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FFCobra Fanatic
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1,978 Posts
Discussion Starter #1
I redid the brakes this past spring, replaced the master cylinder, rear brakes, etc. My brake setup is the complete aerospace lineup.. front and rear aluminum 4 piston calipers, using aerospace's aluminum master cylinder. It looks (and probably is) the wilwood 1 1/16th" master cylinder. The problem I'm having is the first compression stroke of the brake pedal is soft, but the next stroke is very firm, like I want it to be. The car does stop, and it stops fine, I just want my first stroke to be firm like the second. I installed residual pressure valves up close to the MC thinking I was getting fluid flow out of the calipers, but they didn't make much difference. So I'm wondering if I have air in the lines somewhere, or in the MC. I did not bench bleed this MC before I put it in... unlike others, it doesn't have the bleed ports on it. Before I bleed it again, whats the best way to make sure I don't have air in the MC? Oh, since the lines enter the MC from under the fender, I'd rather not have to unhook the lines again!
 

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FFCobra Fanatic
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12,975 Posts
Hard to go wrong with a vacum bleeder. Lets you connect the bleeder at the caliper and draw air/fluid thru the line from the m/c.
"Most" times if pedal is soft but hard on second stroke. it caused by unadjusted drum brake if used or piston retracting too far back into bore so that first pump/stroke of the pedal is mostly just moveing the piston closer to the rotor.
Air in the line would result in a soft pedal on second stroke alos,"most" times.
you don't have to bench bleed the m/c. it just makes the bleeding procces quicker if you do since it primes the m/c faster/easyer.
Can't hurt to try rebleeding the brakes. Harbor Freight has an inexpensive vacum bleeder that works well for ocasional use. At least it would rule out air in the system being the cause.
 

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Senior Charter Member
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2,837 Posts
Ed, I've got a good vacuum bleeder I got from Griot's Garage. You're welcome to it. PM or email me.
 

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FFCobra Craftsman
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23,281 Posts
Also check your calipers.I'm not familiar w/ those specific ones but look for anything that would cause the pads to be pushed away from the rotors.Some cars have springs between the pads to reduce drag.Ck that all calipers are exactly parallel w/ the rotors. If not the first pedal pushes the pads at the rotors and everything twists a little to get the pads in contact fully.Second pedal feels good.Ck rear rotors for runout.If they have runout, that pushes the pads away and the first pedal has to get them back into position and the second pedal feels good.I say rears cause if the fronts have runout, you will usually feel it in the steering.All I can think of now but just wanted to get you thinking other than air in the lines cause usually air will cause a more constant mush feel but it can be hard to destinguish.
 

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Charter Member
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972 Posts
If the pedal is solid on the second stroke, I doubt if you have air in the lines. Like the others said, look for a brake pad or shoe that is retracting too far or being pushed back after the pressure is released.

Dennis B.
 
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