Convertible DRIVEABILITY question

[Guest steveskyhawk]

We all know the approximate number of Reatta convertibles produced in 1990 and 1991. What a shame that production was cut so short. The GM employees that were assigned to the Reatta project must have been devastated. It is no wonder the record keeping was such a mess at the end.

I have driven both 90 and 91 Reatta Convertibles and have found them to be nice driving cars. When passing over railroad tracks etc with a 90 I do notice some flexation commonly called "cowl shake" but I dont find this objectionable. With an aviation background I assume that if something dynamic doesn't bend it will break instead. Anybody that has ever flown on a transport category aircraft has seen dramatic wing flexation.

I have also driven both 91 coupes and convertibles. All the Reattas I have ever owned have had a definite personality. Every one was different. The 91 convertible stands alone however. I get a false feeling that a 91 convertible is bigger and heavier than all the rest. It tracks better and to be honest feels much more rigid than even a coupe. I even get the sensation that the wheelbase is longer in spite of the fact i know this isn't true. The 91 vert is different.

I talked to a GM engineer that worked on the Reatta project and he told me there were many structural changes made to the 91 which created a different (objectionable?) harmonic. Is it possible that the 90 had an unfavorable harmonic and in trying to fix this problem the car was made too rigid thus creating a more unfavorable harmonic? The big question is why were there seemingly no actionable problems with the 90 verts but the 91s were so bad that 2/3 of them didn't qualify for retail sales?

I suspect emotions ran wild during the last days of Reatta production. Those vested in the project probably never saw the car equipped as they envisioned it. I suspect the "cowl shake problem" was overblown. With sales lagging and the potential for for huge tax incentives resulting from the all electric (EV1) development it seems probable that they just needed the building.

[Barney Eaton]

At the 2008 Reatta roundtable held at GM Service Parts Headquarters, there were several former GM/Reatta people present.

Don Cantleberry (assistant chief engineer at the time the Reatta was built) told the story of the 1991 convertible modifications.

According to Don, the 1990 had "cowl shake" problems that prompted some complaints from Reatta convertible owners.

That problem was addressed. One 1990 "fix" were the weights added to the rear bumper mount. This was recalled because the weights failed.

There were several new reinforcing stamping added to the 1991 production convertibles. I believe he said 9 stampings. We have a video of the meeting and that could be reviewed for more detail.

It would be interesting to get a 1990 and 1991 on a lift to see if all the different stampings could be identified.

1991 Reatta production did not start until the last week of Nov, 1990. Eleven early pilot convertibles were built and all were supposidely scrapped.

Those vin's were 90002, 05, 08, 09, 11, 12, 13, 14, 15, 16, & 17. The last four went to Cadillac (reason unknown) and were all white/tan/tan.

The first "deliverable" convertible was probably 900242 and records show it was supposed to be scrapped but Carfax indicates it was titled and had 16K miles on it in 1993. If anyone has the abiltiy to run a carfax the entire vin was 1G4EC33L5MB900242 that should tell us what the mileage is today.

Anyway, it was winter in Lansing and Buick engineering wanted to test the cars. All production convertibles were transposted to Miami FL.

The local Buick dealer had a multiple story parking garage and Buick engineering used the top floor for their Reatta convertible testing.

The convertibles were each driven on a test loop in Miami. It seems that someone said it was around 7 miles, different types of road surfaces, train tracks, etc. From that drive the engineers placed each car into a catagory...... Sellable, Sellable to employees, Scrap.

According to Mr. Cantleberry, the "cowl shake" was solved BUT a harmonic problem was created. There was not time to solve the problem so when the cars arrived back to Lansing they went 3 different ways. One employee that purchase a car said it came with a full warrenty except for the harmonic/cowl shake problem.

Using the raw number, there were 305 built. The list I received from the Toleto Buick dealer shows 102 Employee purchased, 61 scrapped, and 6 with "other" disposition, that would equal only 136 sold thru Buick dealers.

