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Discussion Starter #1
Dear all,

I haven't been very active on this forum, and I'm sure there are already discussion on here on 'brake upgrades', but I would appreciate any direct feedback on my or links to previous articles which are relevant.

That said, my situation is as follows:
  • I have a '67 Giulia Super which I use 'enthusiastically' for classic car events around Europe
  • As I like to have some better braking performance, I've upgraded the front brakes to Wilwood 4-Pots (to be specific - the Wilwood Midilite 4-pot, Z-120-7472) with Montreal ventilated discs and Ferodo DS2500 pads
  • At the rear, I've kept the original ATEs, albeit got (new) refurbished ones
  • In between (on the tunnel behind the handbrake lever) I've got a Tilton screw type brake bias valve
I've attached some photos of the car and brakes.

And the issue I already experience for years is:
  • The pedal pressure is not consistent; often I have to press the pedal once to actually get it firm and only thereafter can I really 'lean on it', which of course is really not ideal when driving at speed
  • The idea that I have, is that it mostly happens after I got out of a corner; so braked for the corner (probably pushed the pedal twice so it was 'hard'), cornered, and then when I get to the next corner, the pedal is soft again and needs to be pushed once again to firm it up
  • However, when I get it 'hard' and drive only in a straight and then brake on the straight, the pedal is still firm
Naturally, over the years I've already worked over many (many) things to check if that would resolve the issue, e.g.
  • Of course I've bled the brakes to ensure there is no air in the system
  • Replaced the brake master cylinder and brake booster already three times, to see if another (new) one would fix it
  • Replaced the brake fluid various times and ensured again there was no air in the system (drive it seriously, let it sit overnight and bleed it again to really ensure all the air is out)
  • Replaced the initial Wilwood Midlite calipers to a different type of Wilwood Midlite calipers with smaller pistons to better the brake master cylinder size (the parts distributor confessed he made an error with the calculation on correct piston diameter size... :mad:)
  • Replaced the Tilton brake bias distributor for a new one, because the first one (lever type) looked to have a leakage
  • Replaced the brake lines to ensure there is no leakage / squeezed sections
  • Replaced the vacuum valve in the head (which is connected to the booster)
  • Cleaned-out the rear brake pistons, as they were clogged up with some brake dust
And still the issue remains...

So any suggestions on:
  1. What could the source of this issue be ?
  2. What brake set-up you recommend for 'enthusiastic rally use' and some 'light track use' (e.g. track day) ?
Thanks
 

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Since you say the brakes work perfectly well after that first push, it sounds something like the affect of ‘pad knock-off’ to me.
In simplest terms, there is excessive movement of discs/callipers during cornering, literally pushing the brake pads away from the discs, which is only rectified when you apply the brakes again. Next corner...repeat.
Causes?
Wobbly discs - not secured properly, or warped (tho I’d guess you’d feel the latter thru shuddering). Excessive slop in wheel bearings (worn out or not adjusted correctly, allowing too much movement).
The experienced racers here in the BB might point to further causes, but it could really be that simple.
 

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Discussion Starter #3
Hi Ranz,

Thanks for your reply. That sounds very reasonable indeed.

I did check the discs being fastened and wheel bearing play, so perhaps it's some 'flexibility' in the uprights ?
 

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That sounds unlikely.
I’m afraid my expertise is exhausted if you don’t find play somewhere there...
Another BBer May chime in...
 
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