I had/have a problem with the brakes on my 89 maro.When i would touch the peddle it would suck the pedal on down by itself and hold for a few secs then release.And while holding the pedal it would pulse up and down about an inch.No shop around here ever heard of such a thing but one and he said it was because i left the t-5's clutch setup installed and had the pedal tied down to the firewall so he removed my clutch fluid resevior cap and said that would fix it.By some streak of luck they worked right twice then back to pulsing.Looks to me like the clutch sys is completely independant.I have swapped out the entire brake sys 3 times with no avail.I then installed a drawthru turbo and they started to work pretty normally but im soon to remove the drawthru and need to fix this prob.

Anyone ever heard of this??

Car is a 89 5.7 carbed auto.

 

I've never heard of a car's braking system tied into it's hydraulic clutch system before, that's for sure. That would cause no end of maintenance problems not to mention possible accidents..
No expert here, so silly question time in the hope that it leads to a solution:
Could the rear brake shoes be grabbing? If they were installed the wrong way round (leading shoe in trailing shoe position) that may cause a problem.
More likely FWIW, pulsing might be caused by warped discs, but that would manifest itself as vibration through the steering wheel at higher speeds too.
Could the engine be providing variable vacuum to the booster? (brake servo in UK?)

Certainly is an interesting problem. Best of luck.

 

Rear shoes are on as book shows and they dont lockup(grab).With the turbo supplying vacuum to the brakes they work great--at 40mph i slammed them and the rear left 10 foot black marks before lifting up and setting over about 6 inches--the front just held and never scooted but they had to have been holding all they can to lift the rear like that plus stop so quick.

They would pulse sitting still.No shaking or vibration while braking while driving.To me it seems like you said the vacuum signal was fluctuating but what would cause that??

 

Any ideas anyone??

 

One just occurred to me. Say the servo was leaking, but only when sufficient vacuum had built up - once it reduces then the servo works again? I may have got this *** backwards, but....

Mark.