Spongy brake pedal, there's air somewhere. Advice on bleeding it out?

[Pyr0monk3y]

I installed my stainless steel brake lines today and in the process, the master cylinder drained dry.

Once the lines were installed I filled the master cylinder and hooked up a mighty vac to each corner (order:LR,RR,RF,LF) and put vacuum on each caliper until I got fluid. After that, the pedal still went straight to the floor. I then re-bled the brakes by having someone push the pedal. After a couple rounds of bleeding each caliper this way, the car will stop and the pedal is firm but it takes half the travel to build pressure. When I push the pedal I feel a little play like normal, then slight pressure, and finally a very firm pedal which stops the car nicely. The period of slight pressure feels like air.

The pedal is significantly lower when it builds pressure than before I replaced the lines. So much so that it is difficult to heel-toe. After checking several times, I cannot find any leaks anywhere.

Any ideas?

I'm thinking there's air in the master cylinder but I'm unsure of the best way to get it out.

Thank you for your help!

[wannafbody]

You might need to remove the master cylinder and bench bleed it. Anyone else have any ideas?

[Pyr0monk3y]

I bled the master cylinder on the car and pedal feel has improved. However, the pedal is still softer than it was before I started. I will try bleeding the calipers again when I can find a helper.

[Codersozer]

Try gravity bleeding them. Open all the bleeders and the master reservoir cap, then connect a hose to all 4 calipers, and give the pedal a slight push to get everything started, then wait a couple hours (adding fluid as needed) and see what happens. Its worked for me, I had the same problem when I switched to steel braided lines.

[DK AFFECT]

Bench bleed the master cylinder.

[Pyr0monk3y]

It's fixed! All I did was enlist a more mechanically inclined friend to help me bleed the calipers and master cylinder.

I can definitively say that stainless lines do improve brake feel. It's no placebo effect and I'm not lying. It's very obvious when I have heat in the brakes by the feedback I get through the pedal. I never had that feedback before. The amount of dead travel in the pedal is identical but once the pedal firms up, it feels firmer. Also, between applying normal stopping force and full lockup, there's no pedal travel, just more pressure. It's too early to tell for sure but so far, modulation is no more or less difficult. The extra feedback should help in theory, but in practice, my stopping distances are no different.

[Agent☣Orange]

Have you considered a master cylinder brace?

[Pyr0monk3y]

Yes, I'm going to try to build one. FM's design seems attainable with the tools I have. I would just buy it but they are asking a bit much IMO. A group buy could persuade me.

[Andy]

Lets see if we can get a group buy going on the FM brake master brace and or the FM shock tower brace.

[Andy]

I just now sent an email to FM asking if they would do a group buy on the brake master brace or the shock tower brace.

[Pyr0monk3y]

lol, I just did the same. Maybe we will get their attention.

[Agent☣Orange]

Good initiative guys!

[WASABI]

Pyro, sorry I didn't see this earlier, but here is an illustration I did a while back that explains the bleed order. It's imperative to go from the furthest caliper away from the master, to the closest.

http://www.fagerquist.com/miata/mod/brakes bleed order.jpg

And, always make sure there is fluid in the brake reservoir, so you don't suck in air.

[Pyr0monk3y]

I was bleeding in the right order, and I think the master re-primed itself pretty well since I never saw any evidence of air in it. The problem was some confusion between the guy turning the wrench and the guy pushing the pedal. I sent the pedal pusher home and got some help from a mechanic friend. He opened the bleeders and I pushed the pedal. I made damn sure to keep the pedal on the floor until the bleeder was closed and then I pumped the brakes a couple times to build pressure.