Black88inmd

Alright guys, got an odd brake problem with my SA going on. Searched around for a little while and didn't find anything conclusive. Maybe someone will have an idea.

Basically whats happening is after bleeding the system and adjusting the rears I'll have absolutely fantastic brake feel and stopping power for about two days worth of driving. (lets say 200ish miles) however after about the first 50-100 miles the pedal will start getting quite soft and braking power will rapidly decrease.

It seems to be that I'm losing pressure between the front brakes and rears. Guessing this simply because I can use the hand brake along with the pedal and bring my braking power back up quite a bit, to where it's safe again.

Pumping the pedal will work for awhile but will eventually become mostly useless.

A new master cylinder came with the car, put it on before it ever got driven. The rear shoes were shot so I replaced them along with the pads on the front over the weekend. The system has almost complete fresh fluid in it as I've put about a large bottle and a half through the system. Fronts I get fresh coming out when bleeding and can see it in the master cylinder.

The rear cylinders appear to be brand spanking new. Just a little blast from the air compressor and all the dust blew off them back to their semi-shiny silver casting color.

Right now I'm pretty damn confused. I would say the rear shoes need adjusting but theres no way in hell they get worn down that badly with just a few days of driving.

About the only thing that hasn't been gone over is the proportioning valve for the brakes, but I have a hard time believing thats the problem.

Any ideas so I don't waste too much time chasing this grimlin?

flat_black_rx7

well i have the same issue with my honda actually. i found that i have a slight air leak in two of the lines.

first thing i would do is take some soapy water and spray the lines by the master cylinder to check for air leaks there.
next if you have a lift/jackstands, get the car in the air and follow each line to the specified area and do the same as above.
if you dont have any leaks i would then say you have faulty wheel cylinders/calipers.

this is just from a technical stand point. may or may not work. gl

Kentetsu

The rear brakes should automatically adjust themselves, but it sounds like its not happening. Not sure if these adjust themselves while in reverse, or through the parking brake (most likely)...

Black88inmd

I know about the usual drive in reverse do parking brake pull dealio, but I swear that I read either here or in the manual that they're non-self-adjusting.

All of the lines by the master cylinder are as tight as they get so I'm quite doubtful that it's leaking there. I'll look under the car and see if I see any signs on leakage real fast since I have it in the air now. Although I haven't lost a drop of fluid since I've had it.

Black88inmd

Just grabbed the manual and flipped to the page about adjusting the rears. They of course of the procedure of jacking it up and manually adjusting them from the rear. Just a simple anchor pin with a lock nut. Anchor pin of course goes inside the drum and just has a semi-oval (best way to describe it) piece of metal which changes the position of the lower side of the brake shoe.

But I don't see any way that it can be manipulated other than that to adjust it.

All of the fittings at the wheel cylinders are nice and tight as well. Doubtful I have any leaks around them. Especially with no fluid going missing.

Like mentioned earlier, just about everything is new for the brakes besides the lines and calipers. However the calipers moved nice and freely and don't seem to be the issue. However I haven't gone as far as rebuilding them. But once again, doubtful because of the lack of a noticeable fluid leak

flat_black_rx7

i also dont lose any fluid, i just got air that gets in the lines. this puzzles me? maybe a new proportioning valve is in order? maybe thats the issues. pressure lose at the valve?

Black88inmd

Thats what I'm lead to believe. I'll have to see this weekend if the rears are really that loose. Can't really believe they're getting worn down so fast. I'll update with anything I find out if I can get around to it this weekend. This is surely a little unusual.

85rotarypower

Sounds to me like your master cylinder might be the culprit. Even non working rear brakes would not cause the problems your talking about if the front brakes are working fine. Either your master cylinder is pulling air into the system somehow, or its leaking by the seals slowly.

ukcodger

Is it the new rear shoes bedding in - is the shoe radius correct, i.e are the shoes wearing on a spot point, possibly the new leading edge?
Have you done a readjust and this is happening every 200 miles?

GB7

iTrader: (1)

had a similar problem with the 79 . no leaks in the system but kept getting air in the rear brake lines . solution new wheel cylinders [old ones honed past tolerance and although they did not leak they did not hold a tight seal as to not draw in air]
look under the dust cap on the rear wheel cylinders see if its wet . good luck

corsaconvertible

I need new anchor pins for my 1980 rear drum brakes. Several internet searches came back empty. Anyone have a source? Thanks, Tony Hansen

j9fd3s

iTrader: (3)

Mazda shows NLA, 8531-99-331A good luck!

Banzai

iTrader: (13)

Sounds like a leak in the system somewhere, probably from a seal rather than a connection. A leak can be either in the form of fluid getting out due to system pressure or air getting in making it spongy. Forget the pads / shoe wear as being the culprit. Not enough use and wear to make that kind of difference. You should manually tighten up you rears before driving. Lift the rear, spin the wheels and adjust untill they just begin to drag. Ea side.

Also, just because a new part was installed does not mean it can be ellimated from the list of possibile problems. Almost everyone has a story about that new part that was not right.

