GMC Hydrovac booster problem

[papastoyss]

I tackled replacing the fluid leaking hydrovac brake booster on my son's 98 GMC 3500 series truck.Is there a procedure for bleeding the system? I loosened the fittings at the hydrovac w/engine running & no fluid came out. Also , now the column shifter won't come out of park. I checked all fuses w/ a test light & brake lights are working. There is a switch that fits over the pin on the brake pedal pushrod, I went back & made sure it was connected & clipped over the pedal rod properly, I didn't disconnect the wiring from this switch  when replacing the hydrovac unit.HELP!!!

[enjenjo]

I have had no problem bleeding them, they will self bleed, but it takes a while. Are you sure you didn't leave a plug in one of the lines?

Some where on the shifter there is a solenoid that releases the shifter with the brakes applied. You sure that wasn't knocked loose

[wayne petty]

unlocking the gear shift..

this is a link that shows the shift interlock device..

http://www.dormanproducts.com/itemdetail.aspx?ProductID=33325&SEName=905-101

not trying to sell you anything..

if the cable section became disconnected from the brake pedal or misadjusted.. yep.. its going to not want to come out of gear..

did yours break??

here is the electrical diagram for it..
http://www.gmtruckcentral.com/wiringdiagrams/1998/Shift-Interlock-Circuit.pdf

a video on the brake interlock switch on the passenger side of the column.

this describes how to adjust it ..

http://www.justanswer.com/chevy/749ch-chevrolet-chevy-cant-shift-park-chevy-wont-go.html

and you might want to invest in one of this external torx socket sets so you can deal with the E4 or E5 torx head screws on the steering column screw heads.. http://www.harborfreight.com/6-piece-14-in-drive-e-socket-set-68017.html   hint.. other than on professional tool trucks i have not found this E4 thru E7 sizes..

as for the fluid...  look up from under the front of the truck.. the pressure port on the back of the pump..  is the pressure line screwed into a drop down device instead of being screwed into the back of the pump.. that device is activated by the computer on some models at freeway speed to cut down on the flow to the power steering to reduce hypersensitivity at higher speeds in the steering.. could it have closed all the way off.. or the pressure valve piston in the pump rear be stuck all the way in so there is almost no power steering fluid flow..  



and this was just a random info booklet on that year of truck.
https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Chevrolet-Trucks/1998-Chevrolet-Truck.pdf

[papastoyss]

I disconnected the wiring from the pressure switch on the p/s pump & cranked the steering lock to lock while pumping the brakes & holding RPM at 1500 for about 10 minutes.The system finally bled out the air. I replaced the brake light switch & the shifter interlock problem was cured.Instead of a normal plunger type switch this switch fits onto the brake pedal pin for the booster pushrod & is activated by the angle change in pedal to pushrod when applied.It is non adjustable & is retained by a #@%*^%#$ clip that I had to go to a dealer to find. THANKS for your help!

[kb426]

That didn't sound like fun. Learning all the secrets does test the patience level.