ROG100

There are some availability issues with RHD power steering hoses and this may also apply to LHD hoses as well because quantities are low at Porsche.

I am querying hoses used for the 87 to 95 cars only.
The only difference between RHD & LHD is the run of the hose from the rack to pump and rack to Cooler hose. The cooler hose (mainly rigid pipe and runs in front of the radiator) and the reservoir to pump hoses are the same RHD or LHD.

So that is the background and the query is ----

For the pressure and return hoses there is a year split - 87 to 90 and 91 to 95. So there are different part numbers for early v post 91 hoses.
The only difference I believe between 90 and 91 was the introduction of the higher pressure pump. Pressure increased from circa 75 psi to 100 psi IIRC.
The increase of circa 25 psi is really insignificant when it comes to a hydraulic hose so why the difference??

Specifically the RHD return hose from the rack to the cooler hose - low pressure as it is the return. The early hose is 927 347 449 03 and the later hose is 927 347 449 05.
The early hose is not available and may be NLA. The 03 does NOT supercede to the 05. The later hose is available and I do not see any reason for it to not be backward compatible.

Thoughts??

dr bob

Roger--

Are the pumps physically different? I have a high-pressure pump in my parts bin but I'm not close enough to the car to see. That would explain the pressure hose differences and reservoir-to-pump but not rack-to cooler or cooler-to-reservoir.

SeanR

The only difference (that I can remember) between the earlier and later ones for those years is the routing at the rear of the fender by the firewall.

FredR

Roger,

I have mine on the garage floor at the moment ready to take to my local hydraulic shop to see if they can rebuild it. If there is a difference between the model years specified my guess would be that there may be a change in the size of the restriction orifice in the centre of the high pressure hose assuming your data is correct.

If they do open it up I can try to measure that for a reference point if of interest.

Some have deleted the orifice and report no ill effects other than a slight change in the steering input effort [a bit lighter].

Rgds

Fred

DuncanF

Roger,

I have a RHD S4 built in late 86, so 87 model year, and I replaced all of the PS hoses six months ago. I bought 927.347.449.03 off of Rose Passion in France and they still list it as available on their website although that doesn't necessarily mean that they are. Sounds like I may have been lucky if they're now nla.

Edit to add that there seems to be a big price difference in the two hoses for some reason. GBP 100 for 927.347.449.03 and GBP 235 for 927.347.449.05.

Regards
Duncan

GregBBRD

As usual, the engineers knew that they were doing...

The orifice does a couple of things:

First of all, it keeps the pump from being stalled (and thus ruined), if the front wheels are suddenly thrust in the opposite direction. The idea is that the pump volume always has the ability to always overcome the potential return volume.

Secondly (and perhaps more important) it keeps your wrists from being broken (or worse) if the same event occurs....it becomes a limiter of how fast the rack can be forced in the wrong direction, by hitting something (pothole) that forces the rack the opposite direction.

There's enough people making huge mistakes on this Forum.....let's not encourage them to make more!

GregBBRD

Yes. Completely different pump with different mounting bracket.

PorKen

It's not a jacked up Ford truck with a high ratio rack.

IIRC, the restrictor is for noise - limits air pulled into the system if turning the wheel quickly.

928Myles

Roger
are there aftermarket hoses available for the RHD cars like there are for the LHD ones?

Myles

ROG100

DuncanF - I buy from the same supplier (Porsche) as Rose Passion and the hose 927 347 449 03 is out of stock both here and in Germany 8>(.
The reason for the cost difference is Porsche has recently restocked the 05 so the price went up.
the 03 shows as a none production part which means it is most likely NLA - hopefully not.

Greg that is why I am asking so I can decide if the 05 is backward compatible. You gave some information but did not answer the question. Maybe you do not know but hopefully you do.

So the possible difference is the pump - however Porsche does NOT differentiate between the two pumps at all.
Way back the 87 to 90 pump was 928 347 089 00 and the 91+ pump was/is 928 347 089 01.
Now both these numbers supercede to 928 347 089 AX - so if you buy a rebuilt pump (AX) from Porsche it covers all applications from 87 to 95 which maybe tells me that the hoses will fit.

The pump would only affect the pressure hose as the return hose locates at the same point on the rack for all years 87 to 95.
As they use the same banjo fittings I will assume that the return hose WILL work.

Back to the pressure hose - so two points for consideration - pressure difference relative to the orifice in the later higher pressure 91+ system and the connection to the pump.

question 1) Does the use of the later hose with the orifice have any detrimental effects when used on the earlier lower pressure system?
question 2) As the pressure hose to pump connection is the same - same banjo bolt - will it connect to the earlier pump. I may just have to buy one and try.

FredR

I have no doubt the orifice was put there for a reason and my intent is to rebuild what Porsche put there. It would be interesting to know whether my thinking about the diameter is correct for the two different pumps.

Your description of the functionality is appreciated- the second point is logical. When I wiped out in my late S4 I took my hands off the wheel just before impact to avoid the very problem you mention- perhaps not necessary with the Porsche design! The first point I cannot get my head around given the pump is a positive displacement affair. As long as ATF is available in the header tank the pump will displace volume irrespective of pressure needed to achieve such up to the point where something goes twang or [more likely] an internal safety valve pops to relieve the pressure.

My HP hose was showing signs of external cracking and there is no way it is going back on the car [same for the LP hoses].

Rgds

Fred

KenRudd

I wish I had known all ^^^^^This^^^^^^ when I was writing this:
https://rennlist.com/forums/928-foru...questions.html

ROG100

I guess as nobody knows the answer to my questions I will have to purchase the later hoses and trial install them on my 87 S4 LHD and my 88 SE RHD and report back on whether they fit and function correctly. If they are indeed backward compatible we will have a way forward.

ROG100

Ken - your picture shows the pressure hose with a metal sleeve and a large rubber grommet. That sleeve is purely for the location of the rubber grommet and NOT a restrictor.

The restrictor is only used in the 91 to 95 system and is a separate part that fits between the return line cooling hose - runs in front of the radiator on 87 to 95 cars and is mostly rigid line - and the reservoir.

PET shows the same part number for this return cooler line as 928 347 350 00 for all 87 to 95 cars but indicates that it is supplied as part of the hose assembly only from 91 to 95. I need to see if it comes with the hose or not. If it does then owners have been replacing the early system hose with the later with the restrictor added. Part number for the restrictor is 928 347 550 00.

SeanR

Rog, the restriction piece is on the earlier cars also. Here's one on the '89. Bad pic I know but it's the clamped part shown. I'm sure some will argue the fact, but cut one apart and you will see it.