Thread: Dual 7" Servo
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Old 21st August 2016, 12:55
Nigbo Nigbo is offline
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Default Binding brakes - hard pedal- my theory

So having fitted my servo and having servere problem with pedal getting rock hard and brakes binding on. All was well for the first 250 miles so the basic set up must have been correct. I did all the recommended things ( return spring on the pedal and rose joint between the pedal and servo input rod).

Everybody here with this problem is thinking it related to alignment but i'm beginning to suspect its not. Having watched at some length a detailed video on how these servo's actually work it seems to me that the problem is related to the atmospheric valve failing to reseat properly when the pedal is released or pressure on it reduced. Its admits too much air in.

Why is the happening maybe related to one thing all BMW engined Sportster's have ( i don't know about other non E series engines ) but the exhaust manifold sits in very close proximity to the exhaust servo.

So these servo's get a big dose of exhaust heat. In addition the heat is not even. My servo gets very hot underneath as its exposed heat rising ( esp in traffic ) from the exhaust manifold collector pipes ( i have 2 on my M3 Evo engine) . Also my bonnet has no venting on it which may make it worse.

So my theory is that given these servo's are fabricated out of pressed steel, uneven heating can lead to it getting distorted and either the atmospheric valve does not seat tightly or the whole chamber is leaking.

Would appreciate anybodies comments /thoughts on my ideas.

I'm in communication with Pirate Jack ( where i brought them from) and waiting to see what they say.
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