20v vented rear brakes on 90q B2

maartenmoerman · 20-09-21, 10:29 AM

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 · 20-09-21, 12:54 PM

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 · 20-09-21, 01:23 PM

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 · 20-09-21, 01:26 PM

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 · 20-09-21, 06:45 PM

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 · 20-09-21, 08:38 PM

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...

20-09-21, 12:54 PM	#2
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	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 __________________ 1991 90 quattro 20v sport 1991 90 quattro

20-09-21, 01:23 PM	#3
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,020	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 __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

20-09-21, 01:26 PM	#4
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,020	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… __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

20-09-21, 06:45 PM	#5
Colin Aitchison Senior Member Classic Audi Club Member Join Date: Dec 2013 Location: Back home in Tillicoultry Posts: 1,325	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.

20-09-21, 08:38 PM	#6
maartenmoerman Grown up member Join Date: May 2010 Posts: 23	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...