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Discussion Starter #1 (Edited)
1994 Cobra Master Cylinder/Adjustable Brake Pushrod Failure Mode and how to avoid

Over the past couple of years we have noticed a slightly high rate of customer reported “leaking” of new 1994 Cobra master cylinders. When bleeding the brakes on our demo car we found that if the pushrod is misaligned near the limit of travel it can contact the circlip, and push the circlip into the master cylinder bore. The result can be damage to the bore and a master cylinder that leaks slowly into the footbox area. The circlip groove is tapered on the far side to enable the piston seals to slide in during master cylinder assembly. This makes it relatively easy to inadvertently push the circlip into the bore. The circlip is also susceptible to bending if contacted by any part of the pushrod. A bent circlip can prevent the master cylinder from retracting fully leading to brakes that don’t fully release.

Misalignment of the pushrod to the master cylinder bore is due to variations in the positioning of the modified pushrod pin location on the brake pedal and the condition and mounting position of the donor pedal box. Since the pushrod end moves in an arc where it is attached to the pedal arm the alignment varies during pedal travel. The alignment will not be perfect but it is OK as long as the pushrod never touches the circlip. Pay special attention to the adjustable pushrods jam nut that can catch, bend and displace the circlip if it happens to be aligned with the loop ends of the circlip. This is most likely to happen during initial brake bleeding procedures when the pushrod is getting fully depressed. Once the brakes are successfully bled the pushrod won’t normally travel in as far.

If your pushrod contacts the circlip you must reposition the pedalbox, (shim with washers) the master cylinder, or both, and or re-work the brake pedal arm to change the position of the pushrod.

I hope this solves some mysteries and helps someone avoid damaging their master cylinder.

Mark Reynolds
Breeze Automotive, LLC
 

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section 8
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vey good info ttt
 

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Blue Oval Scribe
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Mark, I believe you meant to say "reposition the pedal box", not foot box. You might want to correct your post for future searchers of this concern...

Thanks for the heads up...

Mark
 
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