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Faint "fffsssssst" squirt noise from master cyl


Eddie

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I replaced my working original master cylinder with a new 7/8ths master (260z), bled the brakes, the pedal feels rock hard, total pedal travel is good at about 1.75", but when I press it down fast I hear a "ffsssssst" squirt sound, kind of the same sound the fluid makes when it squirts out a suddenly released bleeder when bleeding brakes. When I press the pedal slow there is no noise at all. There are no leaks on any nipples, fittings, or anywhere else, and the pedal feel is good.

 

Is this just the sound of fluid traveling at high speed through an orifice (or similar normal restricted viscous flow) and others have this same sound, or is mine the only one that sounds like this when it's not supposed to?

 

Here's a video of the sound...

http://m.youtube.com/watch?v=41fGC9Sv6Ok&feature=youtu.be&desktop_uri=%2Fwatch%3Fv%3D41fGC9Sv6Ok%26feature%3Dyoutu.be

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Thanks for the replies. I'm not using a booster. The clunking sound is just pedal pressing sound. The squirt sound is definitely coming from the body of the master, not from the pushrod dust boot. It only says "ffssssst" when pressing the pedal down fast, not when slow, and not when being released. Maybe my old master did the same thing, I don't know, but now it does and I have no other non-boosted Datsun to compare it do.

 

I did try bench bleeding it first, but from the time I did that to the time I turned it, angled it, and got it into position, some fluid dripped out, so who knows if that did any justice for it. After I got it installed I bled it again, then all the lines to the wheels. It still felt spongy so then I bled the master again (installed) and saw bubbles come up/out, then the wheels again. Now the pedal feel is good, but I'm not sure if the noise is normal or not.

 

Anyone else's non-boosted master make that same "ffssssst" sound (when pressed fast)?

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I'm thinking it's fairly normal and just the sound of fluid moving.  You might try this......  pull your ebrake on and pump the pedal once......now try getting it to make the sound again.  Most of the fluid movement in the system is going to be the rear wheel cyls.....this should take them out of the picture temporarily.  If the sound goes away, it's just fluid moving in the rear circuit.  There shouldn't be much movement in the fronts since they're disc.

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Thanks for checking and posting what yours sounds, or doesn't sound like. I did bench bleed first with clear hoses recirculating back into the reservoirs, but with the master out of the car and not installed. I think un-evacuable air must have gotten back in as I was angling the master to get it back in position AFTER the out-of-car bench bleed. Looks like it's time to crack open another quart and try again...in-car bench bleed, followed by bleeding to the wheels.

 

This whole thing kind of makes the bleeder valves which are located on top of the master seem useless if they can't get all the air out.

 

Oh and yes I bled with the e-brake on to reduce the chance of air going back from shoe spring kick-back pushing the piston back in and fluid back up.

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The sound is definitely not the rear brakes themselves.

 

I definitely got it now. There must have been a tiny amount of air left that I finally got out. What ended up working to get it out is a bit different than a bench bleed. Here are my theories....

 

A) why manufacturers say not bench bleeding voids the warranty: brake fluid lubricates the internals, so where there's a chance air may still be trapped, that spot in the master may see sub-par lubrication. Also, air has oxygen, and oxygen oxidizes, and can accelerate internal corrosion vs. parts fully immersed in fluid.

 

B) why bleeding from the bleeders on top of the master may be inadequate: Bubbles travel up a sloped pipe, but will stay put if the pipe is flat. If the master is not compressed, each chamber (for a dual master) is a horizontal cylinder. Unless the master is sloped towards the bleeder side for each chamber, you may be left with a small bubble pocket still trapped.

 

Here's what ended up finally getting out the last bit of air (I should mention almost all air was already out and the pedal still felt pretty good before doing the below. Pedal feel is a just a tad more firm and essentially feels rock hard now. Hmmm... it feels rock hard now....what a description. Now it sounds nearly exactly like I remember, only slightly different because I've got a custom pushrod which fits in the 260 master and must be adjusted with SLIGHT preload, vs. the previous 510 pushrod which I had adjusted with SLIGHT play.

 

Note that step (1) did NOT work and should be skipped, but I'm including it as something worth NOT doing......

 

1) Disconnect lines from master to hook up bench bleed tubes - this ended up just making a mess as fluid was slowly dripping (about one drop/sec) while I tried to get the tube fitting screwed in and the reservoir return tubes on. I finally said screw this and reattached the hard lines. This is also where I paused and started thinking of the why's and theories mentioned above.

 

2) E-brake on. Find something to press on pedal continuously (wedged between pedal and seat edge). Bleed via master bleeders by relieving pressure and simultaneous Mitty vac vacuum draw. Alternate front-rear-front-rear as you're bleeding, topping of reservoirs, and adjusting the pedal-to-seat wedge, so the pedal's always being depressed (do not let it slip in the process).

 

3) Continue per step (2) above until pedal bottoms out (assuming you adjusted your pedal height and pushrod length before any of this). Top off fluid and then release pedal. This is where using a Mitty vac is better than a buddy - just before the pedal is released any remaining air is under vacuum, so when you release the pedal, fluid is drawn in from atmospheric pressure.

 

4). Repeat steps (2) and (3) until it seems like you've gotten nearly all air from the master.

 

5). Mitty vac bleed from each wheel, furthest first, periodically topping off the reservoirs.

 

6). Repeat step (2) this many times....f/r/f/r/f/r, followed by step 3. All air should be out of the master by now, and if you don't have a firm pedal feel by now, you either have air still in the lines/calipers/slaves, or a leaking fitting.

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Bubbles won't stay put if bleeding is done thoroughly. Its only old wives tale that bleeders must be at the top. Some cars have them at the bottom and can still be bled effectively.

 

Mity-vac is a good way to go. Otherwise you can put the end of the bleeder hose in a jar of new fluid to prevent air getting back in - and don't crack the bleeder too far open.

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