69 GP erratic braking

[Nexia86]

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]

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]

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]

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

______________________________

 

[Nexia86]

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]

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

 

[Nexia86]

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.

 

[melsg5]

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?

______________________________

 

[Nexia86]

No I don't have it anymore...

 

[melsg5]

Read this link

Got A Soft Brake Pedal? Don't Forget The Booster Pin to Master Cylinder Gap

A common problem and a question we answer more than we can remember is “Why does my pedal feel soft?” in my power brake system. One of the most overlooked things is probably the simplest fix.

techtalk.mpbrakes.com