The Cruisemaster DO35 is a direct replacement for most standard 50mm ball couplings on off-road caravans. Installation is a half-day job with basic tools — but getting the height setting correct is critical.
What You'll Need
Tools: 19mm and 22mm spanners and sockets, torque wrench (0–150 Nm), drill and 12mm metal bit, steel rule, Loctite 243, grease gun with EP grease.
Parts: Cruisemaster DO35 coupling head, Cruisemaster A-frame bracket (check your tube dimensions before ordering), M12 grade 8.8 bolts, washers, and nyloc nuts.
Step 1: Remove the Existing Coupling
Hitch the van to your tow vehicle on level ground. Set chocks under the wheels and place a support under the A-frame near the coupling. Remove the tow ball nut and lift off the existing coupling head. Keep the old coupling as a fallback.
Step 2: Fit the A-Frame Bracket
The Cruisemaster bracket bolts to the underside of the A-frame horizontal cross-tube. Dry-fit before drilling. Use 4× M12 bolts, apply Loctite 243, and torque to 70 Nm.
Step 3: Attach the DO35 Coupling Head
The DO35 head bolts to the A-frame bracket with 4× M12 bolts through the coupling body's mounting flange. Check the coupling head is square to the bracket. Apply Loctite 243 and torque to 70 Nm in a cross pattern.
Step 4: Set the Coupling Height (Critical)
The DO35 is designed to operate with the A-frame level when hitched. If the A-frame angles up or down significantly, the DO mechanism doesn't articulate through its full range.
To check: hitch the van, then measure the height of the A-frame at the front (near the coupling) and at the rear (at the van's front wall). The A-frame should be within 25mm of level across its length.
Cruisemaster supplies multiple bracket heights. If your measurement shows significant nose-up or nose-down, swap to the correct height bracket before completing installation.
Step 5: Lubricate the DO Mechanism
Before first use, locate the grease nipples on the coupling body and apply EP grease via grease gun until grease appears at the edges of the articulation joint. The DO mechanism can wear unevenly if it goes into service dry.
Step 6: Hitch and Check Operation
Lower the coupling onto the tow ball and engage the lock — you should hear a clear click. Pull up on the coupling to confirm the ball is locked. Manually push the A-frame side-to-side and up-and-down — the DO mechanism should move smoothly with some resistance, without clunking or binding.
Step 7: Torque Re-Check After 500 km
After the first 500 km, re-check all coupling and bracket bolts to spec. Vibration can settle bolted joints slightly in the first few hundred kilometres.
Common Installation Mistakes
Wrong bracket height: The most common error. Always measure hitched height before finalising.
Missing Loctite: Off-road vibration will gradually loosen the coupling body bolts without thread locker.
Under-greasing: A dry DO mechanism makes a grinding sound over bumps and wears rapidly.
Cruisemaster DO35 and DO45 couplings plus A-frame bracket kits at RV Parts Giant.