So you've looked at all four corners in detail right? (thats means wheels and drums off, calipers removed from the disks) looking for signs of leaks or wet spots at the connections and seals. Ditto the Mstr Cly? One place often overlooked is the interior footwell. You can get a leak where the pedal arm depresses the piston in the Master and the fliud will run down under the carpet. If you don't lose fluid it must be air. When you bleed it again do you have air? If so, there you go. New or not, I'd suspect the master first.

t_g_farrell

iTrader: (1)

You can check with mazda but I found mine by acquiring a rear axle assembly.

t_g_farrell

iTrader: (1)

First, off lets clear up something on SA rear brakes, they don't auto adjust, ever.
You have to manually adjust them using the two adjusters on the bottom of the
rear brake backing plate. It makes a huge difference to the overall braking feel
if they are not adjusted regularly, like every few months.

Second, your problem is an air leak, not a fluid leak I'm pretty sure. I would suspect
the rear wheel cylinders first, since they are so cheap and available. Pulling the
ebrake just means that manually applying the rear brakes helps, its also a hint that
the problem may be in the rear if using it helps restore the brake feel back to what
it was. Air leaks tend to happen at single seal interfaces in the system when it
experiences vacuum. The other thing to check is the front calipers but I'd do the
wheel cylinders first and see how it goes. Just cause they shine up doesn't mean
they are good.

corsaconvertible

rear brake anchor pins, there are some available at this link:
Mazda RX-7 Parts, Mazda Parts for RX7 rotary

Tony Hansen

Smokeyfb33

iTrader: (8)

I just found black dragon auto's rebuild kits for BMCs. 10 bucks a pop, both models are the same price, drum rear and disc rear.

Kit is a huge improvement IMO. Aluminum pieces instead of oem steel. New seals!

May not be your problem, but I thought I'd share my new discovery.

gerald m

Seems to me from the pics i've seen the actuator rod for the master pushes on quite an angle it might be pushing the piston over to one side enough to cause a problem , The residual valve in the master is suppose to keep just a tad of pressure in the rear system but I don't see how it would let air inside .

If the new master sat for a long time dry it could also cause the piston rubbers to get slack and possibly leak by from front to rear . sometimes new stuff is not so great . ( Just got a new starter couple days ago and the solenoid was wired up backwards ) so just because its new it doesn't mean its OK. Good Luck

7aull

iTrader: (2)

2 yrs of untraceable soft pedal on a new none-OE Master and I finally gave up and had my mechanic have a look. He went thru the whole system & $132 later (labor) he could only fault the Master, by elimination....

FWIW-

Stu Aull
80GS
Alaska

zaridar

iTrader: (3)

So was it replaced? And did it solve the problem?

midnight mechanic

in a vacant lot, try driving and slamming on your brakes. it will point you in the right direction on whether it is the front or the rears that are the [problem.

I would suggest checking the adjustment on the brake rod (between the master cylinder and the pedal) but you say the brakes were fine for the 1st two days.

So something "changed". at this point I would jack up the car again (ya, I know it is a bitch! ), remove the drums, and visually check the rear brakes.

Also, I had a similar experience of the brake pedal being "hard". Turns out it was the vacuum brake assist. I.e. vacuum leak which was traced with a vacuum pump, and fixed with a hose clamp.

When you solve the problem, please tell us what the fix was!!

7aull

iTrader: (2)

nope - not replaced yet. Will post here if/when...

Stu Aull
80GS
Alaska

PreviouslyPlastic

iTrader: (1)

Thought I'd share my experiences with my brake issues here.

When I first bought the car it had a chronic spongy pedal; if the system was fully bled (both fronts and rear line) the pedal would return, but only be "good" for 2 days and would be totally unsafe within a week.

I replaced the rubber hoses with steel braided ones from re-speed but in the process I broke one of the brake hard lines in the rear and had to remake it. The brakes did not improve after this, but the rubber hoses looked due for replacement anyway.

I then discovered that one of the front calipers was starting to leak; I rebuilt both fronts hoping I had solved my issues once and for all. I didn't. The brakes were still bad, but now I could recover "good" brakes by just bleeding the rear line.

I returned to the brake line I had made when installing the braided hoses and thought I may have mucked up the flares; I re-made the line paying close attention to the flares. The problem was still present after fixing this.

I read about the residual valve in the MC and decided to check it out. Upon disassembly I discovered that the rubber diaphragm was torn. I tried to source a new diaphragm, but had to replace the entire MC instead. Guess what, the problem was still there.

I knew the previous owner had replaced the wheel cylinders already, but out of desperation I decided to replace mine (only the passenger side one). So far, the brakes have been holding, it's only been 12 hours though. I will post back with confirmation that I got it.

The reason I only replaced one of the cylinders is that during bleeding air always exists the system before fluid, so I figured the leak was close to the bleeder.

My theory right now is that the wheel cylinder may have been rebuilt one too many times and the cups now sat slightly loose in the bore. Not loose enough to leak any fluid but loose enough that when there wasn't adequate pressure they would seep air into my system.

Almost 1 year and easily 5L of brake fluid later, I think (hope) I'm done with brakes on this puppy.

Kam