brake failure fixed, now won't bleed
 

I'm still driving my poor 7(snow's startin to fly, I got exteme summer performace tires) until I get something for year-round replacement and get the 7 parked...Last week brakes got mushy and needed a pump or two before you'd get any pedal. Day or two later, brake light came on, and I could finally see where it was leaking brake fluid out of...Right between the brake MC/reservoir and booster. Is this a common failure point(MC leaking where booster presses rod into it)? It's my only car to drive right now, so I drove an hour and 1/2 to my Father's place where I could work on it today. I replaced the MC/reservoir/Proportioning valve assemble with one off of one of my parts SE's I have there. It came off an SE with ~120k miles on it, and hasn't been started since 1991...After alot of bleeding(old school, not vacuum pumps or special bleeder screws), got great pedal, and no more air out of three wheels...BUT EVERYTIME I bleed the pass front wheel, TONS of air come out...Every single time, for over two hours. By pumping, or by gravity, air ALWAYS comes out that caliper. If the system is closed, and you press on the pedal, it doesn't drop, and no lines leak anywere. It has st.steel lines at every wheel, and I replaced the rear hard lines and the front/back hard line a year or two ago. No leaks. I ended up just driving it back home tonight, brakes feel fine, light didn't come, don't know if I lost fluid or not yet. Where is the air coming from?

Yes, that is a common place for a leak when the seals in the master cylinder let go. Most likely the seals on the piston in the front caliper are allowing air to seep past them. Time to rebuild the calipers from the sound of it. It's either that or you have an air leak in a line, probably at a joint.

Thanks for the response, I really appreciate it. If it was a leak in some joint in that line, wouldn't it get wet from leakage under pressure? Like if I hold the pedal down with the system closed? I checked every joint of that line, all remained dry. If it is the actual caliper, is there some sort of down N dirty simple test I can do with it removed? Would the caliper also explain all the air when doing a "gravity fed" bleed?(overfilling the revervoir, and leaving the bleed screw opened on that caliper)? Thanks again, I'm stumped...

I had a similar issue with my rear brakes. The left rear brake cylinder was drawing air into the system, but it wasn't leaking. Like you, I figured that it should have shown some leakage. But it didn't. When I replaced that cylinder my problem went away. Stupidest think I ever saw. My guess would be the caliper though, the seals are 30 years old and a lot of rust has built up in there.

You could try isolating the caliper and bleeding it with a vacuum pump to see if it's drawing air past the seals. The good part about rebuilding them would be that you get rid of the rust too. A rebuild kit isn't all that expensive, or if you're pressed for time/work space rebuilt calipers should be available.

1984 Mazda Rear Drum Brakes

Just one of the places that still shows them on a quick internet search. $83 for calipers with pads or $20 for a rebuild kit. I have no experience with these vendors, but the price looks pretty good.

Good luck with chasing down the leak, it can be a bit frustrating trying to isolate them sometimes.

The prices for the rebuild kit on that site are stupid expensive. I ordered mine from Rock Auto and all together they where like $12 plus shipping.

Thanks for the votes of confidence that is almost has to be the caliper. Is it safe to drive for the moment? If it's pulling air everytime I brake...Would/could that pressure build and cause the MC to fail? Or just coincidence? It doesn't feel like it pulls in any direction when I nail the brakes at speed or stop. Pedal still feels stiff and great. Guess I'll get four rebuild kits for the heck of it since all are OG calipers, and I have pretty paint on em. Can anyone recommend a specific kit or brand? There's tons on RockAuto. Does rebilding require any honing or polishing and stuff?

No honing required. The piston actually doesn't ride on the inside bore but its close. If they are rusty inside, simple sanding is good. When I did the front calipers on my RX-7, I blasted the calipers in my blasted cabinet. Don't blast the pistons.

There isn't much difference from the CENTRIC, RAYBESTOS, or DORMAN kits. I could not find a kit for the rear that had the big rubber boot that does on the back side of the caliper. It's really just a dust shield but don't destroy it getting it off. Once you start taking the caliper apart, that paint that is on it is going to get messed up. If your going to tear it that far down, might as well have them powder coated.

Thanks again, is there some simple test I can do to verify this caliper is bad when I remove it? Is it a danger to drive in the meantime(~1 week)?

Well, I got four rebuild kits(2xfrnt, 2xrear) from der RockAuto...Getting ready to get my car out, and need to do at least the front caliper rebuild...I found the StickyIcky on the rear caliper rebuild, but didn't see one for the front...Also, after much research and checking the FSM, it seems there's some "special" , "colored" grease that according to the FSM says "...you MUST use...", and this didn't come with my cheap rebuild kits...Does anyone know wtf these greases actually are, and if I really do need them, can I just buy some, somewhere? Are the OEM kits required?

You just need some high temp brake grease. You can find it at any advancedzone or whatever.

I use the copper colored stuff for my brakes.

But does this one grease replace the two different greases used in two different areas per FSM and other instruction? What were the two colored greases exactly? As far as rebuilding the front, do you just unscrew the piston, or do you have to use compressed air? Is there any thread on the front SE caliper rebuilding? I need more direction...

The front brake piston does not screw out. Place a piece of wood or use the brake pad and place it against the far end of the caliper opposite the piston. Take the bleeder out and use air to push the piston out. Go slow, don't blast it with high pressure and don't put your hand need the piston. Watch a couple of utube videos, they will help.

