-less being "gravity bled" yet again and with a good flow at, I believe, all four wheels.

Vacuum bled again with better results-- though it never got to the point I expected; sucking 100% pure fluid with 0 bubbles.
I read this could be due to seal at connectors or bleeder screw threads (I did not wrap with teflon tape as some recommend.)


Regarding bleeding sequence:
At first, (with pump and hold) I did farthest to closest (RR RL FR FL). Vacuum bleeding recommends closest to farthest (FL FR RL RR). Tried both ways and in various combinations multiple times.

After vacuum bleeding, performed pump and hold again.
Some bubbles at first, then eventually only fluid! Looked very good!
Nice clean fluid coming out, master cylinder fluid level regularly dropping down and being filled up.
Everything appeared to be happening just as it is supposed to. I thought all was (finally) well!!

...but Still no pedal!! The resistance is not increasing at all. In fact, it may even be worse. I've got (almost) no brakes!

Why? Whats wrong?
What did I do wrong?
What did I not do that I should have?
Could I be bleeding them improperly?

If bad flares on my patch are causing this problem wouldn't I find brake fluid leaking at the unions? I don't.

If my patch to the rear line is bad but the fronts and everything else is OK, shouldn't I still have at least some decent resistance in the pedal?


In case this matters, I did remove the rear calipers one of the times I did gravity bleeding but did not mess with pistons. I did disconnect line from caliper once for extra clearance when changing bleeder screw.
No instrument panel lights on.

I have researched this before posting and I was very surprised to find at this forum alone, (searching Suspension & Brakes using brake bleeding) about a dozen or so posts describe a situation very similar to almost identical to mine; coincidentally(?) more than a few were also 240's. In most cases, it seems the answer suggested is to bleed the brakes, which I've already done several times every way available to me or it's the master cylinder. I don't believe I had any master cylinder problem before so if there is now it's new, perhaps created by us during the bleed? I read that pushing too far down on the pedal during pump and hold bleeding can damage the master cylinder seals. Theres a chance my pumping helper may have done this. If that happened, would the symptoms (of damaged master cylinder seals) match my situation? If so, how do I confirm?

As I said, I'm out of ideas. I don't know what else to do but, whatever it is, I need to do it NOW!
What else can I try? Your help is very much appreciated and any advice or suggestions welcomed.

Otherwise, the next step must be to take it in to a mechanic; something I'm sure many of you understand my reluctance to do -- not only because of the expense but, especially now, because of all the thought, time and work invested! Not to mention the further destruction it will do to my self-confidence! (I'll find some other forum to post about my depression, feelings of failure, emasculization, damage to my self-confidence, self-esteem, ego, etc..)

Thanks a lot in advance for any help. I will sincerely appreciate it!

Actionclaw

So, I think my problem, in general, must be one of the three:

1. Master Cylinder problem
2. A leak in the hydraulic system
3. I simply haven't bled the system thoroughly enough or (I'm bleeding it incorrectly)

Have I left out another possibility?

1. If the master Cylinder is the problem I must have caused it because it's only a year or two old and it was fine before I started. I read that an easy way to check the MC is to "turn off the car and pump the pedal. If you get pressure, then it just needs bleeding. If you don't, its your master cylinder." If this is true, mine just needs bleeding as I can pump a dozen or so times still get nothing but, with the car off, get resistance at second press. On the other hand, someone else (a professional mechanic) told me this is not an accurate test.
   
   When I had the MC disconnected for bench bleeding, it seemed to be working; especially at first: bubbles went out, bubbles went in, bubbles out, bubbles in, fewer bubbles out, a few bubbles in...until there were no more bubbles.
   Does this not confirm the MC's OK or must it be under pressure?
   Is there a way to test it while still mounted/connected?
   
   
2. A leak in the system. I hope this isn't the case but it is a strong possibility — especially since I'm not totally confident with my double flaring skills. I did visually check for leakage wherever I had (and a few places I hadn't) worked cleaning off with brake parts cleaner, etc. Right now everything's wet from snow/rain so that won't work. The Brake fluid level has not dropped. Any other suggestions as to how to confirm if there is or is no leak?
   
