Brakes pulling to side

My front calliper pistons were a bit grotty looking so while rebuilding my hubs and swivels, I decided to replace the pistons with SS version. All seemed to go well with rebuild.

I’ve bled the system a couple times, taking out for a spin and bleeding again. I have a pressure vessel system for bleeding so put a fair bit of fluid through - I’m confident there is no air in the system.

When I brake hard, the car pulls to the right. Tonight after bleeding again, I went out and tested. The roads are nice and slippy with frost. Seemed like the front right locked up each time I hit the brakes hard.

I assume it’s something with the Caliper rebuild.... but how do I know what’s wrong? Is there a way to test if the callipers / pistons are working right?

You could take the pads out and put a block of wood in, say 15mm thick. That should be thick enough to stop the pistons popping out, but will give them enough room to slide out a bit. You will be able to see which one(s) move out before the others.
Are you sure it was one of the fronts locking up? A faulty rear brake can very effectively pull you to one side.

Potentially, but I am assuming the front as that’s the ones I rebuilt and I never had any issues before, so would be bad luck if the back failed now.

I could try with the wood. I was worried that they’d all come out but maybe not with the same force or something.... but I guess that wouldn’t make much sense if they all have pressure behind them.

I did take a temp reading at my discs and the front two were pretty even, so couldn’t see anything obvious there

Rorie said:

Potentially, but I am assuming the front as that’s the ones I rebuilt and I never had any issues before, so would be bad luck if the back failed now.

I could try with the wood. I was worried that they’d all come out but maybe not with the same force or something.... but I guess that wouldn’t make much sense if they all have pressure behind them.

I did take a temp reading at my discs and the front two were pretty even, so couldn’t see anything obvious there

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Bad luck, bad timing, call it what you like it can happen and just when you don't want it to!
Using the block of wood lets you see which pistons are moving more easily than others. It's best if you have someone to push the brake pedal bit at a time while you watch the pistons. Do one wheel at a time. If there's just you it just means more leg work going to the brake, then caliper and back to brake etc. Push the pistons back in and repeat the process to get a picture of what's going on.
If all pistons are moving out reasonably evenly on both sides.............try the backs

New brake pads do need bedding in, you may have an uneven pad or even have accidentally contaminated a pad with oil/ fluid. Worth a check.

I changed my front pads last summer and it took about a week for them to bed in, under hard braking they were pulling to one side until they settled in.

People always blame the side it pulls to, what is really happening is the side it is pulling to, is doing its job correctly, it is the other side that is weak causing the issue.
I ahve seen dry piston seals pull the pistone back in after you release the pedal, so giving to much running clearance.
How many miles have you done since the brake work? can take some time for it to bed in and sort itself out.

Give it a week, then if the same, swap pads side to side and another few days, then you can say 100 percent the fault is caliper related.

New britpart calipers are pretty cheap.

Probably not as stupid as me, but you havent put the calipers back on the wrong sides and bleed nipple at the bottom at all?