The grease is brake grease. You only need a very small amount. They sell a little packet for about a buck or you can get a tube for $5-8. You'll never use all from a tube though.

If your going to paint them, make sure to clean them really good. Paint them after you do the rebuild. I painted mine before and it's really hard not to get brake fluid on them during the rebuild. I power coated the bracket, backing plate, and rotor.

Pay attention to how the metal retailing ring goes on the rubber dust shield. Getting it on right is the hardest part. Remember, it's just a dust shield. It does not keep brake fluid in. That's the job of the inner seal.

http://i1133.photobucket.com/albums/...ps45f2ae47.jpg

Thanks, KansasCityREPU. So the simple flat "seal" or "ring" or whatever goes on before the multilayer dust shield and ring? Where does the little rubber plug go? I'd love to see some pics from a good thread if anyone knows of one...Figures I would need compressed air, I took them(the calipers) off my car and back to my apt. where the parts were being delivered to...(Ain't got no compressed air here)

The "plug" is actually the bleeder screw cover. You will need a compressor. Any compressor will work. I have a cheap nail gun compressor and even it will work. Here's a cheap Harbor Fright one. 3 Gallon Air Compressor - 1/3 HP, 100 PSI, Oilless

I also want to stress how much the utube videos help. Their generic, but watch several of them before attempting this. There is a "finesse" to doing this. I fought getting the metal ring that holds the dust cover on correctly. If you decide to test your work and extend the piston, make sure to put a piece of wood or something between the piston and caliper so the piston does not extend to much and come out. If it does you'll be starting all over.

This is a picture of the factory front rebuild kit. You can get them much cheaper from RockAuto. The off brand one that I've bought do not have the bleeder screw cover. It's nice but not required.
http://atkinsrotary.com/store/images...-49-240-01.jpg

Thanks again, yeah, you're right about the bleeder caps(I opened one up). I'll have to take my calipers back to where my car is to have access to compressed air...Speaking of which. Just how much psi should be in the line that I'll be shooting in there? Can you provide any relevant video links to educate me? I still don't understand how to reassemble. ALSO, fsm calls for maybe a polishing of bore and piston with "crocus cloth" wtf is that?

The "crocus cloth" is like a polishing cloth. If you don't see any corrosion in the bore, just clean it good with brake clear. If you feel any ruff spots, maybe use some 1000 grit on the area. Don't go crazy with sanding the bore.

You will need about 10 pounds of air pressure to push the piston out.

Here is a video that shows how to rebuild a 2006 MX5 front caliper. I chose it because the caliper looks very smiler to the first gen Rx-7.

Thanks for the very relevant/informative info and link...But it(the Utoob link) makes NO mention of the giant metal "C" clip involved in my application...

You should be able to see how the C clip goes on by the process of disassembling it.

Post #2 of this Rx-7 rear caliper rebuild "How To" gives a good example of how the clip is installed. https://www.rx7club.com/1st-gen-arch...lipers-855449/

OK, I finally got one apart...Took 25psi and me covering the bleed-screw hole wif me thumb...Me crappy TINY piston finally popped out and I removed it...It don't look so good...Looks burnt or something, won't wipe/clean off...
I think I see where the "c" clip was when I ripped the old boot off...Effing amazing, the whole damn ~30 year old rubber dust boot was still perfectly intact(even after being "aggressively" removed) and exposed to the elements, rust, old crap fluid, being sedentary at least 1/2 it's life, etc...

Got back to my car today, installed the rebuilt front calipers...Tried bleeding for hours again, pumped ~32 ounces of brake fluid through the front lines....Air EVERYTIME still with the pass. side front caliper(as before), and to a lesser extent the other front caliper... WTF????

If the piston is pitted in the seal area you wont be able to sand it smooth and get it to seal. I just bought all four calipers for my car today for that reason. Rock auto sells the pistons by themselves for about $15 each if your caliper seal area(the groove in the caliper) is not rusted. Mine were borderline so I bit the bullet and shelled out $200

Well, the pistons didn't look too good, but polished up real nice with some ~10 micron alumina powder mixed with water and polished with a polyester cloth. they were nice and shiny, no pitting, no rust...Could it be the brake MC itself somehow letting air into the front lines only?

Yeah, if the master cylinder has been sitting for 13 years it would be suspect.

Guess I'll bite the bullet and head to the dealership to fight with the parts guy to order me one...If he isn't willing to, guess I'll go through MAZDATRIX as usual...Of course, I'm not at all confident the rebuild of the calipers went as it should, wish there was some way to CONFIDENTLY eliminate parts of the the system as suspect...I NEED TO GET MY GIRL OUT FOR THE SUMMER!!!

RockAuto has a decent selection of brake masters.

If you don't see brake fluid coming out of the caliper piston area, they are fine. If fluid can't get out, air can't go in.

You probably already know this but...When bleeding the brakes do you have fluid coming out of the bleeder? Also, make sure to bleed them in the right sequence. Start at the passenger rear, driver rear, passenger front, driver front. Also make sure the bleeder is closed, the "helper" is pumping the brakes about 10 times and then holding the pedal to the floor, then tighten the bleeder and start the process several time per brake.