What tools would a garage (main dealer) use to change the brake fluid in a car? Do they have something that attaches to the resevoir and supplies the new fluid at pressure so that the operator can let the old fluid out of each caliper in turn?
never change brake fluid on any car over 50 years....a myth
Brake fluid is hygroscopic.... over time it abosrbs water from the air. Thus the absorbed water diffuses through the hydraulic pipework right down to the caliper pistons.
This leads to a few issues.
I am only guessing, but I have always assumed they used the professional equivalent of the old "DIY" Eezibleed which is just as you described. A bottle for new fluid, connected to a replacement filler cap of the reservoir, and pressurised with air to 5 or 10 psi. Then each brake nipple opened in turn until the fluid runs "clear". Usually starting with the brake furthest from the master cylinder.
I have seen vacuum versions where the fluid is sucked out under a vacuum from an opened bleed nipple on the calliper/psiton.
The brake fluid reservoir screw cap is replaced with one with a tube connected to it which then goes into a container of fresh brake fluid.
Vacuum is preferred over pressure as the effects of a leak is less.... i.e. the system would suck in air via a leak whereas in a pressurised system, hydraulic fluid would be sprayed everywhere!
SMichael Chare formulated on Thursday :
Some reverse flush - pump it in at the bleed nipple, a turkey baster to suck it out of the master reservoir.
Others might use a pressurised 'easybleed' attached to the master reservoir, bleeding at the nipples.
When I was an apprentice some... nearly 40 years ago we had a device called an "EZ-Bleed" which you'd fill up the bottle with fresh fluid, attach one pipe to the fluid reservoir via one of the selection of included (piped) caps and the other end connected to a wheelbarrow tyre via regular foot-pump type valve.
Operation was as you describe, clear plastic tube on the bleed nipple going into a jar to catch the dirty stuff.
Worked really well and didn't require any mower supplies, vacuum pumps etc.
SH presented the following explanation :
+1
A lot of people don't change the fluid but the manufactures recommend it.
its usually every two years....
Well not really sprayed everywhere, if (as was common) you connected your easybleed to a tyre to provide the pressure, it was recommended that you dropped the pressure to 1 bar or so, because plastic master cylinder reservoirs are not designed to take pressure! Yes, it would be messy if you "blew up" a master cylinder, but the flow rate at the nipple or any other normal leak site is not very large.
I've never seen a vacuum system, but no reason why it should not work. Except of course that every seal in the system is designed for positive pressure, so negative pressure has the potential to draw air in at each seal, possibly with dust contamination. With "healthy" seals there should be enough pressure from the elasticity to make sure this does not happen.
I personally think that it should be changed when you have new pads because winding the caliper pistons back forces old fluid back through the ABS unit into the master cylinder.
Professionally I think it is usually done with a positive pressure system (like this
Negative pressure systems risk sucking air past seals not designed to resist negative pressures.
The old fashioned way involves two people, one pumping the pedal and one monitoring the flow from the bleed nipple. The big downside of this method is that it?s too easy to floor the brake pedal and push the piston past it?s normal range of travel where there may be ring of corrosion or debris resulting in seal damage.
I was most unhappy with my VW dealer when they fecked my master cylinder after a fluid change.
Tim
Not any more.
There are two ways. A vacuum pump used at each bleed nipple. Or you pressurize the fluid reservoir.
I have both here (DIY versions) Eazibleed, which uses pressure from a tyre (reduced to about 20psi) is the best. But do make sure you connect it properly, as a leak can result in fluid squirting everywhere.
Problem with the old method on an older car is the master cylinder goes to a part of the travel not used. And if that has slight corrosion etc, may damage the seals. The pressure method leaves it at rest.
As long as you keep enough fluid in the tank:-)
BTDTGTTS
The EaziBleed has an additional reservoir. Which automatically tops up the main one. But you don't have to use it.
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