NYBobP Posted December 23, 2007 Share Posted December 23, 2007 This e-mail came today from one of the GM execs I contacted who worked on the Reatta program. I asked about the cowl shake in the '91's.....<span style="font-style: italic">"the convert never had a cowl shake condition. There was a first order wheel/tire vibration concern in the rear, but the cowl area was more solid than a Corvette."</span>Barney, Padget, Jim, et al; do you agree with this? Was the problem in the rear? Link to comment Share on other sites More sharing options...
Guest TheNewDamage Posted December 23, 2007 Share Posted December 23, 2007 "more solid than a corvette" is a tricky answer. I had a '91 and it had a noticable cowl shake at certain speeds. Especially with the targa roof panel off. Of course it was accentuated by having a single piece hood and fender assembly. I have not yet ridden in a Reatta 'vert so i cant say from personal experience. On the vettes you can see "brushed" areas on the cowl where the seal from the hood rubbed back and forth when it had "the shakes" as I called it, lol. I did a lot of performance driving in the mountains with other guys from Corvetteforum.com for a few years and so saw the cowl shake a lot. Link to comment Share on other sites More sharing options...
Guest F14CRAZY Posted December 24, 2007 Share Posted December 24, 2007 "Cowl shake" = condition in which the cowl, shakes.I got thinking...'91 verts are rare due to the short model year and because a lot of them were scrapped before sale due to the shake. Did '90s have this? I know they do from driving them, but did the '91s suffer more than the '90s? Link to comment Share on other sites More sharing options...
jgmck Posted December 24, 2007 Share Posted December 24, 2007 I have wondered this same thing. What if anything did they change on the 91 ??????????????? I really like my 90 but I am disapointed with Buick over this and wish it could be corrected. I have a 91 Miata that I have never noticed this shake. Is this fairly common with the big GM's (Electra,DeVille,Eldorado,ect)? Link to comment Share on other sites More sharing options...
NYBobP Posted December 24, 2007 Author Share Posted December 24, 2007 FYI...I have not experienced this problem with any of the '91's I've owned. Has anyone noticed this vibration problem and had to have it repaired, or did they all have some kind of a factory- fix before they were retailed? Link to comment Share on other sites More sharing options...
Roadster90 Posted December 24, 2007 Share Posted December 24, 2007 Hopefully this will continue and not only be an interesting , but informative thread. I have a 90 Roadster with 16" wheels (a stock and never altered in any way Select 60 with 39700k), and I only have cowl shake (and a little aggrafretting) when I hit BIG ripples, sunken man hole covers, or chug holes in the road....other than that....beautiful and comfortable ride..... Link to comment Share on other sites More sharing options...
Guest steveskyhawk Posted December 24, 2007 Share Posted December 24, 2007 For what it's worth, I was looking at a 91 vert today and there were tapered pins on the doors and matching recievers in the door jambs. I assume this is to make the body more rigid. Has anybody else seen these and if so do the 90 models have them as well? I finally saw the "triangular brace". I'll bet that ther can be added to earlier models if you can get them. Link to comment Share on other sites More sharing options...
Guest F14CRAZY Posted December 24, 2007 Share Posted December 24, 2007 steve, the '90 convertibles do have the door pins Link to comment Share on other sites More sharing options...
Guest Greg Ross Posted December 24, 2007 Share Posted December 24, 2007 I'm sure it's been written up here before about the road test routine that brought about all those Reattas finding their way to Vocational Schools around the US.All the Verts were trucked to Florida to be road tested over a particular section of rough concrete. Thus divided in to 3 catagories;Scrap, ie: donate to Educational programs, and contract the schools to scrap the vehicle when they served no further educational interest.,Sell to GM employees, and finally retailSell to Dealers.I would have understood this happened with both 90s' and 91s' Link to comment Share on other sites More sharing options...
Guest F14CRAZY Posted December 24, 2007 Share Posted December 24, 2007 Wonder why Florida? Michigan is known for some pretty rough roads Link to comment Share on other sites More sharing options...
jgmck Posted December 24, 2007 Share Posted December 24, 2007 SteveCould you describe where this triangular brace is and/or better yet get us a picture of it on the car ? Link to comment Share on other sites More sharing options...
