Beny

On 12/05/2021 at 20:46, sr2 said:

Sorry for the delay in replying - it is a bit of an unusual one for sure.

One of the big improvements  a Mastervac booster has over the older  Hydrovac  (remote) booster design is that it introduces the atmosphere  from the inside of the car ( the drivers foot well) as opposed to the engine bay.  I’ll just mention here that the major improvement was not relying on a single pushrod seal that the failure of which would often result in a total loss of braking – great innovation guys!

 The filter usually consists of two parts, a coarse foam doughnut and a felt washer where the pedal pushrod enters the unit. The filter sits in the valve body held in place by the felt washer which in turn is held in place by the rear boot. Sadly a lip on the boot forms the seal between the booster and the firewall and to access it you have to remove the booster and master-cylinder (sods law strikes again).

I’ve doctored up an exploded diagram of similar Nissan booster for clarity, (alterations in red).

 

 

Have to say that at this stage I’m clutching at straws with this one. Nothing new here; the more interesting diagnoses are usually the most baffling at their onslaught!

Although an obvious conclusion to jump to I’m not comfortable with a 10 year old booster somehow “digesting” both filter and felt washer through overly vigorous brake bleeding. The ports in the control valve are small and the only Mastervac filters I’ve ever seen fail have been from early 70’s boosters that have lain unused for decades?

I have seen boosters with a small perforation in their diaphragm still performing to spec but needing far more atmosphere than usual to be introduced to the rear chamber. It could well be worth pursuing this, I’d suggest pulling the master-cylinder back a little to see if it is leaking fluid into the booster, on many cars you can manage this without releasing the hydraulics.

Please keep the thread going and let us know what you find.

 

 

 

 

Thanks for reply, I'll have to wait until after next week....the old fella took off to OZ once the border opened and the car is at one of those airport carparks.

Anyway, after I changed the brake pads,  I took it for a test drive and heard the air sound, then I bled all the brakes. One thing I noticed is when I opened up the bleeder on the 2nd brake caliper, no brake fluid came out when I pressed the piston back in, only on the first, just wondering if this had anything to do with it. Other than that, Im stumped too.

EDIT: Also the outter right brake pad was worn more than the other 3, thepiston moved freely and the slides were all good (I grease all the slides).

4 hours ago, sr2 said:

Did you bleed the brakes with the engine running?

No....would that make a difference?

16 hours ago, AllTorque said:

Cool.

The booster has a ‘silencer’ or ‘filter’ that is foam around input rod. Chances are when the new pads were put in or the brakes bled and the pedal was pushed all the way down the foam has fallen apart. 

If the brakes are working as they should,then the booster is sad. 
If you get a hard pedal or poor stopping performance, the booster is dead.

Either way, I would recommend replacing the booster.

Yes the brakes are working fine, its just that whooshing noise. So you cant just replace that silencer? been asking around and this booster unit is expensive (been quoted $480 and thats 2nd hand) and to make things worse, its a real arse to get to the booster as you have to take off half the car just to get it out from the engine bay and release it from the brake pedal. Oh well.

22 hours ago, sr2 said:

Just a couple of questions before I dive in. (Boosters are a lot simpler than most are let to believe).

• Can you confirm it wasn't making the noise before you replaced the pads and bled the system? (i.e. where you listening for it before?).
• What "3 basic booster tests" did you use. If you found them through Mr. Google feel free to provide the link.

I can confirm it didnt make that noise before I replaced the pads. The "3 basic booster tests" were these ones: 

Replaced my dads rear brake pads the other day, took car for test drive and now theres a whoosh sound every time I press the brakes (note: its not a constant hissing sound). Already bled the brakes so no air in the system, the noise is coming from the brake booster. I've tested the booster with the 3 basic booster tests from sitting in the car and it seems all good. Brakes are working fine, not spongy or anything, and the pedal isnt hard, its just the whoosh noise. Brake boosters are expensive (even 2nd hand) especially this car (2011 Nissan Serena), wondering if its a quick fix or a whole replacement required.

Sounds exactly like this on the youtube clip: