TPIShark

OK Guys,

I've tried to help out where I can out there, now I need some advise.
My '76 seems to have an enormous amout of flex in the chassis, to the point where the t-tops don't squeek, they chirp and groan. Additionally, the upper door jambs are starting to be "sanded" by the door weatherstrip! I did a complete body-off completed this year, and all welds are fine. I sand-blasted cleaned, and restored the frame.(Needed to replace two body mount brackets and reinforce the front shock towers, the usual. I have also done a '75 coupe that does not have this problem. I've tried to think about the key differences between the two, and have come up with the following list. I'm looking for some feedback on this before I got to a 6/8 point bar (In which case my wife will never get in the car again.)


Thanks for the help, and happy holidays to everyone out there !

75 Coupe 76

Rubber body mounts Poly body mounts
No rear sway bar VBP rear sway bar with poly mounts
Welded x-member (stick) Bolted -in x-member (auto)

The '75 even has the stiffer "white" KYB's. I switched to the lower-pressure GR-2's on the '76. While I did lose about 10% in the handling dept., I gained about 50% on ride comfort. I drive her EVERY day, so it's important. (I'm not autocrossing, just the dragstrip!)

PatsLs1vette

i had alot of chasis flex in mine after the body was put back on and i made a 2 point roll bar and it helped alot im gone to finishing the bar up this week and installing the other 2 points,so ill have a 4 ppoint and it should get even better.

vettedan

TPIShark- The Shark Bar I will help a with t-top flex. It has help with my '76. Customers have said that a lot of nagging squeaks have disappeared since installing the Shark Bar I or II. Also check the rubber pads on the t-top clamps. They are adjustable, but also wear out. This will help cause t-top squeaking.

Dan http://www.vetteworksonline.com

75 BBC Stingray

No experience, but I was thinking since two people noticed these noises after putting the body back on, could it be that the shims/spacers/cushions for the body mounts are not adequately supporting the body, so that there is some "play" in the attachment points?

TPIShark

Thanks vettedan -

I've been looking at that bar for a while now. I like it because it's a
bolt-in. Any other solution requires cutting the floor and welding to the frame. Definitely a proper solution for a serious performer, but inhibits future body removal, and while I have NO problems modifying the car, I'd rather not cut my new floor pans up that bad. [IMG][/IMG] :smash: I'm also considering welding that cross-member, thought I could no longer remove the trans by itself. When you think about it, the rear half of the frame is boxed/gusseted very nicely. Then you have these long rails with the next real support being the front cross-member/engine cradle, so I'm thinking it's flexing along it's length. But count me in for a Shark Bar 1 as soon as I save a few $$.

TPIShark

When you get a chance, could you describe where it's attached ? Did you start with plain tubing, or buy a kit ?

vettedan

TPIShark-The Shark Bar I attach to all the factory seat belt anchors and is built very stout. I manufacture the entire Shark Bar, except for a few parts that are water jet laser machined. The Shark Bar is fabricated from ¼” thick cold rolled steel flat bar along with 1-1/4” x .134”-wall DOM tubing and is powder-coated gloss black.( polyester powder)
Another area you can stiffen is the shock tower. VBP sells a spreader bar that mounts between the stock tower. You can easily fabricate this bar. The price they want $80.00 or so might not be worth fabricating the bar yourself.
Dan

PatsLs1vette

heres 2 views of it, i bent my own and welded it to the frame and then reglassed floors back in.im finishing the other 2 points this week.smoked tires bought his from jegs in a kit hell post pictures later im sure.where is clarksburg,nj compared to atlantic city.




[Modified by patsnitrovette, 4:49 PM 12/7/2002]

SmokedTires

Here some pix of my 4pt in my car :) .