With further research, I found 9 of the SCRAP designated cars were found on Carfax... this would indicate that somehow they were sold. In addition there are 594 which went to the Sloan museum and 622 the last convertible built was sold by GM back in 2008 at auction, both of these cars were listed as scrap. We know of one of the scrapped cars that were given to technical schools somehow was later sold and now is in Kansas.

As you can see, the numbers get a little fuzzy. Take the 136 sold by Buick dealers, plus the 102 sold to employees equal a total of 238 that ended up on the road. Add the 9 that have appeared on Carfax, the Sloan car, 900622 sold at auction and possibly a couple more (we don't know the fate of the cars that went to Cadillac) Somewhere between 238 and maybe as high as 250/252 that ended up on the road.

Sorry that the 1991 convertible story got carried away but there is no simple answer.

I

[William Rule]

I own, drive and maintain two Reatta convertibles and two coupes. {I also fly and maintain N5608U} My Reattas are maintained as though they were aircraft. To me, the coupes "feel" the same------both 89 red tan------both socal cars----one has 9750 miles the other has 169,444 miles. The convertibles---------one has cowl shake the other does not. I measured this movement by fixing a wire from the driver's upper sun visor to the convertible top mount behind the right seat and observing the wire as I drove over rough roads. The low mileage {62,890} has little or no shake whereas the high mile convertible {148,800} does show some flex! I can "feel" the difference. The high mile car will corner better and is faster than the low mile car. I have raced SCCA and I know how to drive on the edge. And, I live in the sticks [no cops----no traffic].

[Guest steveskyhawk]

Thanks to Barney for that. I really enjoy this type of conversation. Regardless of the conclusion we draw, the story isnt linear by any streach. I cant help but think that some of the engineering conclusions were influenced by the internal accounting/political forces within GM. It must have been heartbreaking to be so vested in this project and to have it terminated so abruptly. After owning multiple convertibles I dont see an objectional trait in either the 90 or 91. I prefer the ride and handling of the 91.

I spoke on the phone with a guy (that claimed to be a Craft Centre engineer). He was selling some Reatta swag that he claimed there was an abundance of back in the day. I asked him about the dimples in the headlight doors and he knew exactly what I meant. He said these dimples in the pot metal covers was an issue but it was decided to tolorate this imperfection. The decision was made to use no body filler whatsoever in a Reatta. He said that if a "tub" AKA "BIW" or simply put a body with no doors etc was damaged it got scrapped. It was forbidden to use body filler to repair it. He went on to say that there was an investigation that alleged that the salvage company (contracted to destroy) was selling these bodies to be rebuilt by third parties. I dont even want to speculate how this effects the VIN sequence but the guy I talked to said there was an investigation by the FBI. After having 3 cars soda blasted I can verify that these 3 cars anyway did not have a tea spoon of filler. (not even where the quarter meets the roof) As a side note that same engineer I talked to had the "Reatta" flag that flew outside the Craft Centre. I didn't have the heart to ask him to sell it. This flag is representative of a man's career.

[wws944]

My 'vert definitely has a different feel when the top is up vs when the top is down. It is more rigid when the top is up.

Back in the separate frame/body days, engineers would design the frames to twist and flex a bit to try to take some work off of the suspension components. But nowadays, the trend is to make the bodies as stiff as possible and use more modern suspension designs to provide the proper handling and ride characteristics. Unfortunately, with unibodies, which the Reatta has, the roof is an integral part of making the body stiff. So it is hard to make a convertible work right without one.

It isn't just Buick. In the video that Barney refers too, one of the panelists said they had a BMW convertible at their test facility for comparison. Apparently the BMW had far worse 'cowl shake' than the Reatta did.

[padgett]

I have had a number of GM cars (Corvair, Camaro, Firebird) that had about the same cowl shake (mostly over railroad tracks) particularly after I removed the cocktail shakers to save weight. Is just an occasional thing and nothing like a speed wobble on a bike. Have had three '90 Reatta 'verts and all felt about the same.

Now that the 100 days of summer have arrived the top is up & air is on and did feel tighter today. Suspect it does need a properly tight top and may be different with vinyl.

Am considering getting the coupe out since is quieter/tighter with A/C but mostly am just driving the heep.

