MK2/3 Polo Brakes
Brakes on a Polo, my word, where do I start. OK, I am talking in context to a MK2 and MK3 Polo brakes.
Front Brakes
The GT’s came with 239mm solid discs on the front as standard much the same as the rest of the Polos, but the G40 came with wider calipers and that allowed them to run 239mm vented disks(vents in middle of disc hence wider). I had '85 Passat GL5 calipers which are the same as the Audi 80/100(early ones) and that has allowed me to fit vented discs of 239mm. These are also the same calipers as G40 ones and most of the early middle-sized VW fleet, of that age. Most VW brakes can be adapted but early Passat brakes, G40, MK1 GTI brakes etc all share the same VW 239mm vented disk set up. The MK2 GTI calipers are similar but they will not fit as the distance between the mounting bolts to the strut are different.
Now be careful not to get confused. Calipers are different to the caliper carriers. The Caliper is a moving part as it slides to adjust for brake pad wear so it cannot be bolted onto the strut. The caliper is mounted on to the caliper carrier and the carrier goes onto the strut. There have been rumours of being able to use pre 87 Audi calipers and carriers to fit 256mm vented disks, but I looked at many suitable Audi’s but all the carrier bolt holes to the strut are too far apart. But I Know of somebody somewhere that’s done it. Anyway, the path to serious braking is more braking surface area, increased friction or more leverage. So that means, bigger pads, better pads, bigger disks.
Disks
The thing that makes polo brakes really crap is brake fade. This happens when the brakes overheat and lose friction, then if your really unlucky the brake fluid will reach boiling point(see fluid section), expand and cause bubbles and cause the brake to go spongy(or even more spongy I should say!). So to avoid this happening Disks can be vented which increase the cooling surface area of the disk and keep the disk cool, helping to avoid brake fade. This allows the brakes to maintain the same level of performance for far longer under heavy usage. If you have a GT or polo with no vented disks and want to experience brake fade, slow down very quickly from 70 or above and by the time you stop the brakes will probably give you the willies! Not good in an emergency. So a common brake upgrade for any polo is to grab hold of some G40 Calipers and carriers and fit them along with vented disks. Although this will not change the initial bite, the braking forces under heavy braking will be increased.
As you increase braking surface area with bigger disks and bigger/better pads, the brakes will produce more heat. This is where cross drilling comes in(X-drilled). Disks can be x-drilled as well as vented for maximum cooling. That basically increases the cooling surface area even more. By the way…….DON’T DRILL THEM YOURSELF! If you are willing to risk weakening the most important part of your car in an emergency then you need your head read!! Leave it to the tried and tested products you buy. More expensive yes but brakes are not to be skimped on if you ask me. Solid cross drilled don’t make any sense either cos venting is cheaper and more effective, except where vented can’t be fitted(ie, GT calipers don’t allow vented disks, so thinner X’drilled ones would be another way of doing it, but vented disks are a better option). Bikes are a good example of this. Disks are far too thin to be vented but next time you see a super-sports bike or a superbike, check out those drilled disks!! Lots of holes!! Believe it or not the primary function of X-drilling is not for cooling!! They are actually for removing brake dust… I’ll explain in a mo.
Grooved disks……sod all to do with cooling. These make a difference to braking performance, but as always there is a compromise. THEY EAT PADS!! Good braking yes, long pad life no! Not sure by how much but there will ALWAYS be compromise between performance and longevity in most things….. pads, tyres, engines, fuel…….you get the picture. I don’t know any car in the universe that comes with them standard, some race cars have them of course and some modded cars, but for the road, perhaps a bit OTT. Now the way grooved disks work is that it helps remove the brake dust from the braking surface area to keep maximum friction between pads and disks. This is actually the main purpose of the X-drilling too. To remove the brake dust the groove just channels it out. The X drilling is apparently more effective as the disk spins it creates a mild vacuum in the vents that help suck out the dust from the pad as it passes. You’ll see that you can buy x-drilled and grooved….. they may look nice but both grooved and x-driiled re a bit needless in my opinion. Also some manufacturers go OTT with the amount of grooves on each disk. Six or eight is more than enough, any more and you loose surface area.
