Bleeding Brake Problem

[Ashman]

So i bled the system again today using the vacuum bleeder while having someone standing by the reservoir to make sure it doesn't empty. The same thing happened...

So off i went to Mazda to ask one of their tech's. I was told to remove one line from the master cylinder, block the hole and then try and bleed those 2 calipers, then the other 2. That may tell me which line is drawing in air and obviously which one needs looking at. So i'll hopefully give that a go tomorrow with the blockers that he gave me. It's funny, they immediately asked me about the RX8 as soon as i walked in, i think they knew...

[Liam22]

Have you bled it with car running? Opens up the valves in ABS unit. Saved me once.

Pete, the wedge pedal down method has also worked for me. Most noticbly on Lotus Elise which is notorious for leaving air in the link pipe between front 2 pot calipers.

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[warpc0il]

When you're keeping the system topped-up, are you using totally new fluid or fluid that has already been pumped through the system and collected in the jar?

When replacing pipes, such that the fluid comes out looking clean, it's very tempting to recycle rather than splash-out for new, but that's a big no-no.

Even if it's chemically clean, the action of being pumped through an unbled system will have introduced air in suspension within the fluid, such that you will never get a firm pedal.

If you must recycle then the fluid must be left standing in a closed container quietly on the shelf for a few days before reuse. It may not look any different afterwards but it is.

Even new fresh fluid will become contaminated with air if you shake the bottle, and before you say "I'd never do that", we've all done that rattle-action with a part-filled bottle to judge how much is left, and that's sufficient to cause the problem.

When we ran the Motorcycle Maintenance Workshop we kept stocks of brake fluid in a cupboard. Even if someone brought down their own to use, we would swap what they'd just carried on the back of a bike for stock that had been sitting on the shelf, as it made that much difference.

If you've only been using fresh, unshaken, fluid for topping-up then all this won't have helped you, though helpfully it might help someone else who's reading this from getting caught next time.

The problem with remote problem diagnosis is that you only have what someone is telling you to work with. There's nothing like being there and watching to be able to say "That's what you're doing wrong..."

[Ashman]

Yeah someone here with more knowledge than me would probably point out the problem pretty quick.

Using new fluid only but I am keeping the fluid that's going through now as it's all new fluid coming out. Only new fluid going in.

I have also bled the system with the engine running multiple times.

[boosted]

Ive only ever lost 1 master cylinder bleeding brakes and that was yonks ago...but i never go fully down, ive trained my wife to go about 2/3..personally i open nipple with the downstroke and when my wife say down i close nipple and then tell her togo up..
Has the technique youve used damaged 2 master cylinders? Or is the 2nd hand spare no good...? Id be inclined if me to buy anew Master cylinder and start over...and bleed only going 80% down...
Using a used master cylinder and bleeding pedal all the way down pushing seal onto unused part of cylinder bore possibly damaging seal..
Prob not what you want to hear but does sound like 2nd master cylinder is dead to me.


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[warpc0il]

How many times have we seen people post "It can't be x because I just changed that..."

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[boosted]

Yep...i did it myself with an rx8 maf...ebay good used maf fully working order...nope same code "cant be the maf then" .....
Yes it was ! 2 garage shelf trophies lol.

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[Ashman]

It's highly possible the master cylinder has had it but until i eliminate everything else i can't just decide it's one thing i changed that's causing it. I've already fitted a known working master cylinder so the chances of it going again are probably quite slim. I'll therefore try what i've been told by Mazda and see what happens. If i can't find the problem then i can always come back to the master cylinder and logically assume that the replacement is faulty and fit a new one. I'd prefer to just buy a rebuild kit considering i have 2 master cylinders now but i can't find one anywhere online, i wonder if Mazda can get hold of a kit...

[Ashman]

Also i want to say thanks for everyone's input, your knowledge has been invaluable!

[boosted]

Whats the history with the car? Brake pedal firm before overhaul? Soz if another post elsewhere..abs light not on etc?

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[bigpete8]

It's highly possible the master cylinder has had it but until i eliminate everything else i can't just decide it's one thing i changed that's causing it. I've already fitted a known working master cylinder so the chances of it going again are probably quite slim. I'll therefore try what i've been told by Mazda and see what happens. If i can't find the problem then i can always come back to the master cylinder and logically assume that the replacement is faulty and fit a new one. I'd prefer to just buy a rebuild kit considering i have 2 master cylinders now but i can't find one anywhere online, i wonder if Mazda can get hold of a kit...

Quick google came back with:
https://www.autodoc.co.uk/car-parts/rep ... /rx-8-se17

(No recommendation from myself as never heard of them)

[boosted]

And Biggred brake company for parts....

