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I was driving on Tamborine Oxenford Rd around lunch today heading towards the Gold Coast on a section with a steep decent and as I was going down all of a sudden my brakes were less than responsive. Up to Mt Tamborine and down to that point there was no spirited driving as the traffic ahead had slowed everyone down. There was however constant braking (heavy at times) because of this slow traffic. I pulled off the road and waited for a about 5 mins to let it cool while checking to see if there was any smoke or smell from the brakes. Only a slight smell but nothing new. After that the brakes were fine again. This has happened on a previous occasion but i figured it was still bedding in after about 500ks from new.

The pressure on the brake pedal was hard so there was no leaking of fluid at least. I have fairly new rda slotted and green stuff pads. Anyone else have problems with these pads when the temp is up or is it another problem?

cheers

GP14 wrote:The pressure on the brake pedal was hard so there was no leaking of fluid at least.

Are you pushing down on the pedal with the same amount of effort but not getting the same amount of bite?
If it becomes harder it means the brake booster has a leak somewhere and thus you are using more effort because there is less vacuum assistance.

Check the hose that goes from the intake plenum to the booster.

1red5 wrote:

GP14 wrote:The pressure on the brake pedal was hard so there was no leaking of fluid at least.

Are you pushing down on the pedal with the same amount of effort but not getting the same amount of bite?

thats pretty much it. Even pushed harder thinking it would help but no go. Will check hose. If booster has a leak would I need to replace the whole thing?

Sounds to me like it might be air in your fluid.
Did you change it when you did the discs & pads?

It only will take a small amount of air in the line to drop performance off.
If you don't do any track work you should change the fluid at least once every two years to keep it in top operating condition.

You might have just boiled your break fluid? How long has it been since it was replaced?

GP14 wrote:

1red5 wrote:

GP14 wrote:The pressure on the brake pedal was hard so there was no leaking of fluid at least.

Are you pushing down on the pedal with the same amount of effort but not getting the same amount of bite?

thats pretty much it. Even pushed harder thinking it would help but no go. Will check hose. If booster has a leak would I need to replace the whole thing?

I can't recall anyone having brake booster failure, all I know is that if you HAVE to replace it, then it's relatively straight forward.
I think I read somewhere, someone here replaced theirs for racing with and NB booster that gave a better feel and/or improved clamping force...?

check all the hoses and fittings (PCV, Idle circuit) that go into your intake plenum cause if any of those are loose/leaking, then vacuum is compromised.

if you take off your plenum-to-booster hose, be careful that you replace it the right way round because there is a one-way valve in there.

Boiled brake fluid = spongy pedal feel & more travel
vacuum leak = very stiff pedal feel & less travel

No we didn't do the fluid when we installed the pads/rotors. I think it was done only a year ago. Will have to check my log. If there was air wouldn't it be affected all the time? It was fine this morning driving to work.

had a quick look at the pipe. hard to tell if there is a leak. The rubber is pretty hard and looks cracked like old skin. I will take it off on the wkend.

Come to think of it the 1st time it happened it was also downhill heavy/hard braking but yesterday was slow driving ie.40km/h downhill. The 1st was spirited and a couple of months ago.

The brake booster reduces the pedal pressure required for a given caliper clamping force. If the booster is playing up, it will mean you have to push the pedal harder for the same resultant brake performance. A larger capacity brake booster won't increase brake performance, it will only reduce pedal pressure.

When you fitted the new disks, did you clean them first with brake cleaner? Did you use grease in the slider pins, and how much? Too much can leak back out onto the pads and/or disks. Also, most pads have a specific bedding in procedure, not just using them gently for a few hundred kms.

NMX516 wrote:When you fitted the new disks, did you clean them first with brake cleaner? Did you use grease in the slider pins, and how much? Too much can leak back out onto the pads and/or disks. Also, most pads have a specific bedding in procedure, not just using them gently for a few hundred kms.

no i didn't clean the rotors, just a wipe with a clean cloth. yes to the grease but didn't smother them. I had help from a well versed car restorer so no problems with the install. did the bedding in procedure so no problems there either.

Most, if not all, new disks have a wax type coating on them when new, which must be cleaned off before use. Wax and grease remover or brake parts cleaner is the go.

I'd be pulling the front brakes apart again, clean the disks and scuff the pads and also change the fluid.

NMX516 wrote:I'd be pulling the front brakes apart again, clean the disks and scuff the pads and also change the fluid.

+1, especially the last part. cannot believe it wasn't changed when new rotors/pads fitted.

NMX516 wrote:Most, if not all, new disks have a wax type coating on them when new, which must be cleaned off before use. Wax and grease remover or brake parts cleaner is the go.

I'd be pulling the front brakes apart again, clean the disks and scuff the pads and also change the fluid.

The greenstuff had a bedding in layer on the pads. I figured that would be sufficient to 'clean' the rotors and bed in the pads with the bedding in procedure.

I'll prob end up doing the fluid next service which will be very soon even if its not the problem.

project.r.racing wrote:

NMX516 wrote:I'd be pulling the front brakes apart again, clean the disks and scuff the pads and also change the fluid.

+1, especially the last part. cannot believe it wasn't changed when new rotors/pads fitted.

like i said, it was only done a year if not less and everything felt good so i didn't do it. I don't track the car and my spirited driving has become much less than it used to

It's not dirty discs as they work fine during normal applications. I fitted new discs and pads and did exactly the same process as you. The bedding surface on the EBC’s works well.

As you're only getting fade after long pedal applications, I still recon you have air in the fluid. This occurs through bad bleeding or moisture in the fluid that occurs due to age.
When it gets really hot the water molecules turns to gas and therefore a spongy pedal. If there’s a lot of air it’s really spongy but if only a small amount you might not notice the slight spongy feel and it’s not until things get really hot that stopping is hard because you’re compressing gas and not fluid.

Change the fluid. Use a good DOT 4.

Yeah I don't think its the rotors. The coating would be long gone by now. I'll be doing the fluid for sure.

Charlie Brown wrote: If there’s a lot of air it’s really spongy but if only a small amount you might not notice the slight spongy feel and it’s not until things get really hot that stopping is hard because you’re compressing gas and not fluid.

Change the fluid. Use a good DOT 4.

That sounds about right. Thanks all for your advice.