Average Boxster Brake Performance - Fluid?

[McSwerve II]

Evening All

The brakes on my old Boxster are average at best, with poor initial bite.

Also when I changed the discs the calipers didn't 'close up' as if there wasn't much residual pressure in the system.

Thoughts?

I thought the calipers could need a refurb, but I wonder if it could just be the fluid (the header tank is full)?

If so can any garage test it?

Any advice gratefully received.

[Locknut]

Lots of people are going to tell you to change the fluid and some are going to tell you that you must use brand X or Y, however I don't think the problem you describe will be cured by changing the fluid.

The callipers will not close up themselves, they need to have the pedal pumped to make them close, so this is not a factor to be considered in your diagnosis. (by "close up" I assume you mean the pistons moving out to make contact with the back of the pads)

I think you might get away with a good clean-up. Dismantle the callipers and make sure the sliders are clean and free to move. Check that the pistons move freely by pushing them back and pressing the pedal a little to make them come forward... but not too far!

If the pistons are seized you will need new or reconditioned units, but cleaning and freeing the sliders will give good results if the pistons are free.

When all this is sorted, you can then consider changing the brake fluid.

BTW all this assumes that you don't have an airlock which would give a spongy pedal.

Edited by Locknut on Monday 3rd June 23:53

[McSwerve II]

Locknut said:

The callipers will not close up themselves, they need to have the pedal pumped to make them close, so this is not a factor to be considered in your diagnosis. (by "close up" I assume you mean the pistons moving out to make contact with the back of the pads)

Edited by Locknut on Monday 3rd June 23:53

Many thanks for the guidance.

What I meant by ‘closing up’ was that when usually when I’ve removed the calliper and pads from the disc, the residual pressure in the system will continue to push the piston / pads together.

So I usually insert a wooden wedge between the pads, so they don’t close in too far.

With this car, you can remove the calliper / pad assembly from the face of the disc, and there’s no ‘closing up’.

Would your bet still be on good clean up??

Cheers

[PaulKemp]

Your calipers, how many pistons?
Single, twin, more?
If single the sliders could be an issue
If doubles then check the old pad wear, the pad with the least wear may mean the piston on that side is seized
You should also compare pads from both sides outer to outer, inner to inner
This will show if its just the way your system works of if there is a difference either side

[Nick1point9]

McSwerve II said:

Many thanks for the guidance.

What I meant by ‘closing up’ was that when usually when I’ve removed the calliper and pads from the disc, the residual pressure in the system will continue to push the piston / pads together.

So I usually insert a wooden wedge between the pads, so they don’t close in too far.

With this car, you can remove the calliper / pad assembly from the face of the disc, and there’s no ‘closing up’.

Would your bet still be on good clean up??

Cheers

The "closing up" behaviour you describe should not happen! How many cars has this happened on? If there is no load on the brake pedal there should be no load on the piston to close up the pads.

[andyiley]

Nick1point9 said:

McSwerve II said:

Many thanks for the guidance.

What I meant by ‘closing up’ was that when usually when I’ve removed the calliper and pads from the disc, the residual pressure in the system will continue to push the piston / pads together.

So I usually insert a wooden wedge between the pads, so they don’t close in too far.

With this car, you can remove the calliper / pad assembly from the face of the disc, and there’s no ‘closing up’.

Would your bet still be on good clean up??

Cheers

The "closing up" behaviour you describe should not happen! How many cars has this happened on? If there is no load on the brake pedal there should be no load on the piston to close up the pads.

+1.

Agree, it is not a behaviour I have come across, and have never heard of it happening before. The caliper should not "close up" the gap between the pads, there should be no "residual pressure" in the system as this would mean your brakes are on, and would be dragging under normal driving conditions.

A good clean up, grease LIGHTLY where appropriate (inside dust seals) and ensure the movement of the pads/sliders (I don't think you have any sliders, anyway) are all Ok.

Change the fluid (should be done every 2 years anyway) and make sure you bleed the system properly (starting as far away from the master cylinder as you can & moving towards the master cylinder) then I think you will probably notice a difference.

[bgunn]

McSwerve II said:

Many thanks for the guidance.

What I meant by ‘closing up’ was that when usually when I’ve removed the calliper and pads from the disc, the residual pressure in the system will continue to push the piston / pads together.

So I usually insert a wooden wedge between the pads, so they don’t close in too far.

With this car, you can remove the calliper / pad assembly from the face of the disc, and there’s no ‘closing up’.

Would your bet still be on good clean up??

Cheers

When the brake pedal is released, there is no 'residual pressure', there can't be as the 'filling' seals in the brake master cylinder uncover the reservoir holes, allowing the fluid from the reservoir to enter the cylinder.