Power Steering Hoses - Question for the 928 Brains Trust
02-23-2017, 12:14 PM
#16
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.
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.
02-23-2017, 12:16 PM
#17
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Thanks Sean - that tells me that the addition of the restrictor has no performance detriment when used on the pre 91 cars with the lower pressure power steering pump.
__________________
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
02-23-2017, 12:24 PM
#18
I removed the restrictor on mine about 8 years ago when that cooler hose was leaking. No issues at all do would imagine that they are on most of the 87+ cars. I'll start paying attention to all the cars and noting what have them and what doesn't.
02-23-2017, 01:35 PM
#19
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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.
.
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.
.
Whereas I will be delighted if what you say is correct, hydraulically speaking it does not seem to make sense given the return line operates at low pressure, the pressure being killed in the rack itself. My hose does not have that rubber bit [probably dropped off] but the metal bit looks to me as though it is a very substantial crimp so my assumption is that it is holding two sections of hose together that have been forced over what logically would be the body of the restrictor and that would seem to be a logical place for it to reside given it is between the source of the pressure and the user of the pressure.
On the other hand I took a look at the return line on my 92 GTS and I could see no signs of anything that resembled a separate piece of kit that could be a restrictor. Whether there is something built into the start of the line where it bolts to the rack could be a possibility but whether it could perform the required functionality at that point I doubt very much.
Perhaps I am being artificially influenced by other threads that have talked about this thing being the restrictor - I have not seen a pic of what is in there. Not at all sure I am correct - just suspicious of what is perceived to be the case.
Rgds
Fred
02-23-2017, 01:44 PM
#20
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Probably the blind leading the blind here Fred - as there is so little knowledge on the board about this subject I am feeling my way.
However the "restrictor" is very clearly shown in PET #34 on illustration 403-01 from 92 onwards.
The rubber grommet is to stop damage to the hose and body as it moves when the steering action is applied. Logic is that they needed it to stay in one place hence the metal sleeve.
Very willing to be proved wrong.
However the "restrictor" is very clearly shown in PET #34 on illustration 403-01 from 92 onwards.
The rubber grommet is to stop damage to the hose and body as it moves when the steering action is applied. Logic is that they needed it to stay in one place hence the metal sleeve.
Very willing to be proved wrong.
02-23-2017, 01:46 PM
#21
Former Vendor
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??
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??
You original question confused me so much that I didn't know how to answer....
You started out taking about high pressure hoses and in the last paragraph, you wanted specific information about the low pressure return on RHD cars.
People in the thread then started taking only about high pressure hoses.....with the discussion taking on a life of it's own about restrictors.
All of the power steering pressure hoses have a restrictor......for the reason I talked about in my post #6. Leaving the restrictor out is like begging to have someone rip your thumbs off or break your wrists, at some point in the future.....it's not very intelligent!
02-23-2017, 01:50 PM
#22
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I have zero experience or knowledge about RHD cars.
Just trying to establish if the pressure and return line specified for the 91 to 95 cars are backward compatible and will fit the earlier 87 to 90 cars.
As for the restrictor - Rennlist folklore says it is in the pressure line where the rubber grommet is placed - Porsche says it is between the cooler line and the reservoir. It even has a separate part number.
02-23-2017, 02:07 PM
#23
Rennlist Member
Probably the blind leading the blind here Fred - as there is so little knowledge on the board about this subject I am feeling my way.
However the "restrictor" is very clearly shown in PET #34 on illustration 403-01 from 92 onwards.
The rubber grommet is to stop damage to the hose and body as it moves when the steering action is applied. Logic is that they needed it to stay in one place hence the metal sleeve.
Very willing to be proved wrong.
However the "restrictor" is very clearly shown in PET #34 on illustration 403-01 from 92 onwards.
The rubber grommet is to stop damage to the hose and body as it moves when the steering action is applied. Logic is that they needed it to stay in one place hence the metal sleeve.
