Technical SLK R170

Mercedes Headlamp Adjustment Repair – Most Models


Here is a quick fix that will restore your failing or ‘wobbly’ headlamp back to a working condition.  If you notice that the headlamp leveller is not working correctly and on inspection the internal reflector seems loose and ‘disconnected’ from the lamp body – it probably is!  Caused by the internal ball and socket arrangements breaking that secure the reflector to the adjustment threaded rods.

If you are lucky the ball and socket arrangement will have just popped out and you should be able to snap them back in place once you can see exactly what you are doing.  The best policy is to remove the lamp unit and work on it at the bench or table.

Usually there is only two or three fixings that hold the lamp into the vehicle body and removal is in many cases quite simple (At least on the R170 SLK we have here)

Mercedes Headlamp Repair 1

On removing the bulb access panel you should be able to see the issue.  There are three attachment points to the reflector, looking from the back of the right hand lamp there is a ball and socket on the vacuum leveller adjuster (could be electric in some models) to the lower left and two points of attachment top and bottom on the right, these are usually a cream/white nylon part, the socket of which is screwed to the rear of the reflector.  Its worth noting that if when you shake the lamp you can hear broken parts inside there is likelihood that one of the sockets has become brittle and broken.  As far as I know, even though these small plastic socket parts look to be replaceable, I have yet find a source. It would mean in most cases a replacement lamp to rectify the fault, used or otherwise its an expensive fix for an otherwise serviceable lamp.

On the R170 SLK once the indicator unit has been removed, by slotting a screwdriver down the 10mm hole at the rear of the lamp body and flexing the latch access can be made to the steel spring clips that hold the polycarbonate lens to the grey lamp body. Once these clips have been removed the lens and body can be carefully levered apart.  The front chrome surrounding lamp trim simply pulls forward and allows full access to the reflector.

Note at this point that if you touch the shiny chrome reflector with your fingers it will mark, equally if you try and rub it with a cloth, even light polishing will damage the reflector.  I have found that using a fresh pair of vinyl un-powdered gloves prevents any handling marks and is a great aid to working with the reflector parts as it prevents any damage.

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Once apart the reflector pivots can be inspected, it will be clear if just pushing the unit back together will be your fix or if further intervention will be needed if you spy broken or missing parts.  In the case of the SLK lamp, one of the nylon sockets had lost one of its three retaining ears allowing the ball to spring out of place very easily.  What was required was to retain the ball and push it into contact with the two remaining ears, giving a secure and durable mounting to the broken part.

Taking a small jewellers screwdriver (app. 1mm diameter) heat it with a cigarette lighter and melt two small holes in the plastic socket, next to the point where it fixes to the reflector body with the single torx screw.  The hole position should be so that they are level with the top flat edge of the nylon ball once it is fitted to the socket.  Thread a paper clip through the two holes and enclose its free ends around the ball whilst holding everything tightly in place.  With pliers twist together the two ends, applying tension to the socket and bridging the paperclip diagonally across the top flat surface of the ball where the retaining ear is missing.

Reassemble the lamp, threading the repaired parts back together, pushing it home into the receiver of the vacuum or electrical adjuster.  If possible always move the sockets around so that the broken one ends up on the headlamp leveller as this can be snapped into place more easily on reassembly than the other attachment points.  Often the sockets are the same moulded part fitted to different points on the reflector and this allows them to be positioned so that any repaired socket is under the least supporting stress (leveller position).

Rebuild the lamp ensuring to use a light smear of clear sealer on the headlamp lens to body gasket if it looks to be leaking or allowing any dirt build up under the lens lip. Clip back all the lens fixings and refit the lamp to the vehicle.  Adjust the beam pattern to the specifications required by rotating either the up/down or left/right adjusters, be sure to make any adjustment with the instrument leveller control set to ‘0’.

Mercedes SLK (R170) Central Locking Problems Resolved


Central locking problems in the R170 series of Mercedes Benz SLK are quite common. The issues are usually centred around the failure of the PSE (Pneumatic System Equipment) pump unit or its connecting air pipework. The pneumatic door lock actuators are simple by design and as a result are found reliable, even in older cars.

