XM and Xantia Strut top failures

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INTRODUCTION

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Open the bonnet of any Xantia or XM and on top of the inner wings on each side, you'll see a green or grey 'cannon-ball'; this is the famous Citroen hydraulic suspension sphere. It's screwed into what is commonly called a “Strut Top” or “Strut Mount” (I prefer the latter to avoid confusion with the top of the strut itself) but to Citroen it's a “ Hydraulic suspension sphere bracket”. This supports the top of the front suspension strut in a casting that connects the strut ram to the sphere and the rest of the hydraulic system.

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This casting is welded to a bell-shaped steel pressing which in turn is bonded to the outside of a rubber dough-nut whose inside is bonded to the outside of a 'top-hat' shaped steel pressing that bolts to the underneath of the wing. The rubber doughnut isolates the body from vibrations transmitted up the strut and also accommodates the angular movements of the strut due to suspension and steering movement (the steering rotates the strut shaft within the strut body, but the lower swivel isn't in line with the strut shaft). The entire casting, steel bell, rubber damper, and 'top-hat' mount form one single component as pictured at right (the white paper towel is to keep dirt out of the hydraulics.


CATASTROPHIC FAILURE

There are two modes of failure: in hot climates like Oz and North Island NZ, the bond fails between the rubber and one or both of the two steel pressings – it literally comes un-stuck; in the UK, salt spray attacks the edge of the 'brim' of the inner top-hat pressing. Water then creeps between steel and rubber causing concealed rusting. When the mount fails for either reason, the top part of the mount complete with sphere and pipe-work is driven upwards by the weight of the car on that corner, “spearing” the bonnet as in this picture. REQUIRED (courtesy of ???).


THE CLASSIC WARNING SIGN

In colder climates, the classic early warning sign of serious rust is the strut gaiter (boot) at 'half-mast as in the photo below right and refusing to stay clipped onto the underneath of the strut mount – because the inner brim of the top-hat has buckled under the uneven stresses caused by the inner 'top-hat' rotting away.

Careful inspection under the bonnet may reveal apparently minor signs of rust on the top face of the 'brim' of the inner (top-hat) pressing as in the photo below left. Those slight rust bubbles have come right through because the photo below right shows what it looked like under the wing.

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Caught in time, after the top of the strut shaft had been given a couple of thumps with a BIG hammer during the dismantling procedure, the rust flaked away showing just how bad the rot was as shown in the second pair of photos (below) taken a just a few minutes after those above. The 'wetness' is due to a slight spill of LHM when the sphere was removed.

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With the strut mount removed and on the workshop floor, the full horror is revealed (right).
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The flange (the brim of the top-hat) is rotted right through and has fractured round more than half the circumference, from 1 right round to 2.

Note how the inner steel 'turret' has been distorted by the suspension loads being taken by only one half of the rubber buffer. As a result, the rim that the boot fits over has buckled (3) so that the boot would no longer stay in place – the classic sign of a failing strut mount.

Changing a strut mount is a a common and straight-forward job that the Haynes manual doesn't cover.

The Haynes procedure for removing the strut complete with mount is nonsense – it's physically impossible unless the sphere is removed first - generally one needs to replace either the strut (rare), or the mount; not both at once.


PARTS

The original mounts for (S1) Xantias are no longer available, but the equivalent Xantia II mounts are a direct replacement provided you also buy and fit the new type boot (gaiter) Part No. 5271 92

The only parts needed are:

Depending on the age of the car, you might want to change the “REBOUND STOP” which is made of a high-density foam that deteriorates with age.

The last 8 digits of the VIN is needed to ensure the correct Citroen part number for a replacement strut mount.

Important Differences

With the introduction of the “Xantia II” (as Citroen call the post-1998 models), the design of the strut mount was changed, supposedly to make collapse (due to failure of the rubber-steel bond) less likely and less catastrophic. The obvious and important difference between equivalent Mk1 and Mk2 strut mounts is the larger diameter of the Mk2 gaiters under the wing (that's why you have to buy new boots/gaiters).

However, strut monts for non-Hydractive, Hydractive/Activa and V6 models are not interchangeable due to more significant differences:-

  1. Non-Hydractive cars have small (3.5mm) bore pressure feed pipes to the strut mount. The connection thread is M8 x 1.25 or, from RPO 08209 to 08518, M9 x1.25.
  2. Hydractive/Activa/V6 cars have large (10mm) bore feed pipes and the mount thread is M16 x 1.5 (check!)
  3. The V6 cars are unique in having a larger diameter strut shaft (with a larger nut). The visible difference in the strut mounts is that the V6 ones have a 20mm top hole, all others are 17mm.

With a little ingenuity, non-Hydractive and Hydractive strut mounts can be converted; a competent machine shop can fairly easily make an adaptor to reduce the larger pipe bore or, slightly more demanding, drill and tap a non-Hydractive strut mount to take the 10mm diameter Hydractive pipe. V6 mounts are unique.

