RE Matsuda

Alright I've been having this problem ever since I bought my RX-2, when my car is turned off the brake pedal feels fine, but as soon as I turn the car on, the pedal will go all the way to the floor without any effort at all. The brakes still work fine, its just I don't get any feedback from the pedal so I have to be really careful about how I press the pedal because its just as easy to get on the brakes lightly as it is to lock them up. I've bled the brakes but that doesn't seem to help.

Would a leak somewhere cause this? I would think a leak would make the brakes harder to press down because the booster wouldn't be getting as much vacuum. Is it possible to have over-boosted brakes? I was wondering maybe the booster is getting too much vacuum so it makes braking effort too easy. Is the line going to the manifold supposed to be all metal? Because I can see two breaks in the metal line that appear to have been replaced by regular rubber hose by the previous owner, possibly in the process of swapping the 13B. I was thinking that maybe if these lines are not the correct size or if the rubber sections aren't supposed to be there then the booster could be getting too much vacuum, if thats possible.

I searched a bunch of the 1st gen threads and they were talking about a check valve, I don't see one on mine unless its right up against the manifold, I would assume the older rotary cars should have a valve as well, but I'm not sure.

Any insight would be much appreciated.

Darth Linux

I've got a very similar problem on my 73 RX-2. To answer your questions:

the check valve is screwed into the manifold, right where the tube is connected to it with rubber hose.

there should be two rubber sections - one at either end.

A leak on the engine side of the booster (i.e. in the hose/pipe) would cause the engine to idle roughly all the time. A leak inside the booster itself would cause the engine to idle roughly only when you apply the brakes.

if you've got the stock manifold on the engine then you already have a check valve. If you don't, then you might not - you can get one at NAPA for about $13 - just ask to see their book and pick out the white nylon with the 1/2 inch inlet/outlets.

Anyhow I've got all the same symptoms and tried everything, including 3 new MCs and nothing helps. The brakes require a very delicate foot otherwise the pedal goes right to the floor. . . . let me know if you get any advice that helps out.

328tr6

Yeah its a 4-port 13B with the stock manifold and Hitachi carb, I don't know if it would make a difference because its not a 12A, but I'm assuming it doesn't since you are having the same problems with a 12A. The next thing I can think of doing that would be to replace the lines with ones that I know can handle vacuum. The hose closest to the booster looks like it was replace and the rubber appears to be too thin and the inside diameter too big. But again I'm not sure if this slight difference could make the brakes so bad.

At least the brakes work and its still pretty driveable, its just annoying when your coming to a stop and you try to set your foot down lightly on the brake pedal but you let it go down a little too far and its just like slamming on the brakes. Its especially annoying if someone's riding along with you and it happens and there like "what the hell was that for?"

I'm thinking about just trying it out with the line plugged up, no booster assist, and see how that is. One of my shop manuals says that smaller cars, especially ones, with drum brakes, don't really need power brakes. My leg would probably get worn out if I did a lot of stop and go stuff, but I think I could live with it. I'd rather have no power and some kind of feedback from the pedal because right now there is literally none.

328tr6

Wow thats crazy, the forum did that random name thing again, the above post was made by me.

Edit: Man, I didn't think it would do it again, but it did, these two posts are actually by RE Matsuda. Maybe I should try logging out than back in....

now

iTrader: (1)

I would have to say there is a problem with the booster itself.
spring inside broke may be?

matt

RE Matsuda

But wouldn't something broken inside make pedal effort harder? Unless the spring is allowing too much air into the booster. It's almost as if the booster is working too well, its assisting the braking effort to the point that the vacuum is literally doing all the work, so the pedal just goes straight to the floor without any resistance.

now

iTrader: (1)

I am not sure but the problem you describe can only be in
one place the booster.

matt

Darth Linux

I guess a good test, for both of us, would be to disconnect the vacuum line to the booster, plug it, and then do some do some driving and see if the brakes approach normalcy albiet with increased effort required.

GrimRPR13

As Darth suggested, it's probably the check valve, but in early RX-2's the check valve was actually in the hose close to the booster. Sometimes folks change hoses without taking the little check valve out of the stock hose. Or, the hose gets put on backwards. An easy test is take off the hose and blow on either end. You'll know right away if you have a check valve in there or not. I've seen this on many RX-2. If you do, then it's on wrong, Good luck.

-Bern

now

iTrader: (1)

the check valve is only to hold vacuum in the booster
when the motor is not making vacuum, like under full
throttle, the only thing that would happen if there
was a problem with the check valve is the booster would
either not work (plugged) or no assist when brake is
applied under full throttle.

matt

Bern

You're right... and what happens when the booster get no vacum at all, like when the valve is either clogged or in backwards, the pedal tends to creep almost all the way down to the floor. It's really wierd, but I've seen it on more than one occasion. The old boosters and assocaited equipment just don't work like they used to Good luck with the fix and please let us know how it works out.

-Berny

RE Matsuda

Well I flipped the check valve around, it wasn't right on the manifold but rather between two hoses coming right off the manifold (unless there is another one). The brake pedal pressure came back, but now I don't think I have any vacuum assist at all. It doesn't feel bad though.

Bern

Actually, I think if your feeling the brake pedal pressure come back, it's the vacuum assist working now. I'm not sure as to your experience with these older cars, but their braking systems are of rather low quality and feel, "compared" to modern systems. How's the rest of yoru system, brake MC, hoses, etc?

-Bern

RE Matsuda

Yeah you're probably right. I drove it around quite a bit today, I just needed to get used to the feel of it but now I can say its definitely an improvement. I've replaced the rear brake shoes and wheel cylinders (I have new front pads, just haven't put them in yet), the booster hoses were replaced not too long ago, so I'm pretty sure some of the feeling is from the old booster, MC and brake lines as you said. Anyone know if there are MC rebuild kits available anymore? I might just get a new 1st gen one from Mazdatrix when/if I do the SE brake conversion.

Thanks for your help guys

Darth Linux

I'm gonna flip my check valve around and see if it makes a difference . . . i'll let you all know.

Darth Linux

well, I turned the valve around and now I have no power brakes at all. The pedal is really hard - almost have to stand on the pedal to make it stop. I'm gonna switch it back - I think my booster has a problem or something, cuz it's either too much boost or none, and neither of those options feel safe . . .

RE Matsuda

My brakes felt really hard when I first flipped it, I was about to switch it back too. The more I drove it the easier it go to stop, I don't if it was just me getting used to it or if the booster was working differently. I've driven it around for over a week now and the brakes feel much better. I don't know if this would be the case with your car too, but I'd say at least try to get used to if and if definitely isn't getting any better than switch it back.

Bern

Darth:
It seems as if your valve was in right before. Your original symptoms seems to indicate some thing beyond the booster vacuum "valve" issue. If you've put in 3 "NEW" MCs then your booster itself might be the issue. It might have an internal issue. Also, I'm assuming that the following have all been done:

-MC and Brakes beld properly
-Brake Pads/shoes not glazed
-brake cylinders and lines not leaking

Bern