Mercedes SLK Central Locking Fix 1


If your central locking is playing up, maybe no doors lock or unlock, perhaps one door does not function, there are a few simple checks to determine what and where the issue may lie. The first thing to try is when you lock the car from the remote key fob – does the vehicle respond and if the ‘alarm arms and disarms’ this is an indication that the key fob is sending the correct signals to the car. However if the car only either locks or unlocks from the fob, there is a chance the fob has a problem with one of the miniature tactile switches inside. These often fall off or break away from the internal PCB, these can usually be repaired (re-soldered or replaced) by carefully breaking open the sealed halves of the fob and resealing when done.

Mercedes SLK Central Locking Fix 2

Actuating a fully functioning key fob will cause the PSE pump to run for a period, as will unlocking the drivers door, opening the drivers or passenger door, unlocking the boot or operating the dash ‘door lock’ switch. Listen out for the pump motor running in the area of the boot floor just below the rear of the fuel filler. To inspect the PSE pump unit, open the boot and remove the spare wheel, then remove the right hand plastic trim lower edge fasteners to enable the ‘foam box’ containing the PSE pump unit to be extracted sideways. There should be enough free-length in the wiring loom and yellow connecting pipes to allow its partial removal into the spare wheel well. If the foam box is ‘wet’ and you do not hear the pump run on lock actuation, then prepare yourself for a potential financial blow.(Circa £200 – £380 for a good used part) It is common for the PSE pump unit to be waterlogged from either water entering the boot from the inner arch area (corrosion) or through faulty boot lid seals and block channel drains (drains behind rear quarter glass gutter, under boot lid) – either way the water is mopped-up by the pump unit foam and damage results. Housed in the base of the PSE unit is a complex electronic PCB that controls its cycle and air distribution sequence. Even if not completely waterlogged a damp environment can do its worst, not only to the PCB but also to the small DC motor that runs the pump itself. It is worth checking the supply fuse, but often no response means replacement required. There are a few companies offering a service exchange service for PSE pumps but as yet I have not found one that does R170 types!

Mercedes SLK Central Locking Fix 3


However if the motor ‘runs’ and seems to run at a healthy speed (buzz) you may be in luck. Mark the yellow hoses and their associated clip in connection points before removing them from the pump block. Activate the pump and see what degree of suction or pressure appears at the air manifold output spigot connections. Suck locks, blow unlocks. The three yellow pipes are connected to: The drivers door only, the passenger door and boot lock and finally the fuel filler flap and cubby box lid lock. You can manually test the function of the actuators on these components by sucking and blowing on the individual pipe ends. This takes a bit of ‘puff’ but it can be done. If when blowing on the respective pipes, you can blow constantly, without building any pressure in the pipe, there is most likely a leak. The pipes are made from a semi rigid wall Nylon and very tough, it is uncommon for them to split or cut. What is more common and is actually a design flaw in this model, is the grey right angle pipe end connectors that clip to the door lock actuators, break. This is due to the over-tight stretch of the air pipe across the door inner. Over time this work-hardens the connector (door slamming etc) and the connecting pipe breaks away, taking with it the plastic spigot on the grey push-on connector. Any air leak will affect the function of the locking. Often if you listen carefully at the latch section on the door edge while the pump is running, any hissing is a sure indication that the pipe connector has broken inside the door and will need attention.

Mercedes SLK Central Locking Fix 5

To gain access to the door lock actuator and its yellow pipework you will have to remove the door card. Start by prizing out the SRS badge and removing the philips screw behind, then remove the chrome trim plate and plastic latch aperture cover from the door edge. Beneath the door handle locate the slot in the underside seam and insert a broad screwdriver, lever off the top half of the handle cover to reveal two more large philips screws. This will take some force to unclip the handle and you may think you are about to break it – don’t worry as long as your screwdriver is as broad as the slot will allow it will pop off – eventually!

Mercedes SLK Central Locking Fix 6

Remove the top triangular trim piece behind the mirror area. Using a trim clip tool or spatula, unclip the trim at its lower edge and speaker section. You can see the position of the mushroom clips in the photograph of the rear of the door card.

Mercedes SLK Central Locking Fix 7

With the bottom edge of the door free lift the handle of the door card upward with some force. Ensure that when the large handle clip disengages from the steel panel of the door, that you don’t stress the tweeter speaker wire, this could if yanked, break the fine wires to the speaker.