Guest steveskyhawk Posted December 24, 2007 Share Posted December 24, 2007 http://www.reatta.org/reader's%20Rides.htmGo to this link and scroll down to the White 91 Canadian Vert where the hood is open. You can see a little of the "triangular brace". Link to comment Share on other sites More sharing options...
jgmck Posted December 24, 2007 Share Posted December 24, 2007 Thanks The only thing that looks triangular to me....... is off of the strut tower on the passenger side. Is this what you mean? I think my 90 has a brace connecting the towers. I guess I have to go out too the garage and look. Link to comment Share on other sites More sharing options...
Ronnie Posted December 24, 2007 Share Posted December 24, 2007 Look over the battery. Link to comment Share on other sites More sharing options...
Richard S Posted December 24, 2007 Share Posted December 24, 2007 Is this a replacement for the long bars earlier cars have running from the strut tower to the front cross piece [not sure what that is called]? If so, why? I don't see any reason why the earlier long bars won't fit the 91 engine compartment. Do the triangular pieces work better? Link to comment Share on other sites More sharing options...
NTX5467 Posted December 27, 2007 Share Posted December 27, 2007 I suspect that you'll find that many convertibles have a certain amount of "cowl shake", which I perceive to be evidenced by the rear view mirror shaking on rough pavement/roads. The first gen Reatta convertible I drove did it with the roof up. I took that as just part of the deal of a convertible not having quite as stiff of a body structure as a hardtop/sedan would have.Over the years, convertibles and "factory" t-top cars have had additional wedges screwed into the door shell and door frames on the body. Kind of as "bumpers" to limit body flex "together" of sorts between the two parts. The pins near the door latches might have a similar function, but might also compliment the possibly different style of door lock on the particular vehicles they are used on.The cowl area is one of the stiffest parts of the vehicle structure, typically. It would be hard for it to "shake", but the structure attached to the cowl might flex under certain conditions. Adding some stiffeners or such to the structure from the cowl area (forward, generally) might help reduce the offending harmonics and bending moments imposed from suspension reactions to road imperfections or other powertrain vibrations. Braces from the strut towers to the cowl might work, just as a cross brace between the strut towers (as many later GM vehicles used) might help too . . . not to forget a different tire choice (with a little more compliant sidewall, possibly) might help tame such conditions.In the case of the flip-front Corvettes, there's quite a bit of real estate between the hinges for the front of the hood and where the latches are in the cowl area. While the cowl would remain "still", the outer ends of the frame horns (and related bumper items) would flex from suspension "workings", which means the front of the hood/fender item is moving too, in relationship to the stationary cowl area.With respect to the way those front frame areas are designed to absorb impact energy, there will have to be a certain amount of compliance in them, rather than otherwise, so they'll collapse correctly to absorb/dissipate crash energies. Not that they are flimsy by any means, just that even a very minor amount of flex can multiply over the length of the hood until it reaches the latching points in the cowl area. Many factors at work here.Just some thoughts and observations . . . NTX5467 Link to comment Share on other sites More sharing options...
Guest Ranger Posted December 27, 2007 Share Posted December 27, 2007 NTX,No, the cowl shake hasn't been evidenced in my experience of owning two Reatta converts by a shaking mirror, the mirror is attached to the windshield which is a part of the cowl. I've owned several other converts that didn't have a cowel shake. It doesn't take a "rough" road to start the shake. Fastening the top to the windshield frame does not add much, if any structural integrigty to the convertible.The non-Reatta convertibles were heavily framed cars, in fact the convertibles I've had in the past were heavier than the coupes/hardtops because of "beefed up frames".I'd guess the reason for the cowl shake in the Reatta just may be that the only thing holding the heavy front end, including the cowl to the rest of the body is the floor pan and a very light frame/unibody.In my experience, the cowl shake happens at a certain speed and tire balancing, rotating, and wheel and tire changes have not corrected the problem. I'd guess we have a weak point in the overall construction of the car.So, in answer to your statement that "the cowl area is one of the stiffest parts of the vehicle structure, typically. It would be hard for it to shake", well Bucko, it does shake along with the whole front end of the car, but it's not a great issue with me, I just speed up or slow down and it's gone. Don't know where you get your theories, but they lose something in translation to the written word.Good Luck,Jim Link to comment Share on other sites More sharing options...
