Subframe Bushings
 

Went out to do what I thought would be a fairly quick and easy job and ran into a problem. The subframe and body have shifted and there is about a 1/2" misalignment. The Subframe has moved forward relative to the body.

Don't really know how or why that happened. Here's my setup, the car is on four jack stands. Two on the front sway bar and two under the rear axle tubes. Could it be because the weight of the front is too far forward, maybe should have had the weight on the wheels?

Anyway, I'm obviously open to any advice, but I think if I use a come a long and attach at the rear end and maybe the lower control arm, I can pull it back into place. If I did that, I'd lift the front using a floor jack so that it can move on it's wheels.

https://i.postimg.cc/44tdmyZ5/IMG-0258.jpg

https://i.postimg.cc/gcRJnjdV/IMG-0259.jpg

You can take a ratchet strap and hook it to the frame, and then around the rear axle. Loosen the bolts and crank it backwards.

That said, I haven't had a 2nd gen subframe move on me while doing bushings. How's your sheet metal looking? Did any gaps change? Sometimes when you swap bushings on the frame, you'll get funky door to fender gaps unless also replacing the radiator support bushings.

I will say, I have aluminum mounts in my 71. They're stiff (in a good way).

Have a look at your fender gaps, usually when the back 4 mounting points are misaligned it moves the core support as well. Core support bushings bolt to the subframe, before shifting anything you need to look at the body gaps. When you move the frame, you don't want weight on it, support the car at the body. If the front body panel alignment is good, loosen the core support bushing bolts at the frame before moving anything. With the weight off the frame and the bolts loose, it should not be difficult to shift the frame where it needs to be. A round prybar up through the alignment holes should be all it needs.

Ditch the bushings for some that are interlocking, and you will never have this issue again.

I suggest the Global West ones, I've used them before, but there are others that may be less expensive, like PTFB.

https://www.globalwest.net/product/f...9-global-west/

https://www.pro-touringf-body.com/pr...-body-bushings

Can't tell by pic but those look like the standard height ones. Unless you want to go thru additional panel alignment, it's easier to use the standard height when you source the new ones.

One comment on the solid ones, you have to at least run subframe connectors, if not the cowl braces. I still have a set of VSE ones, but several others make them now, again, PTFB has them:

https://www.pro-touringf-body.com/product-page/g-braces

That hole you see in the frame, and the one in the body, are the alignment holes, but suspect you already know that. A large drift punch, or two, can aid in the future alignment, after you get locking bushings. The locking bushings will inherently align it to some degree, the drift will take care of the rest.

You can pretty much eyeball it too.

Loosen the core support bushing bolts when you shift it, and the fender & inner wheel well to body/frame bolts. Open the doors like half way too to prevent gap contact. Leave the hood up. And of course, watch panel gaps as you close.

Some kits don't include the core support bushings, it's best to use the matching ones.

This is actually a common problem, and is exactly why now interlocking ones are available.


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Thanks for the replies. I'll try to respond to everything here all at once.

These new bushings are the PTFB bushings. I have a complete suspension and chassis kit trickling in from him including the subframe connectors so I've got that covered.

Seems a little strange to me but in spite of the movement between the subframe and the body, all the panel gaps and alignment seem unchanged. Must be that the fender is just stretching and flexing.

Right now, with the jack stands under the front sway bar, the subframe just naturally comes away from the body slightly when the bolts are removed. There was enough natural separation that I just had to pry the subframe away from the body slightly to get the old bushings out and the new ones in. So the body is not really resting on the subframe.

Tomorrow I'm going to try a couple things. I think that having the full weight of the front on the sway bar is creating a moment which is causing the separation and the shift. As SRGN suggested, maybe if I lift the body just a little at the front end of the pinch weld I can relieve that which could correct everything. Also, I think that just using a come a long between the subframe and the rear and, I can pull it back into alignment.

Dam, That's not good. There is one thing in my opinion about these uni-body cars. Never support that front end like you did off the front sway bar. I puts alot of stress on the center of the car. You also have an IA2 block which is very heavy. At a minimum use stands under the lower control arms. I have wooden blocks made for the purpose. Also, never put blocks at the front off the front frame when it attaches to the body as the front end is way too heavy and will cause a lot of flexing. Sorry to see that happen to you.
Like mentioned tie the front frame to the rear leaf spring perch or the frame rails. I have Hotchkis on my 76 and Global-west on the 72 Firebird. The 72 also has the solid frame mounts.

