self braking

[matuva]

Had a guy coming to see us today with his 1997 K1500.

Till he owns his truck (he bought it about a year ago) he always had troubles with steering :

1. sometimes it acts like there's no power steering, while driving;
2. most of the time, the truck brakes itself when turning, left or right side. PO has hooked the brake pedal with a spring to keep it up. Spring is still in place, if not, the pedal goes down to the floor as the brakes actuates themselves

What he was able to say it that, the power brake booster was changed by previous owner, then a second time by another who exchange it with a "used but known good" one.
The power steering pump has been changed too, though, I suspect (but not sure) the mechanic hammered the pulley to put it back, according the marks I saw on the pulley.

We raised the truck and tried to bleed by turning wheels right to left and back several times with engine running.
At the beginning, we saw the brake pedal going down itself when we were completely on the right, or on the left and insisting.
After a while, we notice the brake pedal stays up.
Thought it was OK, but after the first braking test, here it goes again.

I saw a very few bubbles in the reservoir of steering pump, and the oil doesnt seem to move a lot, is it normal ?

The above of the steering box is a lot oily, should I suspect an air leak there or else ?

We have changed several power steering pumps, power brake boosters, and steering boxes. We have encoutered this problems with brakes self actuating when turning, but each time, bleeding the circuit was more than enough... not this one...

Any idea why it's not working this time ?

 

[buddy]

Wow, that sucks.

Sounds like maybe the master cyclinder needs to be changed. They get damaged if someone bled them all the way out before.

 

[625fireman]

Are you sure the PO has the lines on the booster in the right spot??????? Self braking to me sounds like the lines have been switched. Dont know if this can even be done though.

 

[bk95td]

The GM manual says: check the return line for kinks or obstructions, Remove obstruction or replace line as required. If condition remains, check for damaged reaction end. If damaged , hydro-boost should be replaced.