Enjoy it while you can.

[Guest HessLakeGuy]

Good day:

I put a new set of Firestone tires on my 1991 last September the week of the Anderson, IN meeting. They now have about 900 miles on them and I cannot believe how they changed the cars ride, unfortunately, for the worse. They are the correct size, perfectly balanced and I keep 33 pounds of air in them, but I do not like their stiffness.

The Continentals I have on my 90 convert and 89 coupe give a great ride. I especially like they way the convert rides with them. I have always liked BF Goodrich tires, but I think I like these Continentals better.

So, by changing tires you can also change your vehicles ride, at least with the five Reattas that I own.

I imagine most of you have favorite brands of your own, too.

Tom

[padgett]

I have always liked the ride of 225x60x16 Michelins on factory 16x7 rims. Of course getting over 55" of rain a year, sometimes a couple of inches in an hour, does influence my decisions.

[ol' yeller]

The only driveability issue with my vert is that when the top goes down, the smile on my face gets so large that my eyes get squeezed shut somewhat!

[Ronnie]

Continental 225x55x16 tires were on my Mustang wheels when I got them and they are really smooth even though they are half worn out. I think 225x60x16 would be the ideal size for looks and ride. The 225x55x16s don't fill the wheel well enough to suit me but they don't look bad.

I've had good luck with tires with the exception of Uniroyals (Tiger Paws). Worst tires I've ever owned.

[Guest steveskyhawk]

So it appears to be a consensus among all convertible owners that "cowl shake" is common to all convertibles regardless of year or company of manufacture. Tires and tire pressure can change intensity of this problem. That I get.

What i'm having a hard time with is trying to imagine is how bad was the so called "cowl shake" on the 91 Reatta Convertibles that were allegedly destroyed? I find it nearly impossible to believe that a group of cars that were built exaxtly like my 91 convertible were so bad that they needed to be destroyed. How could there be that much difference?

I suspect that there were many people emotionally vested in this model and were upset with the abrupt decision to end the project. I sure would like to see some paperwork that indicated who, where and when these convertibles were destroyed. I'm guessing that some of them may have been reported scrapped but never made it to the crusher. It would have been a shame to destroy them because of their parts values alone.

All things considered it is no wonder that the paper trail on this run of cars is incomplete and inaccurate. Cars missing, Vin numbers missing. I have the feeling we will never know the whole truth.

Edited June 17, 2013 by steveskyhawk (see edit history)

[padgett]

Uniroyal (low line), BFG (mid line), and Michelin (high line) are all one company now. I tend to buy either Michelin X or BFG Touring T/As depending on whether I plan to drive a lot or in rain.

[Bushwack]

Possibly I missed this in a previous comment but has anyone mentioned suspension.

I've owned 8 convertibles. Cowl shake worse on some (as in terrible) while on two that I have now they are practically non-existent (or I've adapted). As this applies to the present and not the past, on all but one vert, whenever I've changed the struts/shocks, there is a noticeable improvement. Take it up a notch and change the tires at the same time (I find over-priced Michelins good but favor the more reasonably priced Khunos) and cowl shake is minimized. On the flip side, I've changed the struts/shocks on a vert that had newer Firestone tires (installed by previous owner) and I sensed no change in cowl shake.

Going back 20+ years, I can't understand how the brightest engineers at GM couldn't figure out how to solve (or greatly minimize) cowl shake. I'm not a conspiracy theorist but inner politics must have played a keyed role in why the problem couldn't be solved. Was the Reatta not meant to succeed? Did GM feel Allante sales (with its higher profit margin) would suffer? Didn't the Camaro/Firebird have a convertible that year (I'm sure people cross shopped these cars)?

[Guest steveskyhawk]

Ervin Said:

"Going back 20+ years, I can't understand how the brightest engineers at GM couldn't figure out how to solve (or greatly minimize) cowl shake. I'm not a conspiracy theorist but inner politics must have played a keyed role in why the problem couldn't be solved. Was the Reatta not meant to succeed? Did GM feel Allante sales (with its higher profit margin) would suffer? Didn't the Camaro/Firebird have a convertible that year (I'm sure people cross shopped these cars)?"

