4WD MODIFICATIONS - SUSPENSION & BRAKES
Most 4WDs spend their time relatively lightly loaded around town and fully loaded on bush trips. Trying to make a fixed-setting shock absorber handle both damping tasks isn’t easy: hence, the adjustable shock absorber.
At the outset, it needs to be understood that our evaluation of Tough Dog adjustable shock absorbers was not intended to impart race-vehicle dynamics to our LandCruiser 75 Series and HiLux crew-cab OTA Team vehicles.
We wanted to check out whether adjustable dampers could manage ride quality and handling better than non-adjustables, under varying load and road conditions.
We’ve been running Bilstein monotubes on ‘Harry’ – the 75 Series – for several years and have been very happy with their durability and effectiveness. However, after seven major bush trips to remote, rugged areas, over badly corrugated roads, they were starting to show some wear and tear: hardly surprising!
Years ago, the old workhorse had a 50mm suspension lift, a 700mm wheelbase extension and a post-registration, engineer-approved GVM upgrade to 3.5 tonnes. (We checked with the engineer concerned, John Wilson, to be sure that the proposed shocker change wouldn’t void our GVM upgrade conditions.)
The hard-worked HiLux had been fitted with a 50mm-lift OME suspension kit that was also losing its damping effectiveness. This vehicle retained its manufacturer’s GVM, so there were no compliance issues with the shocker swap.
Adjustable Tough Dogs
We took both vehicles to Tough Dog’s Sydney-west HQ, where Simon Vella, the company’s product director, took charge of proceedings. Firstly, he checked front and rear axle weights and spring rates. Then he disappeared into his lab and emerged some time later with appropriate Tough Dog products.
For the HiLux Simon selected 60mm-diameter outer casing models, with 40mm bores.
For the 75, he chose BMX 70mm external diameter models with 45mm bores and 22mm piston rods. Each damper had an adjustable foot valve that varied bump and rebound damping in nine successive steps.
In addition to this variable-flow foot valve the Tough Dog Adjustables have an internal replenishment or bypass tube (on the right, at right) that allows oil flow between both sides of the piston without restriction by the piston valves. This helps control piston speed.
Internal or external bypass tubes are features of top-shelf and high-performance shock absorbers. If you want to read more on this topic, check out our Tech Torque story.
Because of their size, these dampers won’t fit some vehicles, but, although they fitted comfortably to the 75’s shocker mounts they did foul the handbrake cables that ran across the LandCruiser’s rear axle. No problem there, as there are Tough Dog extended brackets to move the wires clear of the shockers.
These rear springs were later changed to Tough Dog types (see below).
Also, a very important part of the installation was an extended bracket for the rear brake circuit’s load-proportioning valve, to match the 75’s prior 50mm suspension lift. The valve allows varying rear wheel brake pressure, depending on the load on the rear suspension. (Late-model vehicles have electronic brake pressure proportioning to do that job.)
In most suspension shops, when a ‘lift’ is done, the rear brake balance is ‘preserved’ by bending the load proportioning valve actuator, but Simon Vella reckons that’s not accurate enough. He’s right, we know, because braking was much better after fitment of the bracket and we had on-road brake-meter evidence later confirm that.
Once we were happy with the shock absorber behaviour we wondered if the leaf springs could be optimised to ideal spring rates. Simon Vella was up for the challenge and made an interesting discovery in the process.
When our 75 Series was modified to move the front spring swinging shackles from the leading ends of the springs to the trailing ends, there had been a slight change in optimum spring length. The front springs I had were actually too long.
Simon calculated that a set of 60 Series front springs would be a much better fit, allowing the front shackles to swing back without touching the underside of the chassis rails.
He chose Tough Dog spring packs with the right number of leaves to cope with 1.4 tonnes load when fully loaded, but provide flexibility at the unladen weight around 1.1 tonnes.
At the rear he fitted 75 Series Tough Dog springs that could handle 2.1 tonnes at full load, yet allow the longer leaves to lift clear of the two heavy-load auxiliaries at the bottom of each leaf pack.
He calculated the ideal spring rates, allowing for the fact that the Polyair bellows above each spring would hold 30psi at full load and 8psi when unladen.
The result was quite remarkable, giving the 75 modern-ute ride quality at the rear and quite reasonable front end ride quality – if not up to Independent coil spring level.
The front and rear spring rates and dampers felt balanced when the 75 was loaded and unladen and the familiar rear-end ‘kick’ was gone, completely.
