I am bleeding my brakes. I am finishing it off the old fashioned way but I borrowed a vacuum bleeder to suck the fluid through from the caliper end. When doing this I think that air is getting by the threads of the bleeder screw making it appear that a ton of air is in the brake system when really all of it is gone. Should there be a thread sealer of some kind on the threads so that air can't get by while using a vacuum bleeder?

Thanks,
k

 

I've never used it, nor seen it called for in a maintenance manual...but HAVE heard of folks doing it. How far are you backing off the bleeder screw? I barely need to crack 'em usually.

 

Isn't there some sort of little o-ring? At any rate, I think the bleeder screw is an NPT pipe thread, so there would be no need for any kind of thread sealer.

 

perhaps your opening it up too much? to bleed the brakes you only need to crack the screw open.

 

I'll try the vacuum again without opening it much but I am pretty sure I only cracked it just a little. At first I thought the vacuum leak was coming from the hose on the bleed nipple. So I closed the bleeder all the way and pumped up the vacuum and it held very well. That ruled out a bad fit of the hose on the nipple. Right when I cracked the screw the vacuum went way down and almost gone...

 

I use a vacuum pump for flushing and bleeding MINI's, other cars, trucks and motorcycles. When I first got the thing I noticed that and had the same concerns. So I finished up old school with someone on the brake peddle. The next brakes I did no one was around to help so I just pumped down as much vacuum as I could with the bleeder closed then cracked it a bit and closed it before I ran out of vacuum. Then when finished with all four wheels the brake peddle was as firm as it gets, maybe even better than before I started. So that helped me developed my own technique for using a vacuum pump.
Yes it does suck a bit or air on some bleeders but as long as you get the bleeder closed before you run out of vacuum you most likely haven't introduced any air into the system. Anyway that's the system I use and it works for me every time. I hang a bent piece of coat hanger wire from the spring to support the vacuum pump so the reservoir stays level, it frees up my hand to tighten the bleeder valve and keeps the hoses from popping off. I leave the box end wrench on the bleeder valve, this helps when its time to close it. Now I don't want to do it any other way, I just wish the reservoir was larger so I didn't have to dump it so often when flushing the system.
Just my experience.

 

Oh, back to your question? No, sealer is not used.
I didn't mention that had I once tried teflon tape on the threads to seal them the first time but decided it was a waste of time. MINI nor anyone use anything on them.

 

norm03s,

Thanks for the info. When using the vacuum bleeder do you see constant bubbles coming through the tube into the container? I do and it has to be from air getting past the threads of the bleeder screw because I have pumped the brakes manually and there is no air in the system.

k

 

That's it exactly.
With my free hand I have wiggled the bleed valve and observed more bubbles.

 

I get exactly the same air-past-the-bleeder-threads syndrome when using a pressure bleeder on the OEM brakes... but yes, if you just barely crack the bleeders open, it limits this. Opening them more than just a tiny bit doesn't really produce more flow, just introduces the bubbles...

 

Thanks for the further confirmation. Is there an amount of vacuum that would be considered too much and damage something in the systems while sucking out the fluid through the caliper? The reason I ask is I have a vacuum pump for dental vacuum mixing investments which would make this job really really easy. It is no adjustable though and will go up to 30 psi suction.

k

 

I think you mean 30 inches of mercury suction.

You can add a tee in the line between the vac pump and the bleeder screw and on that branch put a small regulating valve. As you open the regulating valve, more air will be sucked in through that valve and less will be sucked from the caliper. You don't need much vac to do the job. Just be patient and use a section of clear tubing so you can see the color and clarity of the fluid. Unless you can seal the threads, using the vac method, you will most likely always see some bubbles.


YD