   
3. So, I'm leaning toward thinking maybe I simply haven't bled the system thoroughly enough —which, I guess, is good news. I could just bleed them again and keep bleeding them 'til the cows come home (or til I've run through a few gallons of brake fluid, whichever comes first) but, I think, only after I've positively confirmed that the system is closed, no?
   
   If I'm bleeding them incorrectly, how do most of you determine when to stop bleeding each wheel? when you're seeing no more bubbles in the tube, once you've accumulated a certain amount of fluid in the catcher bottle or only once you begin to get resistance pedal?
   
   I've been using different methods that recommend a different order. Can the bleeding sequence have significant impact on the success of the bleed?

Actionclaw

I only worked on the back brakes and, with the exception of bleeder screws and bleeding, didn't touch the front brake system. If the front and back systems are separate I shouldn't have lost the front brake pressure so I figured, to factor out two variables (a questionable patch and pumping assistant), I would bleed the fronts again using only the MityVac and if the master cylinder is OK, I should see some improvement in pedal resistance.

That's what I did and some progress was made! Something significant happened. What, exactly, and why, I really don't know. Perhaps one of you can offer an explanation.

I bled the fronts again using the MityVac. I kept on repeatedly bleeding each side 'til I filled the bottle with fluid 1—1.5 times (about 16, or so, ounces).

Put it all back together, tested it and noticed a marked improvement! It went from virtually no pedal at all to some resistance; not great—I wouldn't want to drive around like that— but there was a definite improvement.

So while the weather was holding out, I had the tools out and my dirty clothes on and I was feeling inspired, I figured I'd do the rears again, as well. I put up the back end and bled the rear brakes exactly as I did the fronts (with MityVac repeatedly 'til I filled the bottle with fluid 1—1.5 times)...twice: LR, RR, LR, RR. I thought "with the recent improvement after bleeding the fronts, this has to make it even better!" So I put it all back together and tested it to find I once again had NO brakes! What the heck happened?

At that point I figured "That's it! I've got to take it to a real mechanic!" Hoping to drive it in, I put the front up again, repeated everything as before and once again got some brakes; perhaps even a bit better than before — almost acceptable.

I understand why the brakes improve after bleeding the front; that's what's supposed to happen but what's causing me to lose them again after bleeding the rear? Can anyone explain this?

92rpska-t

seems like no one else wants to help. anyway in this situation i would start by inspecting all the brake pistons. have your helper just tap on the brakes and you make sure all the piston are moving properly. if so mount all the brakes back together have all the bleeder screw open at the same time. have your helper hold down the pedal and keep it down so you can close all the bleeders. have helper release pedal. open one bleeder at a time starting with the furthest as you already know pass rear, leave open with out pumping untill you get some fluid drops then open driver rear (but leave pass rear still open) until you get some drops, again leave these two open, next open pass frt and so on and so forth until you have a constant flow AT EACH WHEEL. Once that is established close all bleeders and pump and bleed 2-3 at each wheel in the same sequence as before. Now you should definetly have pedal. If not i would double check master cylinder for leaks. Note that the master often leaks under dash interior and not always on the fire wall. lf all is good with the master PLEASE double check those brake lines you mentioned were rotted. you might be letting a lot more air enter you may know

sunnysentra

hey,

I think that if you are not seeing any fluid on the fittings, then you have a master cylinder problem. that is usually an issue with pedal to the floor. maybe when the thing was dry, it finally went on you. I would just get a good used one and see if that works. I replaced my MC on my 92 sentra and it was bone dry. I bench bled the thing and connected up the thing and bled in sequence. I used regular bleeders and a bottle raised above the caliper. Never had an issue.

Chris 92 classic sentra

__________________
Part of the AUTO / MANUAL SWAP CLUB