Fixing the Weakest Part of Your Frame
When we were trying to get our Blazer ready for this year's Easter Jeep Safari at Moab, we realized our frame had the classic cracks where the steering box mounts to the frame. Knowing that we couldn't fix something like that properly on the trail, we gave Autofab in Santee, California, a call. The company sent us one of its steering box gusset kits. While on the phone, they also gave us some frame strengthening tips to pass along that'll work to make this and other 4x4s' frames stronger.
Where Frames Break
Big tires and off-road use put a 4x4's frame in a world of hurt. This Bronco tried to twist the steering box off the frame--like a cap off a Coke bottle--until a few emergency weld beads were laid down to get it back to camp. Trucks that use crossover steering like this Ford stress the frame perpendicularly to the main rails and try to punch the box off the frame. If your truck uses a drag link that moves parallel to the frame (fullsize GM and Dodges, among others), it is constantly trying to shear the steering box off the frame. Because most boxes mount with Grade 8 bolts, the frame is typically the weak link and will wave the white flag of failure and crack, slot, or completely break through before anything else does.
Why They Break
Tires on 4x4s are big, pitman arms are small. Consider that even a 31-inch tire has a radius (lever) of 15 1/2 inches, while a pitman arm is 8 inches at the most. The reason solid-axle GM trucks are one of the worst offenders for broken frames is because GM used a short pitman arm and short steering arm on the knuckle, which results in very little leverage on the tires. It can take a lot of force for the steering box and pitman arm to turn a 35-inch tire! Just consider how big the tie rod ends are on these trucks--it's clear the engineers knew how much stress they were creating. If GM had always boxed its frames like on the '88 IFS truck frame shown, we probably wouldn't be writing this story.
Autofab Saves Our Butt
Rather than go through all the work of trying to box our '82 GM frame, we knew we could reinforce it with this Autofab steering box gusset. The gusset bolts in with new Grade 8 bolts to triangulate the driver-side framerail to the front crossmember. Only one 1/2-inch hole has to be drilled for it to bolt on. Hit it with a quick coat of paint and use some thread lock on the bolts and you're done. Consider this piece mandatory equipment for '73-'91 solid-axle GM trucks.
Get the Right Kit
Autofab makes two GM steering box gusset kits: SBGK100 works on '73-'82 GM trucks, SBGK200 works on '83-'87 pickups and '91 Suburbans and Blazers. If you have this factory-installed gusset (below) held in place by four bolts like our '82 diesel Blazer, then you need to use SBGK200. There is even a kit for two-wheel-drive GMs that you can tell your prerunner buddies about.
Why It Works
The Autofab kit (B) works by spreading the load of the steering box out over a larger part of the frame and triangulates with the front crossmember. Autofab recommends this to help prevent the steering box (A) from actually trying to buckle the driver-side framerail. For the ultimate in frame upgrades Autofab also suggested we drill out all the old rivets that hold the crossmembers and framerails together and ream the holes for snug-fitting Grade 8 bolts. Manufacturers would do this from the factory, but rivets are cheaper and faster. Nobody we talked to thought welding the crossmember to the frame was a very good idea.
What If Your Frame Is Already Cracked?
All the braces and weld-on plates in the world aren't going to help you if the frame is already cracked. To fix the frame correctly you need to do the following.
1. Find all the cracks and drill stop holes at each end.
2. Grind out each crack from stop hole to stop hole into a V-shape groove as shown. The V-groove should penetrate almost all the way through the frame.
3. Use a MIG or a TIG welder to fill each V-groove and stop hole with new metal.
4. Use a grinding wheel to remove any excess weld until it is flush with the frame. This will eliminate stress risers and make the repair invisible.
5. If the bolts that hold the steering box to the frame have ovaled out the frame, use the bolt as a guide and fill in the hole with your welder until it is round again. Do not weld up the holes and try to redrill them! Again, grind down all welds so they are flush with the frame.
6. Paint the repaired surface and bolt the power steering box back on with your Autofab gusset.