Changing Brake Discs and Pads
Discussion
Having been told by my OPC that the discs/pads are 80% worn and them having "graunched" for a month since, I have decided to change the discs and pads on my 996. However I am considering doing this myself as it appears fairly straighforward. I have read the relevant step by step list over on Rennlist, but I have a few questions:
1) Is there anything practical that I should know beforehand eg it's impossible to get the disc off so don't bother. NB I haven't done this before and will be buying all the parts/tools specifically so ALL advice well received.
2) I plan to change the damping shims as well - is this correct?
3) I don't plan to change the pin kit, the caliper bolts or the sensors (I have no light on) unless there's a problem with them. Is this correct?
4) I'm a bit nervous about getting air in the system, any good tips? And do I have to have a pad spreader (and where does one get a pad spreader)?
All info much appreciated so that I too can save money/enter automotive DIY heaven!
GK
1) Is there anything practical that I should know beforehand eg it's impossible to get the disc off so don't bother. NB I haven't done this before and will be buying all the parts/tools specifically so ALL advice well received.
2) I plan to change the damping shims as well - is this correct?
3) I don't plan to change the pin kit, the caliper bolts or the sensors (I have no light on) unless there's a problem with them. Is this correct?
4) I'm a bit nervous about getting air in the system, any good tips? And do I have to have a pad spreader (and where does one get a pad spreader)?
All info much appreciated so that I too can save money/enter automotive DIY heaven!
GK
I'm no expert, but the job is fairly straightforward.
If you're replacing the discs aswell as the pads, you can use the discs to lever against to spread the pads. Be careful though - as you spread the pads the fluid will back-up into the reservoir and possibly overflow - keep an eye on this, and syphon off the excess.
The discs should come off ok - but depends on how old they are etc..... If you have trouble, you should use a soft face mallett. Make sure you have a decent wire brush - you will have a lot of cleaning up to do - especially around the hub area before you put the new discs on. Use copperslip (copperease) when reassembling - a fine film will do, and will help in the future - make sure you keep it off the friction surface - but put onto the sliding surfaces of the caliper and pad backing plate.
You shouldn't have a problem with air in the system - unless it's already there - you don't need to open the bleed nipples - but if you want to this is where air could possibly enter. I've done this job a fw times before, but only once on a 996 - but essentially all cars are the same. Hope this of help.
If you're replacing the discs aswell as the pads, you can use the discs to lever against to spread the pads. Be careful though - as you spread the pads the fluid will back-up into the reservoir and possibly overflow - keep an eye on this, and syphon off the excess.
The discs should come off ok - but depends on how old they are etc..... If you have trouble, you should use a soft face mallett. Make sure you have a decent wire brush - you will have a lot of cleaning up to do - especially around the hub area before you put the new discs on. Use copperslip (copperease) when reassembling - a fine film will do, and will help in the future - make sure you keep it off the friction surface - but put onto the sliding surfaces of the caliper and pad backing plate.
You shouldn't have a problem with air in the system - unless it's already there - you don't need to open the bleed nipples - but if you want to this is where air could possibly enter. I've done this job a fw times before, but only once on a 996 - but essentially all cars are the same. Hope this of help.
Be sure to clean the preserving oil of the new discs as well - local motor factors /Haldords for an aerosol can of brake cleaner.
As mentioned earlier, the mating face of new disc to the hub must be spotless, the smallest piece of dirt caught between the faces will give you brake vibration, otherwise easy-peasy!
As mentioned earlier, the mating face of new disc to the hub must be spotless, the smallest piece of dirt caught between the faces will give you brake vibration, otherwise easy-peasy!
One tip, the discs are held to the hubs by a philips headed screw. You may need an impact driver to remove the screw if it's really tight. To be on the safe side I would pre-purchase a couple of the screws to replace the originals, just in case you damage the heads or have to resort to drilling them out. As for spreaders, I have found that a pair of adjustable pliers(as used by plumbers) works fine if you put them between the pads and then open them outwards. Once all has been reassembled make sure that you give a couple of firm pushes on the brake pedal before driving on the road. This will mate the pads with the discs and avoid the embaressment of hitting the anchors and the pedal just hitting the floor. 
Quite a straight forward job, you will need to purchase the shims though-they are self adhesive and stick to the reverse of the pads. No need to bother with the sensors or new bolts that the OPC will probably try to sell you.
I am quite sure that Rennlist have a guide on how to fit then if you do a search, very handy for torque settings.
I am quite sure that Rennlist have a guide on how to fit then if you do a search, very handy for torque settings.
If you have not got an impact driver the little Philips head screw can be removed by inseting a large philips bit from your drill driver bit kit and giving it a sharp tap with a hammer.
The same area as the philips screw also has two threaded holes into which you can insert two suitable bolts which will draw the disc off if it is wedged tight to the hub.
