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.

I was very lucky.

Yes I've read reread Herbs articles,his Fiream book,and chassis book. Ideas.

This thread prompted me to check this 72 Firebird I just bought a month ago. Sure enough it was out about 1/8". I found a socket that fit perfectly in the index hole. I loosened the 4 bolts on the frame to body mounts and pulled the body forward 1/8". I actually was very easy even with the engine and tranny in. I supported the frame on the lift and was done in less the 1/2 hour. The body bushing are global west Solid Aluminum.
One thing that I notice is and maybe is to do with solid mounts. There is nothing to hold the body in place except for using frame connectors. Maybe the rubber bushings hold the body to the frame more secure. What am I missing here.? There are no fenders or hood on the car at the moment. The car is being restored by myself.
I watch Doug at Global west talk about these solid body mounts. Here is what he says.
Global West's Interloc body mount bushings are solid aluminum, self-locking mounts designed to eliminate frame-to-body slippage in classic muscle cars. Engineered to replace factory rubber mounts, they sandwich the frame, making them highly recommended when installing Global West Subframe Connectors.
Now this 72 I bought has Global west frame connectors that were not welded or bolted to the main frame when I purchased the car. I have since bolted them to the frame after I did the alignment. I guess these unibody cars are really held together by the radiator support through the fenders and wheel wells from moving around. I have Hotchkis frame connectors on our 76 and 68 without any issues.
I mostly posted this for info, but was looking for opinions/thoughts on the subject. I guess what I realized from this post by Jhein is that anybody with these unibody car and having upgraded H/P may want to look at installing frame connectors. A big Thank you to Jhein for posting his experience.

Seems like it would move a lot easier without the fenders in place. My old rubber bushings had a steel backing plate that mated to the body, so that contact was metal to metal. Then the bushing contact to the subframe was rubber to metal.

If your connectors weren't bolted or welded, what was holding them in place?

My parts are trickling in from PTFB. I just got the subframe connectors a couple days ago which is convenient since they are next to go in. I'm going to bolt them in for now but eventually, I think I'll have them welded.

The final chassis mod will be the PTFB pro G-braces. Then the subframe will be pretty well locked in place.

OK, got the subframe bushings done. I put the car on wheel blocks (don't ask me why I didn't do that before...)

I got the right and left diagonal measurements to 1/8" and front to rear on the same side are exactly the same. All my panels are unchanged including the hood. I then test fitted the connectors.

A couple things about the aluminum bushings. The floor pan crossmember surface isn't perfectly flat and not exactly parallel to the subframe. So the bushing doesn't make full contact all the way around. There's a small gap at the rear of each of the rear mounts. Also, the bolts on these are much smaller diameter than the ID of the bushings. So when you tighten them down, the bolt moves off center based on the previously mentioned alignment issue. Seems like maybe that's done intentionally so that the bolt will move and not the bushing? Don't know. Hopefully this is not a problem. Also thinking that I'll need to check these periodically once I start driving it. Although, once the connectors and the G-brace are in, I don't think anything will be able to move much at all.

https://i.postimg.cc/HrDg1v7J/IMG-0289.jpg

https://i.postimg.cc/qtQVnkD2/IMG-0288.jpg

https://i.postimg.cc/YLGJJQrV/IMG-0287.jpg

https://i.postimg.cc/14kT8nRv/IMG-0286.jpg

https://i.postimg.cc/56zhg5kt/IMG-0284.jpg

Question about the subframe connectors. Is there any reason I should, or should not, install them as far forward as possible? That is to say with the forward end pushed up tight against the subframe, or should I leave a small gap? Or does it not matter? I mentioned that I may get them welded, but that's not a firm decision. PTFB instructions say that welding is optional, especially if you have solid bushings. So maybe it's better to not weld?

Here's a link to the connectors in case you're not familiar.

https://www.pro-touringf-body.com/pr...ame-connectors

They were being held in place as they get sandwich between the frame and the body mounts. Haven said that I believe the body moved a bit during transport as the car was on a rotisserie. But even being sandwich doesn't keep everything solid. That is where welding or bolting them in is the final step to being secure. The previous owner of the car had passed away before finishing the upgrade.

I'm curious on the brand name of the body bushings you used. I don't really have an opinion on the bolt being able to move around in the bushing. I would have thought it would have had a more interference fit. The Global west ones I have installed don't move around like that. I can remove one and post a few pics if you like. Once the frame connectors are in place and secure, I can't see anything moving around after that is done.
As far as the frame connectors installation, you could leave yourself a small gap in case you need to tweak things. In my case I was extremely happy I was able to move the body forward 1/8" to line things up. The one thing I did do was leave the sockets I used in the body alignment holes on passenger and drive side and tightened and torqued the 4 bolts in body mount bushings. I also drilled and secured the frame connect before remove my alignment sockets. But I can't see anything moving around after frame connectors are installed. To weld or bolt them in is a personal preference. It's nice to be able to remove the frame in the future for whatever reason. The welds can also be cut off in the advent it's required. I have all 3 cars bolted in. In my opinion, the frame is bolted to the body through the bushings and not welded, so having the frame connectors bolted is secure enough I'm thinking. Where is it gonna go! I think the key to bolting the frame connectors in is to drill the correct size holes for the bolts and use 1/2" bolts with nylock nuts.

Thanks for posting all of this information. You seemed to have purchased all the same parts I have but are farther along on the process of installation. Thanks. 😊

I felt the bolt being tighter in the bushings keeps the subframe located better, no chance for shifting. I have a similar set of bushings I got to those still new in the box!