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Once the door card is free, slip your hand behind and disconnect the tweeter connector (covered in grey foam) and then unclip the door release lever mechanism hook from its operating lever, you will have to pull back the black outer sleeve of the bowden cable and slide it from its retaining slot in the plastic block on the rear of the door card. Now you can put the door card safely out of the way.

Mercedes SLK Central Locking Fix 10

Carefully peel back the plastic membrane from the lock area of the door to reveal the actuator and yellow pipe. Operate the lock from the dash or key and identify the leaks in the area where the pipe joins to the grey push on connector. Usually once you touch this area the pipe breaks off completely! The connector can be levered from the actuator with a screwdriver, it is a snap fit.

Mercedes SLK Central Locking Fix 11Mercedes SLK Central Locking Fix 12

While you can no doubt get replacement grey push connectors for the air pipe, if you damage the pipe end in replacing it and have to cut it back even a few millimetres, it will be too short to reach the actuator. The pipe appears to be heated and sweated onto the connector and I felt it too much of a risk to try to replace the connector in this instance, so I repaired it in such a way as it would be stronger than the original part!

Mercedes SLK Central Locking Fix 13

It is important to release the yellow pipe from the cable tie that also holds the loom section a little further across the door, this gives a few valuable millimetres of slack to take the stress off the pipe and its connector.

Mercedes SLK Central Locking Fix 14

Now to repair the connector. Using a jewellers screwdriver or suitable size small drill, open out the plastic connector ‘break-point’ and pipe to take a short piece of nozzle tube cut from a WD-40 spray can. This tube can be scraped with a sharp knife to reduce its external diameter slightly to obtain a tight push fit inside the two broken pieces of the connector. A piece of about 8mm in length is perfect, using a light smear of bonding glue on assembly if you wished.

Mercedes SLK Central Locking Fix 15Mercedes SLK Central Locking Fix 16

You will now have to mix some epoxy putty (Milliput) to add strength to the join area and complete the repair. If you shape the putty as I have done in the photographs, it will add support for the pipe and prevent the two pieces coming apart in the future, while additionally of course sealing the repaired joint. Once you have fashioned your repair, push the connector back home onto the lock actuator.

Mercedes SLK Central Locking Fix 17

Test your locking and build up the door. I suppose if you were a purist you could try and replace the connector with a new part, but due to the restricted pipe length (the real problem in the first place) you could run the risk of damage. As the repair cannot be seen, in my view it is a simple and quick solution to the problem. This repair technique could be easily used on connectors utilised on the pneumatic headlamp levellers on vehicles of the same era, such as the R129 SL etc.

SLK PSE Central Locking Pipework Connection Scheme

SLK PSE Central Locking Air Pipework Connection Scheme (LHD Models)

SLK Electrical Device Connection/Integration Scheme

SLK PSE Pump Electrical Device Interconnection Scheme

See here for more useful general background info on the Mercedes pneumatic central locking system.

Mercedes SLK (R170) ABS Fault – Rear Reluctor Ring (Tone-wheel) Replacement


ABS faults can be complex to solve but often it is the simplest of things that causes those dreaded lamps on the dash.  If there is an issue with any wheel speed sensor arrangement on any corner, then this will prevent a number of things working correctly, namely ABS, TCS, ESP, BAS, Cruise Control/Speed Limiter and on the SLK power operation of the Vario roof too. So it needs to be fixed. It is now also a critical tested component in the UK MOT annual check – any dash warning lamps of this kind will immediately fail the inspection and prevent you from obtaining that valuable certificate.

Mercedes ABS Fault - Reluctor ring replacement 1

Intermittent ABS light faults are often attributed to dirty or poorly adjusted wheel speed sensors, even poor connections or weakly performing/damaged sensors can flag faults.  These faults are usually reasonably cheap to sort, though problems with the pump or controller can run into many hundreds to fix.  With this in mind, it is prudent to always check the simple things first, then move on to the ‘eye-wateringly’ costly parts when all other avenues have been followed and options exhausted.  So where to start…

Fault finding can be very hit and miss without a compatible Fault Code Reader that can access the MB systems protocol. There are many on the market to choose from and probably the most capable will be from the Autel range. Be sure what you are buying covers the ABS system, as often less expensive readers only cover engine fault codes and leave the purchaser no better off when it comes to tracking faults in the ABS, SRS or other Body electronics. I use two or three tools, the most flexible and economical is the Autel 702 Maxi-Diag Elite, this can be purchased for under £150 if you search around for the best deal.

