drop arms for lifted P38A

[PaulP38a]

If I had not previously owned a P38A I may not have noticed this, and just put it down to "real" 4WD's driving like an agricultural vehicle. But since I have had another P38A with Bilstein Shocks, Arnott Gen III's and good off-road tyres, all which had minimal adverse affect on highway performance.

So, my current P38A "tractor" with above mods plus the HRA 2" lift kit has had me perplexed for quite a while why it tends to wander on the highway. Then Sam from RangeLand asked me about this one day and it dawned on me that my steering geometry is skewed due to the lift, i.e. the castor angle on the steering is out.

Then I went to a steering specialist today and he took one look at the car and noticed that the front left (passenger) wheel sticks out more than the front right wheel... due to the lift causing the front diff being pulled sideways just a touch.

I guess I have a few options:


remove the lift kit, dropping the car to standard heights (no fun in that)
find drop arms or some spacer plate to bring the castor back in to line and the diff/wheels back to centre;
leave it alone and put up with substandard handling.

Since the P38A has EAS, I imagine it must have some way of compensating for varying height anyway, and the effect this has on steering geometry.

Is there a fourth option, or suggestions for option 2 above?

Cheers, Paul.

[Scouse]

There's no factory compensation for varying heights. In fact, if you look very carefully when adjusting the height while driving, the steering wheel goes off centre ever so slightly with the changes.

You just need an adjustable panhard rod to adjust the diff back to centre but as for correcting the castor, maybe off set bushes in the radius rods (if there is such a thing for the P38) would be a quickish fix until new arms are sourced (unless you want to cut/weld the axle ends ;)).

[andrew e]

Adjustable panhard, so you can set the position at your nominated driving height. (thats the easy part)

For the front arms, you could have them heated up and cranked a few degrees, to suit your normal height which is now 2" higher. Its either this or cut the brackets off the front diff, and re-weld them in another spot. Specialist job either way. I will ask around if you like.

Andy

[Hoges]

just an observation:

Yep, all of the above... the RR steering geometry is optimised for cruising at (factory) highway height. Any deviation is a compromise... hence the speed restrictions... plus the added stress on UJs

You'll notice that as the suspension rises to max height from "Access" the length of the wheelbase varies ever so slightly.

If you were to fit an adjustable panhard rod to counteract the axle displacement, it really needs to be an automatically adjusting one which changes length depending on the height setting... no doubt some bright spark will come up with a design :cool::D

[andrew e]

Paul, i spoke to a fabricator today, and he said he can make you up some adjustable panhards for $200 each. I Dont know about cranking the front arms though, are there any blacksmith out your way? i can supply you with some spare arms if you like.

custom jobbies would be out of the question as the factory ones have that sideways bend in the middle
Andy

[PaulP38a]

Thanks for the responses blokes. This is a fiddly one.

I do actually use the various height settings on the car so whatever I end up doing is going to have an adverse effect on the other settings:


most of the time, the height is locked at standard for driving around town, and the car will fit in my garage if the roof racks are not on;
drop it down to highway mode if doing more than 80Kph for any more than a few minutes;
up to standard or high if playing off-road;
down to access height if visiting an elderly relative who needs a lift.

Looking at the scenarios above, the car spends most of it's time at standard height, but the steering/tracking issue is really only a problem at higher speeds and at highway height.

I like the idea of adjustable panhards and $200 each sounds fair.

Dunno about heating up the front arms though... sounds a bit risky. The little I remember from materials science at uni *many* years ago tells me that this will likely weaken the arms. I'd imagine the arms spend most of their time in compression on the road, but a few decent off-road bumps would introduce a fair amount of tension and shear forces.

Then again, all the arms really need is a small kink to flatten out the few degrees of rotation that the diff is being pushed forward/over itself.

Argh, and of course this is leading to more stress on the prop shaft and UJ's... my brain hurts :eek::D

[Hoges]

Gentle question:;) Do you really need the extra 50mm of lift as a standard accessory... or could you still get by with re-jigged EAS settings which would enable you to cruise at the design height but exploit the additional lift offered by GenIII's "on demand" ?

[fester]

Have you checked the front arms bushes and looked at whether you can get offset ones. This is the most common method of correcting castor on Cruisers/Patrols up to about 3" lift. Over that they go to custom arms (best approach) or castor plates.

