Body flex?

[knownenemy]

MIG welding is exactly the type of welding that should be used when working on these cars.

L body cars are stiff but suffered from poor welding from the day they were new. I remember working on Omni and Horizions back in the early 1990's that had strut towers falling apart because of too few spot welds and poor spot welds.

When I restore GLHS 420 I plan to add spot welds inbetween the original welds along the frame rails and strut towers. I'm also going to try to engineer a rear strut tower brace built into the floor and frame connectors.

I found these pics a while back and saved them for a layout of what I'll do to GLHS #0896:



I'm probably going to go in a different direction with the tower mounting than this one,
but the idea for connecting it to the floor is a great one.

I'll use a ring type tower connector,
and go around the top of the tower completely.

[85boostbox]

LeBaron convertibles had chrome moly tubing running inside the rocker panels. This tubing was tied to supports at the front of the rocker and to the steel bracing that ran across the rear seat area.

This is what I plan on doing. Luckily my body on my charger is solid except the seams right below the pedals. Which is also solid but has a small strip of rust.

Mine will not be ran in the rockers though obviously. It will be channeled right next to the inner rocker. I'm going to have to modify carpet obviously, but I believe it will help.

[ATaylorRacing]

When I had a 6 point set up in my 11 second GLH it was easy to tell how much stiffer it was on the street. Matchbox does not have one....when I jack it up to change to slicks it is about impossible to open the rear doors!

[Dr. Johny Dodge]

This is what I plan on doing. Luckily my body on my charger is solid except the seams right below the pedals. Which is also solid but has a small strip of rust.

Mine will not be ran in the rockers though obviously. It will be channeled right next to the inner rocker. I'm going to have to modify carpet obviously, but I believe it will help.

the old seventies challenger convertables had a reinforcement bar put inside the rocker structure it's self

[5DIGITS]

I found these pics a while back and saved them for a layout of what I'll do to GLHS #0896:



I'm probably going to go in a different direction with the tower mounting than this one,
but the idea for connecting it to the floor is a great one.

I'll use a ring type tower connector,
and go around the top of the tower completely.

Agreed and the floor connection is a nice idea !!

[contraption22]

With the entire drivetrain mounted in the front of the car on soft mounts, I am not sure how much chassis flex behind the firewall really occurs in drag racing an Lbody. I have seen the front core supports flex a lot. Tying it to the Kframe helps with that.

[Reaper1]

The '87-'89 LeBaron Convertibles had massive bracing in the front footwells under the carpet as well as the central transmission tunnel brace. The later ones utilized strengthened rockers so the center tunnel wasn't as wide and could therefor use the same center console (the older ones were unique). The Maserati TC also used strengthened rockers.

[85boostbox]

With the entire drivetrain mounted in the front of the car on soft mounts, I am not sure how much chassis flex behind the firewall really occurs in drag racing an Lbody. I have seen the front core supports flex a lot. Tying it to the Kframe helps with that.

That was already on my agenda.

[knownenemy]

It's really great to see some of the most knowledgeable members chiming in here.

My huge concerns about losing weight need to be incorporated while also strengthening the structural rigidity.
This sounds like an impossible thing to do, but in checking over the car,
I'm finding many things that can be altered for the better,
and a lot of things that can be completely deleted.

[tommyturbo]

I've got an 89 GTC, and well I can agree that it is pretty stiff for a conv of it's age, and I can jack up the front tire and raise the rear off the ground also, It also can get pretty flexible if you drive on roads with the right amount of waves or seams in the concrete at just the right speed, it will start to cause the body to resonate and flex wildly. I notice it on certain freeway sections of Los Angeles if your driving with the top down.

[ATaylorRacing]

... I have seen the front core supports flex a lot....

I had to have the core support rewelded soooo many times in Matchbox when it had a stick. Must have driven home from the track at least 3 timers with the motor almost laying on the firewall and stuck in 2nd gear. Fixed it with a new core support...extra gusseting ...and an automatic...eventually bolted in a big metal bar rom the cross member to the front motor mount.

[5DIGITS]

With the entire drivetrain mounted in the front of the car on soft mounts, I am not sure how much chassis flex behind the firewall really occurs in drag racing an Lbody.
I have seen the front core supports flex a lot.
Tying it to the Kframe helps with that.

I agree, the rear strut tower support and it's connection to the body is more beneficial for handling.