Old strut mounts can be refurbished by elastomer.eu formerly Kingas.

TOOLS

  • 27mm socket - to fit top nut; some are said to be 24mm - ?? for V6
  • Torque wrench to fit this socket
  • 27mm ring & OE (or 24mm as above)
  • 10mm & 13mm sockets
  • Strap wrench, heavy duty (use this for choice to avoid unsightly 'chewing' of the sphere)
  • Chain wrench, heavy duty (in case strap wrench won't undo sphere)
  • Breaker bar, ratchet and short extension to fit sockets and wrenches above
  • 10, 11 & 12 mm ring+open-end spanners
  • 8mm (?? for Hydractive cars) flare nut spanner (essential)
  • 6mm hex key (long)
  • Big hammer (4lb minimum) – a big sledge-hammer is best (seriously)!
  • Jack to support the lower suspension arm.
  • Axle-stands with pads to protect the paint on the jacking points.
  • Broom (or similar) to prop the bonnet wide open and a strap to hold it vertical.

Odds & Ends

  • Hardwoood or Plywood pad to protect strut nut from lighter hammers
  • Underseal and paint brush
  • Primer, masking tape and newspaper
  • Spray can of brake cleaner
  • A couple kitchen rolls and something to chuck oily paper into.
  • LHM
  • Wet and dry in grades to rub down any rust on inner wing
  • Very thin strong cord or fishing line (50lb+ BS) – a metre or so

METHOD

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Doing the job carefully for the first time, and taking notes and photos as I went, it took me under 3 hours all told – with the aid of these notes you should be able to do it in less than that.

In advance, thoroughly pressure wash under the wing to remove all the muck, especially around the strut mount flange.

