69 GP erratic braking

Nexia86

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Hi all,

so recently I changed my brake booster since I felt the kind of brake support it used to provide wasn´t there anymore.

So after the swap for a new booster, the actuation of the brakes was still quite late and the brakes would apply all of a sudden at the last 1/4th of the pedal way. So I decided to also change my master cylinder. Of course I bench bled the master cylinder and bled all brake lines.

So since then I have a better feeling in the brake pedal but still it is kind of erratic as sometimes I can easily depress the pedal to the point when the brakes apply and sometime I feel kind of a resistance in the pedal. The braking overall is not a linear braking progress but more like:

pedal way 0-70% = almost no brake power
pedal way 71-100%= boom, here it comes

I almost used 4 liters to bleed the brake lines and found some big air bubbles trapped. So I really don´t believe there is still air trapped.

Any idea what is going on here?


Thanks
Manuel
 

melsg5

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Did you check the clearance between the old booster pushrod compared to the new one.
Unless you had a hard pedal or some other way detected a leak it is unclear why you changed the booster which seems to have started your problem.
 

Nexia86

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the pedal was hard with the old booster, yes. I have not checked the pushrod length of the new brake booster, maybe I should. I actually considered it, but the pushrod of my new booster did not seem to be adjustable, so I dind´t try it.

I have this booster: SKP SK5471106

Probably have to look into it again whether I can adjust the pushord which is the only thing that makes sense for now to look at.
 

melsg5

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Are you saying the old booster was hard with the engine running?
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Nexia86

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With the old booster I had little break support, also the brakes applied pretty late. In the end it might have been an issue with the master cylinder at the first place, I don´t know. So now I have a new booster and new master cylinder and need to get it working properly.

I need to find out how to adjust the pushrod since I can´t find a nut or thread to adjust.
 

melsg5

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Google brake booster rod adjustment.
You have checked for a sticking brake caliper and adjusted the rear drum brakes?
 

Nexia86

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I just checked the rod of the booster and I can't find a way to adjust it. Pls check the attached picture, this was taken when my wife put her foot on the brake.

It does not look like anything I found on Google.
 

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melsg5

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Do you have the old booster and if so have you compared the distance from the mounting surface of the master to the end of the pushrod in the booster?
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