P38 Steering box

[uninformed]

Hi all,

I asked this in the international forum but this might get more Def’r eyes 👀 

who here has fitted a P38 steering box to a Def’r or Disco? How’d you go about it.

How did it change the geometry?

How do the two boxes compare for ratio and plumbing?

cheers

Serg 

[FridgeFreezer]

Why would you want to?

[Snagger]

On 7/18/2022 at 12:15 PM, FridgeFreezer said:

Why would you want to?

It’s a far more reliable and robust unit and has much lighter feel.

 

I have not seen it done, but as the unit is much taller than the Adwest type and has bolt holes spread further apart, it should be very easy to make a mounting plate with the correct fixing pattern that bolts to the chassis using the original unit’s bolt holes through the chassis.  Do remember that the P38 unit is attached outboard of the chassis, so if you want to retain the original position (and you have checked it won’t foul the timing case or any other assemblies, and I suspect might), then you would need the box from a LHD model for a RHD vehicle and vice versa.  I think it’d be easier mounted outboard as per the P38 with a trim to the wheel arch mud shield and a longer drag link (I used the donor P38’s drag link and made a steering damper bracket with a piece of steel 90 degree angle extrusion and a couple of U-bolts like many aftermarket kits).  I did need to cut the drag link down a bit at the swivel end and have it drilled and tapped to take a Defender rod end, retaining the P38 rod end at the box end (might be the same type).  If you do that, do ensure you have opposite threads at each end of the rod for length adjustment!

I don’t know if the Defender lower steering column fits the P38 box or is the right length, but the P38 lower column does fit the Defender upper column splines and can be adjusted to the right length without any modification.

[Daan]

Blackbird kit:

[FridgeFreezer]

21 hours ago, Snagger said:

It’s a far more reliable and robust unit and has much lighter feel.

OK - why not the Disco 2 box which is also stronger and (I believe) runs the same pressures?

 

[Snagger]

Presumably just because it is a less know conversion.  It should work well, but I don’t know many who have tried it and haven’t read much about it.

[uninformed]

On 7/19/2022 at 11:37 PM, Snagger said:

It’s a far more reliable and robust unit and has much lighter feel.

 

I have not seen it done, but as the unit is much taller than the Adwest type and has bolt holes spread further apart, it should be very easy to make a mounting plate with the correct fixing pattern that bolts to the chassis using the original unit’s bolt holes through the chassis.  Do remember that the P38 unit is attached outboard of the chassis, so if you want to retain the original position (and you have checked it won’t foul the timing case or any other assemblies, and I suspect might), then you would need the box from a LHD model for a RHD vehicle and vice versa.  I think it’d be easier mounted outboard as per the P38 with a trim to the wheel arch mud shield and a longer drag link (I used the donor P38’s drag link and made a steering damper bracket with a piece of steel 90 degree angle extrusion and a couple of U-bolts like many aftermarket kits).  I did need to cut the drag link down a bit at the swivel end and have it drilled and tapped to take a Defender rod end, retaining the P38 rod end at the box end (might be the same type).  If you do that, do ensure you have opposite threads at each end of the rod for length adjustment!

I don’t know if the Defender lower steering column fits the P38 box or is the right length, but the P38 lower column does fit the Defender upper column splines and can be adjusted to the right length without any modification.

It would be outboard, the reason im looking into this is to fit an engine swap. Im hoping to take a look at a P38 box in person soon. Pitman arm may be a problem being shorter than Def'r. Maybe the D2 pitman arm is longer and just maybe same spline??? 

I still have to measure up the geometry, Panhard gets lowered at chassis end. Might help with being more parallel to drag link, but the drag link is already ~100mm longer than Panhard, P38 box would add ~130mm, and then add on my +75mm wider track (each side) means a ~300mm difference (not ideal at all) 

Making a drag link is the easy bit (I have RH and LH taps for the TREs) I Already made one for my current set up and a clamp on damper bracket.

 

 

 

Edited July 23, 2022 by uninformed

[Snagger]

I have the P38 box and drag link (shortened) on my 109.  That has a Discovery front axle, so the same dimensions as your axle, including the swivel housing steering arms.  The P38 box and drop arm have plenty of travel for the coiler axles - I have the stop locks set way further than you can do on a coiler because lock is limited by the radius arms, where the Series models have the leaf springs under the chassis instead of outboard.  Even so, I ran out of tyre clearance to the chassis rails before I ran out of steering box movement.

I’s recommend fitting the P38 pump too, to make sure you have the full operating pressure.  It makes the steering really light, but still quite precise and has much better feel than the standard Defender steering (it was much more stable feeling than my wife’s 2009 90).  The pulleys are interchangeable (even where going from serpentine to V-belt).  The different pump numbers relate to pressures (should all be the same for P38s, regardless of engine type), cast inlet pipe orientation and pump rotation direction, which could differ between engine types, so make sure you get a compatible one for the hose clearance and rotation direction.  You could just swap the pressure relief valve from the P38 pump to your existing pump if it’s in good condition.

