lousy brakes

[bcarter]

Gotta get these brakes fixed.

Racing today, with the pedal so low that it goes down further than the gas pedal, going into the carousel, trying to heel-toe, brake pedal went so far down my foot slipped off while trying to get the gas, got caught in between the two, and I spun off. Guy in second got by me, then spun at the end of the straight, so I won the class anyway.

Sheer luck.

Gotta get these brakes fixed.

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[BrianB]

I wonder if there is something to the emergency brake being diconnected that would cause do much pedal travel? it seems as though you've checked everything OK! Typically,aside from air in the system, too much caliper piston retraction would cause such pedal travel. I'm wondering if the rear caliper piston is somehow free to retract with the emergency brake disconnected from the caliper?I,ve noticed more pedal travel on my RX after disconnecting one of the rear E brake connections after finding a problem with it not releasing. An adjusted Ebrake may keep the rear caliper pistons closer to the pads!?A possible check might be done by adjusting your brake bias as much to the front as possible and see if it reduces the pedal travel.
BrianB

[bcarter]

Seems unlikely to be E brake, as most of us don't run them, and the problem appeared mid-season, after running well til then.

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[GEO46]

Did it occur(sc) just after replacing rear brake pads?

[BrianB]

Try putting the car on a lift, an see where each individual brake makes rotor contact and at what pedal height. If there is no air in the system, then the pistons are retracting too far due to runout or bad seals,a rebuilt MC with a honed bore and minimal seal contact,allowing fluid bypass can cause the same problem. I'm still wondering if the rear caliper pistons which are mounted on a threaded spindle can retract further than usual with the Ebrake not holding them close to the rotors. This may not occur immediately after removing the Ebrake but may loosen up due to brake torque wanting to turn them on that threaded spindle. The MC piston retuning may pull the rear pistons back once they've loosened up.
When the pedal is low, lifting the rear caliper to see where the rear brake piston is in the bore might answer this question.
BrianB

not the e-brake, took mine out while building, brakes are hard and really good.

gotta wonder on what your prop valve situation is though, you can have trapped air with a thousand bleedings if a bubble stays in valve. try bleeding lines at prop valve.



[This message has been edited by 7'sRracing (edited September 22, 2002).]

[BrianB]

If you have replaced the brake booster, check the brake booster pushrod to master cylinder piston clearance. At 20in-Hg vacuum there shuld be .004-.012in clearance. More than this will result in excessive pedal travel From your previous posts, you mentioned having a hard pedal then loosing it after the booster was active. The Haynes manual,workshop manual tell how to do this.
BrianB

not likely, hes got a hard pedal without vacume.

[This message has been edited by 7'sRracing (edited September 23, 2002).]

[Festus E. Simkins]

Have been reading this thread with interest. A friend of mine had the problem of a soft pedal. We bled brakes, changed calipers, check MC & Brake booster. We then got down to checking every line on the car and found a extremely small leak in a brake line. This thing would not leave a puddle of fluid or give any highly visible indication of a problem. It took us about 2 hours of looking at everyline and feeling every line until we found this very small leak. we replace that section of brake line and the problem went away. I mean this was a strange problem.

Drive well.

[Festus E. Simkins]

Excuse me I forgot to tell you what we think the problem really was. It seems that the area of the brake line that was giving us a problem was acting like a 1 way valve. When you pushed on the brakes only a very small amount of fluid would escape. However, when you let off of the brake pedal it would SUCK air into the brake system and thus start giving a soft pedal. like I said a strange problem.

Drive well.

[bcarter]

OK, one at a time.

First off, the brakes worked OK'ish this weekend. I was able to brake without pumping too much, just that the pedal travel was poor, and soft, also had a lockup problem on left front. Heel-toe was exciting, and I am now a foot contortionist.

Geo46 - You know I think it was after I replaced the rear pads, but they are installed properly, I even made my own tool to screw the pistons back in, and align them for the studs on the pads.

BrianB - the rear rotors are true. The pistons rest against the pads, and the pads are right up against the rotor where they should be. I am not getting excessive retraction of the pistons.

