pearlwhitesix

Does anyone know the size of the caliper bolts? The two main bolts that hold the calipers to the spindle.
I have the 4 pot calipers in my 4.2

Also looking for the size and thread pitch of the long pinch bolt for the upper control arms.

Thanks!

Just Me

I *think* 21mm. And darn tight (140#-ft spec)
You mean 4-pad, 2-piston HP-2s, right? I know of no 4-piston calipers ever made available by Audi on that model.

Pinch bolt je ne sais pas

4Driver4

I strongly advise you to buy these bolts from the dealer.

IIRC, the pinch bolt is a 10mm and the caliper bolts are 12mm. Not sure about length or thread pitch or hardening.

SloopJohnB@mac.com

Agree. These are what are called critical fasteners. They're called critical for a reason...

pearlwhitesix

I appreciate the concern, but I have access to hardware graded higher than factory spec, I'm not just going to home depot or something

The pinch bolt especially is weak from the factory, never had a bolt completely strip itself like the factory bolt when I tapped it out of the upper spindle.

Is there an Audi resource that provides part #s and hardware sizes, I'm used to Porsche PET.
I have Elsa but that is not very helpful.

My caliper bolt heads are rounded off as well I would rather replace with something that will last than overpay for a weak factory bolt.

pearlwhitesix

also when I said 4 pot I mean my calipers use 4 brake pads each, I believe the 2.7t uses the same calipers. I couldn't remember if it actually had 4 pistons, now that I think about it I'm pretty sure it only has 2 pistons per caliper

A6Gary

Unless you have the material specs or the actual grade of the factory fasteners, you should purchase them from a the dealer (or an equivalent on–line supplier using the OEM P/N). Without that critical information, you can easily use a weaker bolt/fastener than the OEM version. ETKA should provide you with the fastener size and P/N for these bolts.

4Driver4

So your assumption is that a harder bolt is better? Are you an engineer?

Just Me

its the lucas HP-2. Some 2.7s use them, most dont. Nearly all B5 S4s had them.

SloopJohnB@mac.com

Well, that puts you in the engineer's place. Yes, you can put higher rated bolts and engines can be put together with ARP studs/nuts or head bolts, BUT you don't know the appropriate clamping force for the system that Audi figured out from basic principles and extensive testing.

In other words, you can put a grade 8 socket head cap screw in there with aerospace nuts, but chances are the same torque will give inadequate bolt stretch for the same clamping force...aluminum uprights, etc., higher clamping force distorts the upright. OTOH, higher quality doesn't necessarily mean different Young's modulus, so knock yourself out.