Very willing to be proved wrong.
Seems that those who talked about "removing the restrictor" were talking a load of bunkum. Excellent news from my point of view in that it makes rebuilding the high pressure hose that much easier.
Just leaves me wondering what pressure that "restrictor" creates- clearly there is a flow restriction within the cooling coil. The only other thing I can think of would be if there was also a restriction in the high pressure hose but if that were the case then PET logically would also state so.
We continue to learn!
Regards
Fred
02-23-2017, 02:09 PM
#24
Former Vendor
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.
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.
The difference between '87-'91 pressure hoses and '91-'95 pressure hoses is only a routing change at the power steering rack end....the banjos and pump attachment is exactly the same.
Unless Porsche supplies the bracket that attaches the pumps to the alternator bracket with the pump, there is no way the pumps will interchange.
02-23-2017, 03:03 PM
#25
Former Vendor
Thanks Greg - the answers I need apply equally to LHD & RHD - apart from the run of the pressure hose and the return line from the rack to the cooler line everything else is the same.
Just trying to establish if the pressure and return line specified for the 91 to 95 cars are backward compatible and will fit the earlier 87 to 90 cars.
As for the restrictor - Rennlist folklore says it is in the pressure line where the rubber grommet is placed - Porsche says it is between the cooler line and the reservoir. It even has a separate part number.
Just trying to establish if the pressure and return line specified for the 91 to 95 cars are backward compatible and will fit the earlier 87 to 90 cars.
As for the restrictor - Rennlist folklore says it is in the pressure line where the rubber grommet is placed - Porsche says it is between the cooler line and the reservoir. It even has a separate part number.
Everyone seems to be mixing stuff up between high pressure and low pressure hoses.
Once again....the restrictor in the high pressure hose from the pump to the rack has a restrictor.....for the reasons that I provided in post #6.
Period.
All.
The restrictor in the low pressure return hose (that you are asking about) was put there to slow down the fluid return rate, so the fluid had time to "exchange" heat in the front cooler.
Completely different restrictor for a completely different purpose.
The '87-'91 pressure line and the '91 to '95 pressure line are not interchangeable, because of the way they mount to the chassis (unless you don't mind the steel portion of the line not being secured with the special clamps and just dangling there.)
I've saved every power steering line I've removed in the past 15 years in a box. I've cut these apart and welded AN fittings on the ends of the steel pieces. I've had these pieces replated. I've made replacement high pressure hoses (with restrictors) and tested all of these pieces....some have been on cars for many years. Everything works perfectly.
The problem: This effort costs more to do, than the original hoses cost, from Porsche, so it is not "cost effective" (as long as the stock pressure hoses exist.) However, as soon as the original hose are NLA, I will provide these hoses.
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MickDoyle (01-30-2020)
02-23-2017, 05:47 PM
#26
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Thanks Greg - so two restrictors (I said it was the blind leading the blind) so the swaged fitting at the top arc of the pressure line that has a large rubber grommet is also acting as a restrictor?
So indulge me a little bit more please. IIRC the pressure line 87 to 90 also has the restrictor in it - correct.
My issue is trying to establish backward capability of the later 91 to 95 hoses being able to be used on the 87 to 90 cars.
Thanks for the help GB.
So indulge me a little bit more please. IIRC the pressure line 87 to 90 also has the restrictor in it - correct.
My issue is trying to establish backward capability of the later 91 to 95 hoses being able to be used on the 87 to 90 cars.
Thanks for the help GB.
02-23-2017, 06:10 PM
#27
Former Vendor
Thanks Greg - so two restrictors (I said it was the blind leading the blind) so the swaged fitting at the top arc of the pressure line that has a large rubber grommet is also acting as a restrictor? The only function of the crimped piece is that it holds the internal restrictor in place....so it does not migrate in the hose. t just happens to be a convenient place to put the rubber "bumper" grommet and keep in the corrrect position, so that is probably why they put the restrictor there.
