Land Rover Discovery Suspensions: Caster

[Hank]

Yes, rotating the swivels restores the caster angle if the axle has been rotated. I can see why it's a solution that works. If the original pinion angle could be retained (i.e. the axle not rotated), would that also be a solution to the caster problem?

You've lost me here.

You can't run the "original" pinion angle once the truck is lifted. I mean, you can, but you'd need a DDC shaft most likely (depending how tall you were).

 

[Hank]

That's how you would do it on a Toyota. But I thought Series trucks had "bolt on" swivels like the coilers?

 

[michaelgroves]

You've lost me here.

You can't run the "original" pinion angle once the truck is lifted. I mean, you can, but you'd need a DDC shaft most likely (depending how tall you were).

That was what I was thinking - if you run the original pinion angle, then the caster remains in spec., but it's at the cost of a severe propshaft angle. I'm just trying to establish if that's the trade-off. In which case, if the lift is mild enough to allow a propshaft to work over the steeper angle, then caster can be kept in spec. without doing anything to the swivels.

 

[michaelgroves]

That's how you would do it on a Toyota. But I thought Series trucks had "bolt on" swivels like the coilers?

Probably - I don't know. I was talking in general. If I were doing a mild lift on an expedition vehicle, I would prefer not to modify the swivels, so I am looking at what the options are for lifting, but still maintaining correct caster.

 

[muskyman]

ok lets start here.

1) you can not start changing any geometry in the suspension system without looking at all factors and the affect they have on the system as a whole

Drive shaft

the factory front driveshaft on disco's and RRC are set up 'out of phaze' that means that the two end flanges on the stock driveshafts are not aligned as they would be in a 'best practice' situation or application.

Land Rover did this to compensate for the fact the front end has a misalignment of the drive and driven flanges from the factory.

This issue with this specific application is a short coming that needs to be addressed when you start lifting one of these trucks. once you move at all from the factory position the misalignment becomes greater.

Caster

From the factory the Disco's come with a small amount of positive caster. This small amount is to lower the resitance that the power steering and the driver have to overcome while driving and steering. the higher the caster the more the resistance felt at the steering wheel to turning and the greater the recentering force the truck will exhibit while driving.

As you lift a radius arm truck the radius arms cause a rotation of the axle housing. this rotation moves the caster angle from where it is to a negative position. Negative is when the upper king pin leads the lower king pin.

caster is designed into a steering system for a number of reasons. the main reason is to stabilize the rotating steering pieces or knuckles in this case under the load weight of the truck. Another key reason often not thought about is to stabilize the front housing under braking condition.

Bushing alignment

the factory bushings that locate the front radius arms at the frame are designed to have the radius arm go through the bushing at the bushing center line. As you lift a radius arm truck the radius arm loads that bushing even when the truck is sitting at its static height. This then limits the amount of flex that bushing can withstand before it starts to bind. This causes premature failure of these bushings. One other factor that a Overland truck owner would be intrested in is noise. The greater the angle of the radius arm to the frame the more energy(NOISE) is directed at the passenger compartment as the suspension cycles over bumps.


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OK....take these conditions and think about where to go from there.

So we need to think about correcting these factors as we lift the truck.

The first step is to decide on a final lift height, once we have that we want to correct the above factors for that new chassis position.

1.5" really in most cases takes almost no correction at all. If someone really wanted to optimise for that height and add safety to the truck they could but really 1.5" rarely causes enough issues to start making dramatic changes.

Lets talk about a 3" lift for the sake of discussion, at this height the truck will have degraded handeling to the point that all the above issues should be addressed.

At 3" we can fix two key issues right off with the correct radius arm. By selecting the correct custom radius arm for the lift we can turn the pinion and aim it at the drive flange of the transfercase. That same custom Arm should have a corrected off set built into it to allow us to return the frame end at the bushing to go through the bushing level with the bushing centerline.

We have now corrected the most affected plane of the front driveshaft to be correct. we can now use a adjustable Panhard bar to move the axle housing side to side in the chassis to correct that plane as well. keith at rovertracks builds a adjustable panhard bar just for this purpose.

Now all that is left to restore the factory feel of stability is to return to a positive caster position. With a Land Rover we are lucky enough to have swivel balls that can be removed and re-drilled to correct this. This is a simple proven way to get back the lost caster.

This combination of corrections will produce the best results and the most stabil driving conditions in a lifted Land rover.

 

[Mike_rupp]

Thom & Hank, please give up now. Have you ever heard the phrase "falling on deaf ears"?

Kelly, thanks for your valuable insight to driveline & suspension designs. Brilliant comments.

Keith, I'm not sure what to make of your post. "get the Dweb out"? The reason that I had to counter Scott's new venture into suspension design is that most people here take Scott's word as gospel, for good reason. Most of what he advocates makes sense taking as gospel. I'm sure that there are plenty of newbies that might consider taking his suspension approach simply because of who he is. I disagree. It's an approach that has distinct disadvantages.

Assuming that you have kids Keith, let me ask you one question: are you the kind of guy that congratulates your kids if they say that 2+2=5? Do you not want to hurt their self-esteem?

If not hurting one's feelings is valued more than achieving the correct answer to an issue I'm sure that my stay here will be short lived.