:cheers:

TPIShark

Thanks again - I already have the VBP spreader up front - forgot to mention. This piece made a huge difference in "turn-in" ability. Car feels more like it has 16" wheels now instead of the factory alloys with 245-60-15 BFGTA's (Which, by the way, have been providing excellent service until snow- absolutley useless in snow) So much for recent redesign of tire. :nonod:

TPIShark

Nice work. Thanks for the photos. '76 was first year for steel floors, but still
have 'glass in area shown. (Steel only goes to rear bulkhead) which is cool. On the underside, is there some type of bracket, or does tubing simply contact top frame rail? Clarksburg is "between" 195 and Rt. 33, west of Freehold. In short, I'm about 3 min. from Great Adventure, closer to those outlet stores ?

Ray.

TPIShark

Thanks a lot Mike. This is the Jeg's kit ? I really like the fit and finish. As an experiment today, I'm going to try and disco. that rear sway bar temporarily in case it's making the rear suspension too tight, might also be contributing to my traction problems. If it makes a huge difference, I might consider removing it. I'm mainly concerned with straight-line performance for the track, and with the aluminum heads, brackets, FI, so forth, the front has to be close to 200 lbs. lighter than stock. (Factory installed rear bars were primarily for big blocks, I think.) The 75 I built was VBP bar up front, with no rear, and while I never autocrossed it, it handles fine. I let you know how I do.

Ray. :flag

PatsLs1vette

Hey tpi shark i welded plates to the bar first then welded them to the frame,also were always around that area near the outlets,number one spot for the wife to shop.Maybe we can hook up some time.We use to race at new eygpt speeddway when it was asphalt i built motors for a modified team thereand we ran a few times on dirt there too,so i know the area.

PROSOUTH

TPI Shark -
My '76 seems to have an enormous amout of flex in the chassis, to the point where the t-tops don't squeek, they chirp and groan. Additionally, the upper door jambs are starting to be "sanded" by the door weatherstrip!

75 Coupe / 76 Coupe

Rubber body mounts / Poly body mounts
No rear sway bar / VBP rear sway bar with poly mounts
Welded x-member (stick) / Bolted -in x-member (auto)



I was reading this post and I noticed all of the way down that no one commented on the difference in the body mount types. The '75 had Stock Rubber Mounts. Right? Then the '76 has the new Super Poly Mounts.

It would seem to me that this is the difference. I would be inclined to believe that the stock mounts absorbed a considerable amount of the frame flex from the chassis and did not transfer it to the body. Then the addition of the Poly Mounts, that are very stiff and did exactly what they were supposed to, be stiff and not provide any give in the mount.

Sounds like the Polys are doing their job. The chassis may have been somewhat stiffened by adding a firmer attachment to the body without the "give" between the two. However this has resulted in the squeaks and rubs you spoke of because of the increased transmission of flex from the chassis up to through body all of the way to the t-tops.

The only cure I see is to add further frame stiffness to eliminate flex before it can be transmitted to the body or change back to the stock mounts or both.

I am looking at a Roll Bar myself, Dan has a nice bar for upper body strength, but I want one to stiffen the frame so it needs to be attached to the frame restricting the flex at the point of occurrence and not after.

I personally see no need for the Poly Mounts on my car. The Corvette is not a unibody style chassis and the need to firmly attach a sub-frame to the body in hopes of a stiffer unit is not needed. However this may be relative in some steel bodied / full framed cars, but I don't think it is a good approach in the Corvette. In my opinion the promotion of chassis flex through Poly Mounts to the Fiberglass Body is not worth the end result of body cracks, rubs etc. I do not feel that the Corvette body is structured to withstand the stress, nor show any appreciable gain by doing so.

I agree with the frame mounted roll bars providing needed structural support to strengthen the chassis on the Corvette. I have plans to install one on my '80. The only approach I see is to cut holes in the floor pan and attach directly to the frame. I don't think there is an easy way to do this. At this time I have plans for only a 4 point bar.

I also agree with the post above that states that it is a long way from the front suspension to the rear frame section supports with only one crossmember in between. I have often wondered about an X support of some kind to strengthen the area behind the transmember or just an additional small cross brace tying the rear frame section where the T-arm mounts to the center of the transmember from each side.