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However if you don’t initially want to run to that expense and you may be able to find a friendly independent mechanic who can read the system for you and tell you where the problem lies.  Do remember that if you go to a dealer for a code read, it is likely to cost around £45 to find where the problem lies.  You will then have to take it back to get the fault cleared once repaired, so as you can see you are getting pretty close to the cost of owning your own powerful diagnostic tool that will stand you in good stead for the future. If you have an older Mercedes vehicle pre 2000, then you will have less choice of code reader and things get a little more complex – you can catch up on older vehicle diagnostics here.

There are common faults that can cause problems throughout the Mercedes model ranges, no different with ABS than any other system. If you get unwanted ABS activation at slow speed, when rolling to a braked stop.  This is often caused by the wheel speed sensor on one or more wheels not detecting its rotational impulse cleanly.  This is called ‘falsing’. The controller is being fed an inaccurate stream of speed signal impulses that makes it think that one of the wheels is skidding and it applies (wrongly) the ABS to that wheel.  On W124 models, this was often caused by the magnetic speed pick up sensor devices on the front wheel hubs attracting metal rust debris, ending up looking rather like a christmas tree of iron filings.  The pulsed electrical induction signal from the sensor as its paired slotted ring on the rotating part of the axle whizzes by, is masked by the ‘growth’ of collected iron and rust on the sensor head, making what should be a very clean and precise tiny electrical signal, into a low level ‘blur’ in layman terms.  Simply removing the sensor and cleaning it up in a great deal of cases will result in a cure for this problem. If this does not cure the issue you will have to look more closely at the condition of the slotted or toothed ring that can be seen at the base of the sensor hole, this part passes the nose of the sensor as the wheel rotates.  On the front wheels of the vehicle this ‘reluctor ring’ or ‘tone wheel’ is often a vertically orientated slotted disk mounted behind the brake disk, attached to the rotating hub. Unless corrosion has taken its toll, the front tone rings seem well protected from the elements and do not often give trouble.

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On the rear, most Mercedes cars have flat slotted punched-out reluctor rings ‘sweated’ onto the outer surface of the outboard CV joint casing, just as it passes through the hub carrier.  Often out of the factory this forms part of the complete half shaft and if it gets damaged a few years down the line, or as it often does – corrodes, then the complete drive shaft/joint had to be replaced at quite a tidy sum.

…Enter the wonderful world of the ‘Far East’ on that popular auction site. A wonderful factory somewhere in the world now produces just the 48 window (slots) 92mm reluctor ring (also common to SL R129 and many others) that you can fit to your existing half shaft and get things going for under £10 component cost. Needless to say it is quite involved to fit as you obviously have to remove the drive shaft from the vehicle to carry this out.  Link to reluctor ring seller.

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This article covers the fitting of a rear drive shaft reluctor ring to a 2001 Mercedes SLK200 R170, though the procedure will be common to many other MB models.  If you discover the faulty ring is on the side that has the exhaust passing by the drive shaft then you have a little more work ahead, as it often involves the partial removal of the exhaust system to obtain full access.  If however, if it is like in this case – on the right rear of the vehicle, no such removal is needed.

Reluctor ring replacement

You may wish to initially remove the wheel sensor to protect it from accidental damage. Then you will need to obtain a 32mm 12 point socket. With the hub centre embellishment removed from the wheel (Alloys), with the handbrake set, in gear, while on the ground, peen out the locking tab on the hub nut.  Fit the socket and with the aid of a breaker bar, remove the centre hub nut from the end of the drive shaft.  Spray a good quantity of penetrating oil onto the shaft end so it travels down the splines within the hub. You may need to slip a tube over the breaker bar to ‘crack’ the hub nut off, as if not recently removed it will be very tight indeed.