There’s a lot to be said for having your vehicle fitted with ‘tuned’ front and rear suspensions. There’s no point going to the cost of this individual treatment until you have the vehicle set up for typical daily usage and for bush trips.
It’s a waste of time and money to have a ‘tailored’ suspension fitted and then alter weights and balance.
For example, our ute’s empty weight is 2.6 tonnes, but with the slide-on camper on its back; both fuel tanks and the water tank full and all our camping gear and tucker on board, the 75 tips the scales right on its upgraded GVM of 3.5 tonnes.
A good suspension engineer needs to know exactly the weight he’s dealing with, for optimum results – and optimum results are what we got!
On and off road
Right out of the shop we noticed ride and handling improvements in the unladen 75 Series, even with the shocks on their lowest damping settings. Interestingly, there was noticeably less driveline vibration when lifting off from rest and we hadn’t expected that.
Simon Vella explained that the heavier construction of the Tough Dogs, with their large rod diameter and substantial rod-guide section, gave them better ‘stiction’ when the axle tried to react to lift-off torque, keeping the diff nose and prop shaft universals more stable.
The rod guide area of the Tough Dogs is particularly robust as this photo shows.
With our Tray-Tek slide-on camper on the back of ‘Harry’, weight went from 2.6 tonnes to 3.3 tonnes and with full fuel and water tanks, to 3.5 tonnes. At that loading we set the front shocks to the second damping setting and the rears to the fourth stage.
Preliminary testing indicated those guesses were pretty right, but we need a longer trip, on varying road and track surfaces, to check out the optimum settings and that happened during 2020.
Early impressions are more axle control when unladen and loaded – particularly at the back end – and flatter cornering. Ride quality is about the same as before – very good for a 75 Series, we feel.
The Tough Dog 60mm diameter outer casing with a 40mm bore adjustable shock absorbers that were selected for the HiLux have allowed OTA’s Simon and Sheree M the ability to stiffen the shocks up for the highway travel portions of their trips.
This greatly improves passenger comfort, vehicle handling and stability, along with safety, when the vehicle is fully loaded.
The adjustable shocks also allow them to adjust the ride to suit the changing vehicle weight and track conditions, throughout a trip.
This feature makes them the most versatile shocks they’ve tested so far.
Big bore, non-adjustable Tough Dogs
In March 2020 we added a third vehicle to our Tough Dog shock absorber test.
The test vehicle was truck journo, Steve Brooks,’ own 79 Series short-cab ute that had done around 100,000km on its standard suspension. It felt tired, he reckoned, doing its main duties as a farm runaround and towing a two-horse float all over the country.
Steve didn’t want adjustables: just some quality shocks that would control the 70 Series’ coil/leaf suspension on the less than wonderful roads in his area.
Simon Vella chose 41mm internal-bore shocks, with 18mm double chrome-plated rods for the task and fitted them, after doing a suspension check that all was in order.
Steve Brooks picked up his vehicle and sent us through his early impressions:
‘It is no exaggeration to state that since Tough Dog shocks were fitted a few weeks back – replacing original Toyota LandCruiser shocks after almost 100,000 km – the difference in handling and ride is extraordinary.
‘Phenomenal, in fact, which suggests I was entirely ignorant of how ineffective the original dampers had become.
‘Roads around our way are generally very poor – little more than an interlocking splotch of roughly repaired bitumen holes, or, a little further afield, heavily rutted dirt tracks.
‘However, on both surface types the ride and handling of the 2012 LandCruiser tray top is vastly improved, with no kick-back through the steering and, perhaps best of all, an appreciable advance in handling stability.
‘My genuine thanks to Tough Dog for the product and the advice, and my old mate Allan Whiting for suggesting the brand.’
We’ll update Steve’s post when he’s done more klicks and some towing. We’re also very interested to know how they compare with the adjustables fitted to the OTA 75 Series.
GVM upgrade implications
Our 75 Series had a post-rego GVM upgrade, so, to confirm it would still be compliant when fitted with adjustable shock absorbers we consulted the certifying engineer, John Wilson, because the conditions of a GVM upgrade include spring and shock absorber models and part numbers that cannot be changed.
However, John Wilson was more than happy to approve the switch to adjustables in writing.
We asked Simon Vella if Tough Dog had done any GVM upgrade packages, using adjustable shockers.
“No, we haven’t done that,” he told us. “Because certifying the components to our satisfaction would be very difficult.
“To cover every contingency would mean brake- and swerve-testing a vehicle repeatedly, with all possible combinations of front and rear damping adjustments.”