when i reach for the brakes my pedal gets much closer to the floor and it dosnt pull up very well. if i sit in the car with the engine turned off and pump the brake pedal, the pedal gets hard (lets keep this clean ) and becomes the right height to what i am used to. as soon as i turn the engine on and put my foot on the brake ,the pedal get really close to the floor and it feels kinda spongy. i have checked brake pads and they are good so im thinking its either the nissan sunny master cylindar or booster that might need replacement/rebuild ,maybe? i have toped up my master-cylinder in the last month,so... do different brake fluids react with each other? i have swaped diffs in the last few months but i cant see any thing that could have affected it. any ideas will be very much appreciated as im not sure what i may need to change or do at the moment

Bleed your brakes...
I don't know much about brakes, but it sounds to my amatuer opinion like you need to bleed them...
Have you tried that?

If your topping up fluid then your losing it somewhere.
Possibly into the booster
Its also possible your adjustment is out of whack thats why you can pump it up then it frops. As things pump up the shoes move out and contact. When you release it the springs pull them back and your pedal drops.
Sounds like your booster is working fine. Might be time for a reco master cylinder.

Clamp off the rear flex line then try your tests again. If the pedal stays firm and hard then look at the rear adjustment. If its still the same check caliper operation and master cylinder.
If you can clamp both fronts then try this too and if its firm even when running the master is O.K.

Oh yeah all brake fluids are compatable except silicone. All glycol based fluids can be mixed if need be. Though you should get a syringe and suck it out of the resi and flush new fluid thru the whole system.

I'm new to the whole 110/1200's scene, in fact I'm new to most DIY mechanics. but the first thing I did when I brought my datto (b110 4 door sedan) was replace the master cylinders in the front brakes. not really knowing what i was doing I was left with exactly the same scenario you describe. problem was that I had reconected some of the brake lines incorrectly (not tight enough fluid was leaking) So I would suggest checking similar with a caution to not overtighten. It's a simple solution that might not be the problem but it worked for me.
Cheers, hope all goes well.

Hey Dattoman,

what do you mean by: Quote:Sounds like the brakes need bleeding.

1. Bleed the master cylinder
2. Bleed the cylinders at each wheel, using the technique Dattoman suggest it can be narrowed down and then you only need to bleed one or the other.

sound like bleeding but seeing how charachteristics change when engine is running it sounds like the booster as that runs off the vacuum from the carbie

I've stopped for 5 seconds...unusual...and I reckon I know what the problem is!

It's got Second hand boosted brakes syndrome.
SHBBS. Very Common disease, especially when the booster comes from a wreckers. People pull out the piston and the reaction disk falls free inside the booster..
I reckon if you pull the master cylinder off the booster, then pull out the piston from the booster, you'll see that the 'reaction disk' is missing. It's a round rubber disk, that normally lives on the end of the booster piston. When this disk goes missing, symptoms include:
1. brake pedal dropping to the floor
front brakes. The falling of the brake pedal is because of the space where the reaction disk used to be, is taken up under vaccuum, thus moving the effective brake travel closer to the floor.
2. extreme front bias resulting in very hot

Please try this, and if I'm right. You have to call me 'the master of SHBBS'.

Cheers,
Chris.