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Now raise the vehicle so the differential is at least high enough to be able to swing a 21 inch breaker bar beneath the car (those inboard CV-to-output flange bolts will be incredibly tight) Chock and make sure your working area is safe then remove the 6 reverse torx bolts from the inboard flange of the drive shaft.  These have been thread-locked with a compound that must be the almost as strong as the bolt itself!  It will take some muscle to remove these pins, so be prepared.  Always seat the reverse torx socket on the pin with a copper hammer, not only does this ensure the socket is seated as far as it will go onto the head but the ‘rapping’ helps to jar and break the joint.  Remember – good well fitting tools are important here as if you twist up the head with an ill-fitting socket, you will be left with a huge ‘near impossible’ job to remove it.

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Once all six flange bolts and tri-plates are removed the shaft can be pulled down towards the front of the vehicle.  In some cases you will have to remove the plastic cover over the fuel pump to gain adequate opening to ease out the shaft end.  Its a tight fit, but it will come clear and hang down just below the nose of the diff.  Now take a copper drift and stout hammer and whack the end of the drive shaft, it should with a few blows begin to move, once it starts to move tap it with care so it passes through the splined hub centre.  Support the shaft as you tap and once free, guide it out from beneath the vehicle.  While it is off, check the CV rubber dust boots on both ends for damage/wear/cracks/splits as this is a perfect time to change them.

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Remove all traces of the old reluctor ring and file the surface clean to prepare it to accept the new ring. File deliberately more material off the outer edge to allow a slight taper lead-in for the new ring.  Once you are satisfied that the area is nice and clean and smooth, prepare to tap home the new ring onto the CV joint casing. Heat up the new reluctor ring with a blow torch, don’t go too mad, just enough to make it hot.  Then with a gloved hand, place it centrally and tap gently around the perimeter of the ring to drive it home into position.  In this case it was easy to see the exact location and position of the old ring, if you are not so lucky then use a torch to inspect the opposite side of the vehicle to get the correct placement dimensions you need.

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Once the new ring is fitted, the drive shaft can be assembled back into place and the other parts built up around it, much in the same way as they were removed.  Be sure to tighten the hub nut to the same position as it was prior to removal so the lock tab can be tapped back into place.  If you can obtain 6 new flange bolts for the reassembly, then that would be best, failing that be sure to wire brush the old screw lock compound from the threads before reusing.

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Once the vehicle is back on its wheels on level ground, insert the code reader into the OBDII diagnostics port, then read and clear the ABS speed sensor related faults from the controller. Finally road test. You will most probably now have no warning lights on the dashboard and be able to enjoy once more a fully functioning set of connected vehicle features that were all lost while the fault was present.


Because of the proximity of the exhaust and restrictions of access for the removal of the left hand drive shaft it is possible to remove the lower link bolt (lower wishbone to hub carrier), the ball joint of the tie link and hub end of the pushing link (lowest fixing on the hub carrier)  See diagrams below to identify component attachments to be removed. Once these fixings are removed it is then possible to pull the hub at the bottom just far enough out to allow the drive shaft outer CV joint to slide out its hub spline and hang down to clear the carrier so the new reluctor ring can be fitted.  Just remember to pre load the suspension as if the vehicle was standing on level ground before retightening the removed bolts.  This is a practical alternative method to removing the drive shaft completely from the vehicle.

Fig-117 Fig-116


Mercedes SLK Vibration on Overrun – All Gears – Propshaft Centre Bearing Replacement


We recently picked up a 2001 facelift Mercedes SLK200 from South Wales and on the way back to Staffordshire it was obvious all was not well with the driveline.  As soon as the vehicle started rolling at even the slowest speeds, there was a bearing noise usually associated with a gearbox problems.  It was present in all gears and became almost unnoticeable at about 60mph and above. It did not change note in any way if you dipped the clutch (This was a 6 speed manual model) or selected neutral whilst rolling.  The only characteristic to this noise was at slower speeds it was slightly lower in tone and when power was applied, even lightly, the noise lessened.  Immediately you had toed-off the power, the noise returned. There was no apparent vibration through the gearstick, although the noise did seem to be coming from the gearbox/transmission tunnel area and was quite loud at sub 35mph speeds.

While this type of noise and the issues connected are discussed in relation to a Mercedes SLK R170, it is probable that similar issues could exist on many models of vehicle not just Mercedes and not specifically just this model.

