Convertible rockers

[Mach1 Driver 560]

I'm thinking of installing convertible rockers, but notice that the 64-70 convertible seat platform is one piece and has a rather tall section that goes over the transmission tunnel. This is supposed to improve rigidity. 
I have a 69 Mach and I can't help but think that this will interfere with the center console. Normally it doesn't have this added large lump (maybe 1-1/2" high) in the middle of the tunnel. Anybody done this modification?
Also, besides the carpet, what other changes are required to the interior? I suspect I'll have to put a notch for the new inner rocker in the rear side panels? How about the front kick panels?
FYI, Street or Track has an excellent write-up on the nuts and bolts of installing the rockers: http://www.streetortrack.com/Installing-convertible-rockers-into-a-65-68-p-14.html

Thanks

[RPM 1,190]

I highly recommend this to anyone who wants to stiffen up their creak box chassis. The inner rockers along with the 1 piece seat riser really make a difference. I did it a few years ago when my plan was to not use my center console.

Terry, you are correct that the lower center console edge must be clearanced to fit the contour of the hump. I also had to clearance a couple of other pieces which makes me think the convertible console is quite a bit different. Cutting an oem console isn't for everyone. 

The one piece seat riser also has the seat platform 1" higher, which wasn't any option for me or Latoracing. We both used the stock seat platform and spliced in the trans hump piece.

The tunnel reinforcement cuts into the available space at the inner seat rail, making the seat belt install mighty tight. 

Even with the added hours needed to modify the seat riser and console, I'd do it again. 

My kick panel vents were no affected. I'm not using my rear quarter trim panels so I can't comment on that. 

[Mach1 Driver 560]

2 hours ago, RPM said:

The one piece seat riser also has the seat platform 1" higher, which wasn't any option for me or Latoracing. We both used the stock seat platform and spliced in the trans hump piece.

Do you mean it wasn't an option because you wouldn't have had sufficient headroom? That isn't a problem for me, particularly now in my "Golden Years" since I'm 2" shorter than I was in high school. Golden years my ass!

 

 

 

[aslanefe 333]

My question would be what do you use your car for? Track? Sunny day cruise? I would say convertible inner rocker and seat riser is not needed for a sunny day cruiser; too much work with no gain. A noticeable improvement would be modifying UCA to increase caster (moving the ball joint 20 mm back gives +4-+5 caster or buy ready made +3 UCA), 1 inch UCA drop and roller spring perches. I am real happy with only those changes on my 70 Grande.

[RPM 1,190]

7 hours ago, Mach1 Driver said:

Do you mean it wasn't an option because you wouldn't have had sufficient headroom? That isn't a problem for me, particularly now in my "Golden Years" since I'm 2" shorter than I was in high school. Golden years my ass!

Yes, because of the decreased headroom Terry.

aslanefe  said:

My question would be what do you use your car for? Track? Sunny day cruise? I would say convertible inner rocker and seat riser is not needed for a sunny day cruiser; too much work with no gain. A noticeable improvement would be modifying UCA to increase caster (moving the ball joint 20 mm back gives +4-+5 caster or buy ready made +3 UCA), 1 inch UCA drop and roller spring perches. I am real happy with only those changes on my 70 Grande.

----------------------------------------

All I know is from driving mine and my brothers 69 Mach 1s which flexed  and creaked like crazy. He didn't add them to his car and mine is much more stable and stiff. 

 

I agree with the other mods you did, which I also did to mine. 

 

[aslanefe 333]

Yes, you are stiffening the car, there is a benefit; but unless you are restoring the car, already replacing floor pans, etc, it is a lot of work for a sunny day cruiser. I do not feel any flex or creaking on my 70 Grande, but it is an asphalt cruiser that is not pushed hard. It will be waste of time and effort for me to put convertible rockers etc on that car, I wouldn't feel/see any difference because of the way the car is driven. That was my point.

[Mach1 Driver 560]

No, it doesn't make sense for everyone. But, there is no need to remove the floor. The front suspension has to come off, but that's happening anyway. The torque box covers come off. The old seat pans are removed. The floor is strategically cut, holes are made in the floor pans for the rockers to pass through. Everything is welded-up. The sheet metal parts cost $288. Its mostly just time and effort. I'm retired and have an abundance of time. But as RPM states it stiffens the car like no other modification. SFCs do nothing for front to rear torsional twisting unless they have an X frame connecting the two, and even then it only reduces torsion by 3%. I can point you at the data.

BTW, I intend to add SFCs too, but not for the usual reason- I want to make some custom jacking points for my two post lift.

[aslanefe 333]

Make sure you figure out the rear seat buttom and the inside panels too, they may need modifications to fit with convertible inner rocker.

