jayok

My MY01 has its NCT (equivalent of an MOT) on Thursday and I was doing the normal pre-test checks (lights, oil, air, etc). Looking at the rotors (or discs) on all four corners of the car were covered in rust. This by itself isn't unusual, so after 45 minute drive through the back roads that involved quite a bit of braking and accelerating, I returned to discover the rear discs are still covered in rust. It's as if the rear brakes are not applying!

To try and fix this, I took off both calipers, brackets and sliders, cleaned off any rust build up, ensured that the pads were free to move, re-greased the whole lot. It all looked good. Took it for another test drive and their is only a slight application of the brakes on the rear. The car stops fine, but I know 90% of braking is from the front anyway and there's no rust on the front discs.

Do I have stuck calipers or could it be something else? I haven't found too many issues reported about the PCV in the S2's brake lines. Reason I am asking this is I normally get calipers that don't retract properly rather than apply properly.

I won't get to flush the brake fluid between now and the test, but that's the obvious next step. Pads and discs are fine.

WinFreak

Does your handbrake still work?

Have you tried twisting the cylinders in or out a bit when you had the calipers off?

jayok

Yep, handbrake is 100%. No problem holding the car on a hill or underload (i.e. in 1st and holding the clutch bite-point).

When the calipers were off I rewound them back as if new pads were fitted (they weren't), and the pushed out the whole way again, so they are moving. I suppose the pistons could be pitted and preventing any further movement. I didn't try to push the out beyond the pad range.

noodels

^^When the calipers were off I rewound them back as if new pads were fitted (they weren't), and the pushed out the whole way again

you mean unscrewed until a small clearance between pad/disc,and not pump brake pedal to take up slack !

jayok

I wound the piston back into the caliper using a wind-back tool - this was similar to if I was replacing worn pads. When fully wound back, I remounted the pads and caliper and pumped the pedal. It took 4 pumps of the pedal for it to "firm-up" - that is move from the fully wound pad position to minimise the gap between piston, pad and disc (i.e. the disc now floats). Normal stuff. A few pulls/releases of the hand-brake also tightens it up.

My point in telling you this is that the brake pedal applies pressure to forced the piston out, so the fluid is moving. The caliper appears to float freely (i.e. the slider pins, etc are not stuck).

Unless the caliper will go no further

richmc

Did it pass it's NCT? if so surely that would mean the brakes are working.

Hay I can quote myself now! Great that it passed and the numbers were OK, how often do you drive the S, it just may need the pads to get scrubbed in?

Dembo

Is it Thursday yet?

But yes, assuming your NCT includes the same sort of brake test to the MOT, then that'll confirm whether they're working or not. It might just be the pads; if they're a bit old they get brittle and don't do much of anything. Or perhaps the disks are too manky to work.

richmc

Miss read thought it said had not has

jayok

As Dembo said - I'll tell you in 2 days time!

It does include a brake test, include balance and load and we'll get a pretty comprehensive report on the kilo-newtons of force being applied to each wheel. The funny thing with the pads is that there's load of life left on them and when I re-wound the caliper, it seemed to free up a little more.

Now, what's confusing me is that the rear of the disc is nice and shiny (i.e. the pad is engaging) but the front isn't. That would normally suggest that the caliper isn't sliding on it's pins correctly. However, they are completely free! I'm going with a stuck caliper for the moment. I'll get the brake test report from the NCT and how much force is being applied and probably a fail. But a re-test is only €22 and I've 28 days to get the test redone. I'll get the calipers off to Bigg Red during this time and get them refurbished.

I'll keep you posted.

jayok

Well went to the test today and it passed!

The readings for the brakes were:

Front - n/s 2.82kN o/s 2.66kN
Rear - n/s 1.98kN o/s 1.84kN

So, it appears the brakes are grabbing correctly and the force applied on the rear is approximately 70% of the front. Which is within specification of what I would expect the PCV to do. But I'm still not getting a completely clear rear disc. I'm going to change the pads on the rear in case there's uneven wear on them that I cannot see and then just flush the brake fluid.

But, we're looking good for the next year.