SMSP spongy brake pedal

[cookies]

Hi guys

So I was at South circuit yesterday and whilst lining up for my 4th session I noticed the pedal was very spongy. Could easily push it to what felt like the bump stop.

Quick bit of background. Car is an 04 SE with 220rwhp, 225 section rs3 tyres and MCA reds.

I had the same problem at wakefield last year. At the time the car had factory pads and fluid. Very unnerving when you go for the brakes, and all you can get is a gentle slowdown from about 170! As a result of this I went for hawk hp plus pads in the front and flushed the fluid with I think penrite RBF ( was recommended my mania ). The old fluid came out with quite a black tinge to it so definitely needed doing.

Yesterday was first time on the track with the new pads and fluid. Felt great in the first couple of runs, however as I gained confidence and braked later and harder it started to feel a little soft. I thought they were just getting a bit warm after some hard driving. Lining up for session 4 the brake pedal felt like it had at wakefield so I called it a day. Not worth the risk as far as I'm concerned.

On the way home I attempted to activate ABS a couple of times but it felt like I was pushing against a bump stop and i was only getting a gentle braking.

One of the other guys there said it was possibly air in the lines. Makes sense to me given the feeling I am getting.
The question is, how does this happen? I can't see anything leaking under the car and the brakes were great at the start of the day.

Is there any recommendations on the absolute best fluid to use? RBF600 came up in a search I did.

Cheers guys

[CeramicND]

Maybe it's not the quality of the fluid, rather heat build up and the lack of ventilation? I also notice that after a few rounds my pedal gets a touch softer (nothing dramatic though). When I am due for new discs I will be repacing the rotors with 2-piece directional rotors. I am also weighing up the advantages and disadvantages of removing the dust shields. Finally, it would be nice to have some brake cooling ducts to keep everything as cool as possible.

I believe that irrespective of whether you are using $25 a litre or $200 a litre brake fluid, if you are cooking the fluid that quickly other aspects need to be considered.


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[rascal]

The causes of a spongy pedal is pretty much only air in lines, pads, fluid, or possibly if these are covered then factory rubber brake lines expanding.

Since fluid was done recently, and assume properly then I'd suggest that its the HP+ that is causing the problem. They are really only a lower spec track pad and once you get some pace up, which 220whp and tyres and suspension to suit would deliver, they will begin to show their shortcomings. (ie inability to handle the extra heat)

Flush the fluid with any reputable hi temp brake fluid just to be sure its not that, ensuring no air in the system, and fit some higher spec brake pads (Hawk Blue, Carbotech XP range, a heap of other choices) and you should remove the sponginess.

[MattR]

My money would be air in the lines. If you are looking at doing more track work it may also be worth replacing the rubber flexible lines with braided lines in the near future.

What bleeding method did you use when the fluid replaced, and how much fluid did you flush through the system? You may have introduced some air through the bleed nipples or through the master cylinder if using the traditional pump and crack the bleed nipple. This can happen if the brake pedal is pushed too fast or too far.

When I do a brake fluid flush and bleed using the old push the pedal method I usually use nearly a full bottle of fluid to make sure I have all the fluid out and use a reasonable long piece of plastic hose over the bleed nipple to try to ensure I have all the air out of the system.

Give the brakes another bleed, starting at the furthest caliper away from the master cylinder working back to the closest, so LR, RR, LF and finally RF. If you have the time gravity bleed the lines, Tbro did a great write up in the technical section, this will make sure you get all the air out.

The fluid and pads you have been recommended and are using should be more than up to the task of a few track sprint sessions.

[Magpie]

Brake fluid is hydrosopic, that is it absorbs water. Water has a lower boiling point than the brake fluid. Hence if the fluid gets hot enough and has water in it you will get air in the lines. The question is it old fluid or a cooling issue. Are you doing cool down laps and not using the brakes? Consider temperature strips on the calipers to see what the temps are, this also helps with pad selection.

As suggested, another way air gets in the lines is incorrect bleeding or bleed points not tight enough. Therefore, all new fluid and bleed throughly. I use a vacumn bleeder, including full fluid replacement in about 20 mins.

[cookies]

Thanks for all the help guys. I'll have a read through that gravity bleed article. I did use the pedal method to bleed. Used a whole bottle to flush through. I didn't know that your could do it too fast and that would introduce air.
I use a bit of hose about a foot long to bleed.

I don't have any spare fluid at the moment but I bled a little out of each caliper today which didnt make a difference.

I'm thinking I'll take it to mania. Probably the safest bet to get it done correctly until I figure out a setup to do it correct at home.

Thanks again

[NitroDann]

I always just put workshop air pressure into the master. Use different coloured fluids each change to see the new fluid flush through.

Dann

[Magpie]

http://www.bimmerfest.com/forums/showthread.php?t=392957if you want to use Dann's method.

[pepejesus]

Thanks for all the help guys. I'll have a read through that gravity bleed article. I did use the pedal method to bleed. Used a whole bottle to flush through. I didn't know that your could do it too fast and that would introduce air.

Did you cycle the ABS pump when you were bleeding? I pedal bleed my brakes (one person pumps the pedal, other person opens the bleed nipple), and I could not get a good firm pedal until I also cycled the ABS pump a few times and bled after each.

