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Bumpstop Tuning

Posted in How To: Suspension Brakes on March 21, 2019
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Your suspension: Chances are you know what it does, and chances are you know most of the major components that make it do what it does. Shocks, springs, shackles, coils, control arms, radius arms, traction bars, sway bars, links, bumpstops, and the rest all play a role. When properly engineered, they work together and not against one another.

The problem is we like to add suspension lift to clear larger tires and add custom shocks to smooth out the bumps. Throw one or two parameters off, and everything in your suspension must change. We see it all the time—suspensions with longer shocks and added lift have left the factory bumpstops either nonfunctional or basically useless. The fact is these oft-overlooked suspension components are important in keeping springs working like they should, keeping shocks from being damaged, and keeping fenders from cutting tires. If a shock bottoms out, or a spring compresses beyond a certain length, either component can be irreparably damaged. If tires larger than stock compress too far and hit fenders, bumpers, or rocker guards, they can cause dents or even receive cuts, fatal to a tire.

Those scenarios are bad, but we are here to help you learn how to set up your bumpstops to prevent this kind of damage. Follow along as we look at a few different suspensions we’ve been playing with recently to fine tune the bumpstops on each to prevent damage to your rig and its parts.

The Derange Rover’s suspension works pretty well, if we do say so ourselves. The thing is built to be as low as possible while having enough uptravel to hit some bumps without constantly bottoming on the bumpstops. The biggest issues with the Rover was keeping the front axle out of the oil pan and keeping the tires out of the sheetmetal. The bumpstops keep the front axle from crashing into the oil pan while going fast, even if the factory rubber bumpstops disintegrate. It doesn’t look like the rig has much uptravel, and it doesn’t, but with lots of droop it flexes well (one side compressed, the other side extended) and what uptravel is there is well controlled by the Skyjacker LeDuc Series front coilovers intended for a Jeep JK.
On our Early Bronco we quickly noticed that the bumpstops would never work with the newly installed James Duff suspension. The front shocks had a little more than 10 inches of shaft showing. So if the axle compressed to full bump (both sides compressed) it could move up at most those 10 inches.
The problem is there’s about 16 inches of distance between the metal axle bumpstop and the frame (we assume the polyurethane bumpstops could fall off or disintegrate). We want the metal-to-metal bumpstops to reflect the 10ish inches of shock shaft.
The axle end of the track bar is in single shear (yuck), and the big old Daystar bumpstop has a witness mark from the track-bar bolt. Clearly the metal-to-metal bumpstops need to be moved closer so the polyurethane bumpstop can do its job.
Out back we have a similar issue as the front. To figure out a solution, we need to make the metal-to-metal bumpstop shorter than the amount of shock shaft showing. The shocks show about 9 1/2 inches of shaft. So at most the axle could compress those 9 1/2 inches to full bump.
The distance between the axletube and the metal bumpstop is a whopping 16 inches. These bumpstops may have worked when the Bronco was stock, but now they are apparently just for show.
Our solution for the front was to build some spacers to make up the difference between the available shock shaft and the distance between the two metal-to-metal bumpstops. We capped the 2x3-inch, 0.188-wall rectangular tubing with a 1/4-inch plate with a 3/8-inch nut welded in place. That way we can easily add more bumpstop to the top if needed for fine tuning or for tire-to-fender clearance.
Looks like we need about half an inch of extra metal-to-metal bumpstop. This gets us pretty close for now and can be added once we have the full weight on the rig.
For the driver side we drilled a 3/4-inch hole and welded the nut into the steel 2x3-inch, 0.188-wall bumpstop extension. This puts the track bar bolt in double shear. Adding a little 1/4-inch plate that will be welded in place helps tie together the two sides of the track bar mount.
Out back we are going to add these beefier bumpstops also from Daystar (PN KU09017BK). To do that, we made a plate that grabs the factory bumpstop mounts and has bolts for the new Daystar units. We also welded the plates in place to ensure that they wouldn’t leave prematurely.
We then welded two of these 8-inch-long, 2x2-inch, 0.188-wall square landing pads to the top of each of the leaf spring plates. We drilled another 3/8-inch hole in the end so we could add spacers if needed like we did for the front. In our experience you want to leave some adjustability in your bumpstops to fine-tune exactly when things bottom.
Our Samurai project lacks shocks altogether, so a quick measurement on both sides at ride height and then again while flexed (front and rear) lets us figure out the perfect length shock we need. We forced front and rear flex by placing the Samurai on three tires and lifting the fourth corner with the engine hoist and some chain. All of this helped us establish that we would need a shock that is about 22 inches extended and about 16 inches compressed with ride height at right around 19 inches. We sent that info to our friends at Bilstein to see what shocks the company would recommend. We’ll let you know more about that in another article when we test the shocks from Bilstein; that is, once we set up the bumpstops as we’ve shown here to prevent damage to the shocks.

Sources

Skyjacker Suspensions
West Monroe, LA 71294
318-388-0816
www.skyjacker.com
Bilstein
Poway, CA 92064
800-537-1085
http://www.bilsteinus.com
Daystar
Phoenix, AZ 85043
800-595-7659
www.daystarweb.com
James Duff Enterprises
Knoxville, TN 37921
865-938-6696
www.jamesduff.com

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