Xantia Pad & Disc Replacement and Rear Calliper Overhaul

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The extra steps required to replace the discs (and deal with rear calliper corrosion) are in italics.

SAFETY NOTES

New discs must be fitted in pairs and with new pads. Old pads on new discs will have poor braking power until the pads and discs have bedded in – by wearing the same (but shallower) grooves in the new discs as in the old!


Tools If you decide to invest in a tool to wind back the front pistons, beware that many so-called 'universal' kits DON'T include any adaptor that will fit Xantia pistons!


Changing Rear Disc

The callipers have to be removed and you will need new calliper bolts – it's unwise to refit old ones and if you haven't got a complete set of new ones to hand you are sure to break the lot! Calliper bolts are NOT ordinary 8.8 mild steel and standard M10 x 1.5 thread pitch, but 10.9 high tensile steel with fine M10 x 1.25 thread pitch.

TOOLS

  • Wheel-brace (19mm),
  • large engineers screwdriver,
  • long-nosed pliers,
  • big hammer,
  • pin punches,
  • 8” file,
  • wire brush,
  • scraper,
  • LHM,
  • PlusGas or similar release fluid – NOT a de-watering agent like WD40)
Front Brakes
  • either a special piston tool or something like an old blunt flat file to wind the calliper pistons back.
Front Discs:

*Torx55 or 8mm hex key,

  • Impact driver and
  • T30 bit.
Rear Pads
  • 8mm socket (pad retaining bolt),
  • 8mm ring/open-end spanner(pad retaining nut).
Rear Discs/Callipers:
  • 5.5mm socket (disc retaining screw),
  • 8mm flare nut spanner (rigid brake pipe),
  • 10mm socket (mud shield screws),
  • 16mm hexagon or flat-drive (not a standard bi-hexagon) socket (calliper bolts)
  • 400mm breaker bar (calliper bolts),
  • 10mm drill bit (estates) or 9mm (hatchbacks) to clean out the calliper mounting through-holes that will be clogged with corrosion,
  • sharp chisel or centre punch.

FRONT BRAKES

Sequence of operations
  • 1. Chock both back wheels very securely.
  • 2. Un-tighten both disc retaining screws with the handbrake ON (having the wheel bolts still tight takes the strain off the screws and makes them much easier to undo).
  • 3. Crack-off (but not loosen) the wheel bolts on both front wheels.
  • 4. Jack up one side at the front and support the car with an axle stand.
  • 5. Remove the road wheel.
  • 6. Release the handbrake, then disconnect the handbrake cable from the calliper by pulling the end of the inner from the operating lever, then the cable outer from the lug on the calliper,
  • 7. Unplug the pad wear sensor wires (one on each pad) from the double socket on the suspension strut.
  • 8. Lever out the anti-squeal shim from the calliper with a screwdriver under the bottom edge of the shim.
  • 9. Remove the retaining clip (or small split-pin) from the calliper retaining pin.
  • 10. Drive out the retaining pin with either a proper pin punch or a nail (the pins have dimpled end) of the right size ((5mm or 3/16”) – pins vary from being very tight to needing no more than a couple of taps and a push; if the pin is really tight, wire brush what you can get at, apply Plusgas, use a pin punch and tap pin in and out until it will drive out without too much brute force.
  • 11. Gently lever the calliper against the outside pad so that the calliper will slide off the pads (you only need to gain a few mm.
  • 12. Remove the pads - you will see that the piston has 4 slots in it,
  • 13. Swing calliper up and push back (towards engine) so that it stays up resting on the calliper holder
  • 14. Release the hydraulic hose from its clips.
  • 15. Undo the calliper retaining bolts and remove calliper, supporting it securely out of the way – don’t let it dangle on the hydraulic hose!
  • 16. Remove the disc- it may need a few bumps from behind with a BIG hammer; be careful not to rock the car off the axle stand!
  • 17. Thoroughly clean all rust from the face of the drive flange – it’s very important that the new disc sits flat on it with absolutely minimal run-out (wobble). Squirt with WD40 or similar and wipe off excess.
  • 18. Degrease the new disc thoroughly with a petrol-soaked rag or brake cleaner, paying particular attention to the friction surfaces.
  • 19. Fit the new disc, doing up the retaining screws hand tight.
  • 20. Refit the calliper
  • 21. Screw the piston back into the calliper - either with a special tool or by using something like a rectangular bar or blunt file across the slots – until the base of the slots is flush with the face of the calliper; the piston should turn fairly easily but it will be more than finger tight. Opening the bleed nipple as if bleeding is claimed to make it easier.
  • 22. Make sure that the largest cut-out in the piston will be at 3 o'clock (off side) or 9 o'clock (near side) when the calliper is swung back down into its normal position.
  • 23. Scrape clean the curved faces that the pad backing plates sit on and smear with slight trace of copper grease.
  • 24. Fit sensor wires to new pads (upper hole on inside pad, lower hole on outside pad)
  • 25. Fit new pads into carrier and swing calliper down into position - checking that the 'pimple' on the back of the inside pad is within the slot in the piston face.
  • 26. Reverse operations 10 – 3. (clean and lightly grease the retaining pins with copper grease).
  • 27. Take the hand-brake cable end off the calliper arm. With the engine running, firmly press the brake pedal twice, back off the cable adjusters all the way; clean the threads, then adjusted the cable to the correct amount (just loose) on the arms. Spray the exposed adjuster threads with WD40 be VERY careful not to get ANY on the disc or pads.
  • 28. Repeat for other side.
  • 29. Tighten the wheel bolts to the correct torque and check the tyre pressures.
  • 30. Before removing wheel chocks, apply the hand-brake!
  • 31. Be VERY careful about stopping until the pads have started to bed-in. Half-a-mile with the hand-brake on lightly will start the process.