 

[Hank]

Probably - I don't know. I was talking in general. If I were doing a mild lift on an expedition vehicle, I would prefer not to modify the swivels, so I am looking at what the options are for lifting, but still maintaining correct caster.

....my comment was directed to someone else, but the post is now gone.

 

[michaelgroves]

...

Lets talk about a 3" lift for the sake of discussion, at this height the truck will have degraded handeling to the point that all the above issues should be addressed.

At 3" we can fix two key issues right off with the correct radius arm. By selecting the correct custom radius arm for the lift we can turn the pinion and aim it at the drive flange of the transfercase. That same custom Arm should have a corrected off set built into it to allow us to return the frame end at the bushing to go through the bushing level with the bushing centerline.

We have now corrected the most affected plane of the front driveshaft to be correct. we can now use a adjustable Panhard bar to move the axle housing side to side in the chassis to correct that plane as well. keith at rovertracks builds a adjustable panhard bar just for this purpose.

Or:

The panhard rod would be modified just as you suggest.

We could fit a different pair of radius arms - ones that are designed to keep the pinion angle the way it was. I.e. not point it at the driving flange of the output shaft. The new pair of radius arms would also be designed to have the bushing offset you refer to, to obviate the bushing bind. And lengthened etc., as required.

This would mean that we don't have to adjust the caster angle - it's still at factory spec., because the factory orientation of the axle is retained.

But it would mean we would need a special propshaft that can operate at the more extreme vertical angle between the pair of (parallel) flanges.

Assuming we had such a shaft, would this be a perfectly viable alternative, solving all the same problems your proposed solution does?

My next question, of course, would be, what angle is feasible to operate a propshaft over that distance, and what kind of shaft would be needed?

 

[michaelgroves]

Thom & Hank, please give up now. Have you ever heard the phrase "falling on deaf ears"?

They're not falling on deaf ears - I'm asking questions about alternatives, trying to understand precisely where the problems lie. There are usually several ways to achive an objective, and they all have upsides and downsides. Only if we understand the precise strangths and weaknesses, can we possible choose what's best for any particular situation.

 

[Hank]

Only if we understand the precise strangths and weaknesses, can we possible choose what's best for any particular situation.

Honestly, I do not see any weaknesses with turning the swivels and installing it's related parts.

But I do see several weaknesses when it comes to installing a DDC shaft.

 

[I Leak Oil]

I don't think the assumption that most of us here take Scott's word as gospel is accurate. That might be an opinion but probably can't be supported by fact. By the very nature of this board's genre most of us are usually very independant and curious. I agree with the Rupp brother's argument that their solution is the most common and accepted way of accomplishing the goal at this time. Now....Has anyone changed out the side gears on an ARB?
Jason T.

 

[sinuhexavier]

Why is water wet?

 

[Scott Brady]

Thom & Hank, please give up now. Have you ever heard the phrase "falling on deaf ears"?

Nothing is falling on deaf ears. I have already commented that the swivel ball change, etc. makes sense as a good solution, and I have also included it as an option in the article I am writing on my Discovery. I have included it primarily because of this discussion. So, not only have I listened, but I am making sure other people hear it too.

You are taking this way too personal Mike, and I am sorry to see that. Please understand that I have been doing this stuff a long time, and have a solid academic and functional foundation in suspension design, and suspension geometry and physics. I certainly do not know everything, and do not claim to be a suspension expert, but I certainly know enough to see when someone's argument is incomplete or needs proper documentation and support. So I am not just going to take your comments and advise as gospel until you give me something empirical. The comment "That is a bandaid" or "giving up" or that the driveshaft is heavier just doesn't work.

Don't make this personal guys. These discussions are healthy and productive, and stretch or validate common practice. I am sure you are all great people, and I hope to be on the trail with all of you, but don't expect me to just roll over on a subject when no actual data has been presented to the contrary.

As I said a few posts ago, give me the data, show me the documented failures, break out the geometry and theory - I am still waiting, and my Disco still drives perfect and the pinion seal is not even weeping (that cannot be said for the new leak from the power steering box)




Ok, on to the Costa Rica maps.

We are going to stay at this lodge - ************************ Lizards just hang out in the bar. And from the bar, you can slide down a 100' slide, but you have to make sure there are no crocodiles in there first.

So, we can either keep talking about swivel balls, or start planning how we get here.

and here.

Does that help put things in perspective?

 

[kellymoe]

Kelly, thanks for your valuable insight to driveline & suspension designs. Brilliant comments.

Keith, I'm not sure what to make of your post. "get the Dweb out"? The reason that I had to counter Scott's new venture into suspension design is that most people here take Scott's word as gospel, for good reason. Most of what he advocates makes sense taking as gospel. I'm sure that there are plenty of newbies that might consider taking his suspension approach simply because of who he is. I disagree. It's an approach that has distinct disadvantages.

Nobody takes Scott's or anyone else's comments as gospel. The reason I like Expo Portal is because you can read everyone's opinion without the trash talk and make the decision for yourself. On other sites you have to sift through pages of attacks to and pick out the good stuff. Here, it's all up front and you can take it or leave it.

 

[Scott Brady]

I don't think the assumption that most of us here take Scott's word as gospel is accurate.

Thank God eepwall:

edit: soap box