Mark D Stephens: Adventurer, writer, photographer, ambassador of the sonoran desert

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Equipment Review and Evaluation:
"Suspension Theory 101"
PRG Spacer (2") lift and Automotive Customizers Shackles (1.5")

Nissan Frontier Navaa d40 PRG suspension lift AC shackles aftermarket shocks lifted truck
Products purchased from:

Benefits of suspension modification
The point of tinkering with the suspension on a vehicle bound for environmentally responsible expedition travel is simply to improve:
  1. passenger comfort and
  2. off-highway articulation

However, added bonuses include:

  • Increased chassis clearance
  • Increased approach, break over, and depature angles (however marginally)
  • Added capacity for taller tires
  • Improved looks, based on the eye of the beholder

Factory numbers for 4x4 Crew Cab Nissan Frontier (Navara):

Off-Road Specs Crew Cab 4x4
Approach Angle 31.5° 31.5° 32.6°
Departure Angle 22.6° 22.6° 23.9°
Ramp Over Angle (break over) 20.6° 20.6° 20.5°
Maximum Ground Clearance 10.1" 10.1" 10.1"

The roads that this truck navigates tend to be routes with little technical challenge that don't demand extraordinarily tall tires: back country Baja tracks, The Mojave Road, El Camino del Diablo, Canyonlands NP, rural Mexico, National Forest fire roads, and so forth.

All we need with this truck is to maximize those numbers above while maintaining good handling and passenger comfort. And fit on a slightly larger tire, which is 265/75r 16 in this case (32").

Mark's caveats to suspension modification:
1. Beware of the products you use. In the modern American marketplace, quality suspension products are often hard to find and sub-standard parts are abundant for customers pleading "I just wanna lift my truck and I have money."

2. Beware that every modification has a consequence. Playing doctor on suspension parts shouldn't be taken lightly as there are joints, geometry, and well-thought-out components designed by automotive engineers. CV (constant velocity) joint angles, in particular, are quite susceptible to premature failure under the stresses of too much lift. Ball joints don't like changing angles much, either. In the rear, shifting the pinon angle can also cause early failure at the axle seal and u-joints. The list can go on. Tread with moderation in this department.

First impression
PRG Spacers:

AC Shackles:

PRG space lift for Nissan Frontier Navara D40 Leveling kitPRG spacer:
Billet aluminum that's been CNC routed is nearly always blemish-free and impressive. The precision milling by CNC left nothing to be desired here. Mounting hardware - nuts and bolts - were included as well as new bump stops.

Additionally, the product came with installation instructions. I find it hard to believe how many times I'll receive a product that doesn't include instructions. Suspension parts to boot! Raise your glass to PRG for having the care to write out the installation process.

"Easy reading is damn hard writing" wrote Nathaniel Hawthorne.

AC Nissan Frontier lift shackles for leaf springs 2005+AC shackles:
Incredibly heavy, which I think is a good thing. No bushings included, however they are not needed, either. Re-use the OEM bushings. Nevertheless, these shackles are quite muscular and well painted. I wish they were greasable.

I chose to cut the tailpipe to make space for these shackes, too. I have no idea if it was necessary, but at the time it appeared so. AC does not include instructions or any paperwork, which I find annoying - even though shackles are a simple install, some paperwork that explains about tailpipe clearance, and why no bushings are included would show some attention to detail.

*Side note: At the time I purchased these products, these were virtually the only items available. Since then, PRG has produced a new coilover option (as well as others), and add-a-leaf packs are available.

PRG Spacers:

AC Shackles:

Both items were very easy and straight forward to install. Thanks to the instructions provided by PRG, I was well armed for working on IFS, which I'd never done before. Brooke, my wife, even did most of the work (as seen to the right).

A difficult part on the front was committing to the beating you must give to the spindle to get that upper ball joint to release.

The front spacer simply bolts to the top of the OEM coilover unit - no coil compressor needed.

On the rear suspension, some instructions would have been helpful as it appeared as though the tailpipe would be in the way and the shackles did not come with bushings. I'd never worked on leaf springs before, either. No instructions just reflects poorly on the product. Hence, I give these only 3 stars on the installation. Once I learned how to do it, the process was easy and quick.

PRG Spacers:

AC Shackles:

Testing the PRG lift leveling kit spacers Nissan FrontierSpacers are a simple product, and they offer no improvement of the suspension as far as control, handling, and articulation are concerned. They work as advertised: slight increase in chassis clearance.