REAR BRAKES

Notes

The rear pads can be changed quite easily – buying a shim and spring kit at the same time will make a better job and save time. If the callipers are to be removed either to replace the discs or to deal with corrosion, before starting the job get a complete set of calliper bolts (the originals will have been stretched and bent) plus a pair of new hydraulic seals for the ends of the brake pipe in the callipers (all dealer only parts).

Rear pads and discs generally last several times longer than the front ones. It seems to be common for the original rear pads, even on estates, to last for 100,000 miles or more. But by this time, the common problem of corrosion of the mounting face of the alloy callipers pushing the calliper away from the trailing arm is more or less inevitable. This occurs because salt water creeps by capillary action between the calliper and the trailing arm causing galvanic corrosion.
Rear disc binding.jpg
Because the mounting bolts are towards the outer edge of the calliper, the inner part of the calliper (nearest the stub axle) is levered away from the swinging arm wearing the pads wedge-shaped and eventually bringing the inside edge of the calliper slot into contact with the back of the disc as in the photo (right).

The only cure is to remove the calliper and clean up the corrosion before refitting. When the problem is noticeable, the calliper bolts can be difficult to remove without snapping off the threaded section in the swinging arm.

Advance Preparation

The usual situation is that all the fasteners except the calliper bolts will undo fairly easily with the application of a penetrating fluid like PlusGas (not WD40). The calliper bolts are usually very tight (and slightly bent) so to maximise your chances of getting the bolts out without snapping them it's essential to soak them with penetrating oil for as long as possible. While you're at it, also treat the three shield mounting bolts, the pad retaining bolt and the disc retaining screw. Scrub the exposed ends of the bolt threads with a wire brush to remove the muck and the loose rust. Give the head of each calliper bolt couple of GENTLE thumps with a BIG hammer to crack the corrosion before treating with penetrating oil.

Cut a fingers from a vinyl or nitrile glove and have several wire bag-ties ready to seal brake pipes.

Received wisdom is that the faces of calliper and the swinging arm need to be isolated in order to reduce corrosion between them – polythene is a common suggestion. Overhead Projector (OHP) sheets for laser printing are better – dead flat, thin, stiff, and more resistant to heat.

It's possible to swap the callipers from side to side so that the un-corroded external faces become the mating faces. This means you have to have both sides lifted and supported at the same time.

