No Power brakes full wheel lock

[Cobra]

On my 97 at full left or right wheel lock i hear a nasty hissing and lose power brakes the brake pedal will sink almost to the ground before they stop the van. It makes the same sound when the van is not moving and i try to turn the wheels from side to side. I've checked the fluids and they are all good well my power steering fluid is actually a little high it was empty however when i got the van. any ideas? the only thing i can think of is the PS pump

[astroturf]

Sounds like your PS Pump is in need of replacement.

Buy a new unit, not a rebuilt.

Jim

[WoodButcher]

Are you referring to the '97 w/ 3500 calipers???

[Cobra]

yup

[WoodButcher]

I just did this caliper swap on mine, 3" cylinder needs alot of fluid. I posted a thread on the other site
http://www.astrosafari.com/viewtopic.php?f=45&t=12087
and had to make a few mods. Are your calipers meant for a thicker rotor like the ones I got? Maybe shims would help.

[Cobra]

the brakes work perfectly except for that one condition, i'm not sure the thickness of the 3500 rotors but i guess it wouldn't be hard to find out give me a minute to measure

edit:
stock 1997 rwd 1.04 inches thick
stock 1996 SRW G3500 1.53 inches thick

[WoodButcher]

Yeah, 1/2". I have 1/4" of shim in there and I'm thinking to add another 1/8" when I next get the ambition to tear into it.
I don't know if that has any relation to your issue but it may. My PS pump has had issues for some time before I did the big caliper but I have seen no change yet. (whines occasionally when turning hard at low speed)

[Cobra]

no matter what van i've driven they all whined a little bit at full wheel lock but mine i loud.if i can find my vacuum pump I'm going to try a couple things to see if air is trapped in there somewhere. 1/2 inch is a fair difference but nothing that i think the calipers stroke can't cover

[astroturf]

What is the life expectancy of the PS Pump?

How often have you flushed the PS Pumps fluid?

Thanks, Jim

[WoodButcher]

What is the life expectancy of the PS Pump?

How often have you flushed the PS Pumps fluid?

Thanks, Jim

I never flushed but have replaced the steering box so I did drain and refill. I don't know of a way to flush per se but I think what I did would qualify.

[Cobra]

Vans pretty new to me so i haven't changed any of the fluids yet only topped off so it would pass the testing. Who knows when the last oil change was let alone power steering fluid

[Mr_Roboto]

My bet is on the bypass in the gear being messed up honestly. There's probably a pressure regulator for it that's stuck open. Strictly a guess however.