Brake pads and discs

Recent service identified low pads and lipped discs as an area requiring future concern. Since the MOT is approaching I thought it best to deal with these areas. Jack up the car- I used the plank along the sills method to raise one side at a time, and remove the road wheels. Note that there is a wear sensor fitted to a single wheel at front and back- the front sensor is on the left wheel and the rear on the right. I started with the front right which had no sensor. 

Front Pads and Discs.

Removing the wheel reveals the disc and caliper. The disc is held by the torx screw and also by the caliper.

Front dosc and torx screw

 Craning your head inside the wheel arch identify the 2 bolts securing the caliper to the hub and remove these.

Caiper bolts -upper

...and caliper bolt lower.

Note that these are very tight, you cant get an impact wrench in and its tricky to use a long breaker bar unless the car is raised quite high. I broke them free with a ring spanner and a heavy mallet.

At this point it should be easy to remove the calipers by slipping them off the disc. However in my case the discs were deeply lipped and the pads wouldn't pass over the lip. I was obliged to grind the lip down over a length equivalent to the caliper using an angle grinder. Its easy to then remove the caliper, as usual hang this on a bungy strap from the front spring to avoid straining the hoses. The flexible hose clips out of its bracket to give more room for this.

Flexible brake hose cips into this bracket

,

 undo the torx screw and detach the worn disc.

Hob torx removed

Disc removedNote grinding on one section to allow calipers to be withdrawn- obviously only recommended if the discs are to be scrapped.

Clean the new disc thoroughly with brake cleaner and fresh tissues to remove the storage grease.

Clean off all storage grease... lots of spray and several changes of tissue.

Fit the new disc and torx screw.

Fit new disc and screw in torx fastener.

 Before you can fit new pads you'll need to make room for them by pushing the pistons back into the caliper as these will have extended to adjust for wear in the old pads. Obviously as you push the pistons back in they will displace the fluid behind them. There are two ways of dealing with this- firstly just push the pistons in and let the fluid back up into the master cylinder. This obviously raises the fluid level in the master cylinder so you'll have to suck some fluid out as you go or it may overflow and damage paintwork etc. I have read that some master cylinders can be damaged by this backward flow although I've never come across one. However what can't be argued is that this will push older dirty fluid up from the lowest points in the system which may be a concern. The second way of dealing with it is to put a hose clamp on the flexible hose and connect a drain hose to the bleed nipple, directing this into  a container of clean fluid. Crack open the bleeder and pressing the pistons back now pumps the old fluid out through the bleed nipple. Close the nipple when the pistons are retracted and check master cylinder fluid level- you may need to top it up. In my case the bleed nipple was siezed solid and I didnt want to force it. I was therefore forced to back the fluid up through the master cylinder. As an aside here I will say that I was surprised how dirty this old fluid was when it backed up-- especially as Id paid for a fluid flush at the last service. Im assuming the garage couldnt shift that nipple either so that caliper never got flushed and they didnt tell me. Not greatly pleased... The siezed nipple will be a task for another day.

You cant push the pistons back in by hand, youll need to use a retraction tool of some kind. Mine is designed to push on the old brake pads by expanding between them. Note that this tool only works on the front brakes... the rears have to be rotated as they are pushed and that means another tool which I'll need to buy.

Pushing back the pistons using my expansion tool. Note caliper hangs from bungey strap.

You can then clean up the caliper with brake cleaner and a stiff brush before fitting the new pads. These go in pretty much exactly as the old ones came out. Youll need a modest dab of brake grease on the  ears where they locate in the caliper and also on the back of the pads where they contact the piston to help prevent squeal.

Reassembly is as they say the reverse of disassembly-however note that the caliper securing bolts will need a dab of retaining compound (loctite) to keep them secure.

Front Left Pads and Disc

The front left pad is complicated by the presence of the wear sensor. The connecting wire runs from inside the cars engine compartment to the caliper. Its held by several rubber clips along its length which secure it to other wires and hoses.

Pad wear sensor clipped to flexible hose and antilock brakeing wire its length.

 It enters the caliper via the nipple cover which helps hold it in place.

wear sensor aire passes by nipple using the rubber clip

... and clips onto the inboard brake pad. 

Wear sensor visible inside caliper. Thge rear must be removed with snipe nosed pliers before you can remove the caliper... this is the front and the pads some out easily

BMW state that the sensor wire must be renewed whenever the pads are changed, it can be removed with snipe-nosed pliers or eased out with a screwdriver blade once the pads are out of the caliper. Personally I cant see why you shouldnt reuse this sensor provided that its not been worn right down. It can beceased off with a flat screwdriver blade. I changed both my leads though.

