brianrheffron

I find that on twisty but not very fast roads the steering on my 928
is quite hard work but it's OK on faster "sweeping" roads
Are there any known modifications that will lighten the steering on an S4.
I think I read somewhere on this forum that the GTS had different parts
that had this effect.

Chuck Schreiber

100bar power steering pump.

http://www.griffiths.com/porsche/steering/


Quote from website
"If your 928 seems hard to steer in parking or slow turn situations you may want to try out new "HO" (high output) 928 Power Steering Pumps. Our HO pumps offer 25% boost in pressure output which helps reduce the torque strain on your wrists"

I put a 100bar on my 79 and it did make it easier to turn the wheel at parking lot speeds.
I think the 91's and later had the higher output steering pump.

Jerry Feather

Plus one on the 100 BAR pump. And plus one on Griffiths. Jerry Feather

Nicole

Plus a modified steering rack.

dr bob

The spool valve on the little pinion shaft on the later 'improved' rack has a softer torsion spring, plus the rack seals are improved for the higher pressure. Changing just the pump without installing the later rack, especially if the original is a worn early rack, would be an invitation to leaks. IMHO anyway.

Nicole

When we replaced my rack, we first got a ZF rebuild one that made the car steer like an older model - despite the 91+ higher output pump. We swapped it again to a Porsche rebuilt rack that was specific to the later models, and all was fine.

axis of evil

But wouldn't this make it "spongy" at speed?

Nicole

Definitely not in the set-up on my car. It's just right with the 17" wheels.

Note that the 928 steering is also speed sensitive; it reduces power assist at high speed.

I'm not sure how it does that, though.

blown 87

I can not see how it could do that with out some type of electronics Nicole.

I have suggested to one of our resident geniuses that he should make a bar (spring) to reduce effort.

blown 87

I thought it was stiffer, not softer?

Chuck Schreiber

Nicole is correct.
928 was the first car I believe to have reduced power assist at speed.

With the HO pump on my 79, the car had more assist in parking lot, but kept that tight feeling at speed.
I did replace the rack right after that. I'm assuming it was correct model, ordered it from 928 Specialists.

blown 87

What are the parts that reduce the assist at speed?
I have seen nothing on them that makes me think that.

Pump, rack and hoses is about it, rpm sensitive with pressure limiter, how can this possibly know the difference in 4500 RPM in first and 4500 RPM in fourth?

Other cars with reduced assist have electronic racks.

I have been wrong about many things, so please correct me on this.

SQLGuy

I think it may be as simple as rack valving that provides small assist for a small movement of the wheel and large assist when the wheel is being turned further/more quickly.

dr bob

The spool valve has one end connected to the steering wheel and the other connected to the pinion on the rack. The two ends of the valve direct fluid flow to the ends of the rack or back to the pump. Really they just meter what flows back, but it's easier to understand if you think about it putting more pressure on one end of the hydraulic cylinder as the two ends of the valve get further apart in rotation.

So a softer spring lets the valve twist more with less wheel effort, so the hydraulics do more work faster with a weaker spring.


There was another comment about 'speed sensitive power steering' on the 928. There isn't.

Nicole

Just checked my old sales literature, and here is what they said in 1983:

The German 1983 and 1991 brochures say power assist decreases with increasing rpm.


Dr Bob: Does Glendale really have a Yacht Club??? It's a little far from the ocean, I would think...