transmission hiss sound in reverse
 

Hello,

I have a 2002 2wd expedition with a 5.4 triton. Just recently i have noticed that when it is put in reverse there is like a hiss type sound. Now when my wife was pulling out of the driveway the hiss sound was a bit louder and it sort of smelled like air. The smell was like air just let out of a tire. Now when it is put in drive, everything is normal. I have not had a chance to look at it just wanted to get this question out there to get some help.

Thank you

same issue
 

I have the same issue. When I put my 2001 expedition in reverese only I get a hissing noise comming from under the truck everything runs great just a ?

Air sound at steering wheel
 

Okay, so I know what everybody's talking about with the hissing sound in the steering wheel when you turn it all the way, or sometimes at all. Mine was doing that, had started and did it for a while I ended up changing the power steering fluid, still did it but helped a little ended up getting Lucas power steering conditioner, pulled some of the fluid out and poured it in. Immediate fix! Barely does it at all now, and the brakes are much more responsive. I still have the hissing sound in the tranny in Reverse though...

Interesting trick that putting conditioner in your power steering box made the brakes more responsive.

The power steering pump is not only power steering, but it supplies the power boost for the brakes. So any problem with the pump will affect the brakes.

Didn’t know that. What year(s) Expeditions had that?

I don't think any did, Expeditions all use vacuum boosters. He is referring to hydraulic boosters.

"The hydraulic pressure generated by the power steering pump is stored in an accumulator, which is then routed to the master cylinder by the hydraulic booster unit when the brake pedal is applied"