Odd brake disc rust / MOT fail

Big_W

Hello all,
Today the wife-mobile has failed its MoT on front "axle" brake imbalance.  Testing garage recommended replacing all front discs and pads, but I'm not convinced, as both discs and pads have plenty of wear left. There is a definite problem - the attached picture shows the front offside inner pad is not making proper contact with the disc, with rust showing on parts of the disc that should be "polished"  by the brake pad (other 3 front disc surfaces look normal), and on heavy braking the nearside wheel locks, but the offside does not (no ABS on this car).

Car is a late 2002 Fiesta, that typically does only 6 miles a day, 6 days a week. Lest it be relevant, during the early part of lockdown it wasn't used at all for one month, for 4 months it it only did those 6 mile round trips 3 times a week, but is now back to normal.  

I suspect part of the brake caliper is sticking - what do you think?
  

Lomast

I agree sticking brake caliper. Shouldn't be too expensive on a fiesta and easy to DIY if you are confident and have the tools. I would change the discs and pads whilst it's off anyway

Big_W

Lomast said:

I agree sticking brake caliper. Shouldn't be too expensive on a fiesta and easy to DIY if you are confident and have the tools. I would change the discs and pads whilst it's off anyway

Thanks for the reply. Any thoughts on if it would be a problem with the main piston or just the guide pins?  
  
And why change the pads and discs, when they are not worn out?  The rusty area in the middle of where the pads should "polish" isn't significantly higher than the shiny parts.
  
I'm a bit twitchy about this, as although I have done DIY servicing for many years, I've never replaced front disk brakes (have done rear drum brakes) or took a caliper apart. Everything I know about servicing brake calipers I've learnt today....

chrisw

I doubt the rust will polish away very easily, it will damage the brake pad as well.

It's probably the guide pins need cleaning up but pushing the piston back in will ensure that's free as well especially if fitting new pads.

Replacing the discs and pads is really the best option. It's pretty straight forward, plenty of guides on YouTube if you're not sure. A set of pads and discs will be less than £50 from somewhere like carparts4less or Eurocarparts with the sale prices.

Robbo66

Both the pads and discs will have uneven wear as so braking efficiency will be reduced, just cleaning the guide channels/pins wont cure that and is something do when fitting new pads anyway.

mo2312

I agree, looks like a sticking caliper, would take the slide pins out and check for corrosion and check the piston itself seems to be moving freely