design - Land Rover section

 

Optimizing Leaf spring suspension

 

What follows are my personal thoughts and current understanding on the subject of optimizing leaf springs and suspension for expedition travel. There are some amazing things that can be done with leaf springs for a pure rock crawler or Baja racer style rig. However they may not work best for a loaded expedition rig. Expedition travel assumes a vehicle that is basically stockish bodied, is carrying equipment needed for extended travel and needs to behave well both on the tarmac and under off road conditions likely to be encountered.

The only given is that the suspension needs to be strong enough to suspend the travel weight of your vehicle through your worst driving conditions long distance without damage. Anything else is suspension tuning to make it perform more to your personal desire.

To begin with there are two spring types commonly seen on series Land Rovers. Except for the 101 forward control all series Land Rovers came from the factory with semi elliptic leaf springs. A few years back a company started offering parabolic springs from the Spanish Santanna 4X4 for use on Land Rovers. Since then a couple other spring manufacturers started offering parabolic springs as aftermarket replacements for stock type springs.

Parabolic springs have 2 or more leafs of varying widths that are only in contact at the ends and middle of the spring pack. The advantage of this spring is that it can react quickly to bumps and provide a much softer ride than standard leaf springs, especially older leaf springs with rusted together leaves. If the weight range is correct, the spring will articulate to both upper and lower limits of stock shock travel. Properly set up these springs will provide almost coil spring like softness. However since nothing comes for free there are a couple penalties that come with the soft parabolic spring. One is an increase of side sway. Two to four leaves only attached at the ends and middle have considerably less resistance to side torsion than a block of leaves in constant contact along their lengths. So side sway on curves, from quick maneuvers and body tilts for terrain will be more, and the dynamic centre of gravity will effectively be a little higher.

The other item is spring wind up caused by engine torque at the rear axle. This windup will put a little additional stress on U joints (should not cause problems) and will increase wheel hop on loose surfaces. A parabolic sprung Land Rover may have more problems climbing a steep loose surface hill than a stock suspension Land Rover

Leaf springs can not inherently follow bumps as well as parabolics because their leaves are in contact and there are more of them. As grit gets between the leaves and rust starts forming, the increased leaf to leaf friction makes them less able to respond to road surfaces.

There are two things you can do to help your Rover ride smoother with leaf springs, choose the correct spring for your Land Rover's off road weight and reduce friction between leaves.

Heavy duty springs do not mean best for gonzo off road use, it means capable of supporting heavier loads. Leaf springs are designed to respond best to the road surface when they are near their rated maximum capacity. As you reduce weight on the spring from the rated maximum capacity or put on heavier duty springs, the springs become stiffer and less able to respond to road conditions. So an obvious key element in spring optimization is to pick the correct springs for the actual weight you carry off road.

The very first thing you need to do is go to a public scale and weigh your Land Rover fully loaded for your off road travel including full fuel tanks & cans and a full load of drinking water and food. You will want to take a weight with just the front wheels on the scale and one with only both back wheels on the scale. This will give you front and rear axle weights.

When Rover rates their springs they have an on tarmac max load rating and an off road maximum load rating. Rover assumes that between 70 and 80% of your loading will put weight on the rear axles. This might not be your case. Choose a spring for each axle that has a maximum rate closest to but greater than your vehicle's actual axle weights. This should get you the softest ride and best articulation with springs able to handle your off road driving needs. The Land Rover factory allows you to choose from among five front springs with different rates, two 88 rear springs and three 109 rear springs.

I have gathered the factory loaded and unloaded data and matched them to the springs. Then I tortured the data some to come up with close approximations of the maximum off road axle weight for each spring number. You can use the calculated data chart to pick the springs that provide the best spring flexibility for your vehicle and handle your vehicle's off road travel weight.

Once you have the springs that provide the best dampening for the weight of your vehicle, the next step is to minimize the friction between the individual leaves. I like UHMW (ultra-high molecular weight) Polyethylene plastic.

This plastic provides a low friction surface, similar to Teflon tape, but with a much higher abrasion and puncture resistance. It was designed specifically for commercial use on chutes, packaging lines, slides, and anywhere high pressure metal to metal sliding contact occurs. It also provides sound dampening, eliminating squeaks and rattles caused by adjacent parts movement. The plastic's temperature range is -40 to +225 degrees F.

You disassemble the spring pack and stick the tape to the top side of each individual leaf, except for the top leaf of course. This tape virtually eliminates the friction between adjacent leaves in the leaf pack and dramatically increases the spring's ability to react to bumps in the road.

While we are thinking about springs there are there are two additional spring traits I want to bring up.

One is that the longer the leaf spring, the farther it can bend (articulate) both up and down. Some people have placed 88 rear springs on the front of their Land Rover to increase articulation. I personally have not done this yet, but the people I've talked to who have made this conversion say there is no change in steering nor in on tarmac handling.

