07 S60 Increase pressure in Power Steering Pump?

[jpitt-32]

The p/s on my 2003 doesn't work properly - feels a bit heavy and 'gummy' - for some reason which I never found. I replaced the pump, still the same. However one day I placed the reservoir a little higher (having removed it from it's bracket) and also removed some fluid and for the next few days the steering was completely transformed. It felt easy yet heavy all at once and very smooth and pleasant. It felt 'weighted'. Perhaps that's how it should have been from factory.

oragex, thanks for the you tube video. from watching it appears that there's no relief valve built into the these units like an older gm pump. Centrifugal force moves the vanes out to create pressure.

[jpitt-32]

just wanted to update this thread in hopes that it might help someone in the future. I flushed out the old Lucas power steering additive. I've had good luck with this stuff in the past but didn't seem to make any difference in this case. Refilled with CHF 11S. Replaced the factory installed Michelin's with Cooper CS5 Ultra. The tire change made more of a difference in the ease of steering than I expected it would. To my surprise the steering is much better than before. While driving now, the steering has that small easy spot that you use while driving down the interstate. The area that you move the steering so slightly to make corrections in lane height and angle. Before you had to put much pressure against the wheel just to do these minor corrections. " felt as if you were already in a hard cornering maneuver and the car was wanting to re-center itself"... I would never have thought that the tire change would have made such a drastic difference but, I'm happy that it did. Also, I had already had the wheel alignment done before purchasing the new tires in hopes that it would make a steering lighter but it didn't.. Thanks for all the earlier advice on the pump pressure.
Please xcuse the typos... It's late here and I've been up way to long today.

[vtl]

It's not the tires, they hardly change anything in that respect on a highway speeds. I think your problem was in old PS fluid with an additive. Improper PS fluid may form cavitation bubbles/foam on pump's blades, which effectively reduces pressure in rack, not to tell that cavitation itself "eats" the blades.

[jpitt-32]

Do the ZF pumps have a regulator built in like a check ball and spring?

[jpitt-32]

Took a spare pump apart today. It does have a spring that appears to regulate pressure. This weekend I intend to remove my good pump and put a shim between the spring and valve release. I'll post results. Hopefully not the one saying that the seals came out of the rack. Lol