Crazy frame flex! How do I fix this?

[wasted wages]

In the OP's case, "fixing" the body mounts means you are now expecting the body to control all of that flex that it now exhibits. The body is nowhere near strong enough to do what is asked of it with a stock frame, thus broken hard top seams, popping roof panels, and impossible to open doors, even with very mild off-road use.

I've heard of ( but never tried ) putting old valve springs on the bottom of the body mounts ( along with longer bolts) to allow some body flex...

sounds plausible....

Me... I like cages to keep everything nice and square....

When I drove my K5 on the street with the supercharged BBC, the front end of the truck frame flexed so bad that a full throttle stomp at the traffic light would cause me to turn the steering wheel at least a half of a turn, just to make the truck go straight across the intersection....even with crossover steering...

Both front fenders had a crease in them from all of the flex....this was all with new poly mounts from front to back.... The more I tried to stop it from happening the more the truck creased and cracked body parts and started to tear itself apart....the cab was split behind the drivers door near the roof pillar and the front two cab mounts had torn away from the cab floorboard when I decided to cut it up and build it into a truggy...

 

[dyeager535]

With everything else stock, poly body and shackle/spring bushings should make things worse in terms of frame/body movement. Any deflection transferred by using harder materials is transferred to the frame or anything connecting (like shackles) and that's just not good for the body.

Pretty hard to definitively quantify any differences, unless it's massive like a boxed frame or cage, but it *seems* that my poly body mounts make the roof pop in pretty mild situations, where it didn't when I had the stock rubber ones in there. It popped even with the rubber mounts, it just took more suspension movement to do so before.

As to springs, I'm pretty sure that idea is why GM used springs on the exhaust manifold studs. They knew movement was going to happen, and it must help. Even with good headers and stock supported exhaust, my collector bolts were continually coming loose.