Rear vented discs/ calipers - differential clash?

[NorfolkJohn]

Has anyone upgraded to vented discs and matching calipers on the inboard rear location. Trying to fit up and finding the caliper can't be centralised over the disc without spacing it away from the diff flange. This then makes it clash with a strengthening rib on one side of the diff housing. I am contemplating grinding off a 4mm section of diff material on one side - off the rib directly behind the caliper. Has anyone fitted the Rob Beere kit to a series 3 car. How did you get on with this aspect ..? I would like to centralise to maximise pad life and ease fitting the pads in the first place.. I am out by approx 4-5mm.

Any pointers greatly appreciated.... thanks

[MarekH]

You can simply reuse the old Girling calipers but with an appropriate spacer between the halves. (This is also how the fronts on a s3 differ from a s2.) The only modifications then needed are 1/ to shave off a tiny amount of material from the middle of the inner face of the lower control arms, as that will foul the discs when the control arm is fully extended over a humpback bridge, and; 2/ to fab up a wider brass returning fork on top of the handbrake caliper.

There is little or no benefit in doing this upgrade. The "upgrade" is only in the failure mode. When the diff seals start to leak, instead of the oil leaking out and migrating down the half shafts onto the inboard side faces of the discs (resulting in uneven pad wear), the oil migrates down the halfshafts, onto the inner faces of the vents between the discs and now migrates out of there, missing both braking faces of the disc, thus maintaining even pad wear. (One might argue, that vented rotors may run slightly cooler and hence never overheat the diff seals in the first place.)

The only reason I did this "upgrade" is that my car had been standing so long that everything was rusted frozen together and I purchased a new set of unused vented calipers and discs for £90. These were on sale because a chap wanted them fitted to his racing XJS, but was told to take them off as the car would not be homologated for racing with them fitted. I sold the old rusted caliper at Stoneleigh for £60 when I used to run a stall with Peter, so frankly, it was just a cheap way to unstick the old calipers. To add icing to the cake, Martin Robey had stainless steel cylinders in their catalogue erroneously listed at just 50p more than standard ones, so it all ended well.

Braking and/or acceleration will always be tyre to road limited, so as long as your brakes can lock up, there is little to be added by spending money "upgrading" here, especially as the s3 is not known for having poor bakes.

http://www.jag-lovers.org/snaps/snap_vi ... 1287747435

Sorry, thumbnails only. The originals are left sitting on another computer now.

Apologies to Barry.

kind regards
Marek

[PeterCrespin]

That was when booking a stall worked out at about a fiver each for a group effort, all of whom then got in free as stall staff and had somewhere to leave their stuff and sell their resto leftovers - happy days!

In fairness, vented rear discs are not designed to improve stopping power but prevent fade and preserve diff output seals. There’s not so much benefit without air-scoops, but all S3s should have those anyway. Quite how often S3 owners push their cars hard enough to induce brake fade is another question entirely, but the logis is sound

[NorfolkJohn]

Thanks very much for the input chaps. I think ww should go with the new calipers ( old ones look fairly shot) and besides we have paid for them now.. Only question remains - are we safe to nibble a bit off the differential housing rib ? probably need about 3-4mm off one side - either that or grind a bit off the side of the calipers ( not so keen to do this ).. Has anyone any good intelligence on doing this ? risk of weakening he casing ? how much can we remove before going through??

[mgcjag]

Take the rear cover off the diff and inspect the area your looking to grind away is the only real answer.....if someone says yes its ok and you grind and get a leak your buggered.....Also on a S3 diff there should be an oil drain channels from just outbourd of the output shaft seals to under the diff so that any oil getting past the seal diverts out at the botton of the caseing.....they do get blocked with crud over the years so run a wire down to clear them......Steve

[NorfolkJohn]

Thanks for the advice Steve.. will definitely look for the channels and also investigate before any grinding..