Brakes, need help! Please read.

[grk nickafis]

I took my car to two shops and my own shop. I could not figure out the problem so i swapped the booster and master cylinder. Took it to a shop and they bled it and said "I dont know whats wrong with it." The pedal goes right to the floor and theres no resistance but the brakes apply. The front applies more than the rear. I took it to another shop, they said the master is bad because its the 1" not the 17/16" so I swapped it out brand new for a 17/16". The problem is still there, bled, everything's new and tuned. Please help.

[robomatic12]

The size of the master cylinder would not cause your problem, that could possibly effect pedal feel/force required.

You need to check over the entire system for any leaks, it seems like air is entering the system. Did you/they bench bleed the master cylinders before installing them? Are they nissan oem or autoparts store stuff?

Check all the bleed screws, perhaps they arent sealing properly.

[grk nickafis]

this is the third master, its been bled. The brakes work, the feel/force needed to push the pedal isnt there. It goes to the floor without any resistance but it will stop on a dime. I've heard from two people it could be because There is synthetic oil in the lines. Would Synthetic oil effect the resistance of the pedal?

[grk nickafis]

I've done all the pedal and booster tests in the manual and they all check out fine.

[robomatic12]

What brake fluid are you using? Please don't tell me you used DOT5.... it will not mix with any other brake fluids. Use DOT3,4, or 5.1 only.

[grk nickafis]

i put DOT3 Johnsen's. I'm not sure what the other shops put. Could this be the problem?

http://www.johnsens.com/index.php/produ ... ake-fluid1
This one exactly

[grk nickafis]

Someone told me the piston seal on my caliper is bad. Haven't checked it yet

[robomatic12]

If the seal was bad, the fluid would be leaking out of the caliper. Check it out, you would also be loosing fluid.

And the fluid you posted is fine, nothing wrong with dot3.

[grk nickafis]

it may sound stupid asking about the fluid and stuff. but i've honestly checked everything else i dont know what it it. would the booster adjustment make a difference? i'm going to check all my calipers. I even checked my actuator on the ABS pump. all the bleeders are tight. Boosters fine, masters fine. Pedal needs adjusting but not a big deal. im completely stumped. I asked a Z shop local to me. They didnt know.

[robomatic12]

So the reason you swapped the booster was to try and fix this problem? Or it started after you swapped

[grk nickafis]

it started after i swapped. The adjustment on the booster is set Exactly the same as my other booster. The master is brand new and the right model (17/16), the lines are not leaking, the piston seals are fine, no air in the system. pedal goes to the floor.

[robomatic12]

Perhaps you broke something internally in the booster like the diaphgram when you were swapping it over?

[grk nickafis]

but wouldnt it fail the "airtight" test from the fsm?

[robomatic12]

Not 100% sure, I've never run into this before. By the looks of it no one else has lol... Your calipers wern't touched right? The bleed nipples are at the top of the calipers? There is 100% no more air in the system? It still sounds like their is air somewhere. Try mashing the pedal to build up pressure before opening each bleed screw.

[BigTDogg (MA)]

I think air too, but I've been wrong before.

When I bleed I pump 3 times and hold to the floor, then open the valve. It's also key to close the valve before the flow stops.

[awesomekasim]

If your car is stopping on a dime, you arent losing fluid, and everything is tight, then i would definitely think its a brake booster problem.

[BigTDogg (MA)]

If your car is stopping on a dime, you arent losing fluid, and everything is tight, then i would definitely think its a brake booster problem.

Perhaps the check valve for the brake booster is in the wrong way? Just a guess.

[sdkid123]

had the same problem with mine did the same things yoiu did and i turned out to be the master cylinder cap change that and then bleed the brakes i believe its in this order rear left,rear right,right front,front left correct me if im wrong

[awesomekasim]

this is from the FSM about checking if your brake booster is airtight.

http://www.300zx-twinturbo.com/cgi-bin/ ... t&total=56

[grk nickafis]

I've done the air tight test. I will check the check valve, I heard that from someone. I know how to bleed my own breaks, i also have a machine but i brought it to 2 shops to have it bled 3 times.and to get the master changed. I gave them my manual to see the bleeding procedure but if they dont do it right does it cause a problem.

[es.biggs]

A few years ago, a truck came into the shop I worked at at the time, and he complained about his brakes. It was obvious there was some air in the system by the way it felt...we had to bleed the truck for at least an hour to get the air out. That was all it needed, to be bled. Sometimes you just need to do it for a long time, because the air pocket can get stuck in a bad spot where it is hard to get out.

[grk nickafis]

Would you recommend i do it myself or should I take it to another shop because it's cheap to do I have no problems doing it but just wondering.

[sdkid123]

why pay someone else when you can do it yourself?i would recomend doing it yourself you might learn something new and if the problem still proceeds then thats when you find someone else to give you a hand:)

[es.biggs]

It's easy man, anything they do would be no better than you and a friend, pumping and cracking, and closing and pumping more lol

[grk nickafis]

I know, i wanted to do it myself from the begining but i thought i would mess it up but apparently the shops couldn't have done any better.

[DokkTekk]

Can anyone link me to a 'how-to' on replacing the brake master cylinder and bench bleeding?

[grk nickafis]

Brake master is easy.

1- Loosen the lines and plug them to prevent leaking.
2- Loose the brake master and remove it.

3- install the new one and tighten the bolts
4- don't attach the lines yet and put a hose where the lines go and pump the brake fluid back into the reservoir
5- attach the lines and then follow the FSM to bleed the rest of the brakes.

Thats what I did...

[es.biggs]

It's a good idea to bench bleed the MC before installing it...that could be your problem man. They are filled with air when they are new, and if you install it without bench bleeding first, you are introducing a ton of air to your brake system. It would probably take a few hours to bleed all of it out.

Here's a good video:
http://www.youtube.com/watch?v=ZH3PG3ZVcf0

You can route the hoses back into the reservoir on your master cylinder, you don't need to put them in a separate container. If you route them back into your reservoir, you won't have to keep adding fluid either because it will just cycle it back through every time you push the rod.

When I replaced mine, I didn't use a vice to hold my MC while I bled it, I just held the MC and held a screwdriver, and I pushed it against my toolbox so it would have something to rest against when I pushed the rod in.

Bleed it til there are no more bubbles, then bleed it some more for good measure, and you care done!

[grk nickafis]

Jeez, yeah the first time i didnt bench bleed the master because it came off my parts car. the second time i bought it new because my parts car had the 1" bore and i needed the 17/16 bore. I bench bled the second one but i guess it had air from the first time. I'm going to bleed them Thoroughly and get back to you guys. its just kinda cold and wet in Pa and I dont really have a place to do it so it may take a while. Thanks for everything guys.

[DokkTekk]

grk nickafis, brilliant idea on connecting the BMC to the booster and using the brake pedal to bleed it!! This makes this process a one-man task. Question, after bleeding the air out of the BMC, wouldn't disconnecting the hoses used to bleed it reintroduce air into the BMC? And how do I secure the clear plastic hoses into the BMC for the bleeding process?