One test being applied on the 2-door currently being built is the use of a Neon mount from the K-frame to the differential.
Please consider that pushing on an engine mount (especially the rear dog-bone mount) does not provide the same self-centering alignment as realized when a mount is being pulled.
The approach effectively drops the rear mount in the horizontal position so as the differential moves forward during acceleration it pulls rather than compresses the mount.
This provides linear pull and centers the load based on each end of the mounts connection points.
This ''self-centering' effect minimizes variable plunge depth loading within the CV joint, reduces side to side powertrain movement during aggressive launches and therefore increases vehicle stability.
Please note that the selected Neon mount requires that the large end isolator to be rotated 180degrees and an alternate mount could be researched already set-up for the application.
With this approach, the intent is to reverse the mount demand and place the primary load on the increased strength of the K-frame and minimize the secondary support to weaker front core mount.
This could eliminate the front core to K-frame gusseted bars that have been in use and upon test completion, may eliminate the front mount altogether.
This would open the lower front engine bay area up for FMIC induction plumbing, other enhancement hardware or simply allowing the engine harness to be taken off the engine and wired across the lower support.


FYI-
The Ultimate Daytona utilized two front engine mounts that split the loading via the second front engine mount but was a quite heavy apparatus to accomplish the task.

[85boostbox]

It would be interesting of what people have done to really strengthen the core support. Anyone done anything radical?

[contraption22]

I made a bar that connected the core support to the k frame and the bell housing. With the 2.4 swap, Brian Slowe built a much nicer one for me.

[thedon809]

I agree, the rear strut tower support and it's connection to the body is more beneficial for handling.

One test being applied on the 2-door currently being built is the use of a Neon mount from the K-frame to the differential.
Please consider that pushing on an engine mount (especially the rear dog-bone mount) does not provide the same self-centering alignment as realized when a mount is being pulled.
The approach effectively drops the rear mount in the horizontal position so as the differential moves forward during acceleration it pulls rather than compresses the mount.
This provides linear pull and centers the load based on each end of the mounts connection points.
This ''self-centering' effect minimizes variable plunge depth loading within the CV joint, reduces side to side powertrain movement during aggressive launches and therefore increases vehicle stability.
Please note that the selected Neon mount requires that the large end isolator to be rotated 180degrees and an alternate mount could be researched already set-up for the application.
With this approach, the intent is to reverse the mount demand and place the primary load on the increased strength of the K-frame and minimize the secondary support to weaker front core mount.
This could eliminate the front core to K-frame gusseted bars that have been in use and upon test completion, may eliminate the front mount altogether.
This would open the lower front engine bay area up for FMIC induction plumbing, other enhancement hardware or simply allowing the engine harness to be taken off the engine and wired across the lower support.


FYI-
The Ultimate Daytona utilized two front engine mounts that split the loading via the second front engine mount but was a quite heavy apparatus to accomplish the task.

Kind of like the dart and UF 200? They both use a single mount attached to the k frame.

[5DIGITS]

Kind of like the dart and UF 200? They both use a single mount attached to the k frame.

Exactly !!
Did a fair amount of work on both and the new US version of the Ducato (now called the ProMaster).
There are many vehicles now heading in that direction and the intent is to apply what we learned on those vehicles to improve the TD arrangement.

[85boostbox]

I made a bar that connected the core support to the k frame and the bell housing. With the 2.4 swap, Brian Slowe built a much nicer one for me.

Mike, what kind of NVH did you get when you did that. This car will be a spring, summer, fall daily, and don't want my teeth rattled out of my head it is too bad. I'm expecting a rough ride from reinforcing the chassis, so more NVH I'm expecting, but not beyond bearable lol.

[5DIGITS]

It would be interesting of what people have done to really strengthen the core support. Anyone done anything radical?

Maybe not a radical approach, but I've supported the front lower radiator core support a couple of different ways over the years.

The mildest approach was used on my Shadow VNT where a forward facing stick of angled steel (90 degree - 1"x1") was added along the entire lower lip of the core weld seem.
Holes were drilled every 6" and was bolted in place from the back side facing forward with corresponding 1" flat stock on the front.
This was done as structural rigidity is far greater of steel on edge versus the ability to bend it as flat stock.
After this was completed, 45 degree corners were tied from the added stock to the frame rails to reduce the load from the pinch welded core ends, where the core support meets the side rails.

The Charger had a few iterations similar to 'Contraption22' and the method of tying the front support to the K-frame but differed without a connection to the trans.
A similar second method used bent gusseted tubing to connect the front mount directly to the K-frame with what I'd describe as a very long dog-bone mount.
Mounting tabs much like the existing dog bone mounts on the K-frame were welded to the bottom of the front engine mount and tied rearward to the K-frame.
An improvement would be to split the connection to the K-frame into two points (essentially a "Y") to minimize L to R powertrain movement, distribute the load and reduce NVH.

The new method mentioned earlier in the thread will be stress-tested in the Spring and front mount removal will be determined.

[contraption22]

With the 2.2 it wasn't bad because it was all isolated with rubber. The 2.4 system uses Heim joints so I imagine there will be vibration.

Edit, all my OE type mounts were Polybushings.com pieces, not rubber.

[85boostbox]

Yea, I'll be using heim joints... Guess I'll find out in spring lol