Silvia Club of NSW

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PostPosted: Sun Jun 06, 2010 8:32 pm 
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Maybe it's lack of sleep, maybe something else in the system is damaged but my brakes will not bleed.

Typically on s13/r32 when i bleed the brakes i can crack the bleed nipple on the caliper, pump the pedal a few times and it'll pump the fluid through no problem so one man bleeding is a simple enough job.

I put an s15 bmc in hello kitty, fitted a tee to the front port as it's an abs master in non abs car and hooked up all the lines. Bled the master properly (and re did it 3 times over the course of the afternoon) and found that when i tried to bleed the system the fluid/air would come out on the down stroke but then it'd suck air back in on the up stroke, which can't be good for keeping pads on rotors as they wear. I had the gf in the car pushing the pedal

I started on the left rear as per the manual so tried the other side and it would actually pump up the pedal gradually even though the bleed was loose enough that it let fluid past the thread to drip on the ground. Pressure would bleed off in a few seconds and i could push the pedal to the floor again. I don't know if this was happening on the other side as i didn't try the pedal myself.

I thought possibly the rod on the pedal extended too far and was preventing the pistons retracting properly so backed that off with no difference. I've had that issue with clutches before.

Handbrake was off too.

Through out all this the fluid in the master turned murky

I've pulled the master back off and have removed the primary piston, seals look good and bore is fine. Still have to remove the secondary piston which i hope is perished and causing the issue (and also the murky fluid).

Am i on the right track or well off?

And have any s15 owners found the same issue with the bleed procedure and the fluid sucking back up?

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PostPosted: Sun Jun 06, 2010 10:20 pm 
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Takumi
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yeah I'd say the other piston's seal might be damaged.

Usually it's caused by the bore being corroded, so it'll work fine until you go to bleed the brakes and the seal gets run over the dodgy bit.

It happened on the 240Z (the day before a track day of course)

It actually looked like it was bleeding ok, but air would always get back in the system.

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PostPosted: Mon Jun 07, 2010 11:56 am 
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Quad T04
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I had the same thought, had it happen to us a few years ago on the AE86. The actual pedal pumping process stuffed the seal because it moved further than usual and chewed the seal up when you bled it.

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PostPosted: Mon Jun 07, 2010 12:16 pm 
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Luckily i have a week before my track day to sort it.

guess i'll pull the other piston out of it tonight and check. I'd have thought that a stuffed seal would mean it isn't pumping fluid out at all as opposed to sucking back in as well. Also, the master is barely used and in immaculate condition (or was before i touched it) but i suppose that doesn't mean it hasn't been sitting in salt water.

Worst case i'll have a few nights work this week swapping out the master and rear brakes from the other car so i have skyline brakes all round with a skyline master.

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PostPosted: Mon Jun 07, 2010 12:34 pm 
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Quad T04
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On the one i had i don't think it was so much corrosion, it was more varnish that built up at the end of the (in use) piston travel, like a little ridge.

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PostPosted: Mon Jun 07, 2010 10:02 pm 
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Success!

I removed the secondary piston tonight and found a heap of shit in the end of the bore. It looks like it's had a bit of fluid left in which dried leaving shit on the spring and then flaked off when i was bleeding.

The shit appears to have gotten under the seal and obviously prevented it from sealing properly.

The bore looked fine, the seals were good apart from 2 very minor scuff marks so i decided to clean it and give it one more try before giving up.

After about half an hour of trying to bleed the master solo it came good and bled properly.

I'll check it again on the weekend and if it's still holding pressure fine and working ok then it'll stay on for monday. The front circuit and seals are fine so not concerned about suddenly losing brakes.

I think i will still get it recoed after the track day just in case.

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PostPosted: Mon Jun 07, 2010 10:15 pm 
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good news :)

I guess it's probably a good idea to pull apart and inspect any master cylinder that's been sitting around for a while... (but I don't wanna!)

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PostPosted: Tue Jun 08, 2010 1:35 pm 
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It's the first one that's ever caused me problems.

Though yeah, the saving in time and avoiding having brake fluid everywhere would be kinda worth the effort.

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