What you do is keep the front axle in the same location relative to the vehicle and fabricate new front and rear spring mounts. For the front mount it is usually a matter of extending the front frame a little.

Some people have extended the rear spring length by using approximately 5 foot long rear 1/4 ton pickup springs. People who have gone to longer front and rear spring lengths claim articulation as good or better than that of coil sprung Land Rovers.

The other thing I wanted to mention is spring wrap from axle torque. Springs with the axle centered, like the Land Rover's, are the most susceptible to spring wrap. Spring wrap can cause wheel hop on loose surfaces. Timm Cooper pointed out a modification that helps.

If you look at the rear wheel arch, you will notice that the wheels are set 2 inches forward of the middle of the arch. If one were to centre the axles in the wheel arch and leave the spring mounts in place, one would be extending the spring mount to axle distance at the front of the spring by a couple inches and decreasing the distance at the rear by the same amount. This provides uneven tension on the spring halves which reduces spring wrap.

Timm accomplished this on his 88 by redrilling the centre pin mounting hole on the longer springs 2 inches rearward then reassembling the spring pack with the lower shorter springs 2 inches rearwards of the longer springs. He ran this configuration for a few years as only Timm could run a Land Rover. He reported no problems because of the modification. This would mean of course that you would be driving either a NINETY or a ONE ELEVEN.

I accomplished this by using an offset pin adapter that has the pin the locks the axles housing 1-1/2 inches offset from the locating pin on the spring pack  I used a slightly modified adapter from a Jeep fabrication company. Using the adapter required drilling new holes in the 'U' bolt bottom plate.

 

Spring Bushings

Spring bushings perform two basic functions, they allow the spring to move in relation to the frame without wearing the frame and spring mating surfaces and absorb some high frequency road vibration energy. Today there are the original style rubber spring bushings and several variations of poly bushings.

The factory stock rubber bushings are actually very good at what they do for off road travel. Good quality rubber bushings last a long time and do a good job of attenuating higher frequency road vibrations. When the suspension articulates, it twists the springs sideways. Rubber bushings take up most of the twist on stock springs. Rubber bushings have two major flaws though. First they are a bitch to remove when it comes time to replace them and second they don't look high tech cool.

Poly bushings look high tech cool and are often installed because "cool appearance just must perform better". But lets take a closer look...

Poly bushings come in different hardness and are starting to come in a couple designs. Poly bushings are harder than rubber. There are now hard poly and soft poly bushings. The soft poly bushings tend to be about half to two thirds closer to rubber hardness than hard poly bushings.

Hard poly bushings tend to tighten the suspension which is great for highway curves at speed There is a lot to be said for improved handling for performance on highways. However the ride becomes harsher because the higher frequency road vibrations do not get attenuated. They get transmitted to the frame and the whole vehicle feels it. So while hard poly bushings are great for pavement performance driving they are the worse for off road comfort and rattling of vehicle components and can actually accelerate vibration caused metal fatigue.

When sold beam axles articulate they put a twisting force on the springs that gets transmitted to the bushings. Rubber bushings do a better job of handling this twisting force than poly bushings. The lack of give in the poly bushings may be a force working to limit the amount suspension articulation.

Soft poly bushings are still not as good as rubber bushings for absorbing high frequency road vibrations, but they are a lot better than hard poly bushings.

So why install poly bushings at all on an expedition vehicle? Ease of replacement. Rubber bushings are just about the hardest parts to remove from a Land Rover. Bad poly bushings come out easily so you are a lot less apt to make due with tired worn bushings.

At first poly bushings were advertised as lasting longer than rubber bushings. But the standard poly bushing design does not last longer than rubber and often wears out much faster. Once the instillation grease dries out, gets washed away or contaminated with grit, friction between the stationary part and the moving part builds up. On surfaces with lots of spring movement, such as washboard surfaces, the poly heats up from friction. Poly wears quickly at higher temperatures. So the more you actually use poly bushings off road, the faster they wear compared to on pavement use. Plus dry poly bushings squeak.

Recently, some off road product fabricators have been offering modified poly bushings. The modified bushing halves do not quite meet in the center leaving a gap and they have grooves cut into their inner bearing surfaces. They come with special drilled out grade 5 suspension bolts that have grease fittings. You add grease to the fittings which puts the grease in the space between the bushing halves and into the grooves. The moving parts of the bushings are lub'ed, have low friction, which means lower operating temperatures and the life of poly bushings becomes greatly extended. Also you eliminate those poly bushing suspension squeaks. A set of lub'ed soft poly bushings would be almost as good as rubber bushings, probably last a lot longer and be way easier to replace.

Of course plain old factory rubber bushings still does a better job of providing a smoother off road ride, protecting components from high frequency vibrations and handling twisting forces from axle articulation. The only real potential issue I see with lubricated poly bushings is that you can not use undrilled grade 8 suspension bolts. Having broken a suspension bolt once I'm a little leery of anything less than grade 8.

