Yes you can get by with all sorts of things, but the cars to beat are the ones where the probability of failure has been reduced to the greatest extent possible/practical. Not much diagnosis required when that happens.Ĭontrary to what KKK123 would have us believe, the brake cylinders on race cars should be frequently inspected, and serviced as needed. I assume that's what happened on the two you mentioned seeing? According to some here, if one doesn't push the pedal down too far a bad cylinder is apparently ok? I have seen a few cars where the bore was rusty or corroded and the pedal goes down & stays there. The few of times I have seen this the seal was damaged when the pedal was depressed, so it was obvious. Inherent in that is the assumption the bore may be bad, and that the cylinder will be used in that condition. We are talking about using a bleed technique that might avoiding seal damage if the bore is defective. If you have never seen air(or fluid) leak past bleeder threads in good condition, you haven't seen everything yet. If you are saying that brake bleeders have pipe threads, that isn't so. Part of the design of a dual master cylinder is that the floating piston must have a mechanical stop. While I have not seen everything, I have never seen a master cylinder that was designed or installed in a way that would cause seal damage at any point in the pedal stroke. There are cars where strong/forceful strokes are needed to exhaust air from parts of the system. What chain of logical conclusions would lead a person to use a brake cylinder with a defective bore? If you're in NJ you can come see how firm the brake pedal is on my race car, which is still using the MC is started life with. See earlier comment regarding my qualifications. I've NEVER seen a brake bleeder (which is equipped with pipe threads) that is in good condition draw air past the threads. Going quickly can result in bottoming the piston in the MC and damaging the internal seal and also can result in some degree of aeration.ģ. When bleeding the brakes slow and steady strokes win the day. Don't go more than about 3/4 distance on the pedal travel when bleeding.Ģ. Going quickly past this possible s'step" can cause the o-ring seals on the piston to catch, flutter, and possibly be damaged. Due to normal service use the inside bore of the MC may develop a small step at the end of a typical stroke. I've bled only few brake systems in the past 30 years or so, from street cars and medium trucks to several race cars, including multi-piston caliper equipped Trans-Am cars who's per caliper price numbers in the thousands of dollars to my current Spec Miata.ġ. There is also a good chance it will leave a little air in the system. If there is any doubt it's best to rebuild the cylinder rather than trying to avoid an issue that should be fixed.ĭoing as you described will get most of the air out of most cars. A partial brake failure is not the time you want to find out the remaining half of the system has problems too. If the bore's condition cannot support that, the system's redundancy is lost. When a hydraulic failure occurs in the system the master cylinder piston(s) must travel further than normal in the bore in order to apply the remaining functional half of the system. If something in one half fails, the other half can still operate the uncompromised half of the system.
The master cylinder is actually two cylinders in one. If it is necessary to do as you described, one is actually working around a problem that needs to be corrected. No point wearing out the seals pumping all the old fluid out the system One tip: Use a syringe or turkey baster to remove all the old fluid from the master cylinder and top up with new fluid before starting. You just keep pumping up and down until you see new fluid pumping out the bleeder. Once the fluid starts to flow and fill up the drain tube (dipped in a jar), the down stroke will expel a lot more fluid than what it sucks back up when you release the pedal. I haven't tried this on a Miata yet, but I have found that on other cars I've tried (Volvo, MB, BMW, Porsche) you don't need to close the bleed screw when bleeding brakes. A piece of wood as a spacer as someone suggested might help.
When you bleed, just make sure you don't push the pedal lower than you normally would when you stop. Then have someone undo the bleeder screw at the caliper. The pedal doesn't go 'all the way' in normal stopping unless something is worn out. You open the bleeder, press the pedal, close bleeder, release pedal, then repeat.(unless you have speed bleeders"ġ. You press the pedal all the way whenever you have to stop.Īlso you don't "pump" the brakes to bleed. It's only going to go as far as you press the pedal. Where did you read this at? that makes no sense at all.
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