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Does a new brake caliper need to wear in?

Discussion in 'Motors' started by bainbridge, 29 Jul 2021.

  1. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,475

    Location: Bristol

    I replaced the left rear caliper today because the old one was weeping fluid from the piston. The new caliper isn't braking as effectively as the old one. Does it need to bed in?

    Discs are well within the wear limit and the pads are only 25% worn, so I refitted them. Replaced both banjo bolt washers, everything is tightened to the specified torque, all brake lines have been bled. The nobble on the inner pads are slotted into the pistons.

    Before I went for a test drive I turned the wheels by hand while the rear was still up on stands and the handbrake mechanism is moving the piston, as is the brake pedal, but the handbrake isn't holding the left wheel as well as the right.

    I went out for a short test drive, when I got back the right hand disk was warm, borderline hot, but the left disk was just warm. I've double checked my work and the only conclusion I've arrived at is that, because it's a new caliper, the seals are tight and everything just needs to beds in over the course of some miles and some hot/cold cycles.

    Is this the case?

    Any comments welcome, thanks.
     
  2. dLockers

    Sgarrista

    Joined: 21 Jan 2010

    Posts: 8,318

    Never heard of such a thing to create any discernible difference. Are you sure it is bled properly?
     
  3. BUDFORCE

    Mobster

    Joined: 3 May 2012

    Posts: 4,098

    There shouldn't be any "wear in" on a caliper.
     
  4. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,475

    Location: Bristol

    @dLockers yes it's bled properly.

    @BUDFORCE I didn't think so either, it's weird.

    Thanks for the replies. It's a reconditioned OEM unit. I thought it would operate exactly the same as an OEM part. I've double checked everything. When I realised there were differing pressures between the rear calipers, I tested the caliper off the disc and the piston was working fine from the brake pedal and the handbrake, but was extremely stiff to wind back in. I had to use the winding kit, whereas the right hand caliper was a breeze, I used needle nosed pliers in the slots, hence my stiff seals theory.

    I dunno I'm tired, I'll sleep on it and gave another look on the weekend. MOT isn't until September so there's time to resolve it.
     
  5. BUDFORCE

    Mobster

    Joined: 3 May 2012

    Posts: 4,098

    I wouldn't worry about it too much.

    When you get a day spare and the weather is nice, take the caliper off, pull the piston right out, give it a good clean and see if the piston moves freely in the caliper without the seals. It might be the piston is warped or something similar.

    I'm sure you know, but there isn't really any moving parts in a brake caliper other than the piston. If that is moving freely without any brake fluid/pressure and the seals removed then your problem is elsewhere. I doubt the seals themselves would be enough to jam up the caliper.

    If you do this, when you put the seals back use red grease (silicon grease I think) some grease like copper grease for example can perish the rubber seals.
     
  6. jsmoke

    Capodecina

    Joined: 17 Jun 2012

    Posts: 10,829

    Definitely brakes in, the handbrake was pretty soft when I changed the rear caliper and over a few days it tightened up.

    I just changed a front caliper and brakes were a bit soft but after a day or soft they are back to normal.
     
  7. dave28

    Wise Guy

    Joined: 28 Jun 2013

    Posts: 1,455

    Do some miles and then decide, i would think it just needs to settle in
     
  8. bobuk

    Gangster

    Joined: 25 Jan 2009

    Posts: 486

    Did you put the pads back in the same way ?
     
  9. dLockers

    Sgarrista

    Joined: 21 Jan 2010

    Posts: 8,318

    That's not a bad idea
     
  10. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,475

    Location: Bristol

    Good point. I usually put them back in the same position but rain was forecast and I got a shimmy on to avoid the weather, so may have inadvertently switched their position.
     
  11. pugheaven

    Mobster

    Joined: 22 Apr 2008

    Posts: 3,599

    Location: Bryn Celyn Wales

    The only thing I could say there is, the new caliper pistons sticking for some reason. Other than that, take the top off the brake fluid level and pump the brake again around 20 times, with engine on and off... and just see if there is some air in the system somewhere? Can't think of anything else other than it's not setup OR your current NONE replaced caliper is sticking more on the disc!!! You're assuming that the new one isn't putting pressure if it could be that you existing one is locking on too much?
     
  12. IAmATeaf

    Soldato

    Joined: 3 Apr 2007

    Posts: 7,221

    Location: South of the Watford Gap!

    I'd hazard a guess that the pads have become swapped? When my son changed his calipers he also used the old pads but didn't think about where they originally were, the result was very spongy braking. In the end he dumped the old pads and put in new and everything returned to normal.
     
  13. Django x2

    Capodecina

    Joined: 28 Sep 2008

    Posts: 13,763

    Location: Britain

    No so either:

    A) you've not installed it right, or
    B) you've used a pattern part for the caliper instead of OEM or OEM supplier (ie Lucas).

    It's unlikely to be a bleed thing, but it is worth checking. You'd feel that in the pedal though.

    This is very strange considering one pad has clips specifically for the caliper piston and the other floats (ie no clips) on the outboard side of the caliper.
     
  14. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,475

    Location: Bristol

    With the rear up on stands and the roadwheels fitted I was turning the wheels by hand while engaging and disengaging the handbrake. On the right hand (original caliper) side, the handbrake would hold the wheel solid, and then spin freely when released. The left roadwheel, however, would turn under firm pressure with the handbrake on. The car is 12 years old and the original caliper, although old, appears to be working fine.

    I think the switching pads theory is plausible, the discs do have some scoring. I've just shone a light on the outer pad in situ to see if there's any tell tale piston marks indicating that I'd switched them, but I'd removed all trace with brake cleaner and a nylon brush.
     
  15. bainbridge

    Mobster

    Joined: 9 Dec 2009

    Posts: 4,475

    Location: Bristol

    The rear pads on this car are interchangeable and don't have an inner and outer pad. I do usually keep the orientation the same anyway, to save them having to bed in again, but I may have swapped them when cleaning.