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535i Andrew

F10 535i Auxiliary Drive Belt Replacement DIY

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When I was under the bonnet doing my yearly yellow grommet clean out/inspection I noticed that the edges of the belt were starting to fray slightly.  The bearings in the tensioner and idler pulley may also start to grumble as well as a loss of tension in the tensioner leading to reduced performance of the system. It is 8 years old so the rubber will be starting to age before wearing out as its only got 56,100 on the clock. 




The FEAD or front end auxiliary drive is known as the complete set of pulleys, idlers and tensioners that are driven by the belt to power supplementary ancillaries with power from the crank.  My F10 does not have any form of over running clutch on the alternator system (OAP/OAD) so there is no need to change the alternator pulley.  The parts to change on the N55 without dynamic drive (which adds another idler pulley and needs a longer belt) include the belt, tensioner and idler.




Tools needed


15mm socket for strut brace

12mm socket for cross brace

10mm socket for air con lines bracket bolt

E12 Torx Socket

Torx T30 bit/screwdriver

Torx T40 bit – and a spanner that fits this bit!

Torx T50 bit

Torx T60 bit

3/8” ratchet

Breaker bar

4.5mm dia drill bit, 5mm is too big!

Small flat screwdriver

Torque wrench – 30Nm for strut brace and 60Nm for Idler


This job is all about access.




To get my arms and tools into the space at the front of the block, you need to remove the electric fan, before you can remove the fan, you need to remove the upper cross brace and the strut braces.  Trust me it needs to come out, I just ended up getting sore knuckles and scratched to bits attempting it without*.




To remove the cross brace complete with the strut braces, slacken the stretch bolts at the strut towers.  15mm socket




Prise up the two expanding rivets on each headlight flap surround.  2 each side…




…and lift this up slightly to allow access to slacken the 12mm bolts that connect the upper cross member bolts to the inner wing.  2 each side




Flip up the head light access flap to access the T30 bolts and slacken then that connect the upper cross brace to the bonnet release mechanism. 2 each side




Slacken the two T30 bolts at the front of the upper cross member to the trim panel behind the bumper.  These go back to 19Nm on tightening.


Now the pain the sit down bits bolt.  There is a horizontal T40 bolt that secures the upper cross member to the diagonal braces. 




There is no room for a ratchet, bit and bit holder so I stuck my T40 10mm hex bit in the ring end of a ratchet spanner to loosen and then undo it.




Once all the bolts were initially loosened, I used my impact driver to quickly remove all the bolts, it certainly speeds things up and reduces fatigue, get one would be my advice!  Bin the two bolts from the strut brace to strut tower as these are stretch bolts so cannot be re-used.




Once all the bolts are out, move the complete upper cross member and strut braces to the rear so they clear the headlight surround trim.




Lift up or rather pivot the complete upper cross member and strut braces with the front edge resting on the plastic trim to allow access the three clips that hold the nearside bonnet release cable.  Unclip the cable.  The two rubber bushes you see on the underside form a support to the top of the radiator.




Set it aside, its surprisingly light for its size as its all aluminium.




Remove the T30 screw that holds the charge air duct to the fan.




And its bobbin, as it will no doubt fall out later!




Unclip the fan’s electrical connector from the offside of the fan housing and pull up and out the socket.




Prise up the central clip on top of the fan housing.




And prise forward the two on each side of the fan housing (picture of offside)




Grip the fan in the centre and pull up, carefully, making sure it doesn’t snag the bonnet release cable.




Add it to the pile of removed bits, it’s physically huge, 600W version in mine.




That’s most of the access sorted, now to get on with the actual job of replacing the parts which are the tensioner seen hiding behind the coolant hose and the two air con lines.  The idler puller is also hiding behind the air con lines support bracket.  This is the picture I took so as to record the routing of the belt.  Don't rely on your memory to remember how the new belt should be routed.  I had to flick back to this picture when routing the new belt.




A 10mm socket is needed to undo the air con lines support bracket bolt.




Pull out the bolt and catch the spacer that keeps the bracket off the front of the block.


Now to take the tension off the belt.




There is a T60 socket in the tensioner to allow you to get some purchase on the tensioner.  I had to raid my tool box for a big enough Torx bit.  Rotate the tensioner clockwise to release the tension on the belt




Have the 4.5mm drill bit ready to stick in the hole in the tensioner (hole just above the lower air con line) once it lines up with a slot in the tensioners housing at the location the drill bit is pointing too, hidden under the upper air con line. 




You can see why you need the fan out the way while you heave round the tensioner




Tensioner locked off with drill bit.  Belt is now slack.




Lift the belt off the alternator pulley as it’s easy to access at the top of the belt run.




then off the crank pulley




then out the engine bay.




E12 torx socket and short extension was needed to slacken the tensioners single bolt  Carefully pull out the tensioner from the block and manoeuvre it clear of the coolant and air con lines while making sure the business end of the drill bit doesn’t contact the radiator fins.




Tensioner removed, its bolt looked as clean as the day it was fitted over 8 years ago.  You can see the job my drill bit is doing, at the end of the shift I mounted the tensioner in my vice to recover the drill bit as I wanted that back!  Date on the tensioner ties in nicely with the cars production date.  It’s the original and with a slight bit of play in the bearings of the pulley.  I could feel a bit of play but there was no noise from the bearings when rotated, so it was partially worn.




