Convertible K Stiffening

[TylerEss]

My 600 is about as stiff as a wet noodle.

I'm not talking about "oh, it'd be better for auto-x"; I'm talking about fear of metal fatigue after a few years of just cruising and driving. Car's going to have to get torn apart lots this summer anyway, so I'd like to maybe stiffen it up while I'm at it.

I'm thinking that strut and shock braces will be a nice start (to avoid twisting around the car's long axis), but something more will need to be done. I want to keep the car stock "looking", so a rollcage is right out.

Where are other good places to think about adding supports?

[afsautoworx]

wont every be very stiff if its a convertible and no roll cage. i know where youre coming from tho, the lebaron converts. twist a lot too.

[TylerEss]

Yah. I'm not even really so much interested in making it stiff as making it not slowly self-destruct whenever I travel over rough roads or drive it hard though the corners.

[Whorse]

My lebaron convertible is fairly stiff for a convertible. I'd go so far as to say it's comparable to my friends lowered accord on low profile tires with lowering springs and a tower bar.

[TylerEss]

Yah. The J bodies are a lot stiffer than the K bodies, 'cuz the Js got extra reinforcement the Ks didn't.

[Whorse]

That would do it. The GTCs usually came with a slightly sportier suspension as well. I remember reading that the 1989 and 1990 GTC Lebarons had a Shelby Suspension.

[85lebaront2]

Damn, somebody forgot to tell me that my K LeBaron convertible doesn't have body stiffening. It is a whole lot stiffer than my son's 99 stang convertible. On the K body convertibles, there are three major reinforcements, one across the toeboard and front floor making the floor dual layer, one running the length of the car from just behind the heater casing to under the rear seat (that's the one that drives you crazy with the shifter and any kind of console) and one across the rear floor starting at the seat rise and giong back to the rear suspension area. There are two more gussets at the door post, two bolts into the floor area, one of which holds the seatbelt retractor, and two into the door post/quarter panel front. I am trying to convince my local SCCA region that there's not a big difference between the T1 log setup offered in 85 and my "tweaked" T2 setup. Some of them actually believe me!

[afsautoworx]

ive driven some lebaron converts at work and you could feel them twist a lot in the rear, maybe its stiff for a convertible?

[Tim]

If there's room, install subframe connectors. But I'm not even sure the subframes line up like they do on 1960's-1970's Mopars.

[Frank]

I would suggest that you do a few things.... replace your bushings with stuff from Poly Bushings, replace the rear panhard rod (probably a noodle now and bent), and upgrade your suspension some.... heck when was the last time it was replaced? (aka shocks/struts and springs?)


Frank

[Dietro]

Here is a list of some things that can help, (there is no rhyme or reason to their order):

1) Front strut tower bar.

2) Install an entire K-frame from a '89 or newer car, preferably a T-II car. It'll have a larger sway bar and it'll also have the bigger brakes, but that's another thread.

3) Install a rear sway bar and/or box the rear axle with a plate. This is an old trick and some people use it in lieu of a rear sway bar.

4) As Frank suggested, install poly bushings, along w/new ball joints, tie-rods and shocks/struts. None of these add rigidity per se, but they help make sure the energy/motion from the suspension is all straight up and down.

5) Several years ago, SCC ran a story about using some anaerobic foam to fill hollow frame rails and/or suspension pieces. Supposedly Inifiniti does this at the factory and it helps significantly stiffen the car. I know of a CSX that had it done, and it definitely seemed to make a significant difference. Here's the thing though....the "insulation foam" you can buy at Home Depot or Lowes will do the same thing and it is SIGNIFICANTLY cheaper. If all you did was fill your frame rails it would probably help considerably.

[TylerEss]

Sarcasam

I hadn't realized that those features were added to the convertibles to make them stiffer. I thought ALL K-Cars were built that way.

You say your K-car is stiffer than your son's Pony convertible? Hmm. I've never owned any other convertibles, so maybe mine IS stiff--but it creaks and groans a lot when going into driveways and other such "one wheel up higher than the other 3" situations. That's the biggest thing that's got me worried.

Is the suspension crap?

Just replaced everything last summer with Konis/Eibachs/Johnny Spiva. You're right about the track bar, though, it looks horrible.

To make things more interesting, a Pepsi truck hit the car right at the end of the summer--drug the tail of his trailer from just behind the rear driver's wheel well out past the front of the car. Needs a little body work, now.