Mercedes R170 SLK Propshaft

To inspect the propshaft centre bearing it will be necessary to lift the rear of the vehicle onto ramps. Once elevated crawl under the centre of the vehicle with a torch and inspect the centre bearing that you find approximately half way down the propshaft just before its sliding splines.  You should be looking for the prop to be central in the rubber bushing as it passes through. Any sign of sagging downward with the rubber at the bottom of the circular bearing housing, being either split or compressed is a sure sign of a tired support bearing.  Grasp the prop shaft and try and lift it against the supporting bearing, any easy movement here is also pretty indicative of a failing/failed unit.

There is another way of determining wear of the propshaft centre support bearing and that is to elevate one rear wheel and whilst the vehicle is in either park or first (manual box) rotate the wheel.  Get an assistant to look at the centre bearing with a torch. If it is seen to lift as the wheel is turned against the static gearbox the joint must be further inspected.

What actually happens is the propshaft sags in the centre, and on overrun it rotates out of line rather similar to a bent knee.  This induces vibration, this usually lessens when you apply power as the shaft will self-straighten under load and spin centrally once more, only to relax again to the ‘bent knee’ when you lift off the accelerator.  The grinding/whirring noise often heard as soon as you begin to move off, is simply the worn centre bearing race transmitting noise to the transmission tunnel and surrounding chassis through the support bracket.

Worn out propshaft centre support bearing

Turning attention to the ball bearing in the centre of the support, located just as the propshaft section passes through.  If you can see any signs of rusty powder or corrosion dryness this may indicate the races are failing and have become gritty, producing that rubbing worn bearing noise we spoke about earlier.

Mercedes SLK Propshaft Centre Bearing

If you decide to replace the centre bearing it is quite a simple job on the SLK200 R170 and should take no longer than an hour start to finish, other models may involve the removal of some exhaust components to gain full access however assess the job before you start. Begin by undoing and removing the three 19mm nuts and pins that go through the differential input spyder that hold the rubber flex disc.  Now remove the forward rectangular protection plate that bridges the transmission tunnel by removing its four 13mm pins and washers.  Note the position of the captive support spring clip for the oxygen sensor connector, it is attached at the bottom left pin of the plate, if you were lying under the vehicle with your feet towards the front.

Now using tippex or other marking aid, mark off the position of the flex joint and diff input spyder. Pull back the rubber boot that protects the splines on the shaft just ahead of the support bearing, mark the shaft position in relation to the spline position so that on reassembly the two halves can fit together in the exact position as they were in before removal.  Positional marking is important as the propshaft is balanced as a complete unit and if it is assembled differently it could be unbalanced and induce other noise and vibration to the drive-line.

Now remove the two 13mm bolts on the centre bearing yolk.  Grasp the rear section of the prop and push it forward a couple of inches to clear the spigot on the diff input flange.  Once clear of this, the back end can be dropped and pulled free from the spline, withdrawing the complete rear section of shaft with centre bearing attached.  You may have to orientate the bearing to feed it past the exhaust, but in most cases it should not be necessary to remove/part the exhaust for removal of just the rear section.  On the SLK200 2001 facelift R170 you will not have to remove any exhaust component.

Once off the car hold the prop vertically and using a copper drift and stout hammer drive off the centre bearing, invert the propshaft and feed on the new support bearing in the same orientation as the old one was removed and tap it fully home using a similar drift, ensuring you only tap the inner race nearest the shaft to prevent damage.  Once fully seated, the propshaft can be refitted in the same way as removal.

Mercedes drive line flex disc

While you have the rear section of prop off the car, this is a great opportunity to inspect the condition of the rubber flex disc on the drive line.  You are looking for failure in the form of ‘C’ shaped cracks appearing around the bushes that allow fixing to the drive flanges.  Any problems here can be addressed by fitting new flex discs, obviously the front unit would be accessed by removal from the gearbox output shaft. It is more probable that the rear flex disc exhibits more wear than the front due to its position on the vehicle so use the rear disc as a visual indicator of what the front may be like, from this determine if further inspection is necessary.  When removing/replacing rubber flex discs it is important to note the moulded arrows on the rubber outer edge. These indicate the fixing bolt orientation with regard to where the nut of the through-fixing should be on reassembly – Arrow points to nut.