To convert the front disc brakes of your VW to the larger Porsche Brembo type is a fairly easy affair and is more or less a 'bolt on' conversion. Proprietary kits are available from companies like MBT, who will supply you with replacement hubs and caliper adaptors making it a true 'bolt on' conversion, but if you want to save some cash, or simply fancy doing this yourself, it is a pretty straightforward project that anyone with access to a machine shop or who knows where to get machining work carried out, would be able to tackle.
I designed the caliper adaptor myself - it is pretty simple and basic looking but could easily be modified to look better (I may do this in the future). The bearing adaptor is based on sketches available from Ricola Racing that I modified to suit my hub / spindle combination. The seal I sourced from the SKF online catologue.
Porsche Hub fitted with bearing adaptors
What Brakes to use?
The first thing to do is to source the brakes and hubs. The units I used were from a later 944 Turbo. The 944 Turbo has the large 4 pot Brembo calipers (the same as fitted to the 996), vented discs and the rotor that you will need. It may also be possible to use the hub and disc from a 996, but having not tried this I'm not sure.
Earlier and later cars have different hub and disc configurations, it is possible to use either type successfully but I am not 100% sure if the dimensions are the same. It would also be possible to use alternative calipers by modifying the drawings.
Caliper Adaptors
Rotor Differences
The main differences between the Porsche and VW rotors are that the VW rotor is a one peice construction, whilst the Porsche unit has a seperate hub and disc, the Porsche also uses a larger shaft diameter. The Porsche hub can be fitted to the VW spindle using VW bearings by fitting bearing adaptors into the hub. These bearing adaptors are a press fit into the hub that once fitted form part of the hub itself. One of the bearing adaptors can be seen above. The earlier Porsche hubs are different to the later ones, the bearing diameters are slightly smaller and the disc itself not only mounts different but is a different size.
Bearing Adaptors
Below you can see the drawings for one of the bearing adaptors You can download these either in 3D or 2D format from the links at the end of this article. There are two different adaptors - one for the inner bearing and one for the outer bearing.
The bearing adaptor is a press fit into the Porsche hub. The bearing then mounts as normal into the adaptor. This is acheived by using an interference fit - hence you will see that the tolerances are + 0.00 and - 0.03 for the inner diamter of the adaptor and + 0.03 and - 0.00 for the outer diameter. This is a N7 / P7 tolerance that is suitable for bearings of this size. It is advisable to fit them using a locking adhesive like Loktite 620 so that they don't come out when changine the bearings.
Not shown here are two recesses in the 1mm thick section to allow the bearings to be removed. I added these after with a half round file as it was easier than getting the job set up just to machine them. These recesses are positioned 180 degrees apart and should line up with the recesses in the hub when fitted.
Not shown here are two recesses in the 1mm thick section to allow the bearings to be removed. I added these after with a half round file as it was easier than getting the job set up just to machine them. These recesses are positioned 180 degrees apart and should line up with the recesses in the hub when fitted.
Caliper Adaptor
Once the bearing adaptors are fitted and the hub is mounted to the VW spindle the disc and brake caliper can be mounted. the caliper is mounted by the use of an adaptor plate manufacturered from T6 Aluminium. This allows the radial mount caliper to be fitted to the stock VW mounts.
The adaptor above will need to be clearanced to miss the steering arm. If you are fitting a rack and pinion to your car you will probably be swapping the steering arm around and so clearance will not be an issue. I clearanced mine manually as it was too hard to measure it before hand (it took about half an hour with a hack saw and file). I will try to update the drawings with what I have done to mine.
The caliper adaptor is held to the spindle by M10x45mm Machine Screws whilst the Caliper is held to the adaptor by M12x75mm Machine screws.
Caliper Fitted
Seals and Centre Caps
Amongst the last things to consider is the dust seal on the rear of the hub, this obviously needs to have the outer diameter of the Porsche hub but the inner diameter of the VW spindle. This is not a problem as such a seal is available from SKF, the part number for this is 38/62/10 HMSA7V. Finally you will need to drill out and file a square hole in one of the Porsche centre caps for the speedo drive cable. You can use the VW centre cap as a pattern.
3D CAD Models
All of the drawings you need to do this are available for download in 3D format from the DOWNLOADS section. To view them you will need to download Google 'Sketchup'. Sketchup is available for free from Google HERE .
2D Drawings
Alternatively you can view / print the drawings from the following links.
