Headlight Servo (UPDATED) E85-E86

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R7VOX
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Headlight Servo (UPDATED) E85-E86

Post by R7VOX » Wed Jan 15, 2014 12:03 am

Hi all!

The last "How To" on this subject was not as clear as I wanted and the photographs were pretty crap, so I have made quite a few amendments with better photographs

PREFACE

I had an intermittent fault on the headlight servo (Hella part no. 734 857-00 BMW 8 372 381 ) which would fail occasionally on a self test when the ignition was placed into the 1st position. The fault would not be rectified until I accessed the servo and jiggled it about, even then it was hit and miss if it worked.

I managed to acquire a scrap headlight which was damaged and dirty internally that I have been able to take apart to component level. I am currently putting together a "How To" of removing the interior parts for servicing and cleaning, so please bare with me.

In this whole process I will try and explain in as much detail as possible how it all works and what to look out for as I believe to repair something, you actually have to know how it fully works. I apologise in advance if I ramble on.

TOOLS NEEDED

TORX T15 screwdriver
Needle Nose Pliers
Sidecutters
Multimeter
Jewellers Screwdriver (flat head)
Dremel Style Drill & wire brush (soft)
Nail Varnish!
A large cylindrical object (kitchen towel cardboard insert)
Hand Drill (manual) - Optional

STEP 1. REMOVAL

Firstly, remove the front wheel and associated panels to access the back of the headlight with plenty of room. I am working on the driver side (UK) headlight, so the passenger side may be slightly different.

The wires and connecting pins leading to the servo are quite fragile so you don't want to tug and damage any connections when removing the servo

Remove the secondary plug (small plug) by gripping either side and gently wiggle in a circular motion whilst pulling. It will probably have never been removed since the headlight was installed.

On the headlight unit itself, locate the small pink tab (bottom corner left in this photograph). This needs to be slid across whilst pushing on the centre of the plug. A small slot head Jewellers screwdriver is ideal.

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**BEWARE this is really fiddly and also there is real potential for damage to both the small pins and the socket. The socket was damaged removing the plug as I had to figure out how the plug came out. Hopefully everyone else will be able to do it without damage**

This is what the plug looks like with the catch slid into the OPEN position

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You could bypass this step if you wanted to do a running repair like I previously did in the first "How To".

Now the cables are free from the socket, you need to release the servo from the unit. 2 Torx T15 screws hold the servo in place. I slid a piece of curved card underneath the servo to catch the screws so they don't fall into the unit during disassembly.

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Now the unit is released, slide the ball socket end out of the guide (towards the side of the car on the drivers side) and the servo is now fully released.

STEP 2. DISASSEMBLY OF SERVO

Now you have the servo released, it will be fairly straight forward to open it into component parts.

Using a small jewellers flathead screwdriver release the 4 tabs on the face of the motor by gently prying the tab inwards towards the body, pulling gently at the same time doing one side at a time.

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Once the tabs have released, you will need to pry apart the 2 tabs clamping the cable in place.

The body can now be withdrawn exposing the actuator core, the motor and the cover itself. remove the body and the actuator core placing them to one side.

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Before you try the next step, if you have a multimeter handy, check the pins on the plug for continuity, the pins are arranged as follows:-

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If there is no detection or you are getting an intermittent signal then proceed to the next step.

Next requires a bit of patience and delicate handling. to remove the cable from the motor windings. The cable is held in place by 4 krone style pins very similar to a BT phone socket.

This method, although very good for mass production could have been designed a lot better as I feel this is the main source of trouble for most servos due to the way it just nips the cables.

Gently pry away the plastic clip the has the cables attached to it. The idea is to remove the plug and leave the krone pins in the motor housing. If they do come adrift, or it damages the motor coils, dont worry. The motor CAN be repaired which I will deal with later in this instruction. It just means a little more work to fix it, but it is worth saving the £100 even if you need the parts which I will mention later.

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Now the motor is released. you can set aside the cable connector. and its time to get down to some serious business dealing with the motor itself. You can see by the photograph the krones have stayed with the cable connector as they have corroded quite badly. It has actually snapped off the enamelled cable which will require the whole thing to be unwound to give me enough wire to reattach the krones.

