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Discussion Starter #1
when i press the brake pedal it goes down a bit further than it should, but then i press the brake pedal again, it is instantly back to where it should be on the feel & the amount of travel.

I bled the system today, & its still there.

Is this likely to be servo related ?
 

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I doubt if it's related to the servo unit, that will either boost your brakes or it won't (and you'll feel a vast amount of difference). It depends on how much the variation is in the pedal height. My guess is you may have some air in one or more of the brake lines. I bought four Speed Bleeders from Centerline, and they are the best thing since sliced bread for bleeding brakes. They are check valves, that is one-way valves, and once the fluid/air is expelled, it cannot re-enter the line. Or, if the difference in pedal height is pronounced, you may have a leaking master cylinder (internal leak, chamber to chamber).

I have a new truck, and I occasionally feel a slight difference in pedal height as you describe, and my '91 Spider exhibits the same to a degree, so I don't think it's a major issue unless the variation is extreme.
 

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If it's happening only on the first press on the pedal after you park the car (engine shut off) for hours and won't happen again until you park the car again, it is likely that you have a vacuum leak in the booster system. We had the same symptom on my mother's '91 Automatic few years back, which was cured by replacing a booster hose check valve (at the intake manifold) and a booster hose.

Hope this helps,

when i press the brake pedal it goes down a bit further than it should, but then i press the brake pedal again, it is instantly back to where it should be on the feel & the amount of travel.

I bled the system today, & its still there.

Is this likely to be servo related ?
 

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Registered
Joined
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1,015 Posts
Discussion Starter #4
If it's happening only on the first press on the pedal after you park the car (engine shut off) for hours and won't happen again until you park the car again, it is likely that you have a vacuum leak in the booster system. We had the same symptom on my mother's '91 Automatic few years back, which was cured by replacing a booster hose check valve (at the intake manifold) and a booster hose.

Hope this helps,
it happens whilst driving, all the time.

I already use a non-return valve system to bleed the brakes - which I have already done.
 

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Piston knock back results in this symptom. This is where the caliper piston(s) is 'knocked back' into the caliper bore by the rotor as a result of loose wheel bearings.
 
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