Floting rotor setup

[safe]

Whats the best setup for true floating rotors for 911 hubs (not 930) nowdays?

I use the VCI on my 77 Targa and I like them, despite being a little noisy (pretty quiet now with enough brakedust in them).

On my 69 widebody I get knockback, I think, not sure if it's front or rear.
I have to pump the pedal before braking to get a decent pedal on almost every corner. I don't think it's curbs, just flex from the cornering forces, is that possible?

[chrismorse]

How is the disc runout, at each wheel?
Loose bearings
warped rotor?
Which calipers are you running? Could the seals be causing excessive pull back of piston(s)??

good luck,
chris

[safe]

New bearings, minimal play, new rotors, same as the old rotors.
I run 928 S4 calipers and also S4 rotors over the hubs.
Maybe the calipers nesd rebuilding but I don't have any issues on the street and not every corner.

[Locker537]

Stay off the curbs for a lap and see if you still experience the symptom. It's impressive how much some curbing will rattle the pads back.

[Bill Verburg]

I prefer the floaters using McLaren spring clips over the older 930 setup



That said it's difficult to get the caliper rigidity necessary when a caliper adapter is used as on your setup

Is the issue new? or something that has always been there

[safe]

Originally Posted by Bill Verburg

I prefer the floaters using McLaren spring clips over the older 930 setup



That said it's difficult to get the caliper rigidity necessary when a caliper adapter is used as on your setup

Is the issue new? or something that has always been there

It's probably been there, I'm just driving faster when other stuff has been sorted out. It might have gotten worse, but I can't say for sure.

If I could find a pair of front 930 calipers for reasonable money I would change calipers.
I have 930 rears.

[safe]

Originally Posted by Locker537

Stay off the curbs for a lap and see if you still experience the symptom. It's impressive how much some curbing will rattle the pads back.

I get it without hitting curbs too.

[safe]

Originally Posted by Bill Verburg

I

That said it's difficult to get the caliper rigidity necessary when a caliper adapter is used as on your setup
e

Btw, how does caliper rigidity affect knockback?

[Bill Verburg]

Originally Posted by safe

Btw, how does caliper rigidity affect knockback?

knockback is just the pad pushing one or more of the caliper pistons further back into it's bore than usual, In normal operation the pad rotor pushes the pad back til there is 0 clearance, pushed further causes the brakes to need the extra pump to corrrectly operate again

Porsche calipers use oversize through bolts compared to off the shelf Brembos of the same design and Porsche also goes out of it's way to make the calipers and mounts and supporting structure as stiff as possible, Any twist or distortion in the caliper, mount or supporting structure can cause knockback but you generally have to be putting a lot of strain on the system for it to be an issue.

Unfortunately when caliper adapters are used a small compromise in stiffness is introduced into the system compared to the same setup w/o them/

[safe]

Originally Posted by Bill Verburg

Unfortunately when caliper adapters are used a small compromise in stiffness is introduced into the system compared to the same setup w/o them/

Are there differences between different adapter manufacturers that you know of, someone who makes them better?
Those I have seen are aluminum, but a steel one would be stiffer for not a lot of extra weight (I think at least).

I was also thinking that there may be some play in mounting the calipers to the adapters, the calipers can't be super snug on the mounting bolts so I can't be certain that the calipers are 100% square to the rotors.

Edit: Unfortunately the track day season is over now so any testing will be postponed until spring....

[stownsen914]

Another thing to check - worn spindles can be out of round and allow a little movement similar to loose wheel bearings. And cause what you are experiencing. You’d think a wheel bearing shake test would reveal it, but who knows.

[safe]

Originally Posted by stownsen914

Another thing to check - worn spindles can be out of round and allow a little movement similar to loose wheel bearings. And cause what you are experiencing. You’d think a wheel bearing shake test would reveal it, but who knows.

I hope they are ok, they were brand new from Elephant Racing and have been on the car basically 5 active years.
Reinforced spindles like RSR.

[stownsen914]

Most likely fine. The end of the spindle can wear if the smaller bearing race spins on the spindle. It would feel like a worn wheel bearing.

[safe]

I think I found the issue.
The adaptors i have are crocked. The calipers sits slightly of from parallel with the rotors. The mounting threads for the calipers in the adaptors are 1-1.5 mm off from each other.
The adaptors are something that someone made, no any commercial product. I bought the brake parts at junkyard some years ago.