GMC Syclone & S10/Sonoma 3-Link Installation
- Rear Pumpkin Plate – Qty. 1
- Rear Cover Gaskets – Qty. 2
- Upper Bars – Qty. 1
- Lower Bars – Qty. 2
- Frame Cross-member – Qty. 1
- Lower Axle brackets – Qty. 2
- Rear Axle U-Bolts – Qty. 4
- 5/8” x 6” Shock Bolts – Qty. 2
- 5/8” ID leaf spring spacer – Qty. 2
- 5/8” x 3” Link Pivot Bolts – Qty. 4
- 5/8” x 5” Front leaf spring pocket bolts – Qty. 2
- 5/16 x 1” Rear Cover Bolts – Qty. 8
- 5/16” x 1 ¼” Rear Cover Bolts – Qty. 2
- 3/8” – 16 Crossmember Bolts – Qty. 4
Note: When installing the rod ends into the bars, use some anti-seize on the threads. Ensure no dirt is on the threads, and if the ends start to turn hard STOP, carefully remove and re-clean everything to prevent them from galling up and seizing.
- Lift vehicle up and be sure it is secure. If using a floor jack, PLEASE make sure jack stands are bearing the weight and are secure.
- Drain and remove the rear axle cover. Clean and install new center pivot onto rear sandwiched between the cover and rear axle.
- Install the front pivot onto the factory crossmember. This will require removing 1 bolt from the gas tank which will locate the bracket with the JSM logo facing rearward. Johnny joint will be located to the front.
- With the rear cover on, and front bracket on you should now be able to bolt in the shorter upper bar. Adjust bar so that is fits, later we will do the final adjustment. This is done early to help keeps things in place when removing leaf springs.
- Remove both rear shocks.
- Install the new rear watts link crossmember. This will bolt in where the factory shocks bolted. 2 new holes are drilled on the underside of frame to help provide additional support.
- With the rear carefully held up, you can now remove 1 side leaf spring. This includes the u-bolts, and front and rear bolts.
- The stock front hanger, will now need to be drilled to ⅝”. Install the new lower axle brackets to the rear axle via the new supplied u-bolts just as the factory leaf spring attached.
- The lower bar can now be installed, Johnny joint in the front, rubber bushing in the rear. The front will need a supplied spacer.
- Repeat for the other side.
- With all 3 bars now installed, install the aluminum JSM watts bell crank to the rear cross member. This includes spacers and a lock nut. Adding loctite is a good idea also. The 14” long bars with heims will now bolt on with the bellcrank being oriented vertical at ride height.
- Shocks can now be installed, depending on the truck some may require minor trimming of the frame for the upper cup clearance.
- Follow setup instructions.
- The first step after installation is to adjust wheel base. This is done using the lower bars. This can be done visually via the wheel wells, or more accurately from the front wheel back. Obviously you want both sides to be equal so the vehicle doesn’t drive “sideways”.
- Second step is to adjust the pinion angle. This is done with the top center bar on rear axle. You want the pinion angle to be -1 to -2 degrees from the transmission angle at ride height.
- Third is to center the wheels side to side. This is done with the watts bars, by changing the length of them the axle will move left to right. Adjust both so that the axle is centered, AND the bellcrank is vertical at ride height.
- Once everything is setup correctly, make sure to recheck all bolts and locking nuts on all the bars.
Tuning your JSM 3-Link Kit
Being this kit was designed as a bolt in kit, some compromises had to be made, mainly in adjustability. For the average user this actually is a benefit as it will most likely perform adequately as first installed. There are 3 rear lower bar settings available. A truck that is typically 2” lower than stock should use the middle position. The one nears the ground would be for the extremely low ride height, and upper stock ride height as a general rule of thumb.
If you find yourself with some traction problems, the 3 holes can be used for adjustment. A bit of quick overview is needed on the effects though.
If you look at the center of gravity of the vehicle, typically it will be near the drivers knee while seated. We then draw a line from the rear tire contact patch, up thru where the front tire contact patch is at the C of G height. This line is referred to as the anti-squat line. (grey)
With your pencil and scratch paper still handy a few more lines need to be drawn. Picture a side view of the lower bars (red) and upper bars (green). If they were to extend forward where they intersection becomes your instant center. The instant center is where the suspension applies horsepower into the body to move you forward. If this IC point is in front of the Anti-Squat line the rear will squat before going forward. If the IC is on the AS line, no movement is made. If the IC is behind the AS line the rear will actually rise up during acceleration. (look at a Buick GNX launch).
JSM has done a lot of research and reading on this in regard to AWD vehicles. It is hard pressed to find any reliable source on this in regards to All Wheel Drive vehicle. It is our opinion in an AWD application the IC needs to be near the AS line, and that was designed into the kit. Should you need/want more weight transfer the lower bar can be adjusted. As a baseline start with the lower bar parallel to the ground.