  1. Suspension control lever to HIGH with the engine running.
  2. Loosen the wheel-bolts on both front road wheels while you wait for the car to rise.
  3. Position the axle stands carefully under the front jacking points (if in doubt look in the handbook).
  4. Suspension control lever to LOW with the engine still running. After the car has stopped sinking, wait a good 20 sec before you stop the engine.
  5. Prop the bonnet wide open (near vertical) with something like a broom as pictured (right) and, if you're outside, hold the bonnet in place against gusts of wind with a strap.
  6. De-pressurise the hydraulic system fully by opening the release valve 1½ turns max (this is the 12mm 'bolt' on the front of the pressure regulator - what the Accumulator Sphere screws into) and wait for 20 seconds after the faint whistle stops.
  7. Stuff lots of kitchen roll under the suspension sphere and under the pipe going into the rear of the strut mount to catch the inevitable trickles of LHM.
  8. Unscrew the sphere from the strut mount; it shouldn't be much more than hand-tight, if it's really tight, did you de-pressurise fully?
  9. Stow the sphere (hole upwards) somewhere clean and out of the way in a generous 'nest' of newspaper.
  10. Clean up spilt LHM as you go.
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  11. Undo the 10mm bolt holding the pipe support bracket to the top of the strut mount and then
  12. the gland nut of the pipe into the rear of the strut mount (photo at right).
  13. Remove both front road wheels
  14. Stuff the old strut boot with kitchen roll (use plenty) to soak up the flood of LHM when the strut shaft is undone.
  15. Undo the strut top nut with a 27mm ring spanner while being ready to hold the strut shaft still with a long 6mm hex key. If the nut is really tight, loosen it with a socket on a breaker bar. Undo the nut only until its top face is slightly proud of the top of the shaft leaving a small gap between nut and mount as in the photo (right).
  16. Hold a pad of hardwood on top of the nut and give it a thump with a BIG hammer - weight is more important than force because you need to jar the whole (heavy) strut and hub assembly to release the taper – after several good whacks with a 2lb lump hammer wouldn't shift it, one gentle bump with a 14lb sledge-hammer released it!
  17. Clean the strut threads so that the nut will turn freely with the fingers.
  18. Tape the strut threads carefully. Once the shaft is free of the taper in the mount, remove the nut and wind a single layer of tape around the threads to prevent them damaging the seals in the new mount. It's much easier to do it now than under the wing. Keep the tape clear of the groove at the base of the thread and use only one layer of tape.
  19. Push the strut shaft gently and slowly down into the strut cylinder as as far it will go. Use something like a long Philips screwdriver engaged in the hex in the end of the shaft. This will pump lots of LHM out through the port in the strut shaft into the old boot. Remove and discard the old boot (item 6) and the kitchen roll inside it. Clean up all the spilt LHM before it goes any further.
  20. Push down on the hub until you can pull the strut outward and forwards so the end of the strut shaft JUST clears the bottom of the strut mount. DO NOT pull it out so far that the drive shaft disengages or back so that the pad wear sensor wire breaks! Be careful not to damage the strut leak-off pipe. Do not pull the strut shaft up until it is back inside the new mount and being pulled up into the taper, otherwise you'll pump lots more LHM all over everything!
  21. Hold down the strut shaft with the 'Philips screwdriver' (as above), and pull the bump stop assembly off it. If you're not going to replace the bumpstop, thoroughly clean the LHM off the bump stop assembly.
  22. Clean the strut shaft and the top of the strut cylinder. Take the new boot out of its plastic bag and slip the bag over the top of the strut shaft so muck from the strut mount doesn't contaminate the shaft.
  23. Remove the old strut mount by undoing 4 x 13mm head bolts that hold the old strut mount in place and lower it down and out from under the wing.
  24. Clean up the inner wing above and below, rubbing down any rusty patches before priming and re-painting. Brake cleaner will wash off the last traces of spilt LHM. Apply a thin coat of under-seal to the underneath surface.
  25. Paint the top mating surface of the new strut mount including its edge where rubber meets steel and the water creeps in with a THIN coat of under-seal. DO NOT get any under-seal in the threaded bosses and don't wait for it to dry!
  26. Fit the new strut mount by holding it up in place and fitting the retaining bolts finger tight only. Apply a slight smear of LHM to the taper and seals inside the new mount.
  27. Fit the new boot to the strut after removing the bag from the top of the strut shaft.
  28. Stuff the new boot with kitchen roll as some LHM will inevitably get pumped out as you fight the strut back inside the base of the new mount.
  29. Push the bump stop assembly up into the new mount.
  30. Tie the thin cord into one big loop. Keeping hold of the knot, feed the loop down through the strut mount and bump stop, using something suitable to stop the knot disappearing down the hole. Under the wing, double the loop over to make a noose.
  31. Slip the noose down over the strut shaft into the groove at the base of the threads and pull tight without any twists. The cord will now give you something with which to pull the (very slippery) strut shaft up through the mount – but not yet!
  32. Fit the strut shaft into the new mount: Push down on the brake disc and position the strut shaft inside the strut mount. Now wipe the shaft and your hands really clean and dry of LHM. With one hand, feed the end of the shaft into the hole in the bump stop, with the other hand carefully pull the strut shaft up into the mount with the cord. Once the shaft is inside the taper, you'll have to use your long hex key to lever the shaft into alignment with the taper – no need to align the horizontal port in the shaft with either port in the mount. You'll probably have to remove the cord before the thread is above the taper and you may find that you have to loosen the mount's retaining bolts to tilt it slightly.
  33. As soon as the top of the thread is above the top of the mount, hold the shaft in place with the hex key and remove the tape. Don't worry about the threads being a bit oily for the moment, slide the nut over the hex key and screw it down the threads to pull the shaft up into the taper. This should not require much force but you will need to use a spanner.
  34. Do up the nut as tight as it will easily go with just the spanner while holding the strut still with hex key.
  35. Tighten down the 4 x 13mm bolts that hold the mount to the inner wing.
  36. 'Refit the sphere with the new seal, being careful that the seal, lubricated with LHM, in the groove in the mount and won't get pinched.
  37. Refit the pipe and support bracket. Don't be brutal with the gland nut (there's no rubber seal) better it weeps slightly and needs tightening than you shear it off!
  38. Remove all the kitchen roll from the new boot by pushing down its top and clean the strut cylinder of any traces of LHM (otherwise you may get an MoT fail for a leaking "damper".
  39. Fit the top of the boot to the rim on the strut mount, starting from the inside of the wing and working round both sides towards you.
  40. Under-seal the joint between the new mount and the inner wing.
  41. Refit the road-wheels – to do so, you may need to compress the strut slightly with the jack. Remove the jack as soon as the wheel-bolts are nipped up.
  42. Close the relief valve (only nip up – over-tightening will damage the valve).
  43. Start the engine, when the STOP light goes out, raise the suspension to HIGH and remove the axle stands. Keep your foot OFF the brake pedal otherwise you might end up having to bleed the front brakes
  44. Tighten the wheel bolts to the correct torque.
  45. Check for LHM leaks above and below the wing.
  46. Stop the engine.
  47. Refit the strut top nut with thread-lock: With the weight of the car on it, the strut shaft can't move, so you can safely undo the nut. Thoroughly degrease both nut and the shaft thread with brake cleaner before applying thread-lock to both the shaft thread and the mount seating face. Refit the nut and tighten down with hex key and spanner.
  48. Tighten the strut nut to 65Nm (48 lb-ft) with torque wrench and socket.
  49. Make sure there's nothing under the car.
  50. Start the engine and do a thorough Citaerobics session to purge the new strut top of air.
  51. Check the LHM level in the reservoir with the suspension on HIGH and top up if necessary.
  52. Take the car for a test drive, then check again for LHM leaks above and below the wing.

Job done!