I saw a kit with 4 front radius arm bushes so I'm gunna guess they have two bush mounts, one for and one aft, like most radius arm set up (not an owner yet sorry). You could go to somewhere like Pedders and see if they can match the bush size up to supply offset ones. You could also make up some castor plates. These bolt to either side of the standard mount set up and use the same rear hole but have a lowered front hole to set the castor. The original front hole is just used now as a fixing point. But these are normally for big lifts on Cruiser/PAtrol like 5" and over. Cruiser owners also look at slotting the front hole downwards then locking in the desired place with a fat washer tacked over the hole. On a cruiser you can get 2 degrees of castor back by slotting the hole down by 14mm (size of hole in first place)

Not sure how easily these relate to the P38 but at any rate you would need to decide at what height you want the castor to be correct and be happy with that. Depending on the difference between fst highway and town height both could still be acceptable. Offroad height is not too important as speed is not normally high.

Adjustable panhards whilst good will not change your wandering that much if it;'s your castor that's affected most. 2" Cruiser/Patrols do not normally bother with or need panhards. Of course all this is relative to what factory settings are and the length of the originals and the arcs they travel.

Custom radius arms for the Cruiser/Patrols set you back about $1,600 so you'd want to be sure you really need them especially seeing as yours are one offs.

[andrew e]

Have you checked the front arms bushes and looked at whether you can get offset ones. This is the most common method of correcting castor on Cruisers/Patrols up to about 3" lift. Over that they go to custom arms (best approach) or castor plates.

I saw a kit with 4 front radius arm bushes so I'm gunna guess they have two bush mounts, one for and one aft, like most radius arm set up (not an owner yet sorry). You could go to somewhere like Pedders and see if they can match the bush size up to supply offset ones. You could also make up some castor plates. These bolt to either side of the standard mount set up and use the same rear hole but have a lowered front hole to set the castor. The original front hole is just used now as a fixing point. But these are normally for big lifts on Cruiser/PAtrol like 5" and over. Cruiser owners also look at slotting the front hole downwards then locking in the desired place with a fat washer tacked over the hole. On a cruiser you can get 2 degrees of castor back by slotting the hole down by 14mm (size of hole in first place)

Not sure how easily these relate to the P38 but at any rate you would need to decide at what height you want the castor to be correct and be happy with that. Depending on the difference between fst highway and town height both could still be acceptable. Offroad height is not too important as speed is not normally high.

Adjustable panhards whilst good will not change your wandering that much if it;'s your castor that's affected most. 2" Cruiser/Patrols do not normally bother with or need panhards. Of course all this is relative to what factory settings are and the length of the originals and the arcs they travel.

Custom radius arms for the Cruiser/Patrols set you back about $1,600 so you'd want to be sure you really need them especially seeing as yours are one offs.

I have not checked, but i very much doubt anyone makes a offset bush for a p38. The only slight chance, is if a D2 one is the same, and someone makes them for a d2. They are nothing like a patrol / rangie classic bush.

you cannot make custom arms, as the factory ones have a dogleg in them to miss the chassis rail.

Paul, your car at any height compared to a factory p38 is 2 inches higher, correct?

Andy

[PaulP38a]

Gentle question:;) Do you really need the extra 50mm of lift as a standard accessory... or could you still get by with re-jigged EAS settings which would enable you to cruise at the design height but exploit the additional lift offered by GenIII's "on demand" ?

The 50mm lift is mainly for the 33" muddies. Even then, I get slight rubbing at standard height. [yeah Andy, I know - cut the guards... Ok, but we're doing it at your place :D and I want some of those plastic/rubber guard covers that Sam has on his Disco]

Do I need it? No not really, but I do like the extra height for off-road work :). To change it back to non-lifted would probably involve changing the shocks back to standard Bilsteins as well. Mine have the fronts at the rear and modified LandCruiser shocks at the front to really make use of the Genn III's extended travel.


Paul, your car at any height compared to a factory p38 is 2 inches higher, correct?
Yep, front and rear sits 50mm taller than stock... or at least it will when I cut down the new front HRA bump stops. What were they thinking? These buggers are 120mm long, and I've got about 50mm of downwards travel on standard height!! Aren't standard bump stops about 60mm?

[Hoges]

"Aren't standard bump stops about 60mm?"
yep,,, but they're also very soft , concertina shape and hollow meaning that when they are compressed there's less than a couple of mm at most between the axle plate and the bumpstop stub...not real comfortable as others can attest...:(

[Scouse]

If you cut down your bump stops, will the longer dampers compress enough or will they 'top' out?
That's usually why longer bump stops are fitted.