One disk upgrade option is a 285mm kit upgrade. For this you need 15 inch wheels and G40/Audi/Passat calipers. All the kit does is space out your carriers to fit the 285mm disk, so it doesn’t actually increase braking surface area, but it does increase leverage by a great deal. Imagine you are undoing a tight wheel nut. You have a wheel brace that’s 239mm long and one that’s 285mm long which is going to be easier to remove the nut……..same thing applies when applying any leverage force. Apparently the 285mm increases braking by 100 percent over 239mm disks. Now to get the most of the big disks you should get bigger calipers and pads off say a VR6 and adapt them to get more braking surface area…… but I would imagine the way it is would do!
If you decide to go for rear disks (more later on that) solid non grooved disks are normally OK for rear disks as they do no where near the same work as front ones. All I would say is leave your car in gear if you have rear disks cos if you’ve been driving hard, the brakes will cool and loosen the handbrake when parked…not good on a hill!! OK Next…
Pads
Pretty much covered that in the compromise bit. I would say its worth it, but you pay more and they last less, I wouldn’t ride my bike with standard pads, can’t say the difference it made to the car cos I modded the brakes in one go. I have standard pads in the rear, simply again, cos the rear does very little. Upgraded pads made a huge difference on my bike.
Calipers
If you want to spend silly money, you can get four pot or even six pot calipers (more pistons per caliper, VW brakes have one per caliper(single pot). But you are talking 2-300 quid PER caliper!! So if you want to know more… mark.hunter@blueyonder.co.uk ahh this is the ultimate way to silly needless brakes…… ;o) you’ll see what I mean soon enough.
Brake Lines
VW fitted steel brake pipes as standard, pretty silly if you ask me. If you get them replaced make sure its with copper ones or copper/zinc ones, they don’t corrode, so that should be it for life. If you do get steel, make sure you paint them with Hammerite or something. Copper is really easy to work with, more so than steel and copper/zinc, but copper/zinc is harder and less likely to chew up if you need to change bits (or fix!) later on, but that’s me being pernickety. I used copper, cos it was me working with it! Don’t ever use pliers or anything hard to bend pipes, you risk kinking them. I have learnt the hard way! Other than that, no difference in performance.
Also BRAIDED FLEXI HOSES. I went for Goodridge stainless steel flexis cos I liked the lifetime Guarantee!! You’ll need a 6 line kit (or you can get a custom 4 line kit made) for rear disks, or 4 line kit for drums. I think they make a difference to the feel and response of the brakes, plus they look nice and once they’re fitted you should never have to worry about them again. On the bike they make a HUGE difference, but the little things are more noticeable on bikes.
Master Cylinder
Tough one, I’ll do the MK3’s first. That’s easy….. if you want more power(less leverage and feel though, not that you have any with the servo anyway!) fit a 22.2mm Passat effort or late Golf GTI 16v one (same thing anyway). They bolt straight on and you just plug up the unused hole with the supplied screws. Easy. Steve Millo has done this so ask him!!!!
Now the bit more tricky MK2!! No servo on the MK2 so brakes do even less per foot pound(boom boom!). The later 22mm master cylinder CAN be fitted , but I would advise better front stoppers first. I didn’t think it would be possible to do this, but I did it, I will describe shortly.
First I investigated fitting a MK3 servo, possible but would require a serious amount of re-constructive surgery to the bulk head. I don’t like the MK3 servo anyway so I didn’t bother. Remote servos ARE available from somewhere, I don’t know where but I didn’t look hard. Perhaps Rally Design or somewhere like that. As I have beefy brakes I thought more power less leverage option would be a good idea. Careful cos leverage in the mk2 is important. You need good brakes with the bigger master cylinder cos it will stiffen up the pedal giving more power, but if you whack it on with crap brakes it will still reduce pedal travel, but will be harder to push for same power
Ok. To fit the bigger master cylinder without servo to mk2, I thought I would need to cut the bulkhead or lengthen the master cylinder mounting bolts (on the pedal cluster) but while doing it I devised a way to do it easily. All you do is shorten the pedal push rod by about an inch and a half, and get hold of a MK3 polo fluid reservoir and fit it BACKWARDS!! Fits perfectly! Only problem is you can’t remove the push rod without moving the master cylinder once fitted. Only really a pain when adjusting (should be 1mm play in pedal travel) but once done, it will never bother you. Depending on whether you have an early MK2 Polo or later MK2 Polo you may need to play around with the brake pipes. Early MK2 has 5 outlets, one for a brake light switch. Easy, fill up one hole with brake line switch and make set up like on later MK2/MK3 polo. Ie put in a T-piece on one circuit(make sure you get this right….. remember front left/rear right and front right/rear left). Brake light switch on later MK2 Polos are on pedal cluster anyway so… who cares! And there you go!
