Defender, Discovery I and Range Rover Classic Brake Calliper Overhaul

While most owners are aware of the fact that brake pads and discs degrade with age, use and corrosion, many don’t realise how badly callipers, especially their pistons, can also degrade.  Bad callipers can leak or have pistons which are seized, either preventing the pads being pressed aginst the disc, or in partial seizures, pressing the pad to the disc but then not allowing it to release on pedal lift, thus cooking the brakes and leading to brake fade, blued/scored/warped discs, rapid pad wear and possibly even boiling of the hydraulic fluid.  Overhauling the callipers is relatively simple work, though some of it is a little fiddly and exasperating.  It needs few special tools, but a vice is extremely helpful.

The first job, obviously, is to remove the wheels and clean the callipers as much as possible in place.  A jet wash is ideal, but degreaser, a screw driver, a tooth bruash and hose or bucket of water will suffice.  Standing the vehicle on a jack is not safe; the vehicle’s other wheels must be chocked and the corner being worked on must be very securely mounted on an axle stand.

With the calliper cleaned up, you next need to get the pistons to protrude as much as possible to allow them to be removed later.  Remove the brake pads by withdrawing their R-clips and retaining pins and pulling the pads straight out.  If the pads seem tightly held, then it’s as well that you’re doing this now – it signifies seized pistons.  The pads should be slightly loose, but if they catch on the rim of a worn disc, use a lever or an old screwdriver to force the pads back away from the disc before withdrawing them.

With the pistons now exposed as far as the disc permits, clamp and disconnect the flexible hose and remove the calliper from the swivel housing (two 13mm double-hex head bolts).  Make sure the vehicle is well supported when you do this, unable to slip off the axle stands, as considerable force may be needed to undo rusted bolts.

It was at this point that I had my callipers blasted and primed.  If you prefer, you can use a hammer and cold chisel to remove thick flakey rust and a wire brush to remove surface rust, as I did previously on other callipers.  The important thing is to clean the calliper exteriors before stripping them down in order to prevent damage to the calliper halves’ mating faces, drillings or bores.  I apologise that the photos only start here, not showing removal from the vehicle.

Now that the exteriors are fully cleaned, the strip down begins.  Place the calliper in a bench vice, using its mounting lugs to grasp it.  I use an old towel to catch the fluid spills as the calliper is split.  Remove the bleed nipple(s) first (10 or 11mm hex ring spanner or socket).  Then remove the calliper’s four cross-bolts  On my callipers (old and new), these are 16mm hex head bolts, but some callipers use Allen ket type bolts; either way, the sequence is unaltered.

This allows the calliper halves to be split.  If they are still held together with all four bolts removed, then they are being held together by corrosion around the edges of the mating faces.  A tap with a hammer or better with a rubber, hide or copper mallet will quickly separate them.  Note that vented disc callipers have a spacer in this joint – it is just held in by the same bolts and should be removed from whichever calliper half it is stuck to.  There will be two spacers per calliper.

The mating faces have fluid pathways to connect each piston to its opposite number.  These are sealed with square sectioned O-rings.  I haven’t been able to source replacements for these, and have been told that aren’t sold separately.  I’m not sure if that’s true, but they certainly don’t come in the overhaul seal kits, so remove these very carefully and keep them safe.  I have not come across a bad or even mildly marked or distorted  O-ring in the ten callipers I have refurbished, so it is unlikely you will need replacements either.

Now comes the removal of the pistons.  I just used mole grips and wiggled the pistons out as they were clearly scrap – the mole grips are a very crude way of removing the pistons and will damage them if used without extreme care.  However, not shown in the photos is the same technique but with a gentle grip and double wrap in their jaws of a strip of bath towel to protect the stainless pistons fromt the grip’s jaws as they were removed from the other callipers.  The stainless callipers had the benefit of not being seized, but the process was quite protracted to avoid damaging them and much patience is needed.

Now that the pistons are out, the main seals and the outer wiper seal and retaining rings must be removed.  Use a small screw driver to prise them all out.  Throw the seals away, but if any of the retaining rings come out without being deformed, keep them – they might be invaluable when fitting the new seals later on!  The wiper seal and ring may have come out with the piston if it was very rusty, just as in my photo, in which case the ring is likely to be suitable as a spare.

