'90 reatta convertible suspension question

[Philbo]

I posted this over at The ROJ too, but thought I would ask here too.

 

Long story short, when I go over sharp bumps in the road, the car kind of "wobbles" not in the steering, it's more like the rearview mirror shakes back and forth a little bit.  I've inspected the suspension and everything seems tight. It's likely the shocks are shot as old as it is.  I have never owned a convertible before though, is this "normal" for a convertible and I'm just used to hard top cars?  It doesn't feel dangerous or anything just more wobble than I would say I'm used to.

[rogold99]

I think its called "cowl shake". The convertibles are prone to it, even after the factory reinforcement of the chassis. 

[Y-JobFan]

Some convertibles are really bad with cowl shake, the Reatta’s overall aren’t to bad compared to other convertibles. That said I have noticed some Reatta’s are worse than others.  Tires, inflation can make a difference as well. 

Edited December 27, 2019 by Y-JobFan (see edit history)

[Barney Eaton]

I agree with the others...........if you are not hearing noises when this happens,  it is unlikely your suspension.

Because of the lack of a hard top to stiffen the body,  when one end of the vehicle twist over a speed bump, you get some flexing front to rear.

There is an exaggerated feeling because you are setting on the seat that might move one way with is anchor,  the center rear view mirror is at the top point of movement

so it might appear that things are moving inches when in reality the max movement might be less than an inch.

Automotive experts say that ALL convertibles have this condition but some are less noticeable.

Back in 2008 when we had a Reatta Roundtable in Flint,  the assistant chief engineer said they added 9 new (additional) stiffening stamping to the 1991 convertibles to improve the condition

and he felt it was successful.......however he said a new "harmonic" issue developed on some cars.  (the harmonic issue was not explained)

In an effort have satisfied customers for the 1991 convertible,   all the '91's were trucked to Miami and Buick engineers road tested all the new convertibles over a route they selected.

Based on their "engineer" seat of the pants test drive the convertibles were divided into 3 categories.  

(1) Everything was satisfactory and the car was sellable to the public

(2) The car did not meet their criteria for a #1 but the cars could be sold to employees, with the understanding that "cowl shake" was not part of the warranty.

(3)  Unsellable ........these include the 45 new 1991 convertibles that were donated to tech schools around the country.

Over the years several of us "old timers" have pieced together what we feel is approximate number for the above categories.

These numbers are not "official" and can change when new info becomes available.     There were a total of 305 convertibles built in 1991.

#3 cars appear to number 58 ..... this includes engineering test cars, 4 that went to Cadillac, and a couple of museum cars that were the property of GM

#2 cars stands at  102

That leaves  145 that were sold to the public.

I may write a more detailed summary for the Reatta Div  newsletter,  but I am not sure there is that much interest.

 

 

 

 

[padgett]

I know back in the day there was a section of I-75 between Ocala and Gainesville that almost any car would vibrate badly around 70 mph - so much so that a whole industry including billboards on the Interstate sprung up for shops that could cure vibration.

 

Never had a 91 but my 90s never shook badly though had some. Most noticeable difference was the extra deep "frame rail" to stiffen the chassis.

 

I always wondered why, if there was a problem, the Reatta never got the "cocktail shakers" used on F-bodies.

[NCReatta]

I recently picked up a 91 Reatta that still has the 20lb dampener weights under the rear bumper. These were the subject of a service bulletin and most were removed. 

 

From my understanding, this was one of the many things they did to try to reduce vibration. 

[Barney Eaton]

That was a cheap attempt to mimic the "cocktail shakers"  GM put in the Firebird, Camaro, and Corvair convertibles.

Fortunately,  computer simulation and better understanding of engineered design have help reduce these problems.

Almost every new car ad says something about the chassis is 50% stiffer,   70% stiffer.   how do they do that without adding

50% more weight?   All in the design and testing of new vehicles that did not have a separate frame. 

 

For anyone not familiar with the "cocktail shakers" installed starting in 1965 on Corvair, then in '67 on Firebird and Camaro.

Here is a picture of one ....front of a Corvair...bolted to the body seam of the wheel well,  they weight about 25 lb each 

Edited December 29, 2019 by Barney Eaton (see edit history)

[Philbo]

Wow lots of good info.  Thanks everyone.  It's really not that bad on mine, but I live is South Carolina, some of the roads are pretty rough here so that doesn't help.

[Nittany]

Philbo,

 

As mentioned on the other site, replacing 30 year old struts, shocks, ball joints, etc and verifying the condition of the tires and alignment are key to Buick's wonderful ride.  Of course, correcting issues with brakes and drivability are also extremely important when you first purchase a used Reatta or any used car.  I'm sure next summer you'll be enjoying some topless driving!!

[Philbo]

21 hours ago, Nittany said:

Philbo,

 

As mentioned on the other site, replacing 30 year old struts, shocks, ball joints, etc and verifying the condition of the tires and alignment are key to Buick's wonderful ride.  Of course, correcting issues with brakes and drivability are also extremely important when you first purchase a used Reatta or any used car.  I'm sure next summer you'll be enjoying some topless driving!!

Next summer? Heck, it's in the mid-high 60s here in south carolina. I'm enjoying convertible driving right now haha.  I do plan on suspension work at some point, but it's farther down the list right now.  I have new tires, but haven't gotten them mounted yet.  We'll see what kind of difference that makes.

[padgett]

"in the mid-high 60s" its been that cold here but not for long.