So indulge me a little bit more please. IIRC the pressure line 87 to 90 also has the restrictor in it - correct. ALL pressure lines from all years have the restrictor!
My issue is trying to establish backward capability of the later 91 to 95 hoses being able to be used on the 87 to 90 cars. As I mentioned, not going to happen, unless you leave the mounting pieces for the steel line (which holds it to the chassis) off and let the entire hose/steel assembly dangle there.
Thanks for the help GB.
So indulge me a little bit more please. IIRC the pressure line 87 to 90 also has the restrictor in it - correct. ALL pressure lines from all years have the restrictor!
My issue is trying to establish backward capability of the later 91 to 95 hoses being able to be used on the 87 to 90 cars. As I mentioned, not going to happen, unless you leave the mounting pieces for the steel line (which holds it to the chassis) off and let the entire hose/steel assembly dangle there.
Thanks for the help GB.
02-23-2017, 07:07 PM
#28
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Thanks Greg - that really cleared a lot of the questions.
So remembering that at the moment we cannot get the early hoses and they may be NLA is there any way we can modify the PS line/body to enable it to be clamped in place? From your comment I am also assuming both the return and pressure line have this bracket?
Nobody is criticizing you - certainly not me - I am just trying to establish a way forward as I now have two customers without hoses. Yes I know they can be rebuilt but not always the easy answer for some. I, as always, appreciate your in depth insight to these issues. Without you we would be in the crapper.
As I mentioned, not going to happen, unless you leave the mounting pieces for the steel line (which holds it to the chassis) off and let the entire hose/steel assembly dangle there.
Nobody is criticizing you - certainly not me - I am just trying to establish a way forward as I now have two customers without hoses. Yes I know they can be rebuilt but not always the easy answer for some. I, as always, appreciate your in depth insight to these issues. Without you we would be in the crapper.
02-23-2017, 07:55 PM
#29
Former Vendor
Thanks Greg - that really cleared a lot of the questions.
So remembering that at the moment we cannot get the early hoses and they may be NLA is there any way we can modify the PS line/body to enable it to be clamped in place? From your comment I am also assuming both the return and pressure line have this bracket?
Nobody is criticizing you - certainly not me - I am just trying to establish a way forward as I now have two customers without hoses. Yes I know they can be rebuilt but not always the easy answer for some. I, as always, appreciate your in depth insight to these issues. Without you we would be in the crapper.
So remembering that at the moment we cannot get the early hoses and they may be NLA is there any way we can modify the PS line/body to enable it to be clamped in place? From your comment I am also assuming both the return and pressure line have this bracket?
Nobody is criticizing you - certainly not me - I am just trying to establish a way forward as I now have two customers without hoses. Yes I know they can be rebuilt but not always the easy answer for some. I, as always, appreciate your in depth insight to these issues. Without you we would be in the crapper.
I just absorbed a bunch of abuse in a different thread about using colors....
02-23-2017, 08:58 PM
#30
Inventor
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The restrictor is for noise, "ripple attenuation": investigation-of-fluidborne-noise-reduction-in-automotive-hydraulic-powersteering-systems
The restrictor's distance from the pump may be key to reducing the particular noise the Engineers were concerned about.
Except power steering racks don't work like that. The rotary valve limits hydraulic flow to only what the driver inputs through the steering wheel.
Some easy reading - http://auto.howstuffworks.com/steering4.htm
To reduce the pump-induced noise in the power steering
system, several approaches were used in the automotive industry;
for example, the addition of a section of hose, a restrictor, or coaxial
tuning cable with hose.
system, several approaches were used in the automotive industry;
for example, the addition of a section of hose, a restrictor, or coaxial
tuning cable with hose.
Some easy reading - http://auto.howstuffworks.com/steering4.htm
Last edited by PorKen; 02-24-2017 at 01:35 PM. Reason: more fuel