Possibility of *micro air* into brake system ?

[UNC201]

What is the possibility I'm introducing *micro-air* into my brake system. I've been using both a motive and also a *pnemutatic-cap* for my brake jobs over the past couple of years.

In theory, it's the compression of air that is assisting in one man brake jobs. However, even after bleeding all the calipers via this method, I generally do a go around with the 2 man pedal pump to get that last 5% of brake firmness.

From a theoretical standpoint, do you think/feel that *micro air* may be introduced into the system via the above method.

I've never have had any issues....just theorizing/speculating.

 

[unDummy]

Nope, brake bleeding is slow process. Plenty of time for air to climb to the top of the reservoir, assuming you're feeding brake fluid to a full reservoir, not shaking your brake fluid or bleeder excessively prior to starting.....

It takes a while for the 'pedal' to get firmness and to 'pump up'. This is because the master, and all its slaves(wheel cylinders/calipers), need to be pushed into position. Pistons self adjust, using the fluid, with wear. Seals are also 'return springs' and need to 'set' into their finish location. It'll take several brake usages for 'all' to find their comfortable working position. I believe that this is what your gettting from the 2 man pedal pump(classic ol' bleed finishing technique).

 

[mechtech2]

ditto unDummy

 

[shoz123]

I like using a vacuum pump to pull the fluid out of the bleeders. Easiest way I've found yet.

 

[Quest]

+1 to Undummy 's comments.

 

[Craig in Canada]

I remember a brake bleeding discussion in another forum I'm a member of a couple of years back.

Several (knowledgable) people stated that they always got a firmer pedal from the old fashioned method. (bang caliper with mallet - pump pedal - hold pedal - snap bleeder open - snap shut - release pedal - repeat)

The mechanic's theories were that the snap action of snapping the bleeder open and shut dislodged any little bubbles that were clinging to the tubing walls and other parts throughout the system. Gravity bleeds, pressure bleeds and vacuum bleeds simply don't do this (the claim). Instead the fresh fluid flows past some of the bubbles, leaving them in the system. The smaller the bubbles, the bigger the problem.

Those paying attention and owning cars of sufficient sport construction to actually have good pedal feel in the first place could tell the difference. It may not be noticeable on every car or to every person, but these folks found it to be repeatable and it makes some sense to me. The key of this method is to create little "shock waves" by opening and closing the valve sharply. Think about banging your water taps shut in your house - if any pipes aren't securely fastened to the studs they bang in the walls from the pressure wave.

I don't find it that hard to get a helper for 20 minutes every year or two to do the job as a two person operation so I stick with the old process.

 

[Merkava_4]

Quote:

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I don't find it that hard to get a helper for 20 minutes every year or two to do the job as a two person operation so I stick with the old process.

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I'm in the opposite situation, I can never find someone to sit in the car and pump the pedal when I need to; that's why I'm hoping to have some kind of a one man bleeder set-up the next time. I've been thinking of getting the Motive Products bleeder that pressurises the master cylinder, but I don't know how well it would work. In theory it looks like it would be easy.

What do you guys think about this bleeder?