[PaulP38a]

If you cut down your bump stops, will the longer dampers compress enough or will they 'top' out?
That's usually why longer bump stops are fitted.

Good question Scouse. All I know is that at the moment it doesn't take much of a bump on the road until I feel/hear a thud. Here's a pic of the 3 bump stops I have...
http://www.cordwell.net/wp-content/uploads/2009/05/3-bumps_resize.jpg

The original yellow ones are fitted at the rear and were on the car when I got it from Hardy.
The red ones were on the front, but one of them was split so I ordered a replacement set from HRA - the blue ones.

As Hoges rightly pointed out, the yellow stops are quite soft.
The red ones are quite firm, and the blue ones seem to be firmer again.

Interesting that the red ones are exactly 50mm taller than the oiginals... exactly equal to the lift kit on the car. The lift at the rear is via 50mm blocks mounted under the airsprings, so a 110mm bump stop makes sense.

At the front no blocks are visible, so the lift is either spacers at the top of the airsprings... or possibly the extended shocks? Hmm, just doing some maths on the shock lengths. I'll ponder this and come back with my findings.

cheers, Paul.

[PaulP38a]

Here's the maths I could figure based on...
- What I call "Standard" are Bilstein B46-2214 shocks at front and B46-2215 at rear.
- What I call "My front" are modified Bilstein B46-1477 for LandCruiser 80 series.
- What I call "My Rear" are Bilstein B46-2214 (normally used for P38A front).
http://www.cordwell.net/wp-content/uploads/2009/05/ShockLengths.jpg

So the front shocks have 32mm more travel than standard, and 33mm more at the rear.

Observations from these numbers:


The closed length at the front is 53mm taller than standard, so the bump stops should be at least 53mm longer, assuming shock is near vertical.
the open length at the front is 85mm longer than standard, so what gives first - the airspring or the shock?
closed length at the rear is 26mm longer so the bump stops should be <X>mm longer than standard, where <X> = 50mm (height of lift blocks) + extra shock height corrected for angle, approx 18mm if angle is 45deg... <X> = 68mm taller than standard.
open length at rear is 59mm more than standard.

Does this make sense or are there additional factors I've missed?

Thanks for your consideration and suggestions on this... I promise to write something up and publish it if/when we get this sorted for the reference of other P38A owners who want a bigger "air gap" :)

Cheers, Paul.

[Scouse]

The closed length at the front is 53mm taller than standard, so the bump stops should be at least 53mm longer, assuming shock is near vertical.The original bump stops are designed to squash quite easily, so I don't think the standard damper would be close to full compression when on the stops normally. Therefore your harder bump stops give a bit more clearance than is measureable when compared side by side.

You'll find the damper is the limiting factor in the downward travel of the suspension. It is on other models & there's no stop built into the bag at all. The bag can pop off the alloy/plastic mounts if longer dampers are used with standard bags.

[andrew e]

the way to setting the right bumpstop height is:
1, remove all your bumpstops.
2, drop the suspension down with no air (normally bumpstop level) - dont drive anywhere :D
3, measure the height between the diff and where the bumpstop should be.
4, add an inch to this measurement, and that is how long your bumpstops should be.

Andy

[PaulP38a]

Thanks guys, I was planning to try something along the lines Andy described over the weekend. 1" seems about right for those harder stops.

Cheers, Paul.

[blackrangie]

have you talked to bruce davis landys in sydney?

Are p38s able to have slotted swivels for castor correction or is it a different setup?

[BigJon]

have you talked to bruce davis landys in sydney?

Are p38s able to have slotted swivels for castor correction or is it a different setup?

No swivels. They have upper and lower balljoints with an exposed rubber booted cv joint. The only way to change the castor at the axle ends would be to cut and weld.

[PaulP38a]

have you talked to bruce davis landys in sydney?

Not yet, but the local steering specialist in Queanbeyan recommended them too. I will probably call them soon once I get my suspension height sorted.

Cheers, Paul.

[PaulP38a]

Well, I probably made the handling worse today.

Removed the bumpstops, deflated the EAS and measured the heights from bump stop plate to top of diff... 60mm at the front and 0mm at the rear.

Cut the blue HRA bumpstops to 90mm for the front and reused the yellow orignal bump stops for the rear.

Decided to swap over the height sensors while I was at it... left to right that is, which meant I had to recalibrate the EAS. Oh joy! So I thought I might as well give the car a bit of extra height to see how it goes... :)


Highway/Low height is same as before... 485/495mm (front/rear) measured from top of wheel cap to bottom of guard, and 60/55mm bump stop to diff - approx 30mm more at the front stops;
Standard height is now 40mm taller than before... 525/545mm and 100/120 bump stop to diff;
Wading/High height is now 35mm taller than before... 565/600mm and 140/165 bump stop to diff;
Access height is now 15mm off the diffs.