They are PTFB bushings

Here's what I think about this whole subframe mounting system. I've always thought it was not the greatest. Having actually worked on it, I feel that way even more so. My car was restored in 2012. It was not driven until I got it. It has about 10k miles since the resto and the rubber bushings already had significant wear and deformation. So there's that. Then the fact that you can move it around so much is interesting. I guess maybe that's for in the event of collision damage? Anyway, I guess that's why all these mods exists.

As far as the rubber bushings being more secure, that's an interesting question. They're large, soft rubber so they're designed to flex. But, being rubber, they're able to conform to irregularities and imperfections in the fit between the frame and the body. So they can flex, but they probably won't move. Alternatively, the solid bushing can't flex but maybe more likely to move if the forces are great enough? I definitely agree that if you install solid bushings, the subframe connectors seem like a really good idea, almost mandatory. And similarly, I think if you have rubber bushings, the connectors may not be as good of an idea?? The amount of wear that I had on my rubber bushings after just 10k miles demonstrates (no surprise) that kind of forces and flexing that happens there. But, who knows how these repo rubber bushing compare to factory bushings as far as stiffness and durability?

There are urethane bushings if you want something stiffer than factory rubber that might last longer.

I had a spare bushing from Global west, so here is a pic of it for reference.

I used the GW aluminum ones on one my first gens, they worked and didn't slide. On a second gen I set up for a friend for autocross, we actually used no bushings, bolted the frame up, and welded the frame to the body. Dropped the car almost an inch with no change in geometry. Fabricated frame connectors, and really stiffened up the whole car. I've never had a subframe shift unless it hit something, I use the torque specs for whatever bushings are installed.

I was just speaking in hypothetically. I don't really think the solid bushings will move. They're clamped down pretty tight. They are definitely high stress points though. But with the subframe connectors and G-braces the forces there will be reduced significantly. The whole subframe should be pretty well locked into place as much as possible without welding it to the body as mentioned.

I used thinner bushings and then the Herb Adams kit that dropped out the core support one then gradually thinner. Neither were great for a Shaker hood and fan to shroud clearance.

I was held up a bit because I wanted to talk to Dave at PTFB about these fitment issues before I proceeded. He was at the Pigeon Forge Bandit event so I couldn't reach him until this week. Anyway, everything is at it should be with the bushings. So I got those torqued down and I got the left side subframe connector in. Had to drop the rest of the exhaust so I could get the holes drilled on the inside but that came out pretty easy. Anyway the other side should go faster. Still waiting for my leaf springs and control arms. But I should be able to start on the exhaust once I'm done with the other connector.

If you look at the VSE guide, it mentioned you have to trim the inner fender wells and shroud to do the drop bushings.

Yes, it impacts the shaker fit, but there too is a solution, as I recall it's to trim the air cleaner base, but I would have to look it up again. Personally, I fitted the shaker to the hood, which is one of the options. Yeah it doesn't 'shake', and it does sit higher in the hood opening, but in the end I found it was a better solution, you can swap intakes, filters, carbs, etc, without having to worry about fit.

I've seen where folks have sectioned the shaker scoop where it look 'normal', but after a little time you can deal with it sticking up a little higher.

I rolled my fender lips too, and it allows wider tires/wheels. That gap between the fender & well can be filled with sheet ABS and/or rubber to help with keeping road splash out of the bay, but it has never been an issue for me. I may actually end up doing it this time around but will cross that bridge when time comes.

Lowering the body improves roll center and helps with aero, which is needed over say 130-140mph, for stability. If that's not a concern then you can skip the mod.

There are 2 height drop bushings, and it did the max drop. The one in between doesn't require the mod, so choose your poison.

EDIT: I can dig out the page that shows the fan shroud trimming, but it's very similar to the well trimming.

EDIT 2: Found it, attached photo.



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Anti-Squat, anti-dive explained:


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Thanks for posting.

One thing I haven't mentioned is my tires. I've had sticky tires on the rear before but when I put them on the front (I think it's a 200 TW tire) it did some sort of undesirable things. First, I could feel all the imperfections in the road surface. Any running low spots/channels, whatever they may be called tends to pull the tires into them. It felt like it really changed the way the car felt when trying to go straight. Also, it really seemed to amplified all the flexing that's possible in the subframe. I really didn't like any of it very much. So we'll see how it feels once I'm done with all these chassis and suspension mods but I may end up going back to a less sticky tire on the front.

Good suspension setup with a proper alignment will cure that. I also run 200 TW all four on A PTFB full comp suspension.

I'm glad to hear that because that's the suspension I'll have when I'm done.

Not sure if it's a correct term or not, but have always heard that 'condition' called 'tramming'.

This also can be elevated when you run 2 different types of tires on the front than the rear. Lots of people mis-match due to trying to use the widest tires possible, and some brands don't make tires in all sizes. Or by running non-radial street stickies in the rear.

I've run drag radials front & rear several times on a couple cars, and did experience some tramming, but it wasn't too bad. But most are a handful in the rain.

I've run summer tires into the cold months and those were like driving on ice when it got cold out.

Since I tend to drive my cars a lot and in different seasons I only run all season tires now, and live with the fact that it will suffer from a stand-still. I generally get about a year out of rear tires, and 2 or so years out of fronts. With drag radials I got half or less than that.

It's best to have a second set of tires if you plan on doing a lot of road courses or autocross, you save money in the long run.


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Yes, thank you, tramlining. I couldn't remember the name for it. It seems I did almost everything possible to make it worse. Wider, lower profile tires with a soft compound and no improvements in alignment, suspension or chassis (yet) to help offset any of that.

https://www.tirerack.com/upgrade-gar...ses-tramlining

I guess 'tramming' is a slang of tramlining, and couldn't remember the correct term.

Great link, thanks, I'm going to copy and save that for future reference!

Global West and Speedtech have good recommendations for alignments to follow, FYI.



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