Quote:
Originally Posted by embee
I have a suck/blow Mityvac too, a very useful tool. They also do suck only versions, quite a lot cheaper. I empty the reservoir of old fluid first using it, refill with fresh stuff, then bleed at the caliper. The big advantage is that you can get a continuous flow to draw the fluid through the system to hopefully purge all the air.
As said, air does get in past the nipple threads while bleeding, but in reality this doesn't matter because while you are pumping it the low pressure in the bleed line is always drawing fluid out of the brake system so no air can get back in while it is still flowing. Make sure you tighten up the nipple while the flow is still coming out.
I've never had any issues getting a firm brake using it. Just make absolutely sure you don't empty the reservoir while using it as this will take air directly into the system and you'll have to start again.
It makes the process so easy it means you tend to do it more often, keeping the fluid fresh.
There are alternative very similar items to the Mityvac, I don't have any experience of them so can't comment, but it's not rocket science so they're probably perfectly good. Mityvacs are used in industry and are good quality tools, well worth the money IMHO.
The one niggle is the small plastic vac bottles which come with them are very light and always fall over with the vac tubes attached. I made a steel holder for it using a square plate (old scaffold tube foot) and a slotted tube welded to it, the slot lets you see how much fluid is in it so you don't overfill and pull fluid into the pump.
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One thing I like about the Mityvac vacuum bottle is that it holds a bit less than the brake master cylinder reservoir on most cars ( when reservoir filled right to top of thread ) so I know when bleeding car or van brakes that when the Mityvac bottle is getting full it is time to tighten the bleed nipple, release the vaccum, empty the Mityvac bottle and top up the master cylinder reservoir again - saves you from sucking air into system, which you could easily do if vacuum bottle larger. I am not so refined as you and just wedge the Mityvac bottle between a couple of house bricks.