Post Brake Bleed Problems....
 

Firstly, I have spent all day on the forums searching, no joy.

I have just replaced the pads and rotors on my 8. Apart from a seized lower front caliper slider, it all went without a hitch.

Today, I bleed the brake system.

I started with the Master Cylinder, then the rear left (being furthest away from the the master cylinder on my right hand drive RX8), then rear right, then front left, then front right, then the master cylinder again. I did the whole procedure 3 times in total, just to be sure. No air bubbles, nice clean fluid coming out. Reservoir was kept topped up at all times.

The brake pedal was nice and firm by the end of it, not squishy.

I took it for a test drive, and immediately, the pedal was like mush, really had to push it a long way before the brakes took effect... checked, no leaks in the lines, or from the bleed valves, no drop in reservoir level.

Now I know the pads and rotors are new, so they won't be very grippy at all until I bed them in, but I am concerned about the lack of pressure in the pedal.

Have I forgotten something? Any ideas.

Cheers

when you go for the test drive the vacuum boost puts extra pressure on the fluid . It is possible you do have air in the system and didn't feel it till the test drive .

Understood.

However, I am wondering how there could still be air in there, after I pumped nearly 700ml of brake fluid through the bleeds, and it was all clean and clear of bubbles?

I am going to take the 8 for a bedding in up SH1 late next Sunday night, will see if that improves anything. Problem with this epic job I am on, I ain't got time to bleed....

Did you bleed the cylinder at the very end? My friend and I did this and it fixed all our problems.

Do you mean 'did I bleed the master cylinder' after bleeding all the calipers? Yes...

It is fairly typical to have to go back and bleed a 2nd time after driving it around some. The air gets trapped in both ends of each line, and in little bubbles in the joints, etc...

Re-bleed everything again, you will find the air that was still trapped in there. A 3rd time isn't always needed, but isn't uncommon.

WCS and I installed speed bleeders last week and changed the fluid to synthetic DOT 4 by flushing the system out through the bleeders. We used two full bottles.
On the test drive the brake pedal exhibited long travel and a whooshing or gurgling sound. We bled the master cylinder and the brake pedal firmed right up.

Lesson: Even though we used speed bleeders and carefully watched the fluid level during bleeding we still managed to introduce air into the MC... No problem though. Easy fix.

This is true. My friend and I redid almost every caliper by the time we were finished.

Ok, after a bit if further reading, everything points to some air still trapped in the MC.
At the moment when I bleed it, it's all fluid. Do I continue to bleed it, in the hope that more air will come out?

/\ try pumping the pedal then leaving pressure on it while you loosen off the bleed screws . Making sure you tighten the screw before letting up the pedal .

As I wrote in post 7 of this thread, the air bubble I had in the master cylinder made a whooshing or gurgling sound. A quick bleed of the MC bleeder cleared it up quickly and the pedal firmed up. We only bled through two cycles of the brake pedal (pressure, open bleed, depress pedal, close bleed during end of stroke, tighten bleed, release pedal) * 2 to clear the MC

You have to bleed it till the brake pedal firms up so if bleeding the master does not work then you will have to start over at the passenger left calliper and repeat the process till the air is bled out.
IIRC our 12" bleed tube held roughly two pedal depressions worth of fluid so you need a lot of pumping to clear each brake line.
Still recommending speed bleeders.

Ok, interested by your comment, pressure, open bleed, then depress pedal, close bleed. I have been getting my helper to pump the pedal a few times, then hold it all the way in, then open the bleed valve, close bleed valve, release pedal. Is that the wrong procedure?

Generally the goal is to make sure that the valve is closed before lifting(thus preventing air sucking back inward when pedal lifts). So correct procedure would be as you said.

1.) Pressure on pedal
2.) Open Valve (pedal should push further in all the way to the floor)
3.) Continue pressing pedal and stay at bottom
4.) Close Valve
5.) Release pedal and repeat process.

