body flex

[hefty53]

i have a 1975 chevy blazer 6" suspension lift, 3 " body lift, 38.5x16.6x15.5 super swampers, full roll cage, tbi motor, 14 bolt in the rear and dana 44 in the front. when i drive on the highway i expect to have vibrations, but i seem to get alot of body flex. I can watch the windshield to roll cage gap get bigger and smaller. I can also see the top of the door seperate slightly from the back of the body. also when the truck is sitting the door gaps are weird, the exact opposite of what bad hinges look like. my rockers are not in great shape and my rear fenders are shot but the rest of the truck is perfect and solid. could it just be the rockers, is this normal, or do i have a bigger problem.

by the way it doesn't seem to make much of a difference if the top is on or not.

 

[k20]

check your body mounts, bet yours are shot.

 

[hefty53]

i put brand new polyurethane mounts in last winter with the body lift

coold i have loose mounts, cracked frame hidden near mounts or driveline mounts or could some structural part of the body be shot?

 

[BadDog]

On the full top blazers, the rockers and rocker boxes (structural boxes behind the rockers) are responsible for holding the door opening dimensions. My guess is that your rocker boxes are rusted out. However, a full cage tied into the front correctly shold hold those dimensions as well. If the rocker boxes are weakened by rust or damage, the easiest fix might be to improve the tie in on the front a-pilars.

Also, body lifts are notorious for causing body problems including cracked body mount surfaces on the body which could lead to excessive flex and bending, so that is something else to check. I've seen the body mount pucks actually break through the body mount surface almost as if punched through. Basically, at first glance it appeared to be ok, but the body was just suspended over the lift puck which was setting under a hole. When flexed, you could see the puck actually moving into the body or pulling away! In general, I have no use for body lifts...

 

[hefty53]

i have the cage welded to a 4" x 5" plate which is welded to the floor right before the floor starts to slope up. the next tie in on each side is in the stock roll bar location.

 

[BadDog]

I don't much like welded to the floor due to effects of HAZ on the sheet metal, but that's a different issue as long as it has not cracked there already. Might weld a kicker onto the tube to triangulate the cowl area to the forward tube, tying in up near the head light dimmer with a plate bolted through the floor. There is also a bolt on the inside of the dash shell that you could use with a strap tied to the front cage leg. Something like that would make the firewall/cowl area more rigid.

If the rockers and boxes are in fact the problem, due to rust or whatever, there is also the option of replacing them. Those pieces are still made and available from several places including LMC and you might even find them at a helpful dealer. You would be surprised how cheap some of that stuff can be even from a dealer. No idea if they still have any stock.

And finally, you could replace the rockers with what we call “rock sliders”. Basically, cut all the old rocker out below the door deal (hopefully can be salvaged) and then graft in a piece of (typically) 3” wide by 2” (or 3”) tall square tube with around 0.188” wall thickness. This replaces the rigidity lost to the decayed rocker boxes and gives you a strong surface to fall onto and “slide” on when wheeling over rocks or ledges. Of course you might need to get creative to make sure it’s tied in sufficiently to stabilize the body. Best bet it is to fab tie-ins for the cage to the new rockers as well as tying it to the frame.

Just shooting from the hip here, but those are the kind of things I would be looking for.

 

[hefty53]

what are your thoughts on tying the role cage into the frame, that was the original plan when i built the cage but some one felt that if the body flexed it could rip the sheet metal up where the cage attached and went through so i never connected it to the frame.

in terms of my rockers they are only bad at the seam which connects it to the rear body panel.

the boxes look good but some one put underscoating on them so i have no idea what they look like inside.