Rob Edwards

Forgive the dumb newb question - is this the "bolt-thru center"?


I don't have a big black caliper here right now but can probably get one- I'd guess one would need to mount a big black caliper on a steering knuckle and measure from the caliper bolt center to the centerline of the spindle? Is that the measurement you need? Tricky to do on the car, but I have a spare knuckle/spindle here.

xschop

The lateral measurement. Is that a dirty M030 caliper below in pic?
The M030 calipers go on M030 rotors (304x32) same 77mm offset as GTS rotors. The calipers (Bigger Blacks) I have at shop are definitly much bigger than GTS calipers. Just want to know if they have same bolt to rotor center pattern. It opens even more options on the 928 GTS or M030 951/968 spindle/hub.
Dinsdale says they could be off a newer Audi S model.

Rob Edwards

M030 is some sort of 944 thing, right? That dirty caliper is a 928S4 front caliper.

Forgive my thick-headedness, but I still don't understand what measurement you need- by 'lateral' do you mean the distance between an imaginary line between the caliper mounting bolt holes and the centerline of the rotor disc?

Like this?

xschop

Exactly. and how does it compare to the S4 caliper? S4 caliper should be the same M030 caliper as the rotors intercahange. If youve never seen my old posts, the LS430 calipers could be modded up on M030 or GTS spindles fairly easily.

xschop

Did the GTS get a bigger Master cylinder when it when to the 36 x 44 piston calipers?

Rob Edwards

Nope, same BMC from F 92GS8 61000 ('86) - to 1995.

xschop

The piston area of the GTS caliper (36x44) is 2537 mm sq
These Black Brembos I have (40x44) are 2776 mm sq
So definitely wont be an issue with a factory MC

Rob Edwards

I'm a dummy, I measured the mounting hole center-to-rotor center on my F50 calipers at 55 mm. Then drove to Greg's to measure the same on the big blacks on my GTS. Never occurred to me until I got there that the front spindles/steering knuckle and hubs on the racer, the GTS, my old GT, and any 86.5 and S4 are the same, so that any 86.5-95 caliper is going to have the same mounting hole-to rotor center dimension- 55 mm.

Duh.

(That said, the F50 rotors are spaced out from the mounting surfaces a bit: )

xschop

I'm in the same boat. Was doing two different brake swaps this past weekend with the same caliper and rotor on 2 diff spindles.
So what are the dims on your F50 rotor, Rob?
I haven't made it back to the shop yet, but I'm suspecting that Brembo modded an F50 caliper to fit an Audi. I'll post full dims when I get a chance. The compressor bleed valve froze at the shop. First time I ever saw that happen.

xschop

Ok, this Brembo caliper can take either Cayenne rotor 330mm or 350mm.
I measure the same 55.0 mm dimension with a 70mm depth bolt hole.

xschop

Other than the Audi symbol stamped on the calipers, no other part#'s but Brembo, but there's no doubt this is a Brembo F50 derivative with taller mounting studs/protrusions. It also can take either a GTS pad with anti-vibe springs or an F50 pad with the two set pins....







http://www.v-eight.com/multimedia/dx...2073291023.pdf

Rob Edwards

Looks awfully familiar. Any specific measurements you'd like off the caliper I have here for confirmation?

EDIT: Zeckhausen has a nice visual guide illustrating the current Brembo calipers and nomenclature:

http://www.zeckhausen.com/Brembo/Consumables.htm

xschop

Yes, previously asked what was your rotor dimension on the "F50" rotor in your pic above. Is see that you modded the GTS spindle to raise the caliper. What is that additional height/dimension?

Rob Edwards

Fronts are 355 x 32 mm, rears are standard S4 rotor size, but are PFC brand.

Will get you the thickness of the spindle standoffs tonight.

Gary Knox

The S4 and GTS calipers are essentially the same EXCEPT for the fact that the GTS calipers are 10 cm 'deeper', thus the brake pad is 10 mm wider (not thicker).

You can mount the GTS rotors on an S4, then use 10cm spacers and 10cm longer bolts for mounting the S4 calipers. Probably get 90% of the braking improvement from the GTS system without using the much rarer and more expensive (used, not new in both cases) GTS calipers.

Using 993 rear calipers on the rear of an '86.5 - '95 928 also increases the brake piston size by slightly over 20%, thus providing more clamping force on the rotor.

Gary-

PS: Been there, done that with both front and rear calipers etc. on the '89 track car I sold last summer