Yeah , you are doing it right . Sometimes you get air sucked into the sytem if pedal is released too quickly and level in master cyl is down a bit . Maybe that happened :dunno:

Brettus described it well. I tried to relate the process in detail.

What you are trying to accomplish is the action of a one-way-valve. The amount of fluid to bleed is relative to the length of the brake line.
Pressure on the brake pedal creates a positive pressure in the fluid next to the bleeder.
When you open the bleeder the brake pedal is now able to push fluid out of the bleeder and also prevent air from getting in.
The bleeder must be closed before the end of the brake pedal travel. Your helper must tell you when the pedal is nearing the floor.
Closing the bleeder stops the pedal. Releasing the pedal re-fills the master cylinder with fluid from the reservoir and the cycle renews.
Re fill the reservoir as required; Before it reaches the low mark.
Repeat several times before moving to the next calliper.

Edit: A little safer method is suggested above compared to some others in this thread.

Side bar: I see no point pumping the pedal prior to bleeding... it may be counter productive because it seems to firm up the pedal so where does the trapped air go? Also one could easily introduce air if the timing of the actions were off at all. : end side bar

Speed bleeders have a one-way-valve in them so you do not have to tighten and loosen the bleeder each time. This is the process for speed bleeders.
Open the speed bleeder 1/4 turn. Pump the brake pedal some number of times while periodically refilling the reservoir. Tighten speed bleeder. Move to next calliper.

I used speed bleeders and still got air in my MC...?? Probably low fluid in the reservoir? Bleeding the MC with the standard method cleared the problem.

Ok, understood. Will have another crack this weekend. Thanks.

As a side note, you never want to go all the way to the floor when bleeding brakes as this is an excellent way to tear the seals inside the master cylinder. Only go a little bit past the point you would reach if you were to simulate a panic stop in regular driving.

When you're bleeding the brakes, do exactly as you were before but only open and close the bleed screw for a tiny amount of time. If the helper reaches the bottom of the pedal stroke and stops before you close the bleed screw again, it's very likely that air will get introduced to the system through where the bleeder screw is actually threaded into the caliper. Close off the bleeder screw while there's still fluid flowing out of the caliper.

Also, I accidentally sucked air into my master cylinder one time when bleeding my brakes at a track in the middle of nowhere at like midnight while I may or may not have been drinking... long story short, had the same garbage pedal feel you have, and it took me almost 2 liters of brake fluid, and about 4 complete brake bleeds over the course of a month to get the god damn air out. Just keep at it buddy.

A little update. Started bleeding the master cylinder today, 600ml of brake fluid bled, still have air bubbles. Got to go to Repco in the morning and pick up more brake fluid, so I can keep going.

In hindsight, I am pretty sure I let the fluid reservoir get way too low when I removed the calipers, so that introduced air into the MC.

Also need to get a new bleed valve for the front right brake, as the hex is pretty rounded :-(

Will update with the outcome soon... sigh.

Don't keep buying more brake fluid. the stuff you're pumping out at this point is brand new. Just start pouring it back into the master cylinder.

Ah ok, I wasn't to keen on doing that incase it was getting contaminates from the drain jar and the clear pipe I was using. I suppose if I check its super clean, then it should be ok.

Get some speed bleeders while you are at the store. You will wonder why you ever did a brake job without them.

The longer the brake fluid is out in open air the more moisture it absorbs and the worse it will perform.

Get the air out by recycling fluid and then do a fluid change at the end maybe?

Another bleed last weekend, brakes getting better, but still not there yet....going to do it all again next weekend....

holy guacamole !

Finally.

One last bleed today, and I now have the Brakes of Zeus!! This time I bleed the brakes with the engine running as suggested, and indeed some air just shot out, all good.

One thing I did notice (or not notice as it seems), is the fluid reservoir is divided internally into sections, so if you inspect the level from the front, it looks as though its half full...however, from the side, one of the compartments was totally empty...luckily I caught it...

Also noticed a small (very small) fluid leak around the line coming from the MC. Tightened the nut, still tiny amount of fluid coming out...anyone else had this?