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Discussion Starter #1
After finding the tread about upgrading brakes, I would be very appreciative if anyone could help be out! I have a 92 NA. I installed 2012 Audi S4 rotors on all four corners, custom hub rings, OE 92 front calipers on all four corners with custom relocation brackets, braided lines, and a Wilwood spot E-brake. OE master cylinder and prop valve. Here's my problem. I have almost zero clamp pressure all the way around. The front is stronger than the rears but still like I said before almost no braking. I bleed the system over and over using traditional, reverse, and vacuum methods. The pedal pressure is very soft and goes all the way to the floor with the first one or two strokes. A little more pressure after pumping a couple more times, but still very little clamping pressure! I also replaced the MC with a new OE 92 one just in case it was bad. Also tried bypassing Prop valve. Still nothing! Would a bigger MC bore help with more flow? Is there too much space between the caliper piston take up with the pad and the rotor? My brain hurts!! Any ideas to try before I scrap everything and buy an after market big brake kit $$$ Thanks!
 

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Thanks! I have all new parts and bleed everything numerous times. I am pretty sure all of the air is out, but it wouldn't hurt to bleed the system one more time.
 

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Discussion Starter #4
The Audi rotors are 22mm thick and the Toyota calipers are for the OE 25mm rotors. Would the take up of 3mm all the away around be the problem?
 

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I suggest that you try a Motive Pressure Bleeder. This is the most reliable method that I know for purging hydraulics. This is VERY different from any vacuum or suction bleeder because it applies direct hydraulic pressure at the MC reservoir and pushes anything and everything out of the lines. It works reliably on the toughest bleeding cases. If you are not able to bleed your brakes or clutch lines with this tool then you have other issues to contend with.

https://www.amazon.com/gp/product/B00CJ5DWKO/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1
 

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Discussion Starter #7
Thanks! I did try the reverse pressure method with an hand operated oil can from each caliper back up the MC. I will try your suggestion. Thanks again!
 

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I agree not much of an upgrade. The rears are thicker and the diameter on front and rears are larger. They look good as well ! I just hope I can make it work?

92 MR2 OE Front rotor Diameter: 258mm Thickness: 25mm
92 MR2 OE Rear rotor Diameter: 263mm Thickness: 16mm

2012 Audi S4 REAR VENTED
330mm diameter
22mm thick
 

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Discussion Starter #11
The only other thing that I did to the system that I didn't mention, was that I lengthen the rear brake hard line by 18inches between the firewall connection and the OE rear line going back.
 

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Not sure if this will help but I had a similar problem with OEM gen 3 brakes. Problem developed from the wrong fluid being used in system by PO and all rubber seals expanded. I rebuilt all the obvious components like calipers and MC only to find two things wrong.

First was the proportioning valve which interrupted flow of fluid to the rears. Had to replace whole unit as this could not be re-built.

Secondary, I found that the MC kit did not have all the required seals. Missed a small O ring on the shaft which caused the fluid to leak passed when pressure increased.

Hope that this helps.
 

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Discussion Starter #15
Thanks! I did find a major problem. "My stupidity" I installed the calipers on the wrong sides this made the bleeder valve below the brake line. That is why I could not get all the air out of the system.
 

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So it is solved?
I believe your braking will be a major upgrade, provided that on your car your rear braking will not lock up first and unbalance the car (like going into a downhill corner). I have 4 identical 2-piece Celica discs all around on my MKI, 25mm, 277mm diameter, aggressive pads, and the biggest difference is high-speed stopping ability, plus the increased need for modulation/threshold braking at low speeds. Best braking the car has ever had.

That extra diameter will exceed the slight loss on thickness as far as the discs staying cooler due to greater mass, heat distribution over a larger surface area, and gripping force applied to the outside of a longer radius.

You of course gain extra weight, which may or may not affect your type of driving and feel. Test really carefully, progressively, preferably on a private course with no trees, walls, or cars, please. :smile2:
 
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