With the frontend of the 4Runner newly fortified, it was now time to turn attention rearward. A pair of Sway-A-Way bumpstops, Kartek bumpstop mounting cans, and Synergy Suspension strike pads had been patiently waiting since this upgrade’s inception.
In contrast to the ready-made Total Chaos shock hoops we’d used up front, the bumpstop mounts were somewhat uncharted territory. Even though the Kartek bumpstop cans and the Synergy strike pads are ready-made items, the final mounting system and mounting position of the bumpstops was going to require some custom work.
Why go to all the trouble? Hydraulic bumpstops offer progressive suspension control that stock-style rubber or urethane bumpstops can’t match. And, they act in tandem with your existing shocks, reducing the loads and the operating temperature that the shocks experience.
Anything else? Hydraulic bumpstops are like bypass shocks in the sense that they offer position-sensitive suspension control. Bypass shocks provide the ultimate in tunability, but they’re physically larger and they’re more expensive than hydraulic bumpstops. If there’s not enough room on the vehicle or in the budget, consider hydraulic bumpstops in place of bypass shocks.
Follow along to see how things fell into place.
A quick update before we begin...
A quick update before we begin with the bumpstops. The shock reservoir mounts we’d welded on last time ended up putting the reservoir hose in the path of the A-arm. Big hits made the A-arm rub on the reservoir hose, something that wasn’t going to end well. The stopgap solution was to move the reservoir down in the mounts, and only use one hose clamp. We’ll probably move the other mount downward so it catches the top of the reservoir, adding extra stability.
Sway-A-Way’s 2-inch-diameter...
Sway-A-Way’s 2-inch-diameter bumpstops are available in 2-, 4-, and 6-inch stroke lengths. They’re adjustable via internal valving and by adjusting nitrogen pressure. The rear suspension travel on our 4Runner is a pretty short 9 inches, so the 2-inch stroke was the best proportional match.
Some measuring was in order,...
Some measuring was in order, which required the rear coils be removed. The rear of the ’Runner is securely supported by jack stands, and we’ve got a floor jack under the rear axle so we can raise and lower it as needed.
The first measurement was...
The first measurement was to see how close the axle came to the frame with the stock bumpstops. This tape measure’s metric scale was easier to read in this case. There’s about 60 mm of space between the bottom of the frame rail and the top of the axle tube.
The bumpstop includes a half-inch-thick...
The bumpstop includes a half-inch-thick urethane ring to act as an additional cushion. We needed to account for the thickness of the ring, and set our bumpstop height as if the ring wasn’t there. We’ll keep the urethane ring, but we’ll set the bumpstop height to allow for metal-to-metal contact within the bumpstop. Our 9-inch centersection comes very close to the rear suspension’s Panhard bar crossmember at full compression, so correct bumpstop height is paramount.
We consulted an expert for...
We consulted an expert for advice about bumpstop mount construction. Sato Fab’s Keith Sato recommended that the stock bumpstop mount be removed, and that our new mount should tie into the bottom of the frame rail, as well as to the vertical face. Step one was to take a cutoff wheel and a flap-disc grinding wheel to the stock bumpstop mount.
The stock bumpstop mount includes...
The stock bumpstop mount includes a plate that ties to the bottom of the framerail, so we kept that part of the plate. Welding the plate to the lower edge of the frame helps tie the frame’s vertical face to the bottom.
Time to build the bumpstop...
Time to build the bumpstop mounts. We used 1/8-inch-thick 4130 chromoly plate for the base, and a pair of 1-3/4-inch, 0.095-wall 4130 chromoly tubes to span the distance between the base plate and the bumpstop can. Tacking the base plate to the mini welding table kept the base plate nice and flat while the tubes were welded on.
A pair of chromoly side plates...
A pair of chromoly side plates acted as shear panels and completed the mount. Holding the mount up to the side of the frame, we realized it wasn’t going to work. It stuck out too far and was likely to interfere with the tire under heavy articulation.
Bumpstop mount version 2.0...
Bumpstop mount version 2.0 was made completely from plate. It placed the bumpstop closer to the frame and further away from the tire. Note the slight angle, which tucks the top of the bumpstop in closer to the frame as well as kicks the contact tip out closer to the end of the axlehousing. Sway-A-Way’s Brian Bell advised that no more than a 10-degree angle should be used because sharper angles create bigger side loads on the bumpstop shaft. We played it safe and went with 7 degrees.
Chipboard templates worked...
Chipboard templates worked just fine for patternmaking.
Here are two new mounts all...
Here are two new mounts all welded up. The base plate is extra long toward the bottom. We’ll trim off the extra length once we’ve settled on a final mounting height.
We’d cut apart our first bumpstop...
We’d cut apart our first bumpstop mount and reused the mounting can. The heat of welding had distorted the can slightly, and we had to hone out the bore so that the bumpstop could fit back in. Remove your bumpstops from the mounting cans before you weld the mounts! If you leave them in, you might not be able to remove them after welding.
The pinch bolt bores needed...
The pinch bolt bores needed some cleanup, too. A tapered reamer made short work of the task. For jobs like this, tapered reamers are easier to use than drill bits.
When you’re welding up a small...
When you’re welding up a small closed space you’ll want to drill a vent hole somewhere to let hot air escape in an orderly fashion instead of through your weld puddle. This vent hole is actually bigger than necessary.