Hopefully with the shorter bump stops, Low and Standard heights will now be a smoother ride.

I've taken a bunch of pics to document my changes and will post them to a web page sometime soon if they can be of use to any of you folks.

In the meantime, here is a pic of the Rangie on Standard height next to my wife's Freelander.
http://www.cordwell.net/wp-content/uploads/2009/08/090809-48.JPG

Cheers, Paul.

[Hoges]

FWIW... the LR EAS Systems Information document (SID) (LR1998) specifies

"...When calibration is complete, there should be 100 ±4mm (4.0 ± .2 in.) between the front bump stop stud and the front axle pad, while the rear, measured similarly, should be 105 ±4mm (4.2± .2 in.) standard ride height."

I can email you a copy if you want.

The problem is, that with standard tyres at correct psi (equivalent diameter to Pirelli Scorpion with 11mm tread), the 100mm/105mm displacement above gives a wheelarch to ground distance of around 815mm! This is much higher than the widely publicised 790mm ground-to-wheelarch centre measurement so often quoted elsewhere... including in LR's own abovementioned SID!!!

Perhaps there is a LR /RR professional expert somewhere who can explain the differences :eek:

[andrew e]

the rear might scrub a bit more now with 33s on full articulation. The angle grinder is ready to cut up that lovely new stright door :)


Andy

[PaulP38a]

Thanks for that Hoges. The SID was an interesting read and more informative than the Workshop Manual. Who do you have to know/sleep with/bribe to get more of those?

Having driven the car for a short distance today on Highway and Standard modes, it does seem to be a bit smoother. I'll find some bumpy roads and try it again - shouldn't be too difficult to find some rough roads in rural NSW :)


the rear might scrub a bit more now with 33s on full articulation. The angle grinder is ready to cut up that lovely new stright door :)

sounds good to me. Where do we get some rubber mouldings for the chopped guards though?

[andrew e]

how about some defender flairs? you dont want to know what some rangie spares flairs (like sams disco) are worth. and they dont go straight on either.

Andy

[PaulP38a]

how about some defender flairs? you dont want to know what some rangie spares flairs (like sams disco) are worth. and they dont go straight on either.

Andy

Sure, Defender flares aren't too huge either if it is the type I'm thinking of, so they won't make the Rangie look too obnoxious :eek:

[PaulP38a]

Reading an interesting article on rangerovers.net about a bloke who seems to have sorted the caster angle issue by dropping the rear mounts.

Lifting the Air Suspension (http://www.rangerovers.net/rrupgrades/airlifts.html#front)

I think this is what I want... instead of bending/cutting the arms, just drop the rear mount by 2"... makes sense.

https://www.aulro.com/afvb/images/imported/2009/08/1157.jpg

Anyone got one a couple of these mounts lying around and is handy with a welder :p

[M.Allison]

So by welding the mounts a little bit more forward does that put anything else out?

thanks mike

[PaulP38a]

So by welding the mounts a little bit more forward does that put anything else out?

Other than extending the height sensor arms, probably not much else should need attention - I hope.

I'm thinking of lowering the radius arm rear mounts rather than moving them forward. Apparently they can be moved forward to help with improving space within the wheel arches for bigger tyres, but I'd then be worried about stuff like steering shaft, angle of airsprings, shocks and bumps, and extending the front propshaft.... seems like too much effort at this stage.

Thinking about this some more.... I wonder if it might be simpler to make up a 2-piece bracket that is secured in to the existing rear mounting point with another hole 2" lower that the front radius arms mount in? To make it even more useful, you could replace the existing crossmember with a bigger/lower crossmember that gives better tailpipe protection and is also secured in to the existing radius arm rear points, and has new radius arm rear mounting points attached.

Hmm, might just work...:cool:

Despite what some people might think, I'm not trying to turn my Rangie in to some kind of off-road competition truck. It has to serve as my daily driver too. Just want to make a few useful mods to take advantage of the awesome capabilities of these vehicles, and have some fun along the way :)

Cheers, Paul.

[andrew e]

i see this alot, but i dont understand why people do it. If you have a flat chassis rail, you slide over things easy. Adding a drop box, like the one in the picture, you will get hung up more than with stock suspension.

My 2c.

Andy