Power Steering Pump Pipe - Questions

[zcacogp]

Chaps,

My beloved S2 has developed an alarming appetite for Power Steering Pump fluid recently. It is getting through it faster than it gets through petrol (it's been surprisingly parsimonious since I changed the AFM) and producing nasty large slicks of oily stuff on the road wherever it has been parked.

Fearing the worst, I dismantled it all this morning and discovered that there is a leak in one of the pipes, the one from the pump to the rack. But what a pipe that is! It's three times as long as it needs to be, and is covered in a thick black rubbery sheath. It's made up of at least five different sections and goes half-way across the car before doubling back on itself. It's leaking from right hand side of the straight swaged connection joining two of the sections, so I'll hie it down to my local Pirtek to see what the boys there can do with it (I'm hoping it will be a simple repair to take it apart and re-make the connection).

However a pipe like that produces questions. Here's a photo:

My questions are:

- Why is the pipe in so many sections, and runs as it does? I am guessing it's because the car was designed to be LHD and the RHD conversion is not as perfect as it could be. However why is it made in so many sections?
- Is it necessary that it is so long? Could I ask Pirtek to re-make it much shorter (taking out the long run to the U-bend and back)?
- What is the purpose of the heavy sheath? I have sliced it open and can tie it shut with cable ties when re-assembling if it is essential, but can I just remove the sheath altogether?


Oli.

 

[Monkeythree]

Oli,
The hose will be that length and construction for tuning out noise. The problem is that PAS pumps pump in "pulses" due to the vanes and these pulses can resonate in the pipes and hose at certain frequencies which results in noise and vibration. The solution is to "tune" the hoses via a combination of hose length and flexible inserts. In laymans terms, these act as dampers of the unwanted resonance resulting in a quiet and smooth steering system.

I would recommend getting a replacement made with the same dimensions and components otherwise it is likely that you would simply undo all Mr Porsches's hard work to tune out the NVH.

 

[zcacogp]

Tom,

Very interesting - thank you. I hadn't thought about the 'tuning' aspect of the problem but it makes sense. Does that also explain why it is made in so many different sections?


Oli.

 

[Monkeythree]

Yes.
BTW, That crimped tube in the centre of the long hose run won't be a join in the hose, it will be to hold the end of a tuning cable which is inside the long hose.

 

[zcacogp]

A tuning cable?

Oh. That's a pain. It is leaking around that crimped bit - to the left hand side of it, as you look at the picture. I had assumed it was a join, and the leak was the join starting to break down.

If it is as you say, and the leak is indeed at that crimped bit, what would you suggest to solve the problem? I was going to ask my local Pirtek (hydraulic hose manufacturers/repairers) to replace the leaky section. The notion of a 'tuning cable' however is making me wonder whether this is a good idea.


Oli.

ETA: Does the heavy outer sheath also exist for 'tuning' reasons?

 

[Monkeythree]

I would get Pirtek to replace the entire long hose but get them to remove the tuning cable from your old one and crimp it into the same position in the new hose so that the noise attenuation is maintained. I would expect they would be quite familiar with PAS lines with tuning cables in them so they shouldn't be phased by the request.

Not sure about the thick outer sheath. We never fitted anything like that to the PAS hoses we used to supply to Ford. I would assume it to be some kind of abrasion protection but I suppose it could be an NVH related solution too.

 

[zcacogp]

Tom,

I've just had another look at the pipe to see whether I could see (or feel) the tuning cable you spoke of and, annoyingly, I'm not sure it is leaking now. I've sealed both ends more effectively and run some compressed air into it and it's not leaking where I thought it was. I painted some soapy water onto the surface and into the joints and it's not bubbling, so I fear I may not be onto the solution.

Annoying. Back to the drawing board. Thanks for your input all the same Tom, it's been an interesting discussion.


Oli.

 

[Monkeythree]

Stick it back on the car without the thick rubber sheath, fill the system and run the engine. If you lie underneath and get someone to turn the wheel from lock to lock, you should be able to see where any leak is coming from. Put some safety glasses on just in case......

 

[zcacogp]

Yes, I reckon that's the best answer. I need to buy some more fluid before I can do this tho', so a trip to Halfords is in order.

I tested the pipe with some compressed air at about 3-4bar (45-60PSI) and there was no leak. I'm now wondering whether that was too low a pressure to show anything up. What pressure do power steering pumps work at?


Oli.

 

[Monkeythree]

Can't remember precisely (and different manufacturers systems vary), but will likely be in the region of 800psi. There is a good chance that your air test didn't have the necessary puff to force a leak to present itself. Now you see why I recommended safety glasses! []

 

[zcacogp]

Ah, so quite a lot of pressure then. Hmmmm. When I ran it up this morning there was a rapid dripping from the angle at the lowest point of the pipe, but it wasn't immediately clear where the fluid was leaking from the system. I assumed it was coming from the pipe within the sheath, but it could have been coming from a not-quite-tight-enough banjo connection on the pump.

800psi? Really? That really is quite a lot.

I guess it's time to re-fit it, with some new fluid, tighten everything up and see what's what.


Oli.

 

[Eldavo]

I have a Power Steering pump on the bench in the garage that I'm resealing and fitting - it's rated at 110bar.

 

[ChasR]

There is a man who makes power steering hoses locally to me. However he does not install the damper since he feels it is trickier to bleed them (or so his customers said) It would also save him time on labour as well... However, he could potentially reinstall the damper back into the line if you asked him I reckon.

But as above, the construction of the hose is to do with noise. Christ, even with all of that stuff on they sometimes make a sound!

 

[zcacogp]

Right, hose was back on this afternoon with some nice clean new Dex3 fluid. Ran it up and stuck my head underneath to see what's what. The leak was much clearer without the sheath around the offending hose; it appears to be coming through the wall of the pipe itself, about an inch from the right hand as seen in the picture in the first post of this thread. The hole appears to be along one of the spiral seams that runs along it, but I've cleaned it up carefully and can't see anything there at all.

I've never seen a hose leak like that before but it's definitely time for a trip to Pirtek for some advice from the boys there. I just hope that they will be able to replace the affected bit of hose.

Thanks for your input. I'll keep this thread updated with the result when fixed.


Oli.

 

[zcacogp]

Update: A visit to Pirtek in Leyton relieved me of £40 but made me the proud owner of this;

The new hose is rated to some daft figure way in excess of what the pump could produce (I think he said 900bar.) He put a compression fitting on the U-bend as the bend meant he wouldn't have been able to fit it in his crimping machine to put any other sort of fitting on it.

Interestingly, the straight swage fitting in the old hose was a constrictor, with a narrow bore in the middle (approx 3mm or so). I asked the guy who did the work about it and he said it was to dampen problems related to the fact that the hose inside wall wasn't entirely smooth, but the new hose has smooth inside walls so it won't suffer for not having one fitted. I can't vouch for whether he is right or not ...

I've fitted it to the car, and re-attached the heavy sheath (with cable ties as I had to slice it lengthways to get it off the old hose) and all seems well; no leaks and no unpleasant harmonics in the steering.


Oli.