Using a small flat screwdriver, prise off the centre cap from the idler pulley to expose the centre T50 bolt.


For reference that’s the front roll bar, mounting and bolts you can see in the bottom of the picture.  That’s the next job to fettle that up, well perhaps after the grumbling front wheel bearings.




T50 long bit to get access to the centre bolt on the tensioner.  I had to apply pressure to the air con line brackets to give a bit more room.




I stuck a foam mat down the gap to protect the radiator fins as a bit of beef is needed to undo this bolt and access is a bit awkward with the air con line bracket is fighting you.




Remove idler pulley from the block.  Unlike the tensioner there was no play detected in these bearings and was silent when spun so it was still serviceable for a time at least.




Replace idler….




…and tighten to 60Nm.




Install new tensioner in its locating slots, it will only go in one way.  Note factory fitted locking pin so the tensioner is in the compressed position to allow the belt to be fitted.




Torque bolt to 38Nm**.




Fit new belt, I went for febi part number 45238, with 8 V grooves and it’s 1390 mm long, made in December 2020 so its 8 years at least fresher than the one I took off.




Fit the air con lines bobbin and bolt once you have routed the belt around the air con compressor and the underside of the idler pulley.  This traps the belt on the block.




Belt correctly routed and ready for the tension to be applied.




Use a T60 bit to turn the tensioner slightly to free the factory fit locking pin with a pair of pliers, gently release the tensioner on to the belt.  I cleaned up the fan and upper cross brace before refitting (my automotive OCD!). Simply lower the fan back in ensuring the clips at the bottom of it slot into the bottom of the radiator. 




Clip the bonnet release cable back into place ensure the correct routing of the cable.




Install new strut brace to strut tower stretch bolts.


Refit all the other bolts securing the upper cross brace to the car.




Torque the strut brace to strut tower stretch bolts to 30Nm




And then tighten thru a further 90 deg.  This was unsettling as you are tightening a steel bolt into an aluminium part, I just didn’t like it but that’s the spec.




Torque the upper cross brace to inner wing bolts to 28Nm..




…and the T30 bolts to 11.8Nm…




…and that difficult centre one to, “aye that’s about right tight”.




Push home the four rivets you removed.




Check parts holding tray is empty except for the two stretch bolts that are scrap.


Start engine and check all is well.



And unless you are me, that’s you finished.  Because I was thinking about something else/I’m a diddy, I had inadvertently over tightened the tensioners bolt to 80Nm.  I had first tightened the idler pulley bolt to 60Nm and as the tensioner uses the same M10 thread and same socket drive, **I had it in my head that its tightening torque was also 60Nm but no its only 38Nm.  Oh bother. I then bought more new strut stretch bolts and a tensioner bolt from Cotswolds, stripped everything back out again after trying to access the tensioners bolt without removing the strut brace and fan, *hence the sore knuckles and replaced the bolt..




…tightened it to 38Nm and put everything back, again.


This is where I miss a Haynes manual, you can prop it up on the engine, hold the torque spec page open with a spanner and keep yourself right, without having to rely on your memory which at my age is now beginning to fail me.  Not that I’ve had a Haynes manual for my car/engine combo since E39 ownership.

Edited by 535i Andrew
Torque setting missed and one corrected.

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Excellent write up Andrew. Very clear and easy to follow. Thanks for sharing your expertise. I must have a look at my belt soon. 120000 miles is approaching fast. Seems an easy enough job on your engine. I wonder if the N57 is more or less the same

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21 hours ago, 535i Andrew said:


Pot kettle black!  :P

For those of you younger than me and considerably younger than @duncan-uk, this is what he means :lol:



Oi! Less of the old!!

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NewTIS @bmwmike.


It took a bit of a heave to get off so I didn’t really think much about putting it back to 80Nm. But you might find 30Nm plus 180 deg isn’t far off 80Nm.


When playing with tightening wheel bolts. If you tighten to say 100Nm you don’t need to turn it much more of an angle to get 140Nm. 

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Sorry had to dash off before finishing.


The torque goes up really quite high when you start putting another half a turn on to them. Sometimes it’s because they are stretch bolts like all the suspension bolts. 

I think some Audi hub nuts are 200Nm plus 180 degrees. That’s a monster torque probably like 350-400 Nm at the end of the day. 


When I do my wheel bearings, they’ve to go to 20Nm then 100Nm plus 90 degrees I think. I’ll try out my peak torque transducer to see what the ultimate torque   is once I’ve put the angle on it. 

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1 hour ago, 535i Andrew said:

Well @bmwmike you made me double check!


NewTIS says 60Nm as does the notes I made at the time. Not sure why I’ve got 80Nm in my mind..


Old age I think….


Im even more confused now haha. So i just stuck a breaker bar on it and nipped it up a bit. Is fine now i think 


Edited by bmwmike

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Went back in this afternoon with @vpcaptain's help to correctly torque the idler bolt to 60Nm. Took off the cross brace and removed the fan again.....


We put the locking pin back in the tensioner to make sure the tension was off the belt and slackened off the idler to then retighten to 60Nm.




Thankfully I had more new stretch bolts to go back in on the strut brace. We tightened them to 30Nm then using my torque transducer we recorded the peak torque following the further tightening thru 90 deg.





Tightening thru a further 90 deg increased the torque applied from 30Nm to almost 70Nm.


Thanks for your help Rob. 


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