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Old 11-10-2022, 02:08 PM
Argess Argess is offline
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Join Date: Jul 2009
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My new MC showed up yeterday and today I managed to install it. I can now manage 700 psi (plus the width of the needle) vs. 550 psi; so just over 700psi. I might be able to get more, but I need to adjust the seat as my leg is too straight (I had moved the seat back to accomodate the piece of wood I was using to hold the brake pedal down a little bit). Didn't have time for a test drive yet, but wether the brakes can lock the wheels or not, I am very optimistic about getting at least 0.8 Gs while braking hard.

When I look back, hindsight tells me I made too much of this, however there were a lot of factors leading to confusion. First of all, my measured brake line pressure of 550 psi should have yielded over 0.8 Gs, but I only got 0.67. The fact that the front MC would slowly drop was not very noticeable and I didn't realize this was happening for a long time. Nor did I realise the front MC eventually bottomed out disallowing any more pressure increase. Some factors were sort of unkown such as the pad material co-efficient of friction and the pedal to MC geometry and what the brake line pressure normally should be. Additionally the use of DOT 5 came into question as the condition of the seals was unknown. The MC bore wasn't thought to be worn with so little use, but it turns out there was damage.

However presistence seems to have paid off. I'll know for sure after a test drive. I need to do a final bleed first (am leaving it overnight to help air release from the DOT5). I also still intend to change the front HPS pads for Yellowstuff pads, but that can wait until Spring.

Now, as for the old MC bore, I originally stated the bore looked fine. I checked it more thoroughly today. I measured it and there was no wear at all based on the internal diameter measured at locations 90deg apart. There were however some extremely light scoring as per the picture below:

These little scratches don't look like they were made by the piston. My best guess is swarf or grit left in during manufacturing. Or possibly a bit of dirt got in while adding fluid. Of course they may be other damage I couldn't find with the boroscope.
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