Sagging Rockers anyone?

[Mach1 Driver 560]

A little background: since our Stangs are unibody and don’t have a chassis, the load is carried by a combination of components. The rear sub frames extend from the tail to an area under the rear seat. From there they are connected by the rear torque boxes outboard to the rocker panels. The rockers and floor bear the center load along the bottom of the car. If you have a coupe or fastback, some of this load is spread to the roof. If you have a convertible, an inner rocker is added back to back with the outer rocker to compensate for the absence of the roof. The rockers extend to the just behind the front tires, where the front torque boxes connect the load back inboard to the front sub frame.

I’ve been investigating how to install convertible inner rockers in my fastback. Street or Track did a good article showing how to upgrade a coupe/fastback https://streetortrack.com/Installing-convertible-rockers-into-a-65-68-p-14.html, but they noted that they ran into a problem that is seemingly on virtually all unmodified cars. The inner rocker they used is a straight box approximately 2.5 x 5.75 x 75. They found that just behind the front torque box (about 10” from the front of the rocker), the outer rocker began to angle up and was about 1/2” too high at the front. Since their new inner convertible rocker was straight, it was off by 1/2” at the front and they had to take measures to weld it properly, since the pinch welds were no longer in a position to weld to.

I put a straight edge under the pinch weld on my Mach and found the same condition- it angles up in the front 10” or so of the rockers. I have a southern California car where it rarely rains and was always garaged. She’s a survivor that has very little rust. You would be hard pressed to find a better preserved car. Here is my theory: I believe that the outer rockers on all our cars fatigue and bend just behind the front torque box. Think about it and it makes sense- most of the weight is in the front, and the weakest point would be right behind the torque box. Following that thought weight wise, I have a 351w with an FMX, and relatively low mileage on the body of the car at 73k. Suffice to say, that if mine does it, most of them do.

So I’m wondering if anyone knows if NEW replacement outer rockers are straight along the lower pinch weld area? Pictures of parts appear to be straight. If so that pretty well proves that the cars fatigue and sag over time. What the heck, they are only 10 times past their expected design life.

[moodster 55]

I don't think they could sag a half an inch over time.  Since the doors don't sag, you would easily notice that at the bottom where the door closes to meet the outer rocker.  You would see a giant gap in the middle.  My car is a california car still wearing the original paint and my bottom gap between the door and the rocker is consistent from front to back.

david

[det0326 179]

Hey Terry 

Don't really have any experience on this subject, never did it or researched it.  I am pretty sure Bob (RPM) on this forum did  this an I think he has mentioned this offset you speak of. I bet he could help.

[Mach1 Driver 560]

Someone on another forum mentioned that the door gap would become a problem, and in hind sight I think that's probably correct. RPM has done the modification, but I don't recall him mentioning the problem.

I'm hoping Ridge Route will ring in to give us his considerable experience. If anyone would know if the bottom of a new rocker pinch weld is straight, it would be him.

[RPM 1,190]

I attached my inner rockers at the rear angled plate of the torque box, not the front vertical plate. So I have no personal knowledge of the sag, only of what SOT writes.

[Ridge Runner 1,112]

Never noticed a sag ,i know the new inner rocker can somtimes be a bit wide and stick up above the top pinch weld and the bottom pinch weld ,i just trim it with a saws all and grind what is left. 

I have done several coupe to fast back conversions and coupe to convertible conversions and i can tell you even with all the outside sheet metal removed rhe rocker and door frame structure is very solid so i cant see it bending or bowing unless there has been some sort of wreck damage

[Ridge Runner 1,112]

This is a 67 with the outer sheet metal removed and the rocker door structure is so solid i can walk on it with out distorting it ,the sub structure will twist side to side but it will not flex end to end ,unless the torque boxes are cut free

[latoracing 256]

7 hours ago, Mach1 Driver said:

 

So I’m wondering if anyone knows if NEW replacement outer rockers are straight along the lower pinch weld area? Pictures of parts appear to be straight. If so that pretty well proves that the cars fatigue and sag over time. What the heck, they are only 10 times past their expected design life.