Once the pads are removed you can lever the sensor off... personally I think it could be reused as long as it hasnt triggered the brake low-pad warning. However I renewed it.

To remove the old wire you have to trace it along its path to its connector. This means removing the two plastic rivet screws securing the splashguard- hold the rims whilst you unscrew the centre and the rivet will pop out.

Plastic screw in rivet that holds the underwing splash panels. Hold the outside and unscrew the cross head screw in the centre to collapse the rivet teeth- it then pulls out of the splash panel

removed 2 of these screw rivets leaving holes...

 ...and freeing up the splashguard so it could be folded back to give access to the wear sensor connector.

Once removed you can fold back the splash guard to trace the wire along its length, There may be another clip behind the guard but the wire terminates in a WHITE connector also held in a clip.. not the blue one next to it.

Wear Sensor connector detached from its clip under the splashguard. Squeeze the tabs at the top (resting on finger) to release the plug.

The connector unfastens using two lugs at the top (ie towards the motor). Press these inwards and pull the connector apart- its got quite a long plug on it. Fit the new sensor wire being careful to align the plug in the connector before pushing it home as the connection pins are quite fragile. Clip it back in place along its length and insert the plug into the brake notched pad making sure it clips firmly into place. It may help to push it down with a screwdriver. Change the disc and refit the caliper with the new pads as before.

New dics, pads and wear sensor wires fitted.

Rear Pads and Discs

Its not possible to remove the rear pads unless the handbrake is off so check that the car is properly chocked at the front and in gear. Bear in mind raising the rear will also remove any handbrake action so make sure its safe before you raise it. 

Jack up and remove the road wheel. I had intended to change the discs but once I could see them it was clear that the lipping was far less serious here and the discs within wear limits. Further a little research shows that the rear caliper brackets are held with single use bolts and I didn't have replacements so I decided not to change the discs.

Rear Pad caliper and disc- LHS without sensor wire.

The rear caliper is a more complex structure with a pad holder within the caliper and...

Caliper and slide pins under the bellows.

hand brake cable attachments and operating levers at the rear

Levers for handbrake cable operation.

As before, note the sensor and the routing of the wire if present.

sensor wire on rhs

Use a screwdriver to lever down the handbrake operator

Lever down the handbrake levers

... and detach the handbrake cable.

Handbrake cable just pops out. I cleaned and greased it prior to reassembly.

Loosen the caliper slide bolts using two spanners operating against each other

The caliper and cylinder then pull off the pads which remain in the bracket. Note that if there is a sensor present you will need to remove that with snipe-nosed pliers before you can do this. You can then lever the pads out

Removing the pads-lhs no sensor. Note that although the disc is lipped, this isnt deep and the discs are still within wear limit of 20.4mm. Haynes manual is no use for this- states that wear limit is embossed on the discs themselves... possibly on original BMW discs but not on these or the new ones Ive purchased.. which are presumably later replacements. The limit appears to be 1.6mm from the new disc thickness.

The pads sit in flexible shims and these just clip out of the bracket. Clean them with brake cleaner and a stiff brush before rebuilding them with fresh pads. Note that you will need a smear of HMP brake grease on the wings and rear of the pads to prevent squeal.

pad seat shims.

Rewind the piston- it needs to be turned clockwise as its retracted using a rewind tool. I bought the tool  from Laser. Reassemble the  piston caliper onto the pad bracket and fasten with loctite on the bolts. If present, press the sensor into its groove using a screwdriver to push it into place until it clicks.

Fit the caliper and then the wear sensor wire where appropriate. It will probably need to be pushed down at the side with a screwdriver pressing on the top of the molded block. Dont press on the top of the sensor (where you used the snipe-nosed pliers)  as this just bends without transmitting the force. 

... and trace the wiring up to the white connector above the body splash panels, there is just enough slack to pull the connector out and fit the new wire. As before the brake wear sensor is white. Reclip the wire along its route as it was when removed.

Tracing the wear sensor wire- unclip and pop out the white connector. Detach as in the front.

Refit the road wheel

Should add that the right rear caliper boot was split and the piston was very tough to retract. This can happen and I now know that its a good idea to irrigate with WD40 befoe attempting to push them back. Its not clear if this piston had been stuck before but when it eventually did go back it leaked some fluid. Consequently this caliper will need replacement or reconditioning asap. However at the moment I have no spare parts so I'll reassemble and order the bits. In fact Id cleaned off the leaked fluid and refitted the caliper- there was no further leakage and brake fluid level was steady; the car even passed the MOT like that. However, I do have new parts on order and Ill swap this for a new one asap.  

Signs of fluid leakage- replacement or reconditioning needed.