Sequence of operations
  • 1. Hand-brake on really hard. Remove the wheel trims, start the engine and set the suspension to (Service) High.
  • 2. While you're waiting for it to rise, 'crack off' the disc retaining screws (5.5mm hexagon socket) while the wheel bolts are keeping the tension off the screws. This is only possible if steel wheels are fitted, with alloy wheels, this step is omitted.
  • 3. Then 'crack off' the wheel bolts on one wheel. Support this side on the jack and take the wheel off.
  • 4. Remove the disc retaining screw, (then the disc will come off with the calliper - often the calliper will lever the disc off as the bolts are undone). Squirt penetrating oil into the hub-disc joint, all 4 wheel bolt holes and the retaining screw hole. Rotate the disc slowly to distribute the penetrating oil.
  • 5. Remove the 'mud-shield' (three set-screws at the back) – not strictly necessary if the disc comes off easily, but it'll have to come off if you end up have to thump it off.
  • 6. Loosen the pad retaining nut and bolt, the curved pad shield will the slide off (slots not holes) with a little gentle persuasion. Give the pad retaining bolt a good wire-brush in situ while rotating the head slowly with a socket. Then, once the nut is undone, the bolt can be withdrawn easily and the spring will fall out. Gently lever the pistons back and remove pads and shims, noting the position of the shims (rectangular bit at the bottom).
  • 7. Replace the pad retaining nut and bolt and do them up reasonably tight so that the two halves of the calliper can't move.
  • 8. Be VERY CAREFUL of the ABS SENSOR and its WIRE – a new one is about £35! Unclip the ABS wire (be gentle with the clips they will be old and brittle) from the brake pipe and tie it back out of the way.
  • 9. You'll may find that by gently levering it against the calliper, the disc comes loose. If you're going to replace the disc, you can afford to be a bit brutal with the disc: give the driving face a good clout on each of the 4 gaps between the wheel bolt holes. Give the outside edge a couple of good clouts (from inside and out) opposite the calliper, rotate 90° and repeat all the way around. Try levering again. If it's still stuck tight, another squirt round with penetrating oil. While you're waiting for it to do its stuff, move onto the next step and come back to fighting with the disc when you've done that.
  • 10. Clean off the gland-nut and the last few inches of the brake pipe then undo the gland nut carefully, sealing the end of the pipe by slipping that cut-off glove finger over it and wiring it on tightly to the pipe above the gland-nut. Twist a small piece of clean rag into the hole to keep out the dirt. Don't use paper products – little bits will get left behind.
  • 11. Remove the calliper bolts - don't be brutal, both bolts may be slightly bent at the calliper/suspension arm joint, so undo the bolts evenly (to ensure that rotation stays synchronised, it helps to 'pop' each bolt-head at top-dead-centre with a centre punch or chisel) so that the bends are not fighting each other and you. You need to apply enough force to move the bolts without snapping them at the bend. Your first objective is to move both bolts slightly so that penetrating oil can work its way into the corrosion in the threads and between the bolts and the calliper body. Then loosen, lubricate and so on until they are completely undone.
  • 12. Clean up everything. Personally, I use a combination of scraping with a sharp paint scraper, wire brushing, and a sharp 'smooth' file (be careful to only remove corrosion – not metal). I spray-paint the machined face of the suspension arm with a thinnish coat of heat-resistant (wood stove) paint.
  • 13. Clean off around the rag plug, remove it and then extract the seal from the hole with a number 6 wood screw – only screw it in just enough to get a grip then you could re-use the seal if you forgot to get a couple of new ones!
  • 14. Replace the rag plug, screwing it in tight, then you can safely rinse the brake dust off the calliper under the tap and give it a scrub with washing-up liquid and an old tooth brush.
  • 15. I found the mating faces of my callipers were deeply corroded so I didn't hesitate to brush paint them with heat-resistant paint for metal (Blackfriars). Clean up the slot faces where the pads rest and make sure the piston pressure faces are clean of paint and corrosion.
  • 16. Re-assembly is simply a matter of reversing the steps above.
  • 17. Getting the gland nut back into the calliper can be a struggle; the trick is to make sure the pipe is 'square-on' to the calliper and push down gently (don't forget to push the seal onto the end of the pipe until it hits the square flange on the pipe). If the nut is aligned with the hole, it doesn't need a spanner to get it started – fingers only! If you us a spanner to try to force the threads to engage you'll only end up cross threading it and chewing-up the calliper threads – then you need a new calliper!
  • 18. The correct torques for the calliper bolts are 54Nm (10mm) and 47Nm (9mm).
  • 19. With the suspension on High, bleeding the calliper is simply a matter of starting the engine and letting the pump push LHM through while you hold the brake pedal down (on High, the rear suspension/brake circuit is fully pressurised). The rear circuits are very long, from the 'anti-sink' sphere all the way to the Doseur (brake master) valve and back to each calliper. Bleed at least 300 mL out of each calliper until the LHM comes through bright green, clean and clear.
  • 20. Once you've finished one side (Don't forget to fully tighten the wheel bolts!), you can do the other.

If you're doing a really thorough job, it'll take about 4 hours per side; if time is of the essence (MoT time?) and you're not going to worry about further corrosion then you could skip painting the mating surfaces of callipers and swing arms, but the problem will come back to haunt you!