Bleeding PAS Noise

amcdonald

amcdonald

Active Member
Hello

The post title can be rearranged but here's the thing. In what is dangerously close to being one of the last things to tidy up on the decade-resto, I have a vibrating / humming noise from the PAS - just in front of the dashboard. Previously I posted on this, as I had to unhook the belt as the noise was too bad (turned out the "U Bend" at the pump was touching the base unit). So I reconnected it and I now have this continuous humming, sometimes it goes away very briefly at a particular wheel turn but always comes back. Holding the pump outlet hose you can feel the vibration clearly.

To deal with possible air in the system, I tried to bleed the box, but the slightest crack of the screw and PAS fluid is spewing out. Definitely no air. I then made the mistake of cracking the screw with the wheel at full lock and it squirted everywhere. So I don't see how you can bleed this at all without making a massive mess. Does this (seemingly super high) pressure point to a particular pump problem. I rebuilt it, so I was always worried about it. Any suggestions?

Thanks
Adrian
 
I have had a VERY noisy PAS on a Disco, and it was caused by a restricted supply hose from the reservoir. The fluid is very hard on hoses, and it is not unknown for hoses to delaminate inside. Check your hoses are not kinked or squeezed anywhere. Replace if in bad condition.
 
All the hoses are new, and no obvious squeezes. Having a restriction in the supply side would be consistent with the symptom I guess.
 
Supply side restriction causes noise in the pump usually - are you sure the noise is from the box?
 
The noise I can hear inside the cabin is right there at the steering wheel, for sure, but when standing outside you can't really hear anything. By touching the pump discharge hose you can feel all the vibration coming from inside or being transmitted along it. You can also feel the vibrations through the wheel when you get it just right and the noise gets louder.
 
The fluid will transmit vibration well, but not sure how to isolate the cause to either the pump or the box. Book says avoid contact of high pressure hose with bodywork, and if pump is noisy, bleed or replace. It also indicates there is a pressure relief valve in the pump, so that might cause vibration.
 
You can bleed the system without using the bleed screw by winding the steering from lock to lock with the engine running several times, just don't hold it on full lock for any length of time. Has the PAS filter been changed?
 
Hmmm. PAS filter? What is this magical device of which you speak?

I had assumed, without looking too closely, the "filter" was more of a strainer and as such nothing that could be a troublemaker. The symptoms are consistent with too low a suction pressure so maybe this is a problem. I just looked at it on the JRW web site and it certainly looks more filtery than strainery looking closely. Add to Cart.

Let's see - thanks!
 
Ugh. It’s not the filter, removed it and tested and noise is the same. Listening to the pump outlet hose through a touching screwdriver to the ear it sounds like an enormous swarm of bees in there, irrespective of where the wheel is turned. Same screwdriver on the pump and box it’s a muffled noise as if the hose is the source. The hose is vibrating a tiny bit too.
 
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