[uninformed]

Good info thanks Snagger 👍

im actually running D1 swivel housings because they have level and drain plugs unlike my Def’r that only had the fill plug.

My housing is 150mm wider than factory, that will add ~75mm to my drag link so hopefully it won’t suffer bump steer. 
 

lighter steering may actually be good for me as I’m running more castor than factory.

[discomikey]

The majority of the reason our customers fit our P38 steering kit is for engine bay room when doing an engine conversion. The kits are pretty popular and there are a lot more out there than you may think.

Converting to D2 steering box doesn't give you any space advantage over the standard defender steering boxes unfortunately.

RE Pitman arm. The P38a gives less throw than the defender one but it is negligible, it will still hit the lock stops both ways on the axle

As with the comments on lighter steering, you do get this so I always recommend a decent steering damper, and always set your swivels on the tighter end of the OEM spec - You shouldn't experience bump steer or shimmy though as with our kit at least the panhard rod locates in the factory position, Geometry is unaffected. 

 

[Bowie69]

On 7/24/2022 at 9:51 AM, Snagger said:

cast inlet pipe orientation

I know this is a bit of a bump, but a gentle tap with a rubber mallet will spin the inlet barb round to whatever direction you want.

[uninformed]

On 11/3/2023 at 8:52 PM, discomikey said:

…………You shouldn't experience bump steer or shimmy though as with our kit at least the panhard rod locates in the factory position, Geometry is unaffected. 

 

Good to hear, but my brain is still unsure lol. The drag link has to be at least 175mm longer I would have thought, that’s a 20% increase in length. Surely this changes the arc it scribes? 
 

maybe it’s unnoticeable to the feel?

 

It’s something I want to plot out full scale anyway.

[discomikey]

On a vehicle with 14+in suspension travel you might start to notice bump steer at both extremes of the travel he extremes are where the issues start to show, The difference between the two steering box drop arms is almost exactly 120mm so good guess there. It's pretty rare that drag links and track rods are identical in length from factory and the differing arcs aren't too much of an issue. From plotting the suspension geometry in CAD using land rover's chassis measurement diagrams to confirm suspension points etc the panhard sweep gives around 12-15mm of lateral movement in total from one extreme to the other, So given that minimal lateral change from a fixed point the lateral change from two similar, but not identical arcs are almost negligible. 

If I were to design from scratch with no constraints, of course they would be identical in length, angel and would be as close to parallel to the ground at ride height without compromising the extremes of travel in either direction. But engineering is rarely so satisfing.

[Bowie69]

Plus, it's a beam axled body-on-chassis vehicle with massively oversized squishy tyres with big lumps of rubber sticking out of them -if you can notice it, then you are doing really, really well indeed.

[uninformed]

12 hours ago, Bowie69 said:

Plus, it's a beam axled body-on-chassis vehicle with massively oversized squishy tyres with big lumps of rubber sticking out of them -if you can notice it, then you are doing really, really well indeed.

All good to have a laugh, but get the geometry wrong and you’ll definitely feel it. And given the time and effort involved to modify it, you’d be Mildly miffed if it was a backwards step.

[Bowie69]

Agreed, but I'd wager no one would spot a drag link 20mm longer than a panhard. 

[FridgeFreezer]

56 minutes ago, Bowie69 said:

Agreed, but I'd wager no one would spot a drag link 20mm longer than a panhard. 

Don't coilers sit skew at standard ride height anyway? Pretty sure RRC always did - front axle offset relative to back axle when at rest.

[uninformed]

1 hour ago, Bowie69 said:

Agreed, but I'd wager no one would spot a drag link 20mm longer than a panhard. 

You realise that the factory set up has the drag link longer than the panhard to begin with, now add 120mm to the already longer drag link but keep the panhard standard….

[Bowie69]

Wasn't actually making reference to that situation when I made the comment. 

[uninformed]

53 minutes ago, FridgeFreezer said:

Don't coilers sit skew at standard ride height anyway? Pretty sure RRC always did - front axle offset relative to back axle when at rest.

Not sure, I wouldn’t have thought much, for two reasons, the original RRC sat pretty low and the links were fairly flat. Panhard and drag link were on a downslope to the axle , but again not much. 2, the engineers got a lot right with the RRC all in all and I figure they would have factored that in?

 

[discomikey]

I've driven this setup on a myriad of different roads, A roads, motorway, B roads, Dirt, etc and I can assure you the 120mm difference in length is negligible from assessment even when driven with a firmer suspension package, with Bilstein dampers and redeveloped anti roll bars. If it's good enough for JLR to sign off the works V8 like that with aforementioned suspension and 400BHP I wouldn't be too fussed about arguing the toss in all fairness. 

 

On 11/6/2023 at 10:39 PM, FridgeFreezer said:

Don't coilers sit skew at standard ride height anyway? Pretty sure RRC always did - front axle offset relative to back axle when at rest.

Yes they do, not by much though, a hair over 6mm from memory. Their tolerances on some of the suspension chassis brackets as manufactured new are as much as +-2.5mm too even on the last of the puma defenders.