Okay so I have an 86 gxl, Auto (in process of 5 spd swap) disabled the AAS, NO ABS. New master cylinder, new (mazdatrix) SS lines, verified caliper slider movement. Hit the brakes and it doesn't start to engage until after half way. Before I changed the master cylinder it would engage and continue to travel to the floor. Now I just changed the master cylinder (bench bled it, then bled the system) and the peddle feels very hard now... after half way. I'm guessing the next step is the proportioning valve?? Thoughts? Experiences?

 

How much freeplay at the pedal and did you adjust the pedal>booster pushrod?

 

Google reverse bleeding. Also, there's a bleeding sequence. Start at the farthest caliper from the master cylinder, work your way closer.

Reverse bleeding works.

 

That is only partially applicable these days.
With safety mandated split circuit systems, there is no connection between the front and rear brakes, so you can bleed the fronts first without any problems.

 

Since 1964 I think actually. But the split is usually front/rear, sometimes crossed, i.e. right front and left rear, etc. The idea is to preclude air intrusion into the system by scavenging it from other lines. I'm not too sure how truthful it is, but I don't mess with success. Plus, it's easy to remember which one's you've already done, and it takes absolutely no more time. I guess you could just call it a "good practice", even if it does nothing more than help you remember which ones you've already bled.

 

Even I, the wizened old ****, can remember which of the four wheels have been bled.

 

I look for "brake pee" from the calipers..lol!

 

I adjusted the pushrod all the way forward. Made a slight difference. It wasn't too far off from all the way forward.

 

No no no no no...

Dammit no.

You don't just adjust the pushrod all the way forward, you have to adjust the pushrod to give a certain amount of pedal free-play. I don't know what the exact spec is, but 1/4" of pedal movement before engagement usually takes care of things. This accounts for fluid expansion and contraction. If you don't have pedal freeplay, you'll end up with brakes that will lock up as the system heats up. The idea is that there are a couple ports (one's a vent and one's a take-up) inside the master cylinder. Freeplay allows these ports to not be completely covered when the pedal is not being pushed, allowing fluid expansion to return to the reservoir. If you adjust all the freeplay out of it, the fluid has nowhere to go and you now have self-applying brakes.

Readjust the pedal to about 1/2" of freeplay, then REVERSE BLEED the brakes. You still have air in the system. I'm telling you this from experience; not just on my own cars, but from being an actual ASE automotive technician.

Edit:
http://www.rotaryheads.com/PDF/2nd_g...ing_system.pdf
Page 7. 4-7mm is the spec, so right about 1/4" of freeplay.

 

Once you rebleed the brakes, take her for a spin, get the brakes nice and hot, THEN adjust the freeplay.
With the fluids at max expansion, you can set for just minimal freeplay at the pedal.
When it cools down, you should be set very close to factory spec.

 

I would read the FSM and follow the brake bleeding process described there.
The same thing applies to the pedal free play.

Just what I would do, doesn't mean it's the best option.

 

It can also take forever to bleed the air out of the 4 piston calipers. You'll have a great pedal when you finish, but the first time you go for a drive all that trapped air will suddenly be free and now the pedal slams halfway down before the brakes engage. So back to the driveway, bleed again, now slightly better during the test drive, back to the driveway, etc. It can take several tries before there's no more air.

Really makes the case for buying or building a vacuum bleeder, or reverse bleeding it. Seems to me a power bleeder would be really easy to make just by screwing a bottle of brake fluid to the master cylinder and slightly pressurizing it with air. Then open each bleeder...

 

I like to use a NEW (clean) oil can filled with brake fluid. You just hook it up to a bleeder screw and pump away. You may need to turkey-baste some fluid out of the reservoir. This forces the bubbles the easy way... up, not down. That's why the regular bleeding sequence doesn't really work too well, because you're trying to work against gravity. Additionally, tap the caliper lightly with a rubber mallet to dislodge any trapped bubbles.

 

That's brilliant. Now I can't wait to try this on my brakes!

 

i've found if you bleed the rears first then there is enough pedal pressure needed so that you can't get the fronts bled, so i like to do it backwards, i do the front first. in the rear the caliper has two bleeders, and both need to be bled

 

Oh my God. I just taught Aaron something

 

Place a jar of fluid on an upside down bucket or something to prop it up between the master cylinder and and the caliper. It must be between them for gravity reasons. Unplug the bleeder and run a hose from the bleeder to the jar. Then have a seat in the car and pump away about 100 times! Check your fluid levels though. Pump slowly! If you pump fast it makes the air bubbles brake up into tiny air bubbles and spread back up to the top of the lines. Do this on all 4 wheels in proper order and you will have rock solid brakes!

Also don't forget the obvious. New pads will increase pedal stiffness.

 

I have bled brakes in both directions. I use a mighty-vac vacuum/pressure hand pump to vacuum the air out of my brakes.

 

I've done the oil can, I've done the vacuum bottle, I've done all that. The next thing I'm going to try is rolling my calipers up and verifying slider movement because the other day when I hit my brakes coming into town coming off the freeway it pulled to the left pretty bad. So I'm thinking either my sliders are sticking, pull them apart and clean/grease them, or I just need to rebuild my calipers.

 

Replaced rear pads - Verified caliper movement and re-greased moving parts. Then last night I replaced the front pads. Went to push the calipers back with the old pads still in it and nothing moved, everything seized up. Went to remove the pads and they were stuck in their. Hammered them out and then I collapsed all the pistons with no problems. Pads were a little too long for the caliper and were just hammered in there (seen this a couple times at work). So new pads were machined slightly to move in and out of caliper. Also found TSB's on them not to use the shims? Aaron you know about this?? After cleaning all the hardware and stuff everything seemed to work great. So now that the front calipers were now moving, I re-bled the fronts (for the 4th time this year) and black slime came out. Drove it home last night after work and everything feels great. New master cylinder (probably unnecessary), new pads, new fluid - Everything works and feels great. I can get all 4's to lock up now (before I couldn't).

 

That's great. So probably the problem was the longer front pads that made them very hard to move on the sliding metal things (that I don't know the name)?

 

Yes, the pads we too long for the caliper. Grinded down the ends a hair on the new pads to make it so they slide back and forth freely and problem solved. Now I have a new master cylinder and all new brakes w/ new ss lines... lol

 

Well, having new brakes is definitely something to feel right about. Not everybody replaces the master cylinder and the ss lines. So you're better than most of people out there

 

Yeah, I'm working on making a anti-flex bracket for the master cylinder now. It's nice having a machine shop at my shop =D

 

I dunno what that is, and what it does?