Both front brakes not releasing fully

[Daston1984]

Good afternoon everyone.

I have recently replaced both front pads and discs on my Gen 2 997 S as they were getting pretty low and I had the MOT coming up. Everything came apart and went back together without any issue with plenty of clearence between the pad and disc meaning the hub would rotate freely on both sides.

Car flew through MOT without any issues and all was good

I had an odd noise and a bit of knocking the other night and when trying to track it down I noticed both front wheels would not rotate freely at all and were quite stiff. I've just pulled the pads out and made sure everything was clean and looking good, moved the pistons back and all spins freely again. However, as soon as the brakes are applied they don't seem to be releasing the pistons much and the disc's are dragging on the pads on both sides. I can't imagine both sets of calipers have failed at the same time and I am sure the MOT tester would have picked up the brakes binding at the time. I'm not really sure what could have gone wrong especially as I've only covered 200 miles at the very most since changing them and MOT.

 

[Lancerlot]

Pads just need bedding in and then all should be fine.
I believe the calliper fasteners are torqued stretch bolts, did you renew them?
Regards,

Clive

 

[Daston1984]

Pads just need bedding in and then all should be fine.
I believe the calliper fasteners are torqued stretch bolts, did you renew them?
Regards,

Clive

Yeah new bolts, not had this on any other car after new pads are fitted. You can feel it pulling the car to a stop when free wheeling.

 

[Daston1984]

Another update, pushed the pistons all the way out and removed the anti squeal shims from the calipers (the new pads look to have an anti squeal backing), this has freed the disc up after the brakes are applied (yey) but as soon as I add the spring clip that holds the pads in the caliper it then becomes too tight to move freely. I assume at road speeds this will loosen up?

 

[malarcy]

If the 997 brakes are the same as the 987 then then “shims” are a press fit into the pistons and are supposed to stick to the back of the pads to aid pad retraction. The genuine ones have a double sided sticky backing to achieve this.

I have seen some 3rd party kits with shims included that didn’t match the oem setup (they just had generic “springs” for anti squeal ) so perhaps there’s some difference there… or the pads are not the correct fitment.

 

[Lancerlot]

Yeah new bolts, not had this on any other car after new pads are fitted. You can feel it pulling the car to a stop when free wheeling.

OK, that doesn't sound right. Might pay you to double check you have fitted the correct pads compatible with your car's rotors. Try comparing the shape and thicknesses of the new and old pad backing plates and shims.

Regards,

Clive

 

[Daston1984]

If the 997 brakes are the same as the 987 then then “shims” are a press fit into the pistons and are supposed to stick to the back of the pads to aid pad retraction. The genuine ones have a double sided sticky backing to achieve this.

I have seen some 3rd party kits with shims included that didn’t match the oem setup (they just had generic “springs” for anti squeal ) so perhaps there’s some difference there… or the pads are not the correct fitment.

Yeah it's the same set up, a bit of metal with a sticky back plate that slides into the pistons. I was under the impression they were to just reduce noise, didn't realise they helped retraction as well. I plan to take the discs and calipers off tomorrow from both sides and make sure everything is 100% cleaned up and sitting correctly. The fact both sides are doing it I am pretty sure it's either something I've done wrong or something daft like them being the wrong pads.

 

[Daston1984]

Think I am getting somewhere.

With the caliper mounted but not torqued up I removed the pads and popped some thin wood in there and pressed on the brake pedal. The wood was easily removed and when pushing the pistons back in you could see the other move out feely on both sides. So at this stage I am ruleing out them being the problem.

Cleaned up the pistons and popped the pads back in, yes there was very slight binding on the rear side of the caliper but there was no physical pressure on the pad I could move it about in the caliper with a bit of force.

As soon as I torqued up the caliper however the outside pads bind hard to the disc. I plan to take a wire brush to the hub in the hope that it's just a build up of crud that's not alligning the caliper correctly.

New Caliper bolts are also on order.

 

[Motorhead]

Sounds like plan.

Just an unlikely thought but if you’re using OEM rather than Porsche parts the discs and/or pads could be very slightly thicker than original, reducing design clearances?

Jeff

 

[Daston1984]

Sounds like plan.

Just an unlikely thought but if you’re using OEM rather than Porsche parts the discs and/or pads could be very slightly thicker than original, reducing design clearances?

Jeff

That was a thought as well, I have read in my hours of Googling of people having to sand down their pads a little especially on some of the aftermarket ones in order for them to fit.

I'm using TRW pads (who are a Porsche supplier) and Zimmerman Discs.

 

[Motorhead]

TRW pads and Zimmerman discs isn’t a familiar combination to me, so that could be an issue. Most owners tend to opt for items from Brembo, Pagid and Textar.

Sanding the pads sounds like a first option, and I suppose you could try bevelling the leading edges very slightly … something we used to do back in day on drum brake shoes to prevent them grabbing!

Jeff

 

[malarcy]

Porsche vary their supplier per model apparently - 987 ( and I assume 997) pads are Textar - if the pads tighten when the caliper is properly bolted down then there must be something in the "vertical " plane of the pads thats causing them to move - maybe poor recollection but when I did mine - pretty sure the pads came free of the caliper with just the retaining spring release - they just "sit there" on the pad "ears" until the spring and pin go in place - so if you tighten the caliper and they move then something isn't sitting right. Do you have the old pads for a side by side comparison of the "not pad material" dimensions ?

 

[Daston1984]

Annoyingly I chucked my old pads away

I believe I have resolved the issue! I took both discs off, gave the hub a blasting with a wire wheel on the end of a drill, gave it all a good coat of anti seize and put it back together making sure that they were as flush as possible.

Also took the opertunity to bleed the front calipers as well.

There is a little resistance but the wheel will turn a good 1 - 1.5 times before stopping (before it would struggle to get 1/3rd the way).

Once the pads have worn in a bit I'll pop new shims in. Fingers crossed she is all good for the FoS in a few weeks!