Mk1 Polo Rear Disc Conversion

Hi all. I’m trying to work out which parts I need to complete this conversion on a Mk1 Rocco. I currently have a HRP pedal box and will upgrade the front brakes to 239 Wilwood 4 pots, I want to get rid of the rear drums and fancy Polo 6N rear set up. Has anyone done this and have a list of parts or any advice? Thanks

 

I think its simply the brakes, discs and stub axles, and I guess some new hoses with the correct end fitment, bolt on job. Not 100% sure about cables, but my point was why do it....unless its for aesthetics? If you just fancy the look then fine go for it, but for performance you don't need any more that the std drums. For racing you don't really need the back brakes at all other than for trail braking and balancing the car in to corners, they are normally just adjusted down to virtually nothing. For rallying disc handbrakes are useful, but a second set of motorbike calipers is preferable if allowed, other wise no advantage. I guess the disc set up is a bit lighter than the drums, but you can drill the drums face and braking surface to save quite a bit of weight.....I would wager its probably lighter than the Polo set up them.

 

You'd be mad not to upgrade the fronts too, unless you're running 13 inch rims.
Mk2 256mm discs, with Vectra calipers fit under 14s, and are night and day better than mk1 spec 239s.

 

Thanks for the replies. The reason I was thinking of upgrading the rear was I thought the drums might not be ideal with the pedal box setup? On the rollers I have very little rear brake power but on the road I need the bias turn towards the front other wise I have poor braking. I was thinking maybe the wheel cylinders in the drum were at odds with the pedal box setup? I am using 0.625 Wilwood Master Cylinders front and rear.

I am running 13” wheels so need to stick with a 239 and was going to purchase this kit: https://momentummotorparts.com/prod...-cabrio-scirroco-caddy?variant=39841961541789

The current front setup is new oem with ds2500 pads but braking is far from ideal.

 

The pedal box will work the same with drums or discs, subject to the right dia cylinders. You need to use a bigger dia cylinder on the back to reduce the pressure, always bigger on the front. I suggest 0.75 on the rear and 0.625 on the front. You have to learn to brake harder than with a servo set up, but the feel comes as you brake harder, unlike a servo set up where you have to be very delicate not to lock the wheels with decent brakes....not idea on a track at speed with lots of G forces! |You can get 0.5 dia cylinders for the fronts to make them require less leg pressure, but I think the pressures in the system start to get on the high side then.

The only issue with drums will be what buildup over time, its not the power of the brakes....on FWD rear at least. I hillclimb and sprint, so different parameters for me, but with you its the inconsistency of the rear brakes that will be the issue not the power, as the fade over time will change the force available, so not helpful. You can adjust as you go to compensate as you go, hence most race and track cars fit adjusters. For me getting heat in the brakes is the issue not getting it away. So I run std rear pads as they heat up quick and don't grab too much.

When you brake the rear wheels on a FWD racer will be pretty much in the air, so any braking force will lock them up making the car unstable in a straight like, as one will lock before the other for sure, and even worse if you trail brake as soon as you turn in she's going to be unpredictable. Like me you don't want aggressive compounds, but you do want a compound that going to remain stable in its friction, so unlike me you might want to use a race compound......but pick one that stable more than aggressive I'd suggest (either drum or disk). Of course far more compounds will be available for disk than drum I'd imagine.....but never looked really as like I say not a problem for me.

In fact, apart from trail braking, just to steady the car before setting it to hit the apex at the right angle I wouldn't really bother with rear brakes personally. Maybe just for tyre warming or spinning it round quickly on the handbrake when needed, neither which are needed on a circuit car lol.

On my MK2 I had removed the brake compensator of course, and fitted a simple screw type adjuster. Went testing, on run 1 the back end was all observe the place, so down to minimum pressure the the rear, so technically off I guess. Run 2, still light, so in the end I got some mole grips and squeezed the copper brake pipe smaller/flatter until the back end was right....in my case about 40% flat, so virtually zero braking on the rear. Perfect! Not suggesting that you go squeezing brake lines, that's just my fix, but you get the idea.

My MK2 is on a std servo pedal box, with just the pivot point moved, and 305mm discs and big 4 pots and some wicked [expensive] pads etc. but std MK4 rear calipers and some ebay pads of some sort. My MK1 full on hill climb car is on a pedal box, so I do have some experience of these set-ups, not making it up lol. Anyway that's my take on it.

 

Thanks for such an in depth reply Tony, that all makes sense to me. I will probably just stick with the drums and spend the money elsewhere. What are your thoughts on the Wilwood 4 pot setup and what effect it will have?

 

What are the fancy pads you use, Tony?

 

Try Hawk HT10 pads (track only). Best tip I can give you.

 

Thanks for the advice, the car sees mainly fast road use tho.

 

Hmm, then they could be too hardcore. You do need some temperature in them to work. But there are many other pads from Hawk and others which can increase the performance. Check the friction diagrams to see which could suit your purpose