I'm having a strange brake bleeding issue. I may have let the master cylinder level drop too low when I removed a caliper. I'm using a vacuum bleeder. When I bleed the left rear, bubbles appear no matter how much I bleed. I don't have this problem on any other corner of the car. I assume this means the master cylinder is okay. I bled in the correct order, the right rear right before the left rear. I unscrew the bleeder <1/2 of a turn. I tried reducing it further and I still see bubbles. When the bleeder is sealed, the left rear caliper does not appear to be leaking when I pump the brakes.

Any ideas?

How much pressures should I use with the bleeder? eg. I'm using 20kpa = ~72psi

 

I have no experience with vacuum bleeders, could it be sucking air from around the screw threads? Perhaps you should try what we use to call gravity bleeding, (might still call it that, IDK,) where you open the screws and let the air come out on it's own.
I also put a piece of wood behind the brake pedal when bleeding the old fashioned way, the theory being the plunger in the master cylinder could get damaged by pressing the pedal further than usual.
*Did you remove both calipers? Could you have flipped them? It's been known to happen.

 

It likely is sucking air around the nipple....

if you have problems a pressure bleed is the way to go.....you might need to push a litre of fluid through it if you got air into your ABS pump. The master cylinders with a nipple are nice...the master can get fun to bleed bubbles in it sometimes too

 

I never vacuum bleed for this reason. I posted a procedure on here previously that that you do solo and is so simple. It only requires a long silicone hose and catch can, or optionally my preference is the catch bag from Speedbleeder. No need to make it more complicated with unnecessary equipment, its compact and easy to have at a race to boot.

The MC bleed nipple is only on the very early year RX8s. The MC changed along the way.


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Ya...knew that...I have bleed some of the 05+ ones without the nipple and they can be a real beotch if you let them suck in air

 

Thanks for the suggestions/thoughts. I actually removed one front caliper. I've normally had great results with vacuum bleeding, I'm not sure why it didn't work as well this time.

 

I used a mity-vac for several years. You are almost certainly sucking air through the threads on the bleeder valve. I've had some luck putting a little Teflon tape on the valve.

Seriously, just get a pressure bleeder from Motive. It's worth the cost the first time you use it.