On the '87 Monte Carlo SS a set of lightweight bars were used to tie the center of the front crossmember to the front frame rails at the bumper mount. These were called "Jounce Bars" by GM and were used on F-41 suspension cars to help stiffen the chassis. On T-Top cars and additional bar was used to tie the front frame rails together across the front further create a triangular support.

I think that we have relied on the technology directions of the all out race car to long. I love GKULL's Roadracer Vette but his full cage is a little further than I want to go. I think that if it was pursued we could come up with a” Corvette Street Car Guide to Chassis Stiffening” (LOL) that would allow us to maintain an accessible/ streetable car with improved chassis stiffening without an 8 or 10 point cage.

I really see a need for improved chassis structuring with the new suspensions many of us are putting in the old C-3s we have. GM could have never foreseen the need to support such a suspension on the street as is available today.

Think about this, GM did not even have a radial tire developed when the C-3 Suspension was developed, and even then the front suspension was taken from a 55'up Chevrolet Sedan.

I think that the 8.5 x 17" / 285' Super Radials I will be using and numerous other upgrades in Spreader Bars, Sway Bars, Coil Springs / Fiberglass Springs (front or rear), Low Roll Center Poly Struts, 6 links, Offset TA's, Tubular A-Arms, Extended Ball Joints and the list goes on needs to be supported with a much stiffer frame in order to utilize all of these improvements.

Any Comment's or Ideas would be appreciated. I have thought about this for quite sometime and have realized that several of us are trying to go in the same direction.

Sorry for being so long winded today, JIM :smash:





[Modified by PROSOUTH, 1:13 PM 12/8/2002]

Stingraycrazy

Hey Mike, I'd like to remove my T bar and get this look with the one piece Aero top.




You think the 4 point roll bar could handel the body flex? :crazy


[Modified by Stingraycrazy, 7:37 PM 12/8/2002]

PROSOUTH

I'd like to remove my T bar and get this look with the one piece Aero top.


Might not be that Crazy after all.

In Paragon's catalog on page 145 is a kit to convert Coupe doors to Convertable doors. This is a plate that goes inside the door and uses a reciever style lock to further latch the door and provide the extra strength needed to enable the Corvette to be a Convertable.

There should be no reason that you couldn't add this to your car and acomplish the full Targa look. JIM

TPIShark

Cool - we'll get together some time and :cheers: I plan on spending some serious time at E-town next year too. (Maybe do that Corvette Challenge deal. There aren't enough C-3's in that thing) Work/home have always side-tracked me for years, but I think my time's finally coming.

PatsLs1vette

I took picture and videos for the one challenge this year but have been working on the house and other things to go back,hopefully ill have the tpi finished enough to run it this year for the challenge.

TPIShark

Don't be sorry - I really appreciate your input. You've obviously been putting a lot of thought into the subject, (as I have), and we're definitely on the same page. Want to take advantage of some of the technology, so we can run with the "new ones" , without building an all-out race car that's not practical for the street. I have high hopes though. GM went back to Mass-air systems as sure as they went back to a full frame like ours. I still think it's an excellent chassis compared to a unibody car, we just need to figure out a few things. For one thing, I regret not fully welding the frame once I had sandblasted it. Guy that helped works in a frame shop and told me too stiff would lead to more cracks so I left it alone. I will definitely keep everyone in the loop and maybe we'll compile that book after all. :cool:

Ray.

TPIShark

Excellent. I have a few minor mods left myself, now that she's running pretty well and getting some serious break-in miles on her. Need a larger air filter, gut the MAF, and get the throttle body enlarged, and I think I'll get some further improvement. Did you have any idle troubles with ZZ4 cam ? I'm still playing with desired idle on PROM as she won't idle below about 750. I'm currently set at 850 and it's a little hard on trans/driveline going into drive/reverse when engine is cold, as IAC holds idle higher.