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'Opening up' a power steering pump or box...?


Bowie69

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OK, I have searched, trust me :)

There have been references to 'opening up the ports' on PAS pumps, or 'winding up the relief valve' in order to lighten the steering on an already PAS'd truck -this isn't for me, but a friend who has Cerebral Palsy, and limited limb strength/movement.

The steering is not heavy, compared to my Range Rover, about the same I would say, so looking for a boost over and above what is standard, for the least outlay possible (like 10 minutes with a drill bit :P ) It's running a standard RRC v-belted pump from ~ 1990 at the moment.

I'm aware of all the hydro assist kits, and possibilities of fitting different pumps etc, but wanting to nail this one down as an option or just a myth.

So any experts out there been there and done this? And is the advice relevant to other PAS pumps, like the P38 V8 variant?

I confess I know very little about hydraulics... so edumocate me :)

Thanks,

Pete :)

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I don't know about the ins and outs of stripping the pump, though I believe that some makes of pump can be rebuilt I don't know about the one LR fitted. Pehaps someone reocnditions them?

Anyhoo, inside the steering box near the top where the steering wheel input is there is a valve that controls the flow of fluid under pressure to the piston which provides the power.

When there is no input an equal pressure flows to either side of the piston, the valve has to be callibrated during manufacture, get this wrong and the car will pull badly to one side.

The bit of interest to you though is that any input to the steering is made against a torsion bar inside the valve, it is there to provide steering feedback (feel) and ensures that the valve only moves small amounts (ignoring the fact that the whole valve is inside a rotating assembly).

If the steering input reaches 4 degrees a mechanical link HAS to take over, so there is often a dog between input and output for this.

But the key bit is the torsion bar, if it is reduced it will transmit less steering feel and allow the valve to turn further, providing more power assistance. At least up to the point where all the power assistance is not enough.

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Gwyn lewis has been playing with steering pumps and found huge differences in operating pressures of several supposedly identical pumps.(300 tdi version)

Gwyn has also played with drilling one of the fittings that screws into the pump (200 tdi version) and found he could alter the flow rate, but if the hole was drilled too big the flow was impressive but even with a larger metal oil container and an in-line oil cooler fitted it was difficult to keep the oil temperature down.

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I've drilled out the high pressure port on a 200tdi pump that also had a larma4x4 hydro assist ram on it, the steering is really really light now even on 10psi Simex on a tarmac surface. The reservoir was then changed to a tin style range rover one due to larger capacity and built in filter. no issues yet.

Very easy to drill out the pump, as the threaded section can simply be removed, drilled and then screwed back in without dumping swarf in the pump.

I also used an isuzu pump when I fitted a 2.8td lump in my range rover, this made the steering slightly lighter than standard.

I'd drill out the pump union a little at a time and see how you get on :)

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OK cool, sounds like it is time for an experiment!

Just to be absolutely sure, the outlet union on the PAS pump unscrews from the main body, this is the bit I enlarge in a drill press by maybe 0.5-1mm at a time without going silly?

I will take a look at the 4.0-P38-serp pump I have as well, and see if that is similar and report back too...

RRB, I confess, even with your excellent explanation I don't think I want to be playing with the parts of the box you are talking about -calibrating stuff and a vehicle being pulled to one side sounds pretty dangerous and hence something I want to avoid, but thanks for your input!

Thanks again guys!

Pete. :)

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Was just thinking back, it will depend on your pump type. I just remembered that we also modified a banjo bolt type too. the restriction was the feed hole at the tip of the banjo bolt.

If you inspect the whole high pressure side of the pump, the deliberate restriction should be fairly obvious as it's always the smallest hole.

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I've drilled to outlet fittings on 300tdi pumps quite a few times.

At a couple of mm oversize the fluid would airate, so i changed the pas fluid to hydraulic oil

I'm now at about 12mm, hydraulic oil and a large cooler keeps the oil ok

You can still here the pump whine under load, but i can lock to lock 38's with one finger

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  • 2 weeks later...

Right, some progress here :)

Today I played with my own P38 4.0l power steering pump, not sure if this is the same as any other applications, but I suspect so. You can see an example of this pump in Nige's 5.2 build thread, where I advised him on turning the inlet pipe around to make fitting it easier.

The outlet port does indeed unscrew, in the same way that Ruuman says above, very handy feature :) For those interested it is a 27mm socket to remove :)

Having removed it, I took a look and measure the hole by putting a drill bit through it, and stock it is 3.2mm. I tentatively took this to 4mm, then 4.5mm, where I noticed some improvement, and then 5mm, at this point when revving above about 3000rpm the pump was clearly cavitating, not a nice noise :)

So a small improvement can be easily made, but to make it REALLY worthwhile, as DD found out, you will need to run hydraulic oil, and if you go a long way, a cooler.

So...... Any ideas on what sort of hydraulic oil to use in place of the ATF? As I confessed before, I know nothing about hydraulics :)

As for a cooler, I guess it will just go in the return line, so anything I can find lying around should do the job, even an RRC autobox cooler I think :)

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I bought the oil from my local hydraulics place, after a chat with them about my issues.

I've had a look at the barrel for you but is their own brand and it only says "hydraulic oil"

A rangy "bog brush" should help enough, i use a 12"x12" single core cooler in the return line to the reservoir.

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Cheers DD,

Will nip down my local farmer place and see what they recommend.

I don't think I will need to go to the same extent you have, it is already much improved over stock, and I'm running an adwest quick ratio box.

Will report back when I have swapped oil out :)

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OK, well I now have 5 litres of 'VG32' hydraulic oil from my local place -Mayflower Hydraulics in Bridgwater, used them before for hoses for my autobox, very helpful as usual. VG32 is their 'basic' one size fits all fluid, and good for up to 3000PSI, apparently, so should be man enough for this application... They do have VG48 and VG64, which are higher pressure fluids (up to 8000PSI or something) which I decided as they only had it in 25l, was going to be no good for me :)

Not changed it out yet, but I have another question, in preparation :rolleyes:

If I were to fit a cooler in line (I have failed to find a Rangie bog brush in good nick yet), most PAS cooler kits or autobox kits are just AN10 (10mm ID in my understanding) fittings at maximum, if this was fitted in the return line is it going to cause issues? I know it's very low pressure, but don't want a restriction like this affecting flow to the point it starts changing the way the steering operates :)

Any views on this? :huh:

Cheers,

Pete.

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Hmmm, now I have woken up a bit more (woke at 4:30, not been to sleep again yet!) I need to check the return line ID, I thought from looking at this:

http://www.allisport.com/index.php/products/25-reservoirs/25-land-rover-tdi-v8-aluminium-power-steering-reservoir

That the return line was 16mm, it actually makes more sense for it to be 12mm, and the feed to the pump, as it is suction, 16mm -their description is just dodgy if you ask me :P

I am guessing here that 12mm down to 10mm will be no problem at all! Just tighten the clamp down on it :)

Migth get to try the hydraulic oil today, will post when done :)

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