The bottom of the outer rocker does taper up 3/4" over a 19" area, front to back. When installing convertible inner rockers, I've had to modify the inners to accommodate this little feature. Your rockers are not sagging, just designed that way.  

[Ridge Runner 1,112]

I dont have pics but i have had a couple of converts and the inner rocker lip does hang below the outer rocker just below the door post ,you will usually see several short welds with the inner rocker hanging below the outer ,i have also seen where they trimmed this overhang with a saws all when the body was assembled ,they also somtimes trimmed above the door sill lip with a saws all ,so they were built this way

[latoracing 256]

When I was playing doctor on Vicfreg's '70 convertible I had more practice with this annoying issue. You can clearly see the inner rocker sticking out from under the outer rocker. Both parts were new.

Being anal, and wanting things like torque boxes to fit without modifying, the inner rocker had to be chopped up a little. The aftermarket inner rocker is welded together, and the original pieces were stamped, in the correct shape. A little trimming on the inside plate...

and a small wedge removed from the formed inside part...

makes things work out much better. 

There is a flange that I forgot to incorporate into the inner rocker to help attach it to the lower A pillar. I butt welded a strip along the top of the inner plate to fix this issue. On future installs I have a template ready to get this part quickly straightened out. 

Hope this explains a little 

Mike

[Mach1 Driver 560]

Thanks latoracing and Ridge Runner- I'm relieved that my old girl is not sagging and was designed that way. It does complicate the inner rocker design though. Among other things, I worked with sheet metal design for 46 years and intend to make custom inner rockers for my fastback that won't require cutting the floor at the outer rocker, and will be much more stout than the replacements currently on the market. Should be fun.

[Mach1 Driver 560]

36 minutes ago, latoracing said:

Hope this explains a little 

Mike

 

Thanks a bunch for the pictures Mike, that helps a bunch. Your earlier post that its 3/4" over 19" is definitely more than mine, but these beasties tend to vary a bit. Mine is 7/16" on the passengers side and 1/2" on the drivers in an area that's definitely less than 12" long

[Mach1 Driver 560]

17 hours ago, latoracing said:

 

 

 

 

There is a flange that I forgot to incorporate into the inner rocker to help attach it to the lower A pillar. I butt welded a strip along the top of the inner plate to fix this issue. On future installs I have a template ready to get this part quickly straightened out. 

Hope this explains a little 

Mike

Mike, this flange is butt welded to the top of the inner rocker cover? What is that, about 14 ga?

[moodster 55]

The inner rocker is 14 gauge.  You'll need a decent sized brake to make the custom piece that Mike is showing.  I took the opposite approach and modified the torque box to make it fit together nicely.

david

[RPM 1,190]

Careful with the (outstanding, and much needed) pictures guys. You'll get the forum shut down again. Some sarcasm and truth was used in this post.

[Ridge Runner 1,112]

I cant figure out what is going on here ,the pics are showing way over size for the screen on my cell ,i can shrink them down but the text gets to small to read ,could this be causing the picture problems for the forum? They show as 559 kb 

[Mach1 Driver 560]

4 hours ago, RPM said:

Careful with the (outstanding, and much needed) pictures guys. You'll get the forum shut down again. Some sarcasm and truth was used in this post.

Take a look at my post in "Its back, so WTF happened?"  Its not a permanent solution, since you don't know what will eventually happen to the picture hosting site, but it would relieve the gigabyte crunch here.

[latoracing 256]

9 hours ago, Mach1 Driver said:

Mike, this flange is butt welded to the top of the inner rocker cover? What is that, about 14 ga?

Yes, one of the few "thick" pieces of metal on the car 

 

8 hours ago, moodster said:

The inner rocker is 14 gauge.  You'll need a decent sized brake to make the custom piece that Mike is showing.  I took the opposite approach and modified the torque box to make it fit together nicely.

david

I attempted to fit my outer torque box over the unmodified inner rocker, when I was installing on my '70 FB. I was lazy and didn't want to mess with the box lol. 

[RPM 1,190]

6 hours ago, latoracing said:

I was lazy and didn't want to mess with the box lol. 

Sorry, I gotta call BS on this.