Having said that I'll probably give lubricated soft poly bushings a try and just carry a couple spare drilled suspension bolts in my spares box.

This is posting to the Dormobile mail list by Bill Davis of Great Basin Rovers:

Two piece front frame bushings have been around since at least the start of the 86 inch Series Ones (1954) and probably back to the 80 inchers. They continued thru at least the Series 2's (1961) and possibly into the early 2a's. I do think they did stop at the Series 2's in 1961 but Rover is notorious for making changes and overlapping them for no apparent reason. Removal is not a big deal if you know the correct process. If you assume it it a one piece it can turn into a mess. Procedure is to check first so you know what you have, saw thru the outer sleeve on both pieces and knock each piece of the outer sleeve from the inside out. If you try to say knock the outer piece thru to the inside, it runs into the inner piece. It can fold up and make a mess. At this point you cannot reverse the process because you do not have a lip to catch on to for this piece and reverse the process.

For informational sake the front frame bushings increased in size significantly with the advent of the Series 3. The bushing increased in size from 1.2 inch to 1.5 inch. They did this because 109's with the smaller bushings would develop cracks in the frame emanating from the bushing from hard usage. This is important to know when ordering bushings especially if you have reframed the vehicle. I think all replacement 109 frames have the larger front bushings.

 

Shackles

When springs flatten they get longer and when they bow down they get shorter in length. A shackle mounted between one end of the spring and the frame handles the expansion and contraction of leaf springs. The shackle mounting location, its static angle in relation to it's spring and shackle length all effect such things as body roll, maximum spring articulation and static vehicle height.

Raising the leaf spring to frame mounting points raises the suspension pivot point closer to the vehicle's centre of gravity. What this does is effectively lower the vehicle's dynamic centre of gravity and makes the vehicle lean less on curves. If you look, you will see a lot of big trucks with real long shackles that mount on the top of the frame and not through the frame. This is to reduce body lean on road curves. This kind of a modification would not be difficult to do on the outboard rear springs of a 109 or with the rear shackles on the front springs. The front frame might be modified by removing the bottom of the box frame to allow the spring front mount to be up inside the frame. A spring over axle arrangement raises the vehicle about 7 inches (height of axle tube plus height of centre spring pack). If the effective wheel to wheel distance is not increased (widen the track) significantly this can cause real problems on side slopes. Going to spring mounts at the top of the frame will both reduce the overall lift and lower the dynamic roll centre of the vehicle making it more latterly stable.

A shackle that sits at about a forty five degree angle with the top mount closer to the axle housing than the bottom mount provides enough movement for upper articulation (spring getting longer) and the maximum amount of travel for downward articulation (spring getting shorter). When a spring moves downwards to maximum lower articulation the shackle swings down to the limit of it's length. The shackle itself increases the lower articulation distance by the difference of it's resting distance between the frame and spring shackle mount and the extended distance. The longer a shackle, the more distance it can add to downward articulation.


This shackle is at the ideal static location for maximum upwards and downwards articulation.

The "Revolver shackle" is a hinged shackle that is a short shackle under static or regular driving conditions and hinges out to become a very long shackle to accommodate radically increased downward articulation.

The Land Rover military shackle is two inches longer than stock Land Rover shackles and can contribute about an inch or slightly more to additional downward articulation. They add about an inch to static body height when used with civilian front spring mounts and about 2 inches when used with 109 military front spring mounts.

Longer shackles are a two edge sword. The factory only placed extended shackles on 109s, NOT 88s. 88's have a very short rear prop shaft. The added lift can easily exceed the factory maximum 'U' joint angle of 26 degrees. Binding the 'U' joint during spring articulation will break something real quickly. The last time I did it, I ended up with a loose front prop shaft and teeth missing from both ring and pinion gears.

The body raise from longer shackles also affects the front steering angle and can cause increased uneven tyre wear and may affect steering stability at highway speeds. Also, any body raise or increased downward articulation can cause interference between the front prop shaft and the cross member that goes under the bulkhead.

Before getting seriously into increased suspension articulation I suggest reading my web page on shocks. They are what limits your stock suspension and will keep you from achieving greater articulation.

Before doing anything that will raise the body from the axles, I suggest reading my web page about adding lift.

These two pages are series Land Rover specific and I believe has some good information. However I do not come close to knowing all there is about leaf spring suspension and body lift issues. I suggest reading as widely as possible before actually proceeding with increasing articulation or suspension/body lifts. Don't trust any source that doesn't go into the interrelation of different parts of your vehicle. Your Land Rover is a large collection of interrelated engineering compromises and you need to account for how a change effects everything else if you want it to be successful.

Be aware of what your changes affect, be careful and most of all stay safe.

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