Rear brakes

[MacOlaf]

Towards the end of a 20 min track session, being pushed too fast by the instructor, I started to have a moderate vibration on hard braking. In the next session an hour later the vibration started after a couple of laps and then the pad wear red message and light came on - so I stopped.
Examining the rear brakes I see that the pads are at about 3mm and the discs approaching the limit of 22 mm). One of the pad wear indicators has tilted over and contacted the disc. Don't know if it tilted and touched or touched and tilted. I notice that on one of Richard's responses he says the wear indicators are about 4mm anyway. The inside of the discs are slightly corroded, not as nice and shiny as the outside. Front pads and discs look fine, and were replaced about 5,000 miles ago, as were rear pads.
Question 1 - could the vibration be caused by the corroded disc or thickness on limit
Question 2 - what experience have people had with Pagid replacement and who to buy from
Question 3 - replacement looks quite simple, does the parking drum brake cause problems

 

[andyjwhit]

Hi Mac, have not done any track days (yet) but my OPC advised rear discs were corroded, 98 C2 Man, and quoted £750 for a new set of discs and pads, local indy quoted £400 for a set of Pagid discs and pads so went for that. Obviously dont have a direct comparison with OPC set up but can confirm for road the new discs and pads work perfectly and would highly recommend them

Bst

Andy

 

[AlexBell]

Hi, vibration in the discs is often due to overheating and then uneven cooling of the disc. Did the vibration come from the rear?

This could be because of old fluids, old discs, wrong braking technique... lots of possibilities.

 

[924nutter]

An uneven inner surface will not bed into the pad properly and will create varying friction as the disc rotates, depending on how irregular the corrosion is, or even slow the car down particularly well without very heavy pedal pressure. Also having done castle Combe many years ago, Pre chicane layout, as a track day, I found that standard unmodified brakes overheated and juddered but this was in my 944s with new pads, fitted and bedded in for the occasion. I pushed hard enough to get brakefade and remember going up the track from tower bend sideways from an 85 mph turn in being chased by a white 911SC; I didn't trouble the apex but both my passenger and myself troubled our underpants. The 911 has better brakes but the speeds are higher and I'm willing to bet there is some kind of square of the speed difference law applcable to the generation and dissipatioin of all that kinetic enregy.

 

[AlexBell]

The standard 996 brakes are remarkably good, I do both track days and auto slalom with mine and never get into trouble. But I change the fluid once a year.

That doesn't mean they can't be improved, which they can, but I always get a bit sceptical when people complain about their brakes on the first or second track day in their life. ;-) (generally speaking..)

 

[MacOlaf]

Thanks for replies

Vibration seemd to be from rear, but hard to place. Also brake pedal seemed a bit spongy, but now fine.

I did a full track day at Donnington last year plus a taster at Castle Coombe, no problems. Brake fluid changed this April and since then have done Curborough sprint, again no problems but sprint does not give the brakes a chance to warm up.

Indy in Peterborough has quoted £340 to fit rear rotors and pads - but forgot to ask if that included new wear sensors and dampening (?).

Design911UK has full set (2x rotors, pads, sensors and damping) for £238, but not sure what make.
carParts4less has full set (Pagid) for £193, but not sure what diameter dampening discs needed 28 mm or 30 mm - any advice.