I agree wholeheartedly. The potentential for funny stuff going on with cars and vins was signifigant. Bear in mind that DMV and company computers were not nearly as reliable as we have now. The temptation to save one of these beauties was probably on the minds of all involved. I dont believe in black and white. The truth is usually in the grey.<!-- google_ad_section_end -->

[60FlatTop]

I'm a lurker here with a Park Ave 3.8 convertible that has engine drivability problems I am trying to sort from your experience. This thread interests me because I have had a wide range of separate body and frame converts of all types. Cowl shudder is memorable on a '71 Ford LTD I had and I don't recall any on a '67 Skylark.

I remember the weights they put on the '60's Lincoln convertibles and they were an echo of the early '30's Packard bumper end balasts. So I have had an awareness of our Flexible Flyers since I was around 15 years old.

As our cars age and go through various owners on the way to us they go through a wide range of service technique; I really like the aircraft level maintenance. Feed Forward, not Feed Back!

My Electra had two owners and shows 53,000 miles. I think the original owner maintained well though not extravagant, the second did repairs, minimal maintenance, and handed me a lot of work.

Here's what I think is important:

Use a four post lift. Especially if the job entails an overnight stay. The lift points on two post lifts appear counter to the flex and resonance points I have seen on cars through the years as well as my personal observations when using jack stands. It means a lot to me to know my car is supported by the wheels or at suspension points.

Something as simple as a fuel pump replacement that needs to wait a day for parts can leave a car hanging in an unnatural position for 48 hours. Experts will say "Oh, don't worry." Sorry, its my car. I won't worry because it won't happen. You can see from the shop I use.

Today chassis driveability may be more related to service history that manufacture. I'm a four poster for 20+ years now. Only a few short trips up a two post when absolutely necessary. Its just the way I want it done and the guy who complies gets a little extra to take his wife out. We are both happy.

Thanks for reading this far.

Bernie

[padgett]

Agree within limits, when you saw the roof off you lose a lot of structural rigidity and cowl shake results (is a harmonic). Cars designed as convertibles generally do not shake.

For some reason GM semi-monocoque cars are particularly bad. Corvette, A & B bodies had a full frame. Corvair, Camaro, Firebird did not. Reatta does not either.

I bought a mid-rise scissors partly because almost every time I jack a car, tires are removed. Hard to do with a four post. Key is to put blocks in strong places as near the axle as possible.

[Guest tempest6cyl]

It would be interesting to get a 1990 and 1991 on a lift to see if all the different stampings could be identified.

Those vin's were 90002, 05, 08, 09, 11, 12, 13, 14, 15, 16, & 17. The last four went to Cadillac (reason unknown) and were all white/tan/tan.

I

I don't recall any changes for structure on the ASC supplied, convertible specific, bodyshop installed welded stampings for 1991 which were all of them except the quarter panel. Granted, it's been a few years (this would have been about 1989 for the 91 MY) and I don't have any of the drawings in front of me but, that's what I recall. Changes to the ASC parts would have been my responsibility. Mr. Cantleberry may be remembering some of the coupe changes that carried into the convertible, I believe GM made a few changes like that or, his memory is just better than mine. If somebody gets around to comparing parts the pictures could wake up a few brain cells.

Cadillac Engineering had the lead for the E/K platform which the Reatta was part of. This was back in the BOC group days. The cars that went to Cadillac were probably for engineering evaluation or testing. Engineering cars were usually white. Cars that went to Buick were usually for marketing uses. We usually had a few cars around ASC for testing which were probably on the Cadillac Engineering books. Not to stir the pot but, I'm 80% sure one of them was a green convertible that we used for topstack cycle testing. If I ever find some archive evidence I'll let you guys know.

