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The brakes are locking up while driving so hard that you have to down shift to keep from choking out. The master cylinder, front brake lines and pads have been changed. The emergency brake has been adjusted. What else can we do?

Your brakes are activating on their own?

Give us a full ID of your vehicle please, mileage too.

It is a 2001 Kia Rio with less than 50,000 miles. It is a standard transmission, manual brakes and steering. Basically a basic car with no extra ammenities. Is this what you want?

The only component of the system that I can envision applying the brakes without your inducement is the booster. The brake booster is a diaphragm-in-a-can that uses the engine’s vacuum to help push the shaft in that pushes the master cylinder pistons. Under normal operation, when the pedal is not pushed the engine’s vacuum is applied equally to both the fore and aft sides of the diaphragm. When you push the pedal, the aft side becomes vented and the vacuum is only applied to the front side, assisting you im pushing.

If the booster were defective such that the vacuum were constantly on the forward side of the diaphragm and the aft side constantly vented, the booster could apply the brakes by itself.

This problem has been posted on this forum before. As I write this I’m wondering for the first time whether there’s actually and adjustment in the shaft that might correct the problem…could the rod be partially “in” rather than at its proper resting position. Guys, any ideas on this???

Yes, there is an adjustment rod and a special tool to make the adjustment. This rod is supposed to be adjusted anytime you replace the master cylinder.

Thanks. My brain was envisioning te wrong end of the rod. The picture is gaining clarity. Perhaps we have a simple solution for the OP.

OP, you still with us?

We will try this and let you know what happens, if you can think of anything else we are open to all suggestions. Thanks everyone.