7's Racing - Bench bled the MC, then again on the car, then just the master and the prop valve, rest isolated out, pretty sure there is no air, and have swapped in three different prop valves from parts cars. These valves "never" go, according to Mazda, and I know two dealers that have never sold a replacement.

Brian B - When I had the booster and the MC checked, the shop looked at that problem, and replaced the pin in the booster. There are various different 1st gen boosters, and various 1st gen MC's, and they don't all match up. The Booster re-build shop say they matched the booster to the MC. I gotta take their word, but this is my guess for the problem area.

7's Racing - right, I have a good pedal before I start the motor. Then it drops a LOT. When I isolated just the master, with all lines closed off, the pedal was rack hard, and above the gas pedal, with everything connected and the motor running, the pedal is way below the gas pedal.

Festus - I have had a really good look at the lines, at all the flares/joints, the lot.

Now, all that said, the season is over. We won our class, and we also got overall Track Championship. Not bad for a nearly 20 year old car, a 58 year old driver and no @#$%%^$# brakes. I'm going to do what I said before. REPLACE EVERYTHING. ( or, considering how well we did, maybe not, who needs brakes anyway, you just lose momemtum)

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[This message has been edited by bcarter (edited September 23, 2002).]

Congradulations Carter, but... you said "These valve "never" go according to Mazda"

wrong, had to change mine, it had water damage and didnt work, dont ask.....




[This message has been edited by 7'sRracing (edited September 23, 2002).]

[BrianB]

Carter,
Congradulations!
But before you buy all that new stuff, check that clearance!If the shop replaced the pin ,it's just hit or miss on the clearance without checking it to set the pin. It involves tricky measurements and math ,the shop may have(probably) got it wrong.
Good luck next year!
BrianB

[Tak]

Two more things to check are the rear axle bearings / holding flanges. If one axle shaft can move in or out, it may be pushing back a rear brake caliper. You should be able to check this by just pushing and pulling on each rear wheel when the car is in the air.
Is your brake booster vacuum source coming off of the intake manifold, or have you moved it?

Tak

[lateapex911]

On the axel issue....I think the rear caliper floats (or slides, to be exact) on a pin, following the travels of the disc as it moves in and out as the bearing wears. As I just replaced a failing bearing, that was pushing the caliper back and forth, I can tell you that I never experienced the problems that you have. (and apparantly, the results either!)

All my "weird problems usually get traced to the MC.

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Jake Gulick
ITA 57 RX-7
New England Region
[email protected]

[bcarter]

Well, first off, I haven't even been to the garage since the last race. I parked it and left. I will look at the bearings, but I don't think that is the problem.

Vacuum line is from manifold with no valve in line.

I think it has more to do with the MC and the Booster. There are various different configurations over the years, and if I replace everything, I'm likely to solve the problem. If I don't, then I know it's something else...

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta

[This message has been edited by bcarter (edited October 16, 2002).]

[moto62]

Originally posted by bcarter:
OK, I agree that it is probably the MC. I went back to the car after 24 hours, and there was NO pedal at all. Must be air. There is no loss of fluid, we bench bled the master, bled the brakes before every race, and spent half of each race keeping the pedal up. Get's confusing, all that pumping, heel-toeing, braking etc. Actually went off once with my foot caught between pedals.

No parking brake.

I have the solution. I am replacing everything !

New MC from Mazda, not rebuilt. Getting the vacuum booster rebuilt. Trying to find a new proportional valve. Then with a pressure bleeder, at HIGH psi, I will go through the whole system, going back to my old (and functioning) calipers, one by one until I can get a pedal.

Try this. After the m/c bench bleed, bolt it on, then bleed it from each of the lines that are attached to it, then go around and do the calipers. Two quarts of dot 5 brake later, the car will stop on a dime through meer thought.(slight exaggeration).
Ray. moto62


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[bcarter]

Thanks for the thought, but been there, done that. I was at the garage yesterday, no pressure at all. I think there must be an air leak somewhere. I am replacing all of the lines, new double flanges may make all the connections better,. Staying with current m/c and booster, but getting new Prop. valve from Mazda.

Off to Europe for two months, so I won't even think about this til Jan...

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G. Brooke Carter
# 10 Challenge Car
Calgary, Alberta