[Guest Richard D]

Just in case you have never felt what cowl shake feels like, beg, borrow or steal a last generation two seat Thunderbird, from the late 1990's. Now here is a car that was designed as a roadster/ convertible and driving over a set of train tracks you can actually see the car shell flex from the cowl forward. If you put one front wheel up on a standard curb if it is the passenger side to open the drivers door you have to push down on the door near the jamb to get it to open without ramming your shoulder into it. Passenger door you would have to lift up on the door to get it to open. When getting my 94 T-Bird ECM changed I overheard two service writers talking about a new T-Bird pulling in they would call it a flex-mobile and no mechanic wanted to touch it.

[Barney Eaton]

Tempest....... it has been said by several, that ASC was contracted to design the convertible top. We also know from you and others that ASC built the tops ready to install on the bodies at the Craft Centre. Your statement implies that ASC supplied the stampings that were used to strengthen the 1990 convertibles........(and 1991 if Mr. Cantleberry is correct)

I always presumed that Buick designed the extra reinforcement used on the convertibles. All of these weldments would have been added when the body was welded at the Craft Centre.

Please tell us what you remember. You probably posted before, but what years did you work for ASC?

[padgett]

Well the body floor stampings for the 'vert were very different, the "frame rails" were much deeper and there was the entire structure just behind the seats.

[Guest tempest6cyl]

Your statement implies that ASC supplied the stampings that were used to strengthen the 1990 convertibles........(and 1991 if Mr. Cantleberry is correct)

I always presumed that Buick designed the extra reinforcement used on the convertibles. All of these weldments would have been added when the body was welded at the Craft Centre.

Please tell us what you remember. You probably posted before, but what years did you work for ASC?

ASC designed and supplied the topstack, structure, and interior trim parts for the convertible with a couple of exceptions like the quarter panels which were produced in the Craft Centre's stamping facility. Half the fun of a program like the Reatta is in engineering it so that the convertible could be produced on the same line as the coupe. As you can imagine, trying to get a second vehicle variation out of existing plant tooling without getting carried away with increasing the Craft Centre's part count has it's challenges. From the time I started on the program with ASC in the spring of 1987 to it's end, I don't recall ever meeting a Buick engineer. All our contact was through Cadillac Engineering as part of the BOC organization.

I come up with about 40 convertible specific sheetmetal parts supplied by ASC and installed in the bodyshop.

3 front rail reinforcements per side

2 reinforcemnts inside each hinge pillar

1 reinforcement in each foot area

1 rocker outer with 2 reinforcements per side

1 rocker inner per side

1 rocker to quarter brace per side

1 front rail extension per side

1 rear rail extension per side

1 crosscar part below the dash

1 crosscar assembly behind the seats (6 parts in the assembly)

1 crosscar dash brace which tied to the tunnel

1 thicker cowl

1 header inner

1 header outer

1 tonneau panel

1 pair of tonneau hinges

1 pair of tonneau torsion rods

The quarter panels and A-pillar inners were made by modifying the coupe tools to make either version.

For Padgett, the floor stampings are common between the coupe and convertible, it's the parts that were added that make the underbodies different. The frame rails are the front and rear rail extensions mentioned in my list. These cap over the coupe rails. You're right about the structure behind the seats, it's all new. In the Craft Centre built process, some of that structure was installed in the first stage. If you knew what to look for, you could tell a coupe from convertible underbody right from the beginning.

[Barney Eaton]

Thanks for the reply........ wish we knew what parts Cantleberry said were added in 1991.

[Guest tempest6cyl]

Thanks for the reply........ wish we knew what parts Cantleberry said were added in 1991.

Have you guys been able to dig up any body repair illustrations maybe from the service manuals ? There might be some hints there. When did the front shock tower brace come into being ?

[Barney Eaton]

The brace between the strut towers has been there from the beginning....even on coupes. The tubular brace that goes from the strut to the radiator support has also been there since day 1. That brace was changed on 1991 convertibles to a triangular plate (located at the intersection of the radiator support and the fender)

[Guest tempest6cyl]

That brace was changed on 1991 convertibles to a triangular plate (located at the intersection of the radiator support and the fender)

That would be one of the parts Don was talking about. GM handled the bolt on braces and they were not supplied by ASC. Is the video of Don's talk available online ?