Okay, I'm losing my mind on these damned things. I have bleed through a quart of fluid or more and then let the car sit a day or so and the pedal is still spongy. I can pump it and get a decent pedal but I certainly know that I still have air in the system. These are the dual piston units used in the kits for Vegas, etc. Anyone got any good tricks for these puppies????

I've had good luck pressure bleeding. I've been thru the same thing as you & that fixed it.

I don't know about these calipers, but I've put some on upside down before. Make sure the bleeders are on top.

I had a pair of strange four piston calipers do the same thing. These had two bleeders on each caliper,one on top one on bottom. Ended up removing caliper from spindle then put a wood block between the pads. Then hang caliper upside down to bleed the bottom.

quote:

Originally posted by Wooley:
I had a pair of strange four piston calipers do the same thing. These had two bleeders on each caliper,one on top one on bottom. Ended up removing caliper from spindle then put a wood block between the pads. Then hang caliper upside down to bleed the bottom.

I bled out the bottom fitting one time when I first installed them, figured the air would rise but maybe that's what is trapping the air. I will give it a try - thanks!

This message has been edited. Last edited by: chasracer,

quote:

I bleed out the bottom fitting one time when I first installed them, figured the air would rise but maybe that's what is trapping the air. I will give it a try - thanks!

I hope this works for you as it did for him. If it does, all I can say is that's one hellava why to design a brake caliper.

Some calipers have two bleed screws at the top, one on each side, you must bleed both.

Another old-timer method, use a length of tubing from bleeder screw to a catch jar. Fill the lower portion of catch jar with brake fluid, open the bleeder screw and slowly pump brakes until all bubbles are gone. Must repeat with all bleeder screws [the top ones, not bottom]

quote:

Originally posted by Larry Woodfin:
Some calipers have two bleed screws at the top, one on each side, you must bleed both.

Another old-timer method, use a length of tubing from bleeder screw to a catch jar. Fill the lower portion of catch jar with brake fluid, open the bleeder screw and slowly pump brakes until all bubbles are gone. Must repeat with all bleeder screws [the top ones, not bottom]

Yep - I actually built a decent one out of a $1.00 jar from the dollar store. Two holes in the top, one for the piece of brake line and the other a vent. Epoxied the top and brake line together, attached a piece of tubing and it works great. My brake system is minimal so those bottom bores on the Aerospace calipers are probably the culprit.

so I have a dumb question. do you bleed the bottom bleeder the same way as the top bleeder or is there a different method to bleed the bottom?

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I never bleed the bottoms, that makes no sense to me. Fluid will settle and move air to the top. They put the bleeders top and bottom so they are universal.

I have seen many times (Wilwood, Strange and Aerospace) where the bleeder assemble (not the little bleeder screw) is not tight in the caliper. You can put many quarts of fluid thru and still not get a pedal. Make sure they are tight then start the process over.

Another trick I have used is to crack the bleeders and gravity bleed them. Use a small hammer and lightly tap the caliper to expel any trapped air.

I normally let them gravity bleed. When an issue arises, i use the Mityvac brake bleeder kit, the cheap kit from Harbor Freight. Done.

You have air in a line somewhere if you have repeatedly bled the caliper. And Most with upper adn lower bleeder are made that way so they are universal/either side. Always use the top one as the air rises. If you do the lower your wasting your time.

I always tap on mine with a mallet or something to get the air bubbles to release. They sometimes will cling to the sides.

You sure you bled your master cylinder! Sounds to me like you have air trapped in there which requires bench bleeding with lines back to itself. If you dont do that you will never get it. Youtube how to do it. If you didnt I would suggest starting there.

Yep - although I did that when I first assembled the system I was thinking about going back to the beginning and starting with the MC. Doesn't make a lot of sense though - the only reason I am doing this is because I changed the pedal ratio. Previously with less ratio they were like a rock and did stop the car although I felt it should be better as I wasn't too happy with the staging routine. So increased the ratio and realized that there was still some air in the system - somewhere. That's the fight now.

Ok, so you changed the pedal ratio and now the pedal feels squishy? Is that why you think there is air in the system? The more pedal ratio you have the squishier it can feel. That doesn't mean there is air in the system though.

quote:

Originally posted by Tom Reyer:
Ok, so you changed the pedal ratio and now the pedal feels squishy? Is that why you think there is air in the system? The more pedal ratio you have the squishier it can feel. That doesn't mean there is air in the system though.

Well if you let it sit for a bit and then hit the pedal it probably goes 50-60% of travel, then if I pump them a few times, the pedal only goes maybe 40% so over the years I have always learned that if you can pump the pedal up like that, then you have some air in the system.

Been a bit but finally got the brake system squared away yesterday.

And a big thanks to everyone that replied to my post! A lot of good ideas and it always helps.

I had two things going on with the system and of course one of them was self-inflicted. When I changed the pedal ratio, I over did it. It was one of those not "exactly" measurements but should be close enough....nope. I looked at the measurements again with a bit more precision this time and corrected my error. I now have a pedal ratio of 6.30 and before I was closer to 8.0+.
Secondly, it wasn't the caliper bleeding that was the problem, apparently - somehow - air got pulled into the master. In the past when replacing clutch master or slave cylinders I have performed a "loop" bleed on them. I decided to try the same thing on this system so I took a piece of vacuum hose and put it between the left front caliper bleeder screw and the top of the master cylinder. About 15-20 stokes and I had a brake pedal again.

Again, my thanks for the great suggestions and help on this one.