Rear Brake pads uneven wear

[Alsace_rangie]

Help/ideas please with an odd problem.

93 200TDi, non-abs

The rear brakes are wearing unevenly, the inside pads are nearly worn to the metal, outside pads hardly used. The pads are only 6 months old, maybe 6K KM. On the last change this was only happening on one side, so I put it down to a pad jamming and gave the caliper a good clean up. Mintex pads fitted.

This time both sides are doing the same thing. I swapped the "slim" pad over, and got someone to press the pedal; both pistons moved fine and both pads gripped the disc. Pistons push back easily.

The inside of the discs are nice and clean, outside getting a bit pitted, I guess from lack of use.

I am loath to replace the calipers as all seems to move. But OTOH the outside pads are not being made to do any work, as evidenced by the disc surfaces.

Any ideas of what to check before I take the expensive route?

[duncmc]

I would think that may be sticking pistons. If the pads move freely and aren't catching it can't be anything else can it? Sounds like the pistons on the outside are corroded a bit to cause sticking but not seized.

[Snagger]

Sicking pistons are the only possible cause. You could replace the callipers, but I have rebuilt callipers on my RRC and 109 (Discovery/RRC brakes) with a Zeus stainless piston kit and they're brilliant - no worries about the quality of the callipers and I know I won't get corroded sticking pistons again on either car.

[Tanuki]

The pitted vs non-pitted faces on the discs can only mean you've got stuck pistons.

Don't mess around - fit new calipers. And while you're in there with everything in bits fit new discs too because the pitted surfaces of the old discs will rip up the linings on any new pads.

Job Done - OK for the next decade.

[daveturnbull]

I find that the inside break pad always wears faster than the outside. I put it down to the fact that that's the side of the caliper the fluid enters, so probably has a slightly greater pressure than the outside, after the fluid has passed through the caliper veins.

[Snagger]

I found on my RRC and the Discovery brakes that are on my 109 that the rear callipers had seized pistons, outboard in all cases. I think they are more prone to rust and seizure than the inboard pistons because they are more exposed to rain and road spray. It doesn't take much to have an effect, and a small amount of increased friction in the piston will have considerable effect in unbalancing piston effort and pad wear.

New callipers will be just as bad in three or four years, hence my recommendation of stripping the existing callipers and cleaning them meticulously before fitting new seals and stainless pistons.

[Alsace_rangie]

Thanks for all the advice, and sorry for the delay but I've been away for few days.

I will try one more thing before committing to new calipers or a rebuild. As the pistons will push in easily, I wondered if dirt (a small amount) in the caliper fluid passages may contribute to any unbalance, as per Davetunbull's comment. So I will push them right back and bleed each side.

Also considering replacing the disc as well. Pity as they are less than 2 years old.

I've never had much success rebuilding calipers. Once the piston is corroded it seems the rest of the caliper (e.g. the seal seats) suffer. Perhaps new calipers and immediately add stainless pistons!

Will post back if I find anything

[Aragorn]

Once the disk ends up pitted, it will rip apart any new pads you install, so even if you have cured the sticking caliper, the problem will still happen.

[Team Idris]

I put my second hand Zeus pistons into a new Paddocks calliper on the front (when I bust a mounting lug). My concern was that the pattern-part might not take stainless pattern-part pistons. I had to do a bit more wiggling than with the rover calliper, but they went in no worse than other callipers I've rebuilt on other makes. So I'll give it the thumbs up as I viable 'future proofing' mod

As a side note, zeus pistons can get rust from the calliper stuck to them. No point scratching them with abrasive paper, as a nylon pad scrubber and genilite gets it off. Which makes me wonder if this might be a good treatment before any pistons get rammed back in the hole whence they came?

[Alsace_rangie]

Ok, got some new pads and set to work.

I had already swapped the inner (thin) and outer (thick) pads over, and noted that the outside disc surface had polished up a bit. So better when the pistons were further out.

My logic was that as the outer pistons moved just fine but weren't putting any pressure on in real use, there must have been something limiting the pressure inside the caliper. So pads out and flattened the pistons as far back as I could get them, hoping that this would dislodge anything and push it back into the line (or at least the area in the caliper near to the bleed screw).

The pressure bled the brake. Some small bubbles and very small particles (only just visible) was all I got. Anyway, new pads in and brakes feel fine. Mind you they got through a vehicle test not long before I noticed the odd wear...

Will run for a week or two and see how it goes. If still no improvement, then new calipers as if the pistons are moving it's not an issue of corrosion.