Barney Eaton Posted December 27, 2007 Share Posted December 27, 2007 I copied this photo from Steves link of 12/24It is not the best picture but it is a photo of a 1991 convertible engine compartment, showing the black triangular brace. The photo does not show the entire brace but notice that the black rod that all other Reattas have is missing. If you are having trouble finding the brace, it is above the battery. Link to comment Share on other sites More sharing options...
Guest NEMO Posted December 27, 2007 Share Posted December 27, 2007 The shake is like a duck walk,sort of like a waddle? hard to place,Its like the front wheels are pulling from one side then the other .More as if you were pulling a wagon with a rope on each side,causing it to rock very slitly,could be a lifting of one side then the other,twisting the floor pan.It all has to do with the front wheels pulling,one side then the other.Maybe if the tranny had a posi pull this would not happen.Both wheels pulling foward instead of only one. If you jack up the front wheels,put in drive,one wheel will not spin.It needs to pull from both wheels all the time .You do not get the shake when you put the car in neutral,rolling along same speed.evon while the car is waddling,it goes away.Try it! Link to comment Share on other sites More sharing options...
Guest Ranger Posted December 27, 2007 Share Posted December 27, 2007 Nemo,Good point, I'll try shifting into neutral when I get back to the convert this spring, makes sense.Jim Link to comment Share on other sites More sharing options...
jgmck Posted December 28, 2007 Share Posted December 28, 2007 NemoInteresting observation! That should translate to a rear wheel drive convert. not being subject to this problem. Link to comment Share on other sites More sharing options...
Guest NEMO Posted December 28, 2007 Share Posted December 28, 2007 With a positive drive,both drive wheels turning together, front or rear,you would not have twisting, effect on the car. Link to comment Share on other sites More sharing options...
NTX5467 Posted December 28, 2007 Share Posted December 28, 2007 With respect to my "theory" of cowl stiffness, it comes from a statement (I read several years ago) of an engineer who stated that with the complexity of the cowl structure, it was one of the structures on a car which was the last one to be redesigned or changed (which also relates to production costs to change it also). Plus knowing that the front door hinges attach to the side of the cowl structure itself and that each of the welded joints in the structure make it a synergistically stronger structure. Other than just the "firewall", the cowl area houses the plenum area below the windshield (usually with curved sections rather than completely flat sections) which supply air to the hvac system, house and conceal the windshield wiper mechanisms, plus (as mentions) serves as the base structure to which the windshield attaches/seals to. Therefore, I concur with the engineer as to the complexity of that body area and its necessary stiffness to do what it does.When you alter your speed over a bumpy or rough road, you are altering the frequency of the vibrations transmitted through the suspension to the body structure. If the transmitted frequency happens to coincide with the resonant requency of the body structure (or parts thereor), then "shake" can occur. In the '69 Camaro convertible, there were dampers placed at each corner of the body to dampen these harmonics.These same suspension inputs will also cause some amount of flex in the body structure. In other unibody cars with separate front subframes (as in the first and second generation GM F-body), a common "fix" for drag racing is subframe connectors. When the first third gen F-body convertibles were finally built, they had visible cross braces for the floor pan. So, yes, convertibles generally need some heavier bracing or additional "framing" in the underbody area to add stiffness to that area of the vehicle--even on a body/frame construction vehicle.All things considered, if the floorpan area is suspected as being the location of the flex, then some additional bracing in that underbody area might be easy enough to design and implement. Such additional structure would alter the resonant frequency of the body structure and possibly shift it to a different frequency which would not cause "the shake". If this was effective enough, it would be highly similar to the subframe connectors (mentioned) in effect and would make the convertible bodies last longer and be more enjoyable to drive.Regards,NTX5467 Link to comment Share on other sites More sharing options...
padgett Posted December 29, 2007 Share Posted December 29, 2007 I dunno. Send me one (non-returnable) and I'll test it. ps a real cowl shake, like a "speed wobble", is a scary thing. In the worst cases the steering wheel will jerk in you hand though rarely lasts more than a second or two. Railroad tracks were the worst for me.pps the 66 Corvair convert in my garage has cocktail shakers in all for corners. Link to comment Share on other sites More sharing options...
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