GlennD

Quick question -

What difficulties would I have installing brakes from a 1991 GT on a 1986.5 928? I see that the pistons are bigger ... what else would I need to replace (e.g. proportion valve due to larger pistons = difference balance on stopping power)?
I assume I can just unbolt the current ones and bolt on the new ones (and reconnect the lines, etc.)

In advance, thank-you

Glenn

SeanR

Just swap the calipers over. There are no mounting differences.

Jon B.

What's happening to the old ones…?

GlennD

Sean,

Thanks. Appreciate the prompt reply


As for what's happening to the old ones ... just getting rebuilt

Glenn

EspritS4s

I didn't realize the '91 GT calipers were any different from the 86.5 on (pre-GTS) calipers. When did the piston size change? Did it change on both the GT and the S4?

GlennD

According to the information I found:

86.5 - 36mm and 42 mm front
87 - 36mm and 42mm front
88 on- 36mm and 44 mm front

rear wheels

86.5 - 28mm and 30mm
87 - 28mm and 30mm
89 - 28mm and 30mm (seal kits are different part numbers from 87/88)
90 - 28mm and 30mm

So, it appears that only the front pistons changed in size (larger) from 86.5/87

Cheers
Glenn

EspritS4s

Good to know. Thanks.

James Bailey

Little or no difference in function given that the rotor and pads are identical.

GlenL

Ya know...

GTS front rotors are not the same as S4 rotors. They're a bit bigger.

But GT rotors are the same as S4 rotors

SeanR

No one has been talking about GTS brakes.

EspritS4s

We're not talking about GTS brakes, only S4/GT. The GTS has larger rotors and calipers.