Grand Design RV recently started offering a 8K axle upgrade that includes disk brakes. The upgrade is currently priced at $7,439. There isn't much information about this upgrade online. I thought I would do some research to see if the 8,000 lb axle and Disk brake upgrade is worth the money.
What is advantage of the Grand Design 8,000 Axle Upgrade? The Grand Design 8,000 lb axle upgrade comes standard with Disk Brakes, a Hydrastar Electric over Hydraulic Brake Controller, Cooper 17.5″ H Rated Tires, and increases the trailer Gross Vehicle Weight Rating (GVWR) by 1,000 lbs.
I was surprised at how many changes come with the axle upgrade. Here's a breakdown of what I found.
Grand Design 8K Axle
The 7K axles and the 8K axles are both manufactured by Dexter. The 7,000 standard axle is configured with a Dexter electric drum brake system.
The 8K axle is nearly identical to the 7K axle with the exception that GDRV installs large Hydraulic Disk brakes with calipers vs the standard electric drum brakes.
The Dexter 8K axles are also a bit heavier. They are constructed to handle the additional load and stress of 8,000 lb. Side by side, the two axles look similar and they both connect to the trailer via the exact same mounting points.
7K axles have 3,500 LB leaf springs on each side (3,500 x 2=7,000 lb). The 8,000 lb axles have 4K lb leaf springs.
MORryde CRE3000 Suspension System
Both the 7K and the 8K axles are mounted to the chassis with the MORryde CRE3000 Suspension system shackles that provides for a smoother ride and greater suspension travel.
Hydrastar Trailer Brake Actuator
The Disk brake system is powered by a Hydrastar Trailer Brake Actuator. The Hydrastar electric over hydraulic (EOH) trailer brake actuator is a fast acting variable pressure system that senses the tow vehicle's breaking power and the push-back from the tow vehicle to the trailer.
The advantage of a hydraulic braking system is that it is faster to respond and smoother than the standard electric drum brake system.
Hydrastar Vehicle Support
Many modern tow-vehicles will not natively work with Electric over Hydraulic braking systems. The vehicle control system cannot see the brakes through the Hydrastar controller which causes most auto systems to display warning messages on the dashboard.
Hydrastar sells the HBA-CAM which is an Electric Over Hydraulic Actuator Adapter Module that connects in-between the vehicle brake controller and the Hydrastar actuator. The HBA-CAM will allow any factory installed brake controller to be compatible with the Hydrastar Brake Actuator for electric over Hydraulic trailer braking systems.
Integrated factory brake controllers used with an Electric over Hydraulic controller often display warning messages to the driver continuously. Modern brake controllers send a signal down the brake line to confirm connectivity. In addition to warning messages, the test signals can cause a “clicking” in the Hydrastar actuator.
The pulses from the tow-vehicle terminate at the Hydrastar instead of the electric brakes on a trailer, which confuses the on-board control system. This is what causes the errors to be displayed. The pulse also momentarily turns on the Hydrastar’s motor that is creating the “clicking” noise. The start/stop of the motor due to how signals are sent to it from the tow vehicle will eventually damage the Hydrastar actuator.
The HBA-CAM splices into the Hydrastar’s wiring on the trailer and can be mounted anywhere. The module intercepts the verification signals and electronically answers them showing everything to be normal to the tow-vehicle monitoring system. This eliminates the error codes and the Hydrastar motor “clicking” stops. The braking performance of the controller is not changed by the HBA-CAM.
The HBA-CAM is not included in the 8K axle upgrade price and has to be purchased and installed separately.
Wheels and Tires
In 2021, Grand Design changed the Wheel and Tire combination for their rigs. They now install standard 17.5″ Rims with Cooper 215/75R17.5 ROADMASTER H Load Rated capacity tires. 2020 and prior Grand Design RV's came stock with 16″ rims with Westlake G rated tires.
The one thing that makes the 8,000 LB Axle upgrade a must-have in my opinion is that the Gross Vehicle Weight Rating (GVRW) of the trailer is increased. For example, the Grand Design 397TH is rated to a max GVRW of 20,000 lb with 7K axles. The 397TH gets a bump up to 21,000 lb GVWR with the upgrade. 1K of extra carrying capacity is nice to have in a large rig that has more space than carrying capacity.
There is also quite a bit more margin for error if a trailer is accidentally overloaded. A triple 7K axle rig can withstand loads up to 21,000. The 8K axles can handle up to 24,000 LB. I am not suggesting overloading the trailer, but the additional capacity will make it less likely that hard hits from potholes or something unexpected at full load will damage an axle or leaf spring.