Larger 15/16" MC and booster installed.. Have some Q's - Miata Turbo Forum -Boost cars, acquire cats.

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Old 06-23-2010, 07:15 PM   #1
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Default Larger 15/16" MC and booster installed.. Have some Q's

Hello to all! Yesterday I finally installed the 2001 non ABS MC and Booster on my 93.. My expectations were: Less travel, harder pedal, and braking would bite sooner (Less lag)...

I also replaced all the brake line fluid and bled the system...

Two things happened: The pedal was a little longer than before, and I presumed it was that there was some air still left on the lines or the MC... So I started pumping the brakes to see if I could get the air out... The pedal improved, but when I was pumping the pedal, the idle rose consistently, and when the pumping stopped, the car almost stalled... I think there is a vacuum issue here, so I wanted to ask those who have done the swap, how did you primed the MC and booster, and wnhy do you think the idle is being affected so much by pumping the pedal?

After a day of driving the pedal is noticeable firmer and shorter-travelled (?).
Should I let the system settle for a few more days and then re-bleed?

Thanks for your input!

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Old 06-27-2010, 04:50 PM   #2
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could be that your booster is torn and causing a vacuum leak. Make sure you have an additional one way check valve installed in the line so the booster doesn't see boost and break. The boosters have a check valve in them, but it's not worth a broken part just grab an inline one and throw it in for re assurance. If that doesn't help you might just need to re-bleed the lines. Another thing could be with the bigger master the firewall is seeing more force applied to it and flexing more try adding a MC brace. Here's the one in my 7. Made a world of difference. If the 2001 booster is significantly bigger than the last it will cause the RPM's to rise from pumping the breaks, but it almost dieing is sign on a vacuum leak.
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Old 06-27-2010, 11:16 PM   #3
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Did you "bench bleed" the master cylinder?
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Old 06-28-2010, 12:16 AM   #4
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Originally Posted by lordrigamus View Post
Did you "bench bleed" the master cylinder?
Where the heck can you get a bench bleeding kit? I can't find any of the fittings anywhere to do this. I've looked long and hard and deep and black.
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Old 06-29-2010, 11:54 AM   #5
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Thanks all for your responses, apparently the MC and booster was not properly bled before installation, the brakes are significantly better now. The pumping still creates the RPMs to rise, but it is probable because it is larger than stock. We did install a check valve in the line and tested it and it works fine...

Will see the brace thing, it makes sense!

Now, since I assume the air that was in the MC is now somewhere else, I will re-bleed the system just in case...

The system still wants to die after pumping, but I guess it is also related to the larger booster demanding more from the lines and then suddenly having enough, causing the car to take a few seconds to balance it out... Does this make sense?


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