996 discs and pads replacement - inner disc face awful

[MrJingles705]

Changed the 996's front discs and pads (plus the rear pads on their own) this weekend - having heard that the caliper bolts could be a bit of a PITA (and generally because I just hate getting the car up onto 4 stands on the drive) I hired some time on the a self-service ramp at http://www.thisisyourgarage.co.uk/

First off - having it up on a 2 post lift really made the whole thing easier.... I know this is bleeding obvious but honestly, if you fancy tackling it yourself (and it's not that hard) I can't think of a reason not to, for what it costs; plus when it it is up in the air you'll spot things you'd never see from the ground. I can highly recommend the guys above if you are within driving distance of Oxford, all very friendly and there is a cafe on site as well which is handy.

Anyway.... as per title, game of two halves!

The problem I thought I'd have - the steel caliper bolts sticking to the ali calipers, because the previous garage had reused them - wasn't really a problem in the end. Top bolts had one turn of the thread filled wil ali but the rest of the thread/hole was fine and they took torque afterwards, so happy with that. Bottoms were absolutely clear. I think hitting them with plusgas (along with a gentle tap each time) may have helped?

The biggest problem instead was the disc retaining screws - glad I had my impact screwdriver! - and the retaining pins, which I had to work forwards and backwards to get them to finally go through.

Anyway, onto the thread title.

I had to do the front discs as the inner faces were awful.... not just lipped, but uneven. I couldn't get a great picture of it I'm afraid, but imagine it was more of a 1:3 slope than a lip that covered the outer 1/4 of the disc. Never seen anything like it on my other cars, and whilst brake performance was down it'd trailed off so gradually that if you weren't driving it daily I reckon it'd be possible to miss the change.

Did a bit of a google and there are all sorts of comments about similar inner face wear.... people guessing it has something to do with how the radiator air is ducting etc? constant wet dry cycles etc. Others blaming bad batches of discs. Not sure myself but I wonder if the amount of salt that got thrown down over winter had something to do with it too (mine daily driver).

Anyway.... my PSA is to check the inner face next time you are working on/washing your car

[edh]

Mine were exactly the same - disc retaining screws were badly corroded (and one side were chewed up so i had to drill them out)

The design of the hub makes the disc screws more likely to corrode & seize. Never a problem on my 944's.

[Polome]

During past 15 years on 996/7 I've replaced 6 sets of front discs. All have needed replacement not through wear but corrosion on inside faces. Tried OPC , Zimmerman , Pagid and a selection of others...i.e. expensive & cheap...none better than the other with corrosion and all at similar milage ( approx 20-25k ) So might just be a design problem...

[skinny]

My theory is that the inner face is covered by the air duct so when it gets wet it stays wet (with the car not moving). It might also get wet on the inside face when driving in rain with water coming in through the brake ducts

[monty999]

Mine were exactly the same on the front, couldn't believe the difference of the condition of the inner face compared to the outer. The rears weren't so bad though. And, yes, it's a real easy job for most DIY'ers.

[IknowJoseph]

Really interested to see this post, thanks! I live local to the garage space you rented, own a 996 with worn our brakes, and don't want pay someone else to fix

MrJingles705 said:

The biggest problem instead was the disc retaining screws - glad I had my impact screwdriver! - and the retaining pins, which I had to work forwards and backwards to get them to finally go through.

Did you need to take any other tools with you? I see they provide some equipment, but should I take something extra? How long did you rent a bay for? I'm most concerned that it's going to take longer than expected and I'd end up with a car with no brakes hanging on a lift at the end of it's time.

[STiG911]

IknowJoseph said:

Did you need to take any other tools with you? I see they provide some equipment, but should I take something extra? How long did you rent a bay for? I'm most concerned that it's going to take longer than expected and I'd end up with a car with no brakes hanging on a lift at the end of it's time.

You'll need:
19mm socket for the wheel bolts
10mm Hex drive for the Calliper Bolts
Pliers to remove the split pin from the back of the Pad retaining pin
The CORRECT size Pin Punch - if your Pad retaining pins are anything like mine, the rears will be fine but the fronts are an absolute B***h due to the heat and dust generated.
10mm socket to remove the brake line bracket from the suspension upright (Front only)
A bit of stiff wire to hold the Calliper up out of the way while removing the disc
Remember to readjust the handbrake.
Anti-seize compound - A LITTLE on each Piston Shim, plus A LITTLE on the Pad retaining pin.
Torque Wrench (130nm Wheel bolts, 80nm Calliper Bolts)

[edh]

..plus an impact driver & cross head bit for the disc screws

In fact worth checking the state of those screw heads before going in to do the job. Freeing those in advance would seem like a good idea

[IknowJoseph]

Thank you both

[MrJingles705]

All info above good - just a few additionals:

• you will want something to siphon off brake fluid to avoid the reservoir overflowinw - cheapo syringe is fin, and I brought an empty coke bottle to throw it away in
• Some cars have the caliper bolts with 10mm Hex, others have a TX55 torx .... mine is the later, believe it's the turbos/wide bodies have the former.
• You should order replacement caliper bolts rather than reuse, otherwise you risk issues further down the line - handily, checking for these will also reveal which of the two bolt head designs you have
• in terms of other parts - I used new pins and retaining clips (pin I could have salvaged probably but the retaining clip was a mess); couldn't save any of the brake pad sensors but luckily bought 4 away
• get a can of plusgas the week prior and hit the caliper bolts and give them a gentle tap with the socket on (DO NOT spray the discs or you'll end up having a very bad time!); consider doing the same (carefully!) to the retaining screw on the disc. Once wheels are off do the same again and then grab a coffee from the cafe, those 2-3 minutes help a little if it is seized.

2 hours to do the job should be enough.... unless like me you hit a bad bolt and it holds you up Providing nobody is booked immediately after you it's possible to extend though..... if you've never tackled a similar job on another car I'd give yourself a bit of breathing room and go for 3 hours.

They *should* have everything you need tool wise, but double check in advance (you can ping them a list when booking and them follow it up);sometimes others could be using the more specific items (e.g. TX55) and you'd have to wait otherwise. As I already had the bit, long punch, torque wrenches etc I took them with me.

They are really friendly up there so if in doubt, ask and they'll advise; they can also order parts in if you wanted (I brought mine with me).

Ramp time is cheaper during the week than weekend - only by £5 though. Register as a member (free) and you can see availability etc.