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.
Initial mock-up revealed that...
Initial mock-up revealed that the edge of our bumpstop mounting plate was going to cross through the middle of a factory frame hole. We needed to plate over the hole. To maximize strength, we decided to plate the frame top to bottom behind the bumpstop. Just as before, chipboard made a fine template.
We’ve used our Swag Off Road...
We’ve used our Swag Off Road benchtop mounting system and Milwaukee portable band saw extensively, and this combo came through for us once again.
The frame contours in our...
The frame contours in our chosen location, so we made the doubler plate match the contours using a ballpeen hammer, a short section of railroad track (used for an anvil), and a bench vise.
This photo shows the doubler...
This photo shows the doubler plate welded on. After our earlier measurements, we found that a machinist’s 1-2-3 block (rotated to the 3-inch position) was an ideal spacer to hold the axle-to-frame distance we needed.
We tried unsuccessfully to...
We tried unsuccessfully to bend the base plate to match the frame contour. To close up the gap between the flat plate and the contoured frame, we welded a skinny strip onto the base plate.
The Synergy strike plates...
The Synergy strike plates are built from 1/4-inch-thick mild steel, and are cut and formed for three-inch axle tubes. Sanding a chamfer into the ends adapted the strike plates for the 3-1/4-inch axle tubes on our custom Currie Fab-9. The middle of the Synergy strike plates should touch the tops of the axle tubes.
We spent some time getting the bumpstop and strike plate into ideal positions before tacking them in place. The goal is to minimize lateral scrubbing between the bumpstop’s contact tip and the axle strike pad as much as possible. Considering all the different angles the axle will cycle and articulate, lateral scrubbing can’t be completely eliminated, so minimization is the goal. The bumpstop’s angle is roughly 90 degrees to the lower suspension links at full compression, and the strike pad is 90 degrees to the bumpstop’s body.
One bumpstop mount, fully...
One bumpstop mount, fully welded. This shows the driver’s side; a mirror image was created on the passenger’s side.
The strike pad is easy to...
The strike pad is easy to weld on. One weld goes across each end, and a short bead is laid on each side at the top of the axle tube.
Our Kartek nitrogen regulator...
Our Kartek nitrogen regulator was pressed into service, putting 200 psi inside the bumpstop.
Check out the generous distance...
Check out the generous distance between the bumpstop and the tire’s sidewall.
An easy place to mount the...
An easy place to mount the bumpstops would have been to place them inside the coil springs, but this mounting position has been known to bend axlehousings. Bumpstops generate a lot of bending load so they should be placed as close as practical to the outer end of the axle.
We’re articulating through...
We’re articulating through a deep rut here. If we’d gone with a 4-inch bumpstop stroke we’d have less articulation, and we’d have bumpstops that frequently contacted the strike pads even over minor hits. The bumpstops have nylon contact tips, and you can hear them when they hit the strike pads. Shorter-travel suspensions should use shorter-travel bumpstops.
The markings show that lateral scrub is indeed minimal. This is what we were hoping for.