Having run my car now for some time I am into the phase of never ending improvement! I have an extremely light front axle load due to design ( and weight reduction efforts! ) of only 230 kg ( unloaded ). I have cross weighted the car to obtain front L/R balance as far as possible. Despite this I have differential locking L/R. I had put this down to loaded condition ( me ) and road effects ( camber etc ). I have changed from Mintex 1144 to Hawk DCT 30 pads which made a major improvement in modulation. Calipers are Willwood 4 pots. However I was surprised to see today at my MOT on the rollers that there is indeed a significant L/R inbalance. The tester did not comment so presumably within acceptable production limits. So what causes this and what can I do about it? I use the car on track and while I do not claim to be the last of the late brakers obviously you test the limits more than you do on the road. Answers on a post card as they say. TIA.

Were there any clues in how the pads you removed were wearing? If any of them had more meat left on them than the others then that might help with diagnosis. E.g. sticking piston in one of the calipers or suchlike.

Are the Wilwood calipers directional - my AP's have an arrow that shows the way the discs should rotate within them. I think they are designed to slightly stagger the sequence of the pistons operating. I've seen some have bigger pistons on the leading side and smaller behind (or is it the other way around?) Is it possible you have two calipers of the same handing so one is on upside down?

Another possibility could be the disc itself - is one more worn/scored/pitted than the other? Or a disc could be slightly warped?

Did you corner weight with you in the car or a facsimiled of you?

If you think about the light weight of the axle and you sat in it the percentage change is probably a fair bit, and enough to change the weight on the tyres.

As the mot test is on rollers and there's no Wright transfer it'll have nothing to do with cornerweighting. Most probably a sticking piston in one of the calipers. Which Wilwoids are they? The powerlights have no dust seal do can get crap in them when the pistons are pushed back for pad replacement.

You don't need weight transfer.

My car climbed out the rollers at an odd angle as one wheel is slightly more loaded with me in it, that's what the tester said.

Shirley the weight transfer would only add to the weight on the front wheels, if it's out of whack to start with it's out of whack?

Good point about the seals. I bought a pad spreader which I had to grind down so that it would fit. Some string and brake cleaner got them going smooth again.

Thanks for the input. There are no visible signs on discs or pads of anything amiss. I can lock both front wheels if required, the left slightly before the right. The car pulls up square. There is no discernible pull to the left with normal braking. On the rollers there was clearly more braking force on the left. The right seemed to be about 60% of whatever the scale is. While non of this is a problem in practice I guess I am wasting some overall braking capability which I would like to recover. The calipers are Dynalites, no seals. Everything looks clean, no sign of corrosion or general muck. The car has been used generally in dry conditions, 4k miles about 50% on track. Sticking piston seems to be most likely but I can easily lock that wheel. How to fix and is it worth the hassle?

Is there a lot of play in the pads? I've had aftermarket pads rock the piston over and make it stick a bit only under load, looked fine when the pads were out.

Thanks for the tip. I will take a look at the weekend.