Brake bleeding: I must be doing it wrong

Don't ever let the master cylinder get empty.  

Only change one hose or caliper at a time, and bleed and top up between.

Don't push the pedal down any farther than it normally travels, unless the master cylinder is brand new.

Always bench bleed a new master cylinder.

A new caliper will gravity bleed most of the time.  A series of short strokes on the pedal will push it through if it won't bleed by itself.

Installing a new caliper with worn pads can be frustrating, particularly if it's a rear caliper with a park brake built on.

I had this issue when I swapped the lines on my RX7, apparently the shop manual has you bleed the master LAST after you've bled the other 4 corners. I did so and my pedal firmed right up. Only advice I can give is to try bleeding the master.

Did you give the caliper a whack with a brass or rubber hammer after the first bleed? New calipers can have tiny bubbles stick to the inside. The whack breaks them loose.

Personally I would never pinch a brake hose. I use plastic wrap under the cap. 

I didn't whack 'em, I can try that I suppose. After that I suppose I'll try bench bleeding the old master cylinder to see if somehow it got air trapped in it since that doesn't cost anything. Then maybe replace lines, then replace the master if still no joy.

Frustrating!

Erich said:

I didn't whack 'em, I can try that I suppose. After that I suppose I'll try bench bleeding the old master cylinder to see if somehow it got air trapped in it since that doesn't cost anything. Then maybe replace lines, then replace the master if still no joy.

 

Frustrating!

So the brake system engineer with 24 years of OE experience and 40 years of turning wrenches recommended gravity-bleeding.  You really ought to give that a try before bench bleeding the old MC.

Ok big shot!

AngryCorvair said:

Erich said:

I didn't whack 'em, I can try that I suppose. After that I suppose I'll try bench bleeding the old master cylinder to see if somehow it got air trapped in it since that doesn't cost anything. Then maybe replace lines, then replace the master if still no joy.

 

Frustrating!

So the brake system engineer with 24 years of OE experience and 40 years of turning wrenches recommended gravity-bleeding.  You really ought to give that a try before bench bleeding the old MC.

The guy who got his journeymans ticket in 1985 agrees with the brake system engineer in this case.  I still fear the ABS programming in my 2000 Silverado, though.

Someone on here said if you suspect air in the abs system, go out and slam in the brakes on loose gravel.  That'll actuate the abs and pump air thru to the bleeders.  I don't know if that works or not, but it's fun to do once in a while.  

Not a brake engineer, and less than 40 years wrenching. So all those other guys are probably giving better advice.  I did win money and trophies in demolition derbies, though, so tearing sh!t up is something I've done well at.  

This thread I relevant to my interests. My 92 S10 brake pedal decided to go to the floor (slowly) when I applied the brakes after bringing it off the jackstands it has been on for severs months. It has rear-only ABS. Once I find and fix the failure (I'm guessing rear wheel cylinder or internal failure of the master cylinder), is a vacuum bleeder likely to be sufficient?

I'm pretty much the same boat as Erich.

I just replaced the two front (four piston) calipers on my 2005 Tacoma. I didn't clamp of the lines, but I put a vacuum plug over the end and made the swap very quickly. When everything was back together, I used my Motive Products pressure bleeder, but I didn't flow fluid through it, I just used it for pressure (5 psi) over a full master cylinder. The master cylinder never came close to getting empty. I got quite a few bubbles out of the bleeders, and then a solid stream of fluid.

The pedal was really soft and went close to the floor. I couldn't come close to getting the ABS to engage. So then I went back and bled them again with the two person method. No bubbles at all.

It's a little better, but I'm not there yet.

I've ordered new tubing for my pressure bleeder, so when that gets here, I'll fill it with fluid and try to flush the whole system with new fluid at 10 psi.

That is, if gravity bleeding doesn't do the trick...

When I was a kid, I used to be the pedal pusher for my dad. He always reminded me to put my left foot under the brake pedal so I didn't push it too far.

Well, as an update, after bleeding another time and noticing no bubbles, the pedal seems a little better but engages lower than it used to, before cracking into the system. Seems to have gotten better over the past week on its own really. I'm wondering if it isn't a bit of an effect of the new caliper break-in period along with new pads. 

I still plan on doing a good gravity bleed when I get time. 

When you changed the caliper, you changed the pads?  Did you machine or replace the rotors?  Do the rotors have a wear ridge on the edge?  If so, that's your squishy pedal right there.

Brand new pads, rotors, and calipers all around. Bought a kit from StopTech

In my experience, new pads (whether with a new rotor or not) can take up to a few days to bed in, and before that can generate a soft pedal feel while the car is running. The pedal should firm up over a few days (depending on how much you drive it) and then one day next week, you won't even notice it, but the pedal is hard.

Another thing to try that have solved some stubborn bleeds: when you crack the bleeder, crack it as little as possible for fluid to come out (an eighth or at most a quarter turn). This does two things: it will ensure that the fluid is pushing out at as a high a pressure as possible, and, more importantly, that no air gets in through the bleeder screw threads. It seems as much as half a turn loose can let some air back through the threads with certain bleeders.