The first picture looks like your mount bolt is crooked. Not sure how that is even possible unless the bolt was somewhat loose or at least not torqued. When I changed my mounts, I had to pull my carpet up and put a pry bar against the speed nut in the floor to stop it from turning and get proper final torque. One nut cage would not hold while torquing even though it felt tight while the nut spun past the rounded part, causing resistance. My thought is the bolts were zipped in at the factory, and the nut cage is a one-time-use design for tightening, making it difficult to torque a second time. After taking my cross measurements to make sure everything was square, obviously.

Could the bolt shank be bottoming out on the nut? Not likely, but it does not hurt to ask.

You can see the locating hole in the middle picture. loosen them all up a hair and get a BIG punch to slide up in the body hole from the hole in the frame to straighten it up. Might need a big pry bar to line them up then slide the punch or rod to line the two holes up.

I bought a similar set of those from Custom Works and kept them in the box! Second on the interlocking bushings!! Doug at Global even custom made me some lower halves years ago to grab more of the Moroso subframe connectors that slide under the bushing.

Yeah, I took that picture specifically to show the alignment hole. I tried prying it using the hole but it didn't really move. My plan is to change my lift points and hopefully that will improve it at least a little. Then, if needed, I'll use a come along to pull it back into alignment.

I think I usually did one side at a time.

When I did my body off, 2nd gen 40ys ago i saw that hole in frame and body and used sized pins for alignment. Then bolted ,fenders inner outer,core support etc. Worked ok. My 2cts

OK, that worked out better than I thought. After repositioning jack stands and using floor jacks for selective weight relief I was able to get it realigned. I had to use my come a long, couldn't do it with a pry bar. But, with the come a long it moved with very little effort. Nice thing was that I released the come a long before I installed the bushings and nothing moved.

https://i.postimg.cc/YSV2tm4K/IMG-0263.jpg

https://i.postimg.cc/R08Cvn3v/IMG-0261.jpg

https://i.postimg.cc/L8x60WRc/IMG-0264.jpg

https://i.postimg.cc/rFKD2cZF/IMG-0275.jpg

A couple other details. When I repositioned my lift points, it spontaneously moved everything back in the right direction. Also, while the come a long was effective it was total overkill. As suggested by 72projectbird a ratcheting strap would have been more than enough. But, when you just want to get it done, overkill is not a bad choice.

If I'm not mistaken, believe the captured nut in the cowl box actually has some play of the nut inside the captured cage.

I had the inner fender well out when I last did mine, and used a pry bar against the nut to help support the cage when torquing. It sux when the cage breaks.

I forget the value, but recall those bolts have a fairly high torque spec.

It's def not 'best practice' to jack the front up by the sway bar. Not only is there potential of bending the bar, but also the potential of stripping out the threads on the bar to frame mount.

With big tires or good grip, under heavy driving, that whole front clip flexes. A lot. Watch the hood gaps as you brake and go into a turn, and you will see what I mean.

It's kind of a snowball thing ones you start stiffening everything up, one fix exposes another weak link, etc.

In my case, and this may have something to do that I used the short bushings, once I put the cowl braces on, I would crack windshields. This mainly happened when I was 'walking' in & out of parking lot ramps at an angle, bc my car is very low. My only solution was at min a 4-point roll bar.

Tying in the front & rear frame horns help a lot too, there's a front brace that's available that goes between the frame and the swaybar. In the back, you can go stealth and reinforce the bumper, or make a brace that goes in trunk between the bumper mounts on the tail panel.

Tying in the frame rails may provide enough twist resistance to where you wouldn't need a 4-point, not sure bc I put a 4-point in already.

Morning brain-dump, rambling...

EDIT: Final note, the twisting can cause 1/4 panels to bend and get wavy, between the door/roof/rear wheel opening. You can see it on some cars.



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That 1/4 panel flex also shows up in the seam of the 1/4 & roof. If at all possible, when replacing a 1/4, use lead at the seam.


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Next is subframe connectors then G-braces.

I meant to say frame 'horns', not rails, but you get the idea(s).

PTFB makes the front tie in:

https://www.pro-touringf-body.com/pr...sway-bar-brace

It basically does the same thing as tying the front frame horns in.

If you look at the VSE Handbook, Herb welded a bar in between the frame horns, might have been on the 'Cheverra' or 'Silverbird' car.

That handbook is pretty much a must-read.


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I assumed your frame was already tied considering the IAII

Apparently I'm a little behind on things. :)

Glad to see you got it back in place. Thankfully no damage.