GMC Typhoon & S10 Blazer 4-Link Installation
- Rear Pumpkin Plate – Qty. 1
- Rear Cover Gaskets – Qty. 2
- Upper Bars – Qty. 2
- 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. 6
- 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.
- Remove both rear shocks.
- Remove the frame cross member. This is held in from the factory with 4 rivets on each side, and has a parking brake bracket. In our experience the easiest way is the remove the 4 lower rivets and cut the outer lower 6” or so away, giving access to either cut the upper flush with the frame, or remove the top 4 rivets. This is the worse part of the job, so be glad it is first.
- With the old cross member out of the way, the next step is to move the brake line where it attaches to frame and goes from hard line to rubber. The preferred option is to drill a new 5/8” hole inboard ~2”, cut off the excess bracket, and reinstall the line and bleed the brakes. If you do not want to bleed brakes, it can be bent out of the way of the upper bars.
- The new cross member can now be installed. Prior to installing the new cross member you will need to slot the holes in the frame. It may be helpful to install the new cross member first to get an idea as to how much (each truck varies).
Tip to installing cross member: The best method is to install at an angle with the passenger side back, drivers side forward. It is a tight fit, but once you get the technique down should slide in/out without much effort.
- With the new cross member installed,
- Time to get the drain pan and pull the rear cover. Drain and clean the rear cover and rear axle. When things are clean and dry the new upper bar mount can be installed. This will be sandwiched between the rear axle and your current cover, with a gasket on each side. New longer bolts are supplied.
- With the upper bar mounts now in place, remove the u bolts from the stock leaf springs.
- With rear axle now just sitting on leaf springs, compress the 2 upper bars to minimum length and install in the upper mounts. This will require a bit of pushing the rear end forward or back, and possible extending of the upper bars. Leave the lock nuts on bars loose, but you can tighten the 4 5/8” pivot bolts.
- Working on 1 side at a time, remove the stock leaf spring from the vehicle. With spring removed, the new lower bracket can be installed with the new u-bolts. There is a left and right. Be sure the shock mounting boss sticks toward the inside of the vehicle.
- With lower bracket installed, the front leaf spring pocket can be drilled out to 5/8”.
- The lower bar can now be installed. The greaseable joint goes in the stock leaf spring hanger with spacer on the inside.
- Repeat steps 9 thru 12 for other side.
- Tighten 4 pivot bolts.
- Fill rear axle with fluid.
- 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 accuracte is dimensions from the front wheel back. Obviously you want both sides to be equal so the vehicle doesn’t drive “sideways”.
- Second step involves checking 2 things at once. First is side to side of the axle. Measure how far the tire sticks out/in from the body on each side. The 2nd part of this adjustment involves the pinion angle. Under the most extreme acceleration you want the engine and rear axle to be parallel as seen in picture below. In order to achieve this, you will typically point the rear down (as aimed forward) 1-2 degrees at ride height.Both the pinion angle and axle side to side location is done with the top angled bars. For example if the axle is shift to the left you can either extend the left upper bar, or shorten the right, or maybe a bit of both.Pinion angle is also adjusted with top bars. A bit of thought and measuring of both dimensions prior to adjusting will most likely be needed the first few times.
- Once everything is setup correctly, make sure to recheck all bolts and locking nuts on all the bars.
Tuning your JSM 4-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.