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I am encountering a strange problem with the brakes on my 69 spider. This car originally came with an ATE double master cylinder and 2 bonaldi in line boosters. Some time ago, I had this changed to a bonaldi single master (because the ATE was out of production). I also got a new in line bonaldi booster, and bypassed the brake proportioning valve in the back. All the calipers are either new or rebuilt. all the brake pads are newish.

The problem is this: The brake pedal travels almost 3 inches before I get any brake action at all. after that everything is normal: good feel, good power, no sponginess etc. I spoke to a knowledgeable mechanic who told me the return spring in the brake master was probably wearing out, so I swapped it out for a new one and bled the brakes. I still have exactly the same problem.

Is this a characteristic of Bonaldi MCs? Is it an interation between the MC and the inline booster? any other ideas?

Help is sincerely appreciated?
 

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I'm still not to familliar with the master cylinder you speak of but on most systems there is an adjustable rod from the booster to master cyl and then an adjuster from the peddle to the back of the booster. If they are not adjusted properly the symptoms would be similar to what you speak of.
 

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I don't know why you have that much travel. Have you had the same amount of travel since the conversion "some time ago" or is this recent? I would first suspect there might still be some air still in there since these systems are hard to bleed. Second if the travel has been there since the conversion I would look to the adjustment of the actuator rod from the pedal to the MC. Perhaps some of the play could be removed that way. Finally, I would suspect the flexible lines might be a bit soft unless they have been replaced in recent times. Why did you bypass the proportioning valve? I always thought that led to excessive excitement when braking in wet conditions.
 

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I would first suspect there might still be some air still in there since these systems are hard to bleed. Second if the travel has been there since the conversion I would look to the adjustment of the actuator rod from the pedal to the MC. Perhaps some of the play could be removed that way.
Yes, I like those explanations also. It is very difficult to purge all of the air from these systems with an underfloor MC and firewall-mounted booster.

I would suspect the flexible lines might be a bit soft unless they have been replaced in recent times.
I'm skeptical of the flex lines as a possible cause. Yes, the old-fashioned rubber hoses do expand a bit under pressure. But, not enough to result in inches of pedal travel. If you don't know the age of your flex lines, replacing them is prudent. And the more modern teflon hoses covered with steel braid will result in a firmer pedal. But I wouldn't expect new lines to address mhunger's issue in any significant way.

Why did you bypass the proportioning valve? I always thought that led to excessive excitement when braking in wet conditions.
I second this opinion also. Without a limiting valve, the rear brakes can lock up under heavy deceleration, which can lead to spins.
 
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