Does anyone know if the front strut assemblies from a 97 Lesabre will work on an 89 Bonneville? I know the bolt pattern in the engine bay is the same. I didn't know if the geometry would be off. I know the actual struts themselves are different, but didn't know if I could just swap the entire assembly out of the 97 and bolt it on to the 89 without any problems.

I'm not certain but I would suspect that they are not interchangeable. Mainly based off of you statement that they are different.

There are some parts that are worth taking chances on for down fitting/adapting. Brakes, suspension parts, fuel and wiring harnesses are ones that I would not.

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I was able to use the strut tower brace from the Lesabre on the Bonneville. It bolted right on. I do know that the REAR struts are the interchangable. Just didn't know about the front. I am aware that the strut design changed in 1990 and I believe most cars from 1990 to 1999 share the same strut design.

I used the Strut/Spring assemblies out of a '92 Bonneville on my '90 LeSabre Limited.
They bolted right in. The springs from the '92 Bonne have more coils, but they are probably very close to the same psi rating as the 89-90 front coils.
And I believe the geometry is the same. I have not had any with tire wear. And they ride OK.
My struts on the LeSabre were probably original, and they were just boating like the SS MINNOW. So I had this rusty '92 Bonneville, and decided I'd pirate the struts off all four corners before I junked it. Some kid bought it for the same $$ I payed for it before I got the back struts swaped. I'm sure they would have fit too.

There is no reason to think your '89 is any different than the 1990. At least the struts.
The spring rates might have changed slightly from one year to the next, but it'll all bolt together, I think.

I just remembered that the spring pocket on the 92-99 front struts may be welded lower on the strut than the 87-91 struts. That is so they can accomodate the taller spring.
If you use the ENTIRE Spring/Strut assembly from the '97, it will work. But you probably would not be able to put the earlier springs back on the late model struts, or vice-versa.

So how did those springs and struts work out. Ride and handlng wise. There is a 92 up Bonne in the JY right now. My 1990 88 is riding like a boat in the front right now.

The handling is hard to say if it got any better, since I don't really drive the car fast.
Actually there is notable body roll, but this car doesn't have FE3 suspension, so it probably wasn't much different when it was new. And the '92 Bonne springs did have 130K on them. They were considerably fresher than my '90 LeSabre'* with 190K, so I went for it.
But the ride does feel alot nicer. There is some boating still, due to the rear struts still being original. But the front settled out fairly good. It was boating and nose diving pretty bad before I swaped the front springs/struts.

After I drive my '88 T-type for a while, then get back in my Limited, it seems like the Limited rides like dream.

Looked in the trunk today on the poncho. FE1 , but anyway the eng was sold and the guy who pulled it cut it out with the cradle, strut/brakes and sway bar. So that'* that. My friend was upset, but what the hay. I'll still get the 17mm rear sway. I want nice riding stuts but not too soft. My rear KYB'* ride nice , not to firm not to soft. Free, newer struts would have been acceptable. My frots absorb the bumps but dont rebound fast enough to prevent them from continuing to rise. I don't know if I'm explaning myself clearly.

Well, finally got front struts, rear springs and 22mm sway. All off a 97 Bonne SSEI. Read somewhere on here that the rear springs will raise the rear 1". Hope not unless the front comes up some. We'll see. Still looking for a 32mm front sway, but can wait till after rear is done.