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Hello Everyone
As many before me i'm trying to figure out the perfect recipe to stop that car at track :)
I've read some old threads that made me confuse a bit more, i can read weird bias balance suggested, master cylinder mods gone wrong and so on.
I am at the point that i have front on oem BBK AP 4pot on 308mm disks. On the rear, front 2pot relocated on 288mm disks, my brake bias is close to 55/45 but i feel it way too much on the rear not allowing me to get in the corners as i would like, PLUS pedal feeling is a bit soft.
What are my options now? Going further on mods and $$$ or rolling back to full stock learning to brake better?
After all the time that this car is around has a final "recipe" been developed?

Thanks :)
 

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Looks like you've done most of the BOE recommendations maybe fine tune by pad selection? Stop! - Brake Pads – BOE Fabrication
 

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You're down a path very few have traveled, and even fewer have tried different combinations possible.

Considering where you are at right now, if your pedal is soft the first thing I would do is make certain there is no air in the lines. The factory 2 pot calipers are known to be a little tricky to bleed, I do a little bit of everything when I open up the braking system for those - ie push the pistons all the way back, take the caliper off and bang it with a hammer while bleeding. Beyond that, the soft pedal you're reporting, I've at least seen one other person on the forums have a similar problem that you're reporting when doing the 4pot up front and the oem 2 pot in the rear. I think the likely issue is that you've changed parameters of a system, without considering the system as a whole - ie the brake master cylinder may not be appropriate for this application. Really there are too few people running your config on track to really know for sure.

If your problem is soft pedal and bias feels off, and you've got air out of lines, I'd say you could probably head down a few paths:

  • you could change pad compounds as suggested, which may fix the bias but likely won't not fix the soft pedal. Definitely the cheapest option.
  • you could purchase the BOE brake bias cage and install that. You'd need to ask BOE how well it would work with OEM 4 pot calipers and be ready to potentially buy their front caliper if things didn't work. Expensive, but with BOE front caliper should fix both issues you have.
  • you could try a different configuration - OEM 2 pot up front with smaller ap 2 pot in rear (CP5316, or CP5317). Will solve soft pedal, may solve rearward bias complaint
  • you could try oem 2 pot front and rear but for sure bias will be too rearward, you'll need to try different brake pads. Should solve soft pedal, may solve rearward bias with right pad combo
  • AP also sells 2 kits for the lotus, one for the front one for the rear. This is also expensive, but there's one person on here that has it and isn't complaining about soft pedal. I don't think they track their car though.
  • what was the stock config for your car? oem 4 pot up front?
What kind of power does your car produce? Do you run slicks?

What is the car doing that you "know" the bias is too rearward? If you change the braking system, you should expect to have to change your braking technique to get the most out of it....
 

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How did you calculate your 55/45 bias? Did you use piston area factored with the centerline pad offset from the axle centerline?

I assume you have also installed AN braided flexible lines in place of the stock rubber flex lines?

As others have said, if you are still on the stock master cylinder, it is likely under sized with the increase in caliper piston area.
 

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@pb81 That is interesting that you think that you have too much rear brake bias. I have s 260 FE that I ran that combination on and it still would understeer if you tried to trail brake in to a corner. I tried running a more aggressive pad in the rear and still could not make that combination work. I would suggest that you check other areas for problems. By the way, I believe I was one of the first ones that converted to split masters to cure the brake bias issue.

Later,
Eldon
 
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