I used to work on printing equipment and machienry to make printing plates.. and some parts of the big complex machines use vacuum generators as they all have air for the pneumatics, when they want vacuum (used to pick up metal printing plates with suction cups in this instance) they use a vacuum generator that runs when suction is required, its controlled from manifold air pressure with a little air solenoid. it has a little muffler on it where the air escapes.. i removed that as it gets wet with fluid.


I just use a long line so it can be near my compressor and away from me. I used one i had onhand that I had as a spare part but they aren't hard to get. I see them used for things like vacuum bagging wood laminate parts with epoxy.. they put the parts in a plastic bag while wet with epoxy and suck all the air out drawing the epoxy into any voids..


you can use a vacuum pump instead but then you need to protect it as fluid will surely wreck those diaphragm pumps. the generator won't be ruined that way.


yes I suppose you can tie down the reservoir so it doesn't blow off with fluid all over..

and yes, air can leak into the line where the nipple threads are because I do need to open it a little for it to work. You are right that by using pressure you may see that line clear of bubbles, better.

in absence of a 10 PSI regulator one could perhaps just use a barely inflated tire with the Shraeder valve removed. That's how old school VW bug supplies pressure to the water reservoir to feed the wiper squirters, they saved the cost of a pump that way.. Ingeneious idea, but it probably caused a lot to also have roadside tire issues and found their spare flat. maybe it forces you to check the spare tire pressure, anyway I thought it a bit strange..

I think often I'd use both, the vacuum to get my car bled and then maybe I'd bother my girlfriend to go step on the pedal and go around each bleeder to see no bubbles on the last couple of pumps. I know she is OK for a half hour but I'd rather not have her involved too long in all that stuff.

with the bottle method a you just run the line into the bottle and add some fluid to the bottle so it can't backfeed air into the line and then into the cylinder. many Hanes manuals and such describe this method.

this still requires the situation where you have the bleeder screw a bit loose and as a result you can have a situation where as the pedal travels upwards it can possibly pull in air. . I only crack it enough that i can get fluid out with a bit of pedal pressure, not wide open.. I'd still like to have someone pump the pedal to finish things off..

I once bought a thing that looks like a big metal syringe for bleeding brakes and it can pull vacuum but I found it awkward because you can't let go , they have others that have sort of a locking pistol grip thing , maybe they work better.

where I do find the big syringe thing handy is if I dont want to get into bleeding but notice the fluid looking dirty, then sometimes Ill just suck the reservoir near dry, wipe it out, and refill fresh fluid. The fluid does recirculate , if a bit slowly. its not an excuse to not bleed them but it's better than doing nothing

At lest that does remove much of the dirty fluid without the need to bleed them. in practice you may still have some dirty fluid in the wheel cylinders or calipers and that may contain some water so proper bleeding is best.

on my old Volvo I took the calipers apart , it has 3 piston calipers, and the pistons were chromed and the chrome was flaking. I didn't know where to buy new pistons, so I copied the dimensions and made new ones from stainless steel instead. it worked fine but stainless is a bit harder to machine than some metals. my costs were just for the rubber seals and new pads after they were seized up..

at lest it won't have that chrome flaking off again. I haven't had the calipers apart on my 944 but I might see the same issue in there. some rust in the caliper bore wont hurt much, all they need to do is retain the seal between the piston and the caliper and guide the piston. the piston outer surface needs to be not pitted to make that seal.

with wheel cylinders used in drum brakes the seal rides in the bore, so the cylinders could be resurfaced but often they need to be replaced due to pitting in the bore of the wheel cylinder.

With a caliper, the piston just moves a tiny bit unless you change pads, and the seal is really between the caliper and the seal which rides on the piston which moves but not a lot of distance. I think as long as I can obtain the seals and dust caps then the rest is not such an issue to fix. I'd just buy new pistons if they are cheap and if prices are crazy or they are hard to find, then I'd make new pistons..

I sometimes send stuff out to a hydraulic cylinder machine shop and they have abilities to refresh hard industrial chroming and polish it. I think they might have the abilities to rechrome pistons if it was necessary. those guys can work within some pretty fine tolerances, some things like hydraulic control valves make their seal just by being in very close tolerance..
regular bleeding will avoid a lot of problems like the caliper pistons loosing their chrome. in reality, It's a thing that is commonly delayed to the point of failure.


I swapped to silicone fluid in my old volvo . it doesnt; absorb water or eat the paint, and it is not compatible wiht normal fluid.
from a performance standpoint it also boils at a low temp and it can make the brake pedal a tiny bit mushy.. I wouldn't consider it if you ever want to drive hard and it wont be a thing racers want. also the system needs to be completely flushed if not rebuilt before the changeover

the porsche shares the clutch cylinder and fluid, otherwise I would switch the clutch to silicone fluid. a clutch does not get hot and the mushy feel is probably not even noticible.. I was swapping clutch cylinders quite regularly but went 20 years on the silicone fluid, so I like it for the hydraulic clutch application..

really I think the only ones that would want silicone fluid is if you have a show car or one that is not driven often and nevr driven hard.. like antique cars,, and then it kind of shines as it won't eat paint and absorb water into the fluid itself.

I think the porshe can use dot 3 or 4 Volvo always seems to want 4 so Ill probably use that but what is the difference? dot 3 might be more common on US cars and maybe the dot 4 is called for more in european cars? is one better than the other in some way? perhaps the right fluid can affect the rubber life of the brae parts? I think dot 3 and dot 4 are compatible.

amazonphil.

Hi Phil

You made a nice long post on what to be concerned with in servicing a brake system.
It seems the posters brakes work fine just the pedal height was the concern.

It amazing sometimes that little a change in our normal routines can be pick up on and others we allow to be ignored.

You have listed a methodology that covers a lot of territory especially when working alone or with two systems of pressure or vacuum applied to certain points to remove fluids or air.
Pumping the brake pedal, as you point out, has many drawbacks besides having to work both ends at the same time and not make a mess by spilling any.

I personally like the pressurization of the master cylinder top.
I rig up a replacement cap with an air fitting that can be disconnected. The line goes to a regulated air source of about 10+ psi.
The plastic reservoir is only held in by rubber O rings and a long Velcro strip alleviates that worry for me, even though, I have never seen a reservoir loosen up. They seem pretty hard to get off but …?

I have Never liked trying to “pull” fluid from caliper nipples.
First off, is that the caliper nipple is a threaded “in” affair and threads can leak by air.
So you are more likely to get an air mix into making bubbles.
This can make you think you Still have air in the system.
You are looking for only fresh clear fluid in the output hose when operating.

I can imagine that Venturi vacuum device is very noisy but it’s a poor man’s suctioning pump.
I never have used one and have only lost a little hearing.
Protect yourself and use muffs, plugs or something if you think it’s loud, as it really is!

Some high frequencies are somewhat painless but damaging just the same.
I have machined some exotic metals and I’m a believer in a damper’s capabilities and needs.
Titanium “after burner” rings of our jets scream when turned.
Take super sonically applied powered metal application equipment, for instance, it is in an insulated room all by itself. I still wore head gear outside it.

Someone posted a link to how rubber is made for cushions for Brunswick billiard tables.
Very interesting as a knew nothing about it.
BUT,
I looked up another one on how rubber radiator hoses are made. Somewhat complex yet simple.
Seeing India versus Europe or Asia, oh my, what variations of working conditions was showed to me.
Thank goodness we have had regulatory standards established and a likewise management mindset got corrected. All done on the backs of my hard working predecessors.

It showed that the NAFTA trading policy has done nearly squat in some other countries. IMHO.

It made me go clean up my garage even better! (:-)

PHIL