Hydroboost engaging without pedal
 

Took the car for a shakedown run and it seems to be fine until after 15 minuets of driving. Seems as if the breaks are slowly dragging progressively to the point where it comes to a complete stop, without pressing the pedal, from a 5 mph roll. Then I shut the car down, restart and it goes away until another 5 mins of driving. Any ideas???

Maybe a back pressure issue? DO I need to vent the res cap? I saw one post where they eliminated the "T" from the low pressure side on the HB and steering box and ran dedicated lines for both on the PS reservoir.. I am not using a PS cooler.

I did hear some type of burping noise when I shut it down but I am unsure if that is from the PS fluid or the PCV issues that I am currently trying to work out.

Loosened the PS cap and seemed to help, I was able to drive longer but by pulling the brake pedal and holding it to disengage the brakes. Seems like a back pressure issue.

My guess is that you have the pushrod too long and it's applying a slight pressure on the master cylinder. Go under the dash and grab that pushrod and see if you have ANY play fore and aft. Also check your dead peddle adjustment. Should have some movement there before engagement.

If nothing else - make your pushrod shorter and see if it helps.

Thanks, I will look at it. I did notice there is not a return spring. Not sure if I need one since springs were for non power brake cars. I'm going to connect one to see if it helps.

I've never worked on a car that didn't have a return spring....

The pushrod is definitely a good thing to check.

Also try eliminating the "T" I have read many similar threads to this and running that dedicated return line seems to resolve the problem many times.

http://www.pro-touring.com/threads/8...es-w-Hydratech

I believe the piston in the master cylinder is held in place with a snap ring. Pull the master cylinder and make sure the snap ring that holds the piston isn't twisted.

If it's twisted (I had it happen to me once), a little bit of pressure would be applied to brakes and the pads would heat up from dragging and that expandes the fluid in the caliper. The fluid expansion winds up applying the brakes.

Also use a caliper to measure the length of the pushrod and make sure it's not a hair too long for the master cylinder.

Well turns out the rod needed some adjusting and my PS pump is needing the control valve fitting to bring it down from 3.5 gpm to 2.2 gallons per minute. Good info to anyone running a Vintage air Front Runner with a hydratech system. Thanks.