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Mon Apr 14, 2014 6:42 pm

I'm stuck and don't know what to try next.
I recently rebuilt the 4 rear calipers, Airheart 175h's, bleed the brakes using the 2 man system. They worked fine. The front brakes and front M/C are not installed, waiting for me to fab some caliper brackets. After getting the rear brakes working, the buggy sat for 2 weeks. Doing a general inspection prior to a test run, I noticed the M/C leaking at the push rod seal. It is an old 3/4 bore Hurst/Airheart. I installed a new CNC 3/4 bore M/C. Bench bleed the M/C as per cnc instructions. Fabricated a pressure cover for the reservoir, tire valve stem on a alum plate, drilled to match. Added 15 lbs pressure, bleed both sets of calipers using the top bleeder , refilled, bleed, over and over, but never got any pedal pressure. Checked everywhere for leaks and couldn't find any. Pulled the M/C and bench bled, again, using a vinyl tube fed back to reservor. This pushed fluid, no problem. Have tried pressure bleeding over and over and over, I get steady stream of fluid with out bubbles from top bleeders, as well as bottom bleeders, but still do not have any pressure on pedal. It bottoms out with no resistence. Any ideas or suggestions?

I've also tried gravity bleeding, to no avail.

I guess my next attempt will be to make a pressure bleeder with a canister, vs just using the M/C reservoir, buying one here is not an option, nothing like that is stocked locally. Maybe I'm not pushing enough fluid thru ? I don't know.

I need to get this fixed for a race this weekend.
Help please.

Mon Apr 14, 2014 7:36 pm

Does it build pressure on the bench or just flow fluid? You should be able to deadhead the outlet and the piston should hardly move in the cylinder. If it travels to the bottom when deadheaded either it has air or is bypassing the internal forward seal.
If it is solid, then it is air in the lines or calipers. The bleeders must be at the highest point to make it easy to burp out the air. You can hook a rubber hoes onto the bleeder and submerse it into a bottle with brake fluid, enough to cover the end of the hose. Open the bleeder slightly and pump away making sure the hose stays in the fluid and you don't run the reservoir dry. This is super easy, one man operation. Once the bubbles are gone you will feel a slight increase in resistance when pumping the pedal, that's when you tighten the bleeder.

Mon Apr 14, 2014 7:43 pm

4 bleeders?
Don't open the lower bleeders - only the highest ones, air always goes to the top and is displaced with the fluid. If the bleeder is not at the highest point you might have to loosen the caliper and tip it while keeping it on the rotor so the pads don't pop out. This way the air will be to the top, if that is the problem,

Mon Apr 14, 2014 8:55 pm

Actual 8 bleeders, 2 per caliper. I only tried a bottom once. Been using the top one. Sounds like a great suggestion. I ll give it a shot in the morning. Thanks

Tue Apr 15, 2014 12:30 pm

Willy, sorry, I only saw your last post. The mc checked out ok. No movement when deadheaded. I usually bleed with the tube and bottle method, gave up after filling res 7 times. It would have worked, I gave up too soon. Problem Solved after bleeding about 20 more times. That was the main problem, tons of air, in part due to fluid line being above bleeder screws? Also, the cnc shaft is shorter than the airheart shaft, i assumed they were the same, so i was only getting about 70 % throw.

I am running 4 single piston 1.75 dia calipers in the rear and will be running 2 of the same calipers in the front. 3/4 bore mc in rear and 7/ 8 bore in front.. independent mc s. This is the way it was set up when i bought the car. At first it seemed backwards, but after researching airheart site and others, it appears to be correct. Can someone confirm this is correct?

Tue Apr 15, 2014 3:31 pm

Great that you got it. Patience and perseverance and a lot of brake fluid.

I cant help you on the setup but if you get a good pedal with the 3/4 bore on 4 calipers a 7/8 should work on front too.

Tue Apr 15, 2014 4:03 pm

Thanks. It has more pedal travel than I like. It was that way before too. I am thking of trying a 5/8 for the rear and 3/4 for the front. Sound logical?

Tue Apr 15, 2014 4:03 pm

Thanks. It has more pedal travel than I like. It was that way before too. I am thking of trying a 5/8 for the rear and 3/4 for the front. Sound logical?

Tue Apr 15, 2014 6:27 pm

The 3/4 will push more fluid to activate 4 calipers but you would loose a bit of pressure. Doubt if it would be noticeable.