The 22mm master cylinder is off these vehicles :
They are all the same. German and Swedish have got them for £29 plus vat or for VAG(higher quality)£55 plus Vat. Not sure on prices from Euro.
Rear Discs
Oh the biggy conversion. Any VAG rear disks should fit with rather a lot of arsing around. Drums are crap. They have always been so, and always will be when compared to disks. As the back brakes don't do much anyway, you should only really think about uprating them if you want a serious handbrake!! But then I know nothing of these Spira drums Alex mentioned a while back but for 120 quid you could probably find some second hand calipers and discs. The rear calipers are a NIGHTMARE. I am not going to hide this. Just to push the piston back, not only do you need to apply silly force but you need to turn them as well!!!
Anyway all the bits do bolt on as they should on any other Golf/Passat/Corrado but the handbrake cables need made. I made mine (as did Adrian Ford) out of Golf cables and shortened them. I kept the caliper end and put nipples on where they meet the middle bit. If you want to do this try and get a GOOD set of bits. A seized caliper is a re-con job. Also, disks/pads are 30 quid, new back-plates 25 each, handbrake cables to cut up are not cheap and 20 ish and if you need re-con calipers, that’s another 100. If your car is getting disks I would advise a Rear Brake pressure Regulator.
Brake Pressure Regulator
This is standard on GT’s and G40’s. This detects the weight in the back of the car by ride height and adjusts the power to the back brakes and helps stop back brakes locking before the front ones. Without this properly adjusted, disks could lock up the back before the front, NOT GOOD! This can cause the car to swap ends and say hi to oncoming traffic!!! In saying that TSR ran their MK2 breadvan G40 with rear disks and no BPR and I never heard of that crashing!
IMPORTANT. I bet a lot of people have forgotten about this when lowering or uprating their back brakes. There is a load sensor on the back axle of GT and G40 Polos which adjusts the amount of power going to the back brakes. So if you have your mates or a heavy load in the back of the car the rear brakes get more power. So when you lower a car the sensor thinks that your fat mates are always in the car and give the back brakes more power. Great, you think. Not so. The last thing you want to happen is swap ends in the wet! This is a dangerous way to have brakes set up (or I could be being over cautious). So if you lower a car or uprate brakes the load sensitive brake pressure regulator must also be adjusted. (Keith, Jen, I bet you guys forgot about that!! cos I certainly did!!).
Fluid
Another mod to your braking system that will firm it up a little bit is to upgrade the brake fluid from Dot 4 to Dot 5.1. This basically means the fluid compresses slightly less and therefore will stiffen up your brakes. You should replace all the fluid in your system if you do this, so it will take a lot of bleeding. Also, brake fluid absorbs moisture from the air relatively quickly, this introduces water and air bubbles in to the fluid, which will reduce the performance of the fluid and contribute to brake fade. Always use Fluid from a new sealed bottle, when renewing fluid. Don’t throw away old brake fluid cos you can use it to help bleeding at a later date (use it to submerge the end of the tube in a milk bottle to catch bleeding fluid, and to stop air being sucked back into the braking system). One man bleeding kits are very useful if you have no mates, but take ages to get going. You can get this stuff from Halfords or similar retailer. Dot 5.1 fluid is about a tenner and one man bleeding kit is about 4 quid or 12 for the full kit (including plastic bottle and stuff but you can use a milk bottle or old washing up bottle or something).
Bedding In
When ever you fit new pads or shoes the brakes need to be bed in. Basically just drive normally for 200 miles or so. During this time the pads wear to the shape of the disk and until then braking power is not at maximum. During bedding in time it is important not to use the brakes too hard or emergency stop. This might cause GLAZING. This is basically when the pad is not fully bedded in to the disk and instead of creating friction, the disk “polishes” the pad giving it a shiny surface and thus crap friction against the disk. Once the pads are bedded in though this shouldn’t happen. Obviously you may need to use your brakes hard in the bedding in process. Glazing might occur, but I drive normally during bedding in and have been a bit heavy footed and never experienced Glazing. If you do, a light sand with sand paper just enough to take the sheen off the pad will cure the problem, this start the bedding in again.
I think I’ve pretty much covered most things. But if I have forgotten something then feel free to join the yahoo group and ask… I’m on there all the time. Some of the above is simplified, for example, I doubt anyone would want to know about dry boiling points and hygroscopic abilities of brake fluid!