The consequence of using spacers is losing droop (down travel). Gaining a little more chassis clearance is the upside, but I'd rather have the articulation. Truth be told, they work in direct opposition of my goal: improve comfort and maximize articulation.

Spacers do not improve comfort - or diminish it - since neither shock nor coil are changed. This part is a wash. If you want to maintain factory ride and get a little lift, spacers are the perfect product.

So! Spacers do exactly what they are designed to do, but they are just the wrong product for my needs. Hence, four stars.

I feel the same way about the shackles. They are just not appropriate for my needs. While they improve the articulation of the rear suspension, they do nothing for load capacity. Shackles also put added stress on the leaf packs and tend to flatten - or even de-arch - the leaves under a load. This is a total bummer, but I should have expected so.

AC shackles, too, work as advertised and are a heafty product.

I'm definitely learning as I go, and these two products have taught me a lot.

PRG Spacers:

AC Shackles:

Bang for buck?

The way I see it, these two products are a quick-n-dirty way of getting up in the air with minimal consequences yet are only temporary solutions for my needs.

In fairness, not much was available on the market for the D40 Frontier (Navara) when I made these purchases. The marketplace has moved along, and I'm saving my money for the right suspension. While both items prove to be a good value (dollar-to-result), both companies offer better suspension components.

After having the extended shackles installed for over a year, I've decided they are really a poor method of lifting a spring-over-axle leaf suspension; however they are a very inexpensive method. The AC product is fine . . . but all extended lift shackles are going to do the same thing: leverage the leaf packs into flattening and/or negative arching. You get what you pay for.

*Note: Extended shackles work much better in conjunction with longer leaf packs. These will likely be a perfect mate with custom leaf spring packs.


Spacers (mini leveling kit)
Nissan Frontier d40 PRG spacer lift mini leveling kit suspension

As stated above, spacers diminish droop, or down travel, and a limitation of this suspension is with the design the system: down travel stops when the control arm strikes the coil bucket. Simply put, it's just the way this suspension set up is made at the factory.

Coilbucket contact mark from the upper control armA spacer - any spacer - is simply going to augment this. I now have a wear mark from the control arm coming in contact with the top of the coil bucker, as seen to the right.

Other users report that they actually hear a clunk when this happens . . . I don't. Due to the mechanics of where the spindle drops to during down-cycling, nothing is going to stop that control arm contact.

Two options to help alleviate the problem, though:

  1. Add a rubber bumper to the bucket or control arm
  2. Purchase aftermarket control arms

Aftermarket control arms have a bump stop that reduce the noise and abrubt metal-on-metal impact. But you can come to the same end by making your own bumper.

* * *

The coil spacers do not affect the handling or comfort of the Frontier's IFS; noticeably, anyway. I expected this much, since we didn't change the shock or spring.

With the Shrockworks front bumper and winch installed, the measurement from centerline hub to fender sheetmetal is 21.5".

Extended Shackles
Leaf spring shackle articulation AC

I quote AFCO Racing:
Shackle length is another factor affecting the rate of a leaf spring. A short shackle will change its angle (and the effective rate of the leaf spring) quicker than a long shackle upon deflection of the leaf. There is a second shackle effect on the stiffness of the rear suspension that counteracts and sometimes exceeds the shackle's effect on spring rate. This second effect occurs whenever the shackle swings in its arc and moves the rear spring eye vertically.

Basically, here's what happens to a Nissan Frontier leaf pack with extended shackles installed:

Flattening leaf springs from extended shackles

The photo above shows the leaf packs virtually inverting without a load in the truck bed. This is due to the extended length creating a slightly different angle to the datum line, thereby decreasing the spring rate and load capacity. This is why lift shackles flatten leaf springs.

A few options exist to help out the problem:

  1. Custom leaf packs (longer)
  2. Air bag load control
  3. Repositioning the shackle mount forward on the frame (which I do not recommend)

Good news, though! These extended shackles improve the performance on the trail by increasing articulation. That's pretty cool.

I fully anticpate installing custom leaf packs and/or air bag springs for load control. We carry 600-700 lbs of equipment in the bed for trips, so it's my belief that the extended shackles alone are a bad idea. We're better off without them. If I hadn't tried them, I wouldn't know all I've learned about leaf spring suspensions. So it's not a total loss. I'll keep these shackles and test them with custom leaf packs.

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Mark D. Stephens: Adventurer, Writer, Photgrapher and Ambassador of the Sonoran Desert