Brakes Lock Up Whilst Driving

[geewizz]

after driving my previa for about 10 minutes the brake peddal pressure gradualy increases until all 4 wheels lock up tight.

iI proceed to bleed the brakes with a self bleed kit which allows the vehicle to free wheel again.although there appears to

be more air evident in caliper nearest the master cylinder.could the master cylinder be the cause of my stop start lifestyle?

[Alexandra]

after driving my previa for about 10 minutes the brake peddal pressure gradualy increases until all 4 wheels lock up tight.

iI proceed to bleed the brakes with a self bleed kit which allows the vehicle to free wheel again.although there appears to

be more air evident in caliper nearest the master cylinder.could the master cylinder be the cause of my stop start lifestyle?

your brake servo is bust change it and you will be fine.

[raymundo]

after driving my previa for about 10 minutes the brake peddal pressure gradualy increases until all 4 wheels lock up tight.

iI proceed to bleed the brakes with a self bleed kit which allows the vehicle to free wheel again.although there appears to

be more air evident in caliper nearest the master cylinder.could the master cylinder be the cause of my stop start lifestyle?

Geewhiz,

This fault usually means that the pistons in the cylinder are not returning fully to their "off" position when the pedal is released. It can be caused by incorrect setting of the brake-pedal stop or the length of the pushrod which operates the master-cylinder. If the master-cylinder piston is not able to return fully to the "off" position, the vent to the reservoir is blocked by the piston. Rubbing of the brakes heats the fluid, which expands, applying the brakes. There could be a fault in the servo, if the problem has come on suddenly, without any recent disturbance of the cylinder etc., so check the pushrod first for free movement. If the fault occurs again, slacken the nuts holding the cyl. to the servo a little and see if that lets off the brakes.

Hope that helps,

Raymundo

[propnut]

In addition to the above advice Previas are notorious for seized calipers caused by corroded sliders. My advice give the entire braking system a service. Caliper seal sets and new boots and sliders can be obtained direct from Toyota. Don't waste your time looking elsewhere trust me I tried.

Also the load proportioning valve needs to be bled in the correct sequence against the calipers. If you don't air trapped there will just keep surfacing.

There is no quick fix, do it right once and for all.