I used a paper clip to jumper the ABS and GND pins - check this out: http://www.mazda-speed.com/forum2/index.php?PHPSESSID=vg7tdmtja1brfr1ardu1c070m3&topic=26846.0.

My method was this:

1. Bleed one corner the normal way, until you see no bubbles etc.
2. Jumper the ABS and get the pump to cycle
3. Bleed once again
4. Jumper the ABS and get the pump to cycle
5. Bleed once again
6. Move to next corner

Probably overkill to cycle the pump twice each corner but I was frustrated with the soft pedal after bleeding all corners at least twice, and this ended up working for me.

Good luck.

[cookies]

Hadn't heard of cycling the abs pump. Going to get more fluid so I might try that today.

Cheers

[MX593]

I ripped up a set of well known Australian made QFM sold as street/track brake pads in one track day. Good for the street, but no good for the track. Had the spongy pedal going to the floor as the warning. No air in the system, braded brake lines and Penrite racing fluid. Swapped to Carbotech pads and have done 2 full seasons of club and supersprint rounds and heaps of mountain touring with no problems. Still have plenty of pad left too.

[Magpie]

Stoptech article...

BRAKE FADE
Repeated heavy use of the brakes may lead to "brake fade". There are two distinct varieties of brake fade:
1) Pad fade: When the temperature at the interface between the pad and the disc exceeds the thermal capacity of the pad, the pad loses friction capability due partly to out gassing of the binding agents in the pad compound. Pad fade is also due to one of the mechanism of energy conversion that takes place in the pad. In most cases it involves the instantaneous solidification of the pad and disc materials together - followed immediately by the breaking of bonds that releases energy in the form of heat. This cycle has a relatively wide operating temperature range. If the operating temperature exceeds this range, the mechanism begins to fail. The brake pedal remains firm and solid but the car won't stop. The first indication is a distinctive and unpleasant smell that should serve as a warning to back off.

2) Fluid boiling: When the fluid boils in the calipers, gas bubbles are formed. Since gasses are compressible, the brake pedal becomes soft and "mushy" and pedal travel increases. You can probably still stop the car by pumping the pedal but efficient modulation is gone. This is a gradual process with lots of warning.

In either case temporary relief can be achieved by heeding the warning signs and letting things cool down by not using the brakes so hard. In fact, a desirable feature of a good pad material formula is fast fade recovery. Overheated fluid should be replaced at the first opportunity. Pads that have faded severely should be checked to make sure that they have not glazed and the discs should be checked for material transfer. The easy permanent cures, in order of cost, are to upgrade the brake fluid, to upgrade the pads, or to increase airflow to the system (including the calipers). In marginal cases one of these or some combination is often all that is required.

There is also a third type of fade and this is pad knock back. Symptoms are foot to the floor nothing, next pump brakes are back to normal. This is more prone to happen on fully floating rotors as they knock the pad back into the caliper, hence first application is nothing as the pads are not in close contact with the rotor anymore. I have only experienced this once and of all the fades thus was the scariest.

To take some advice from Doug, just before a corner use your left foot to test the brakes whist still on the gas just to make sure they work.

[Okibi]

Been getting the same in my SE, using HP+ and some motil brake fluid, flushing before each event. Going to try brake ducts next.

[Roadrunner]

I seem to also have an eternally spongy pedal when sitting idling but on the track it feels perfectly fine. Not touching the floor but pushing hard feels like I hit a little bump stop (is this an inherent SE thing maybe?)
However, jumped in my ND yesterday and it feels exactly the same, so maybe it's my perception of what a spongy pedal feels like.
Maybe jump in someone else's SE and see what their pedal feels like as a comparison.

Is the ABS module/fluid bypassed when not in use?
As in if the peddle is spongy when idling immediately after bleeding, its probably not air in the ABS causing this, as the fluid in the ABS isn't getting compressed by the peddle movement.
But if it goes spongy straight after ABS is activated then its definitely air in the ABS module as the airs now moved into the main lines?

[pepejesus]

Hadn't heard of cycling the abs pump. Going to get more fluid so I might try that today.

Cheers

I would also suggest inspecting the condition of the pads and rotors. With 220rwhp and stock brakes you might be getting pad taper and excessive wear, which is only really fixed by going to a better, non-floating caliper like the Willwoods.

If the issue is temperature-related fade, you would expect that they would feel ok until they got too hot at which point you'd have fade. If they are giving the same soft feel and lack of retardation on the street after the event, when everything has cooled down, temp fade is probably not the issue. Some brake ducting would help with this, and would also reduce pad wear.

It is also possible that the new pads were not properly bedded, possibly caused by an incompatible transfer layer from your old pads, if you didn't replace rotors at the same time.

I reckon it's most likely either some air in the lines, which a good bleed and cycling of the ABS pump should fix, or improper bedding, which you could fix with new rotors or by machining your existing rotors, and carefully following the proper bedding procedure.

I'd also suggest with your power levels to consider a more track-oriented pad at the least, something like the Carbotech XP10/XP12 or GLoc R10/R12 as I think they're now called.