20v vented rear brakes on 90q B2

[maartenmoerman]

I am in need of new rear brake discs & pads for my B2 90Q , so naturally i want to upgrade to something bigger. I'm also doing the front, and have got that figured out with the right adapter, and boxster calipers, but am trying to get this rear upgrade figured out under one big condition, and that is to stay 4x108 PCD.

Is this possible? I have already acquired a new set of calipers, caliper brackets, discs (urquattro 269x22) & pads to make this work, and was just going to redrill the discs to 4x108, but after diligent reading before mounting them, found out that the urquattro rear hubs have a different offset than the b2 90q hubs.

What are my solutions? I've gone trough a few of the threads, but so far, i can't figure this one out easily.

Appreciate your thinking.

[mikes2]

Is it possible you could use a front disc off another car with 4x108 ?

Must be something out there with roughly the correct dimensions.

Audi 80 B4 discs are 280x22 - you could get them turned down to 269mm fairly easily

[Hanuman]

Or a bracket which steps the rear calliper bracket out.

The issue you have is hat height. I’m working a UFO strut upgrade and dealing with similar issues, as the ufo hub is a larger diameter and a different offset dimension.

To aid in this, I copied/pasted the entire Dark Gem* brake disc library to Numbers (Apple version of excel) to aid finding the right discs.

Didn’t Ford also use 4/108? Or a few other manufacturers?




Character names changed to avoid copyright issues

[Hanuman]

Audi A8 discs are a different height, too. I inadvertently ended up with a set of A8 discs which I hadn’t opened for about 18months. The right disc ordered but the wrong disc sent. Ur- 20v has the same discs as V8. But not the A8…

[Colin Aitchison]

I fitted 278mm x 10mm discs with standard pads and caliper with 38mm piston to the rear of my 1987 b2 coupe GT and only had them on for one track day, on the slowest bend on the track braking from 75mph in third to 35mph in second I found myself facing the wrong way more than once due to rear wheel lock up, yes the car did not have ABS and did have the load leveling valve on the rear beam. I think fitting 269mm x 20mm discs and calipers with 43mm pistons may prove to have the same problem under heavy braking.

[maartenmoerman]

I'm also upgrading the front to 280mm with boxster calipers, golf 1 adapter kit, and redrilled/bored 280mm rotors for a Golf.

Not sure if my math is right, but i was thinking this:

- original 90q is 256mm front and 245mm rear. 256/245 = 1.04 ratio
- new setup is 280mm front and 269mm rear. 280/269 = also 1.04

Anybody can chime in, if my thinking here is correct, or do brake dynamics work in a COMPLETELY different way?


Did some more googling and searching 5x112 swap information (you'd be surprised what kind of info you find there). And some person pointed out somewhere that 200 20v brake might fit. Hat height of stock discs is almost 40mm, and the 200 20v brake (part number 447615601A ) is 46mm, but the disc is also 2 mm wider. This might fit with a spacer on the bracket? I noticed, i can get a set on ebay for 31 euro, so might be worth a shot...

[jogi730]

Some Escort Cosworth discs should fit

[maartenmoerman]

Originally Posted by jogi730

Some Escort Cosworth discs should fit

Thanks, just been googling that, and found this:

Audi 200 Turbo rear axle - 269x20 and height 46.2 LK 5x112
Ford Escort Cosworth rear axle - 273x20 and height 42.7 LK 4x108

so still some machining work to do, but that comes very close to the ~40mm height of the 245x10 original ones.

Interesting... Thanks! More food for thought

[jogi730]

Keep us up to date which route you go down

[msh]

Originally Posted by maartenmoerman

Anybody can chime in, if my thinking here is correct, or do brake dynamics work in a COMPLETELY different way?

Apparently. Look at the cars using more or less the same rear disc brake setup as on your car, and you'll find almost everything VAG made until at least turn of the century - with only exceptions being UrS4/UrS6, RS2, B5 RS4 and probably S4, and, in C5q at some stage rear disc size crept up by 1 centimetre; vented rear discs being used, again, only on V8 cars. And these are much heavier cars than yours. If you want to do something to the rear brakes, apart from discs and pads, check the caliper piston size and if it's 36 mm, go for calipers with 38 mm pistons.

In case the car is being built for heavy track use, then, surely, go for vented discs.