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The motor is actually in two windings which are joined together. You can separate the two windings which gives you 2 separate coils. these separate coils allow for the fine adjustment of the dipping function. I counted 4 positions on the manual adjuster for halogen specification headlights in the cockpit.

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These coils have roughly 14m or 285 turns (yes I counted them!) of very very thin enamelled copper wire (slightly thicker than a human hair).

I have included a picture against a ruler and 2 pence coin for comparison.
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The coil may fail for 2 reasons, the crimps, or a short where the enamel has rubbed away inside the coil causing a short rendering the motor function useless.

Checking on the multimeter both coils measured as an 8 ohm load. Whether a short would detect as a different value. I can only summise that it might.

before the final step of disassembly, make a note of which way both coils are wound. I like to put things back EXACTLY the same.

To access the coils themselves pry off the metal shields which gives you the motor in its most basic form.

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I have unwound a coil completely to show how to repair it. (Excuse the dyson tool. I wanted something chunky to coil it round, and since this servo was faulty. I didnt worry too much).

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I would use something smooth with a large diameter and try not to agrivate the enamel on the wire. You dont want it rubbing off if you plan to reuse it. If you suspect that the wire is faulty, head down to your nearest shop that sells enamelled copper wire and purchase some of the same size and value.

TO REWIND THE CORE

Firstly, clean all the krone pins with a dremel style tool and soft wire brush (if they are corroded) notice that there are DIFFERENT ends to the krone, a thin gap and thicker gap. I would recommend giving them a polish as you want the cleanest contacts.

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In the picture I have placed the wire over the plastic gap ready for kroning in. use a nice pair of needle nose pliers and gently but firmly push the krone in whilst holding the wire with your thumb. it will sit snuggly in the slot and the 2 shoulders should be flush with the top of the coil mounting. visually check to see the wire has gone through correctly and you should have a little excess on one side with the other 13.95m of it on the other!

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You could speed the next process up by using a hand powered drill winding the coil evenly along between the guides. I wrapped it by hand because I wanted to make sure the coil was nicely packed and did not scrape the leading wire just Kroned in.

To finish, once you have wound the coil. it is time to do the same procedure to complete the circuit with the needle nose pliers. The kroning action nips the wires and removes either the plastic sheath or the enamel making complete contact.

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Now cut the excess away with a good set of snips, but leave the tinest fragment of wire to prove the Krone has done its job properly. I have pained the ends of the wires (in white) here as both sets will be facing each other and I do not want them creating a bypass circuit.

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STEP 3. REASSEMBLY

Reassemble the metal covers on each coil (each one has different guide holes for the pair) and test on the multimeter for continuity and resistance.

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Reassemble both coils (there are mating sockets on each) and then you have one repaired (fingers crossed) motor assembly.

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Reattach the cable connector to the motor assembly and check to make sure its secure. give it a good wiggle to make sure the krones bit into the plastic sheath. (You could check again with the multimeter for continuity).

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Place the motor assembly into the actuator core feeding the wires into the small fingers at the top.

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Finally, place the cover over the whole asembly and push till you hear it snap together. Keep checking the wires so you don't pinch the cables and the servo is ready for testing.

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When I first had this servo. I tested it on my car and it was totally dead. After the above procedure. I did the test again and checked the 4 available positions which it passed with flying colours. I also did the self test in ignition postion 1 about 14 times. every time totally fine. in the following pictures you can just about see the adjustments.

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I hope it the instruction helps all you fellow Z enthusiasts out there whilst saving you the outlay for a new unit.

I hope if you do attempt the fix it works for you like it has worked for me. Good luck everyone!


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fixit man
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Re: Headlight Servo (UPDATED) E85-E86

Post by fixit man » Wed Jan 15, 2014 9:28 am

wow ..good write up !

CR55EDS
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Re: Headlight Servo (UPDATED) E85-E86

Post by CR55EDS » Sat Jan 03, 2015 2:56 pm

This is a great write up :thumbsup:
2005 3.0i Z4 Roadster|sterling grey
2010 2.0d xdrive X1|deep sea blue
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