problem after 996 upgrade

[peter]

finally got round to fitting the conversion yesterday,new rs2 hardlines,996 calipers etc.all went well have now done about 100 miles.the brake pedal is a lot harder than it used to be and the brakes dont seem any better than the originals!everything bled through ok but i get the feeling something is not right.should i bed them in longer(i have never driven a s2 with this setup).i suppose the pedal will be harder with hardlines, or have i caused a problem elsewhere? both calipers are working properly,no pulling or noises.any thoughts gentlemen.

[BRY]

What is the part numbers on the calipers?
996.35x.xxx.xx

[HPmuirt]

Bedding in of new disks and pads can take quite a few miles. The action of 'bedding in' is actually performing 3 main functions: -

1. True up the faces. This is to wear away high points, mainly of the pads so that the pad and disk are in 100% contact. This is often the largest single cause for the brakes not feeling great as you can easily have as little as 10% of the braking surfaces in contact for the first few miles. This is easily checked as the new disks will be scored with shiney lines where the pad is making contact. This will grow over time until the whole pad area is in contact, but a 'bedding in' procedure will almost certainly cure this instantly.

2. Remove surface contamination from both pad and disk surfaces (oils/greases, zinc coatings on disks, glazed surfaces of new pads, rust etc).

3. Transfer of pad material to disk. This involves coating a layer of pad material on the disk surface at a molecular level, as there are 2 forms of friction generated during braking, with the 'pad - pad material' (on the disk) friction actually producing much more friction and therefore better braking effect than the 'pad - metal disk' friction. Again, the 'bedding in' procedure below deals with this.

Assuming you changed to ATE racing fluid or something silimar and flushed the system very well, then try a full bedding in procedure below and then see how they feel....

Bedding in - The best thing to do is to find a long, straight, empty road (such as a country road between 2 quiet villages). Now perform 10 acceleration and braking runs, where you gently accelerate to a around 80MPH (theoretically you should slowly increase from 60 - 80+MPH according to the car and brakes) and then brake increasingly hard down to 5MPH. Never trigger the ABS, just aim to be at 95% braking on the last few runs.

Also NEVER STOP as you will leave a pad imprint on the disk surface - this is a life rule, not just for bedding in sessions - never sit at the lights with your foot on the brakes, if you braked hard and the brakes are hot. The pad imprint will cause brake judder that is often misdiagnosed as warped disks. In truth, it is virtually impossible to warp a modern disk!

The reason for accelerating slowly is to allow the brakes to half cool before the next stop. This puts the disks through a beautiful step up heat cycle, slow climbing until reaching the highest temp on the last run. You should notice a brake pad smell after the 2nd or 3rd run, which should have gone by the 7th-8th run. This is because you will have reached a high enough operating temp to have burned off all the surface contaminations and since the pad should now be 100% flush and therefore in contact with the disk, you will have transferred the pad material to the disk.

When you finish, the disks should be hot and a very even (slightly blue) colour across the entire contact surface. If for some reason there is still a small area of lack of pad contact, you can do a few more runs.

Believe me, this is the best way to bed in brakes as normal driving for 100 miles will not heat cycle the disk enough and will not generate enough heat to get a good transfer of pad material to the disk. It may also just not be enough to align the braking surfaces, particularly if you are not confident in the feel.

Cheers n

Si

P.S. Always follow this procedure for new pads. If you have new discs, keep the old pads on as the face will be flush and free of contamination. Now bed in the disks as above, as this gives a more even heat cycle and a better transfer of pad material to the disk. At some point later, change over to the new pads and bed those in as above. NOTE that this is only if you are keeping the same pad type and material.

[Ross]

Good write-up Si!

Must remember this one next time I change brakes

[pastures16]

has he got race pads

[peter]

the calipers are the same part no.s as used in the 996 fitting guide on the forum.i used textar pads p no. 2332902.all seemed to fit together well.

[BRY]

Have you tested your bomb?
How many pumps on the brake pedal with engine off before your pedal goes solid?

[s2driveruk]

remember that there is little servo assistance on the S2 at the best of times so, you till have to push pretty hard anyway i find....

[peter]

Have you tested your bomb?
How many pumps on the brake pedal with engine off before your pedal goes solid?

tried it this morning got 30 pumps then it went completely soild.when i restarted engine the brake warning light symbol came on for a few seconds then disappeared.
should the pedal be a lot harder with the rs2 solid lines?

[s2_bo]

Great write up Si!

[HPmuirt]

Great write up Si!

Thanks Bo Just waiting to here if it helped

Cheers n

Si

P.S. (Hey Bo, do you want your Rad back?)

[dan_b]

@Peter - what pads are you using? Are they some exotic race pad (or EBCs) which have bad cold-bite performance?

Have you changed and flushed and fully bled your brake fluid? If so, how did you do it? It's vital to bleed the system fully (and from both sides of the calipers on those Porsche brakes) to get any brake performance.

[dan_b]

should the pedal be a lot harder with the rs2 solid lines?

You should definitely feel a firmer pedal with hard lines vs. standard rubber hose. Do you have hardlines throughout (have you replaced the rubber hoses to the rear calipers with braided flexi hose as well)?

Also check the volume of fluid you have in the reservoir, make sure its not too low. With large multi-piston calipers now up front you are physically moving more hydraulic fluid around to move the pistons, which means you need more pedal effort than before.

[peter]

Thanks Bo Just waiting to here if it helped

Cheers n

Si

P.S. (Hey Bo, do you want your Rad back?)

thanks si,this did improve things slightly but still not as they should be, have done about 350 miles now.When you first touch the pedal you think this will stop well,but then a lot of pressure needed for a decent stop.

[peter]

@Peter - what pads are you using? Are they some exotic race pad (or EBCs) which have bad cold-bite performance?

Have you changed and flushed and fully bled your brake fluid? If so, how did you do it? It's vital to bleed the system fully (and from both sides of the calipers on those Porsche brakes) to get any brake performance.

the pads i am using are standard 996 textar,the system/calipers have been bled fully,everything else is standard.i think i might try and get it on the brake tester at the mot station and see whats going on.