I've had a shimmy (35mph, which is weird) in my front suspension for a while now. I'm now almost sure it's the rear 4 subframe bushings, which were completely rotten out. I've had it on jackstands for quite a while. I replaced the rear transmisson mount, reinforced the frame (which was super rusty), and replaced some worn suspension stuff (sway bar end links, a tie rod end).

I sourced new rear end pieces (the two "horns" that hold two bushings per side) for the subframe from a junkyard, by cutting them off a full subframe (which I now realize might have been a mistake, maybe should have got the whole thing). The donor subframe was laying on top of a 00-05 Bonneville but I couldn't get the drivers door open and it didn't have a manual so I don't know what year it was, if it was a Bonneville at all. It's also possible that the donor was from a different 3800 - there were a couple of Grand Prix, Aurora, and other 3800s in the area. The ends fit almost exactly on my subframe, so if it's different, it's not very different.

The ends were cut just behind the rear sway bar mounting bolt, and seemed to be shaped the same as the original part, as far as I can tell, but since the original subframe bushing mounts were completely gone, it's hard to tell if they were exactly the same.

According to a few posts post1 post2 the Dorman 924-044 is the right part to replace the subframe bushings. The parts databases say it's incompatible but don't give an alternative part; I tend to trust this forum for stuff like this.

I just can't get the lower parts of the Dorman bushings in. They're about 0.15 inches too big to fit in the holes in the new subframe parts, and there's a steel band running around it so it doesn't compress. I've tried to look at similar bushings but can't seem to find any dimensions for any of them.

Are there any similar subframes or anything that I might have confused with a Bonneville one? Or are there different sizes of bushings between model years? Or anything else I might have missed?

I have personally used the Dorman 924-044 on a 2000-2005 Bonneville (can't remember the year, it was a customer car). They fit and worked great.

If I were you, I'd simply hit the inside of the hole on the subframe with a die grinder until they fit. You're probably never going to have to deal with it again.

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Andrew - owner/operator of Bonnevilles Unlimited

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Sounds like you still have meat on the hole openings, so you can make them fit like Haro said.. consider yourself lucky the subframe isn't bored through ...otherwise onto the hockey pucks lol or replacement sub. Dorman is a one size fits all... if I remember the OEMs were color coded by size to fit the specific locations and you will never get the upper steel caps and hardware for what you paid for the Dormans. Don't think any of those still exist... maybe some parts direct dealers.