Brake Fluid Change???

[dogsridewith]

Last two posts sound great. There are several ways to move brake fluid through the system. I do it w/o assistant using a MityVac (suction device, w/ gauge, also used for testing various vacuum diaphragms). Ever encounter or hear trusted account of the Mity Vac pulling in air around wheel cylinder or master cylinder seals...thereby, of course, ruining the bleed job.

[CoryM]

Originally Posted by dogsridewith

Last two posts sound great. There are several ways to move brake fluid through the system. I do it w/o assistant using a MityVac (suction device, w/ gauge, also used for testing various vacuum diaphragms). Ever encounter or hear trusted account of the Mity Vac pulling in air around wheel cylinder or master cylinder seals...thereby, of course, ruining the bleed job.

I've never seen air pulled into the system except for when master cylinders fail (or when someone lets the fluid level get too low). The suction will cause air to pull past the nipple threads and into the system but it immediately goes out the nipple. This is why you will see bubbles in the mityvac even though its well sealed to the nipple. The amount of air that remains is not enough to cause issues for street cars or even be noticeable when testing. On a high end racecar you may want to give it a few manual bleeds, but I've not found that required on the ones I've played with. Professional brake flush machines are just vacuum suckers on each bleeder, and several PSI of fluid on the master cylinder. It's probably a bit better than just vacuum, but mostly it's probably just faster. We also put 2L of fluid through the system which is probably excessive for most cars, but some sure need it.

One day I should do a write-up or video about brake servicing. Very few people do it properly.

[tmontague]

Originally Posted by dogsridewith

Last two posts sound great. There are several ways to move brake fluid through the system. I do it w/o assistant using a MityVac (suction device, w/ gauge, also used for testing various vacuum diaphragms). Ever encounter or hear trusted account of the Mity Vac pulling in air around wheel cylinder or master cylinder seals...thereby, of course, ruining the bleed job.

I have tried the mighty vac and no matter what it pulls air in through the bleeder for me. That is even with covering it with grease as well as using thread sealant tape.

I just use the 2 person method which is cheap. Quick and woke well.

Down the road I'll likely buy a pressure bleeder but for now the 2 person works fine

[bronsin]

Originally Posted by tmontague

I have tried the mighty vac and no matter what it pulls air in through the bleeder for me. That is even with covering it with grease as well as using thread sealant tape.

I just use the 2 person method which is cheap. Quick and woke well.

Down the road I'll likely buy a pressure bleeder but for now the 2 person works fine

I agree mityvac is overkill. Spend your money on something useful!