Dont forget a length of string to tie the callipers up out of the way to avoid damaging the paint or stressing the brake pipes.
Be careful when you reinstall the calliper bolts and tighten them carefully and evenly as they are easy to strip the soft aluminium of the hub.
Lastly 1. if you do bother to replace the bolts, which are actually coated with a compound to prevent bi-metallic corrosion (Loctite on your old bolts is generally deemed to be okay) be sure the replacement bolts are the same length as the originals as there are several lengths available for different models and not all OPC's are aware of this.
Lastly 2. run a file around the edge of the bedding face of your new pads to give a small 45 deg chamfer to facilitate bedding in.
Lastly 3. Bed the pads in properly!
The same area as the philips screw also has two threaded holes into which you can insert two suitable bolts which will draw the disc off if it is wedged tight to the hub.
Dont forget a length of string to tie the callipers up out of the way to avoid damaging the paint or stressing the brake pipes.
Be careful when you reinstall the calliper bolts and tighten them carefully and evenly as they are easy to strip the soft aluminium of the hub.
Lastly 1. if you do bother to replace the bolts, which are actually coated with a compound to prevent bi-metallic corrosion (Loctite on your old bolts is generally deemed to be okay) be sure the replacement bolts are the same length as the originals as there are several lengths available for different models and not all OPC's are aware of this.
Lastly 2. run a file around the edge of the bedding face of your new pads to give a small 45 deg chamfer to facilitate bedding in.
Lastly 3. Bed the pads in properly!
mbutchers said:
If you're replacing the discs aswell as the pads, you can use the discs to lever against to spread the pads. Be careful though - as you spread the pads the fluid will back-up into the reservoir and possibly overflow - keep an eye on this, and syphon off the excess.
I was concerned that the pressure in the system would prevent me from simply levering the pads back, but from what you say this is possible as long as you check the reservoir whilst doing it - correct?
mbutchers said:
Use copperslip (copperease) when reassembling - a fine film will do, and will help in the future
I assume I can get this from Halfords? It doesn't appear on their website.
big.bad.wolfie said:
above all pick up the replacement caliper mounting bolts from your local OPC.
milleman said:
No need to bother with the new bolts that the OPC will probably try to sell you.
Bit confused now, to caliper bolt or not to caliper bolt? Get them to be on the safe side?
gfreeman said:
Lastly 2. run a file around the edge of the bedding face of your new pads to give a small 45 deg chamfer to facilitate bedding in.
Que? File down the surface of the pads to aid grip?
Pads should lever back ok - so long as the pistons are in good condition - just keep an eye on the levels.....
Copperease - yes Halfords should stock this - alot of their stuff isn't on their website.
Caliper Bolts - replace for piece of mind - you should really, as officially they 'stretch' wher fully tightened - I've re-used many times though.
Filing the edge of the pad at 45 degrees will help the pad bed in easier if there are any high points - not stictly neccessary - but a small amout will not hurt - just to take the edge off.
Copperease - yes Halfords should stock this - alot of their stuff isn't on their website.
Caliper Bolts - replace for piece of mind - you should really, as officially they 'stretch' wher fully tightened - I've re-used many times though.
Filing the edge of the pad at 45 degrees will help the pad bed in easier if there are any high points - not stictly neccessary - but a small amout will not hurt - just to take the edge off.
gmmk said:
If you're replacing the discs aswell as the pads, you can use the discs to lever against to spread the pads. Be careful though - as you spread the pads the fluid will back-up into the reservoir and possibly overflow - keep an eye on this, and syphon off the excess.
I was concerned that the pressure in the system would prevent me from simply levering the pads back, but from what you say this is possible as long as you check the reservoir whilst doing it - correct?
mbutchers said:
Use copperslip (copperease) when reassembling - a fine film will do, and will help in the future
I assume I can get this from Halfords? It doesn't appear on their website.
big.bad.wolfie said:
above all pick up the replacement caliper mounting bolts from your local OPC.
milleman said:
No need to bother with the new bolts that the OPC will probably try to sell you.
Bit confused now, to caliper bolt or not to caliper bolt? Get them to be on the safe side?
gfreeman said:
Lastly 2. run a file around the edge of the bedding face of your new pads to give a small 45 deg chamfer to facilitate bedding in.
Que? File down the surface of the pads to aid grip?
Duh??? Where on my post does the word surface appear??? The EDGE. Reccomended in all good pad manufacturers instructions.
To rebolt or not to bolt is entirely up to you. There is no way a 12mm bolt will stretch when only 60 odd ft-lbs is applied. If you trawl the US websites of the Renn variety you will find a many superb write up on changing 996 discs and pads, and this specific question is also raised many times. Many experienced respected spannermen do not bother and re-use with a dab of loctite. You pays your money....
Take the cap off the brake fluid reservoir to assist the fluid's return to the reservoir, but keep checking the level.
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