Now that the callipers are fully stripped, they need internal cleaning.  I use a length of old welding rod to push any debris and dirt out of the fluid pathways.  A piece of coat hanger wire is probably too thick, but there are plenty of sources of stiff wire to do this job.  The bores need scrubbing as they tend to build up a coating of slime, like a grey snotty grease.  I suspect this is a fungus from water in the fluid, and is worse on neglected brakes – my older callipers were terribly contaminated, but these were only mildly so.  The seal grooves need meticulous cleaning of all dirt and corrosion.  It’s worth noting now that the wiper seal retaining rings won’t fit if there is even the slightest trace of rust in the groove, so clean them back to pure, clean metal.  I then use a can of penetrating oil, with the straw in the nozzle, to blast through the fluid ways and clean out the bores before wiping away all the residual rubbish with a towel (towels are great: lint-free, good at picking up grains and very absorbent).  A tooth brush can be useful for cleaning out the grooves, as would be a hooked tool like a bent brawdal or dentist’s pick.

With the calliper halves fully cleaned up, it’s now time for some reassembly.  I start by putting all the main seals in.  The instructions say to do this dry, but I prefer to lubricate them by dipping them in a jar of fresh brake fluid.  Make sure they’re properly seated, and try to even them out by working them around their grooves as best you can.

Next, the instructions say to fit the wiper seals and retaining rings, but I find that makes fitting the rings harder,  piston fitting more difficult and seal pinching very likely.  So, I go slightly off piste here and use this sequence to easier and more reliable effect:  fit the wiper seals inside the retaining rings (this is the fiddly bit, as they’re bigger than the rings and want to pop out), and then work them around inside the rings to even them out.  Then fit the seals and rings over the open ends of the pistons, such that the ring sits to the open end of the piston and the seal to the closed end.

Now dip a ringed piston into the jar of fluid and insert them into its bore, pressing it gently down with finger pressure alone.  It should go down all the way with only a little effort.  If it jams, it’ll be because it’s slightly crooked in the bore; apply pressure to the high sigde to straighten it up and continue.  As the piston descends, the wiper seal and ring will reach their groove, but they won’t quite fit in.  Keep pressing the piston down until the top is just proud of the ring.

This is where a cleaned up old piston, a similar sized socket or other suitable drift comes in handy – you need to tap the retaining ring into the groove.  It’s an interference fit, so it’s very easy to get an edge to pick up on the groove’s shoulder, wrecking the ring, so take it slowly and easily, tapping gently as you work your way around the circumference of the ring, always using the drift to spread the force over a wide arc of the ring.  I wreck every other ring using the instruction’s technique of fitting these before the pistons, but this way I only wrecked two out of the eight (two callipers, remeber).  I hope you were able to save some of the old rings for this!  Repeat this step for all the other pistons and seals in turn.

Now the calliper halves are completed, you need to mate them back together.  Make sure the mating faces are meticulously clean, including the O-rings’ recesses.  Where relevant, make sure that the spacers for vented disc brake callipers are likewise prepared.  Clean the O-rings on a clean cloth and then refit them to their seats.

Clean the threads on the four cross-bolts.  They were fitted dry, but I prefer to lubricate them slightly to ensure good, even torque and to give some corrosion resistance.  Line the parts up, making sure any spacers are ftted the right way around (there should be one and only one O-ring on each joint) and then insert the bolts.  Turn the bolts until the slack is taken up, but then prigressively tighten them to 60’lbs so that they are fairly evenly tight throughout the proceedure to prevent warping, just like on head bolts.  Finally, the bleed nipples are refitted.

At this stage, the calliper is now fully reassembled.  To give a decent finish and resist corrosion, I paint them, though many won’t bother.  I have had good results using Hammerite smooth – it seems to cope well with the heat and dirt and only softens or peels if spilt fluid is left on the paint for a significant amount of time.  Rinsing off spills with water after every bleed seems to be sufficient to keep the paint intact.

Refit the calliper in the reverse of how it was removed.  I make sure the mating faces of the lugs on the calliper sand axle brackets are clean first to make sure the alignment is good and that the calliper can’t move – that includes removal of any rust or paint as well as loose dirt.  I then apply a smear of copper grease to prevent rust before fitting the mounting bolts with a drop of blue (semi-permanent) thread lock.  They should also be tightened to 60’lbs.  Refit the pads (a light smear of copper grease on their backs will help prevent squealing), reconnect the pipe work, bleed the system and you’re done!

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