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[Ashman]

It's highly possible the master cylinder has had it but until i eliminate everything else i can't just decide it's one thing i changed that's causing it. I've already fitted a known working master cylinder so the chances of it going again are probably quite slim. I'll therefore try what i've been told by Mazda and see what happens. If i can't find the problem then i can always come back to the master cylinder and logically assume that the replacement is faulty and fit a new one. I'd prefer to just buy a rebuild kit considering i have 2 master cylinders now but i can't find one anywhere online, i wonder if Mazda can get hold of a kit...

Quick google came back with:
https://www.autodoc.co.uk/car-parts/rep ... /rx-8-se17

(No recommendation from myself as never heard of them)

I saw those but they're out of stock, have been for weeks. I did ask them to notify me when they're back in stock but nothing so far.

[Ashman]

And Biggred brake company for parts....

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I couldn't find a master cylinder kit on there, i looked for entry level too as well as using my reg number as the reservoirs are the same(?).

Still i've never heard of them so bookmarked

[Ashman]

So today i removed one pipe from the reservoir, blocked it off and then tried bleeding the 2 calipers that run off that line and the pedal is the same. So i swapped lines and did the other 2 and it was identical. So i thought i'd eliminate the braided lines i fitted by swapping them back to the rubber lines and bled the system again and was the same.

It's looking like master cylinder again so it'll probably need a rebuild or a completely new one. I'll see where my finances stand at the end of the month and maybe order a new one, at least it's done then.

If anyone wants to take a look you are more than welcome, there may even be an alcoholic beverage waiting for anyone who can make it stiff, hard and usable... (this is my polite way of asking for help lol)

[boosted]

Give Clive a ring at Mazda Rotary Parts...if there available he will know. He gets oem parts and access to mazda parts database..if theres a rebuild kit out there he will know.

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[boosted]

Im on Tapatalk mate whats your location...

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[boosted]

Milton Keynes...im in Gran Caneria at mo..anyone local take alook...?

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[ChrisHolmes]

It's highly possible the master cylinder has had it but until i eliminate everything else i can't just decide it's one thing i changed that's causing it. I've already fitted a known working master cylinder so the chances of it going again are probably quite slim. I'll therefore try what i've been told by Mazda and see what happens. If i can't find the problem then i can always come back to the master cylinder and logically assume that the replacement is faulty and fit a new one. I'd prefer to just buy a rebuild kit considering i have 2 master cylinders now but i can't find one anywhere online, i wonder if Mazda can get hold of a kit...

Quick google came back with:
https://www.autodoc.co.uk/car-parts/rep ... /rx-8-se17

(No recommendation from myself as never heard of them)

Of topic but.....£50 for a brand new TRW / Sumitomo front brake caliper!!!!

[Ashman]

Whats the history with the car? Brake pedal firm before overhaul? Soz if another post elsewhere..abs light not on etc?

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Sorry mate i didn't see this comment earlier. The car was sitting on the forecourt at Mazda in MK for around 18 months, it was a trade-in so i'm assuming it was in use before that but it did have issues. When i bought it the brakes were completely shot, the calipers needed slider pins, new bleed screws, discs, pads and i bought braided lines too. The brakes did work before i replaced them, they were just really bad given that they were completely rusted and worn. All i did was remove the brake lines and replace with braided lines, clean and paint the calipers and fit new sliders and bleed screws and refitted with new discs and pads. Then we bled the system and since then the pedal has gone straight to the floor as though there is no pressure built up. I've put 3 liters of fluid through the system and it's come right back out the other side with absolutely no pedal pressure at all. I've replaced the master cylinder, ok it was a secondhand one but the chances of 2 going pop are slim. I've tried blocking off one line from the master cylinder and bleeding those calipers and then vice versa and it's all the same. I've even put some plumbers tape on the bleed screws to minimize the risk of air being sucked back through the threads. It's as though i am doing something wrong but i have no idea what it is...

Sorry for the wall of text, it just kinda flowed from my frustration

[ChrisHolmes]

A wild suggestion! Blank off all the outlets from the MC and if the pedal goes to the floor then you know the fluid is going past the seals. Could be stupid suggestion!

[Ashman]

Give Clive a ring at Mazda Rotary Parts...if there available he will know. He gets oem parts and access to mazda parts database..if theres a rebuild kit out there he will know.

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I will shoot him a message, thanks man

A wild suggestion! Blank off all the outlets from the MC and if the pedal goes to the floor then you know the fluid is going past the seals. Could be stupid suggestion!

Not a stupid suggestion at all mate, though i'm not sure if forcing the fluid to go through the seals would be a good idea if they're as fragile as i think they are. It's a shame i have no way of pressure testing the master cylinder with a gauge so i can see if the pressure is falling or not, though again i would have no idea how much pressure is too much.

[ChrisHolmes]

That’s the point, the pedal should be rock hard, if you can get movement then fluid is passing the seals and that’s the problem identified, bad sealing in the MC

[Ashman]

It's definitely worth a try.

[warpc0il]

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