Bent the control arm, though my guy assures me the body's still straight enough to align all 4 wheels (after the suspension is rebuilt AGAIN). Guess now I've got the motivation to replace the track bar. I'll try filling in those frame rails, too. Since that stuff's so cheap, I guess it can't HURT.

So basically, I just shouldn't worry about the stiffness? It handles well enough (or, it DID...).

Does everybody's car creak like that? I'm gonna see if I can find some friends with convertibles I can drive to get a feel for my car vs. others.

[denviola]

Most if not all convertibles have some stiffening in the frames, windshield pillars, etc. If not, the windshield will break under normal stress loads from bumps and body flex. Read some articles quite a while back about a restorer that was making a 40s 4 dr conv from a sedan body. He added X-bracing to the frame and rear of body, as all convs had that mod in the day. Now with unibody I believe all assembly line converts have stouter frames, etc. When the conv was reintroduced in the early 80s after being gone since 76 (I think), all Chrysler converts were sent out to have the roofs hacked off and the convert mod installed. The dealer I worked at had a spec sheet on the mods which included the additional bracing. Wasn't long before they were a regular assembly line option again.

[Andre Parker]

Since you don't want a roll cage, maybe something with hoops behind the seats kinda like some of the Z3 bimmers I have seen with them. It would limit rear seat passanger room, but could be thoughtfully done and look and perform decent.

[inmyshadow]

I have a dodge shadow convertible. It has some flex, mostly noticable with the top up. It makes alot of noises.

Also dodge shadows have tons of reinforments. The frame rails are boxed-in in the interior. Underneath there is plate that extends the whole length of the frame rail. It connects to the both of the car and frame rail with huge rivits. Its about maybe 1/8in thick. This plate is awesome for jacking the car, but I had to buy a low profile jack clear those plates

The stock towers are trianglated, alot like a 350z. Its pretty beefy and the back seat cushion bolts to it.

Where the b-pillar was cut is reinforced also. It helps support the top's rack.

Now my friend has the same year convertible with less miles then mine. His car shakes alot more then mine. He could feel the difference over rail road tracks mostly. So the strength of the chassis could be affected by alot of things.

The only thing I've done to strengthen my car is with my strut tower bar. It helped with the windshield flex alot.

The shadow was a ASC converted car. So it might have an advantage over the chrysler designed convertibles when it comes to chassis strength. Plus shadows have manual tops, so I don't have all that extra dead weight of a power top. I've weighed my car at ~3000lbs without me.

[TylerEss]

Hmm. I think I'll just give 'er the old strut tower bar and maybe a shock tower brace if the convertible top doesn't get in the way. After that, I'll just try not to worry about it.

Thanks everybody!

[supercrackerbox]

5) Several years ago, SCC ran a story about using some anaerobic foam to fill hollow frame rails and/or suspension pieces. Supposedly Inifiniti does this at the factory and it helps significantly stiffen the car. I know of a CSX that had it done, and it definitely seemed to make a significant difference. Here's the thing though....the "insulation foam" you can buy at Home Depot or Lowes will do the same thing and it is SIGNIFICANTLY cheaper. If all you did was fill your frame rails it would probably help considerably.

Any idea if/where I could find a copy of this info? Something I've thought about doing to my GLHS for various reasons.

[Dietro]

I just googled, and came up with THIS. The info about the foam is near the bottom. They say not to use Home Depot foam because it won't dry.....I know for a fact it will dry. I had a can I used for something around the house. It was 90% full, and if I didn't empty it, it would have made the entire can useless, so.....I partially filled the frame rails in the minivan on jack stands in my garage. It is dry, and if I ever got so motivated, I'd fill the remainder of the frame rails, and not think twice about it.

If yoiu decide to use the Foamseal stuff they did, HERE is the website. And checking their ordering PAGE, their prices have dropped considerably...

[mech1nxh]

TODD...
thread piqued my intrest..went to the site and called them , as the page has not been updated since /00.....yup..../00.
phn# still good, called to late in the day for info , will update here later...

interesting, we used to use "mr foamy" to secure roof ribs on "B" vans , as
mopar could never seem to get them attached correctly....lol. the foam always dried completely....
I want to see if ITW still makes thier product as the Sport Car Compact article
says some of ITW'S formulas have densitys of up to 10# per foot......
yikes!!!!

[85lebaront2]

Damn, maybe I need to get some of the void filling foam mix we use on the nuclear carriers. It has a low density and pretty good compressive strength.