[Mach1 Driver 560]

45 minutes ago, aslanefe said:

Make sure you figure out the rear seat buttom and the inside panels too, they may need modifications to fit with convertible inner rocker.

Some people say the convertible rear seat isn't as wide, but it doesn't come close to the inner rockers, so I don't know why that would be. I think all I'll have to do is cut a notch out of the plastic inner panels for the rockers. I'll have to investigate.

[Mach1 Driver 560]

I found this template for cutting the console: Jim Osborn Reproductions Convertible Console Cutting Template 

Its for a 65-66, but the profile seems to match. I'm sure its safer to just make a cardboard template using a Home Depot contour gauge: 

[latoracing 256]

The rockers on a convertible do not interfere with the seat as they are flush to the raised rear section of the floor. The rear seat in a convertible is narrower due to the top well structure. There is a little more bracing in the lower section of the convertible that interferes with a regular seat bottom fitting along with the wider rear inner quarter panel trim pieces.

 In installing the 'vert rockers in a coupe / sportsroof, they stop at the front of the rear torque boxes, unless you are really ambitious and install the 'vert rear torque boxes as well. I never tried to install the quarter trim pieces in my car (mini tubed) but it shouldn't be a huge modification to fit the panels, if they need trimming at all. (I have been wrong before lol)

The one piece seat riser is debatable as the '69/70 cars did not use this structure upgrade. I installed it with the thoughts of running the lower seat pan reinforcements as well, so it might actually pay some dividends in structure rigidity. (I also have a multi point cage in my car) As I cut and removed a bunch of the seat riser, it might be doing nothing but adding weight to my car and my exhaust routing kept me from using the "stock" reinforcement pieces. I haven't given up on that yet.

The inner rocker upgrade brings these cars into a more modern area structural level. Go out an look at the girth of most new car's rocker areas, they are huge! This upgrade is well worth the time and expense IMO

MIke 

 

[Mach1 Driver 560]

2 hours ago, latoracing said:

The one piece seat riser is debatable as the '69/70 cars did not use this structure upgrade. I installed it with the thoughts of running the lower seat pan reinforcements as well, so it might actually pay some dividends in structure rigidity.

Huh, I didn't know that the 69/70s didn't use the one piece seat platform. A platform is sold for 65-70 but I suppose that is just because it fits all those years. That got me curious so I looked in my Osborn 70 Weld & Sealant Assembly Manual (I hope there aren't many changes from 69 to 70 as a 69 manual is not available).  It shows 10812-3 Front Floor Cross Lower on each side, and two platforms, one on each side on the top 10672-3 Front Floor Cross Upper.

So it wasn't clear- it sounds like you thought about installing the lower pans, but did you do it? How about you Bob?

[Vicfreg 771]

On my 1970 Convertible, I also added sub-frame connectors.  This may be an alternate solution if you don't want to go all the way with the other modifications discussed earlier in this thread.  No doors in these photo's ...the car is stiff.

 

[latoracing 256]

3 hours ago, Mach1 Driver said:

So it wasn't clear- it sounds like you thought about installing the lower pans, but did you do it? How about you Bob?

With the way I designed my headers, the stock pans will be "slightly" in the way. I have templates to fabricate some "custom" versions, but haven't gotten back under the car quite yet.

As far as your trimming of the inner rocker goes, this is how mine came out using cardboard.

[MAC390 327]

Really nice fab work.

[RPM 1,190]

3 hours ago, Mach1 Driver said:

So it wasn't clear- it sounds like you thought about installing the lower pans, but did you do it? How about you Bob?

Installing the lower pans didn't cross my mind while doing the rockers and seat riser. Once I started on the 6 point roll bar I figured it was moot.

[RPM 1,190]

Just now, MAC390 said:

Really nice fab work.

Mike's work is right up there with the best. 

[Mach1 Driver 560]

1 hour ago, latoracing said:

With the way I designed my headers, the stock pans will be "slightly" in the way. I have templates to fabricate some "custom" versions, but haven't gotten back under the car quite yet.

As far as your trimming of the inner rocker goes, this is how mine came out using cardboard.

Very nice work. When you get around to it let us see what you did to the lower pan- I'll probably need to do something similar.

[Mach1 Driver 560]

Following is a timely and very interesting post in a thread titled “Torque boxes vrs subframe connectors”, on 1-27-18 in VMF. Both patrickstapler and Huskinhano are senior members of VMF and are very knowledgeable and respected. Patrick’s profile does not mention his occupation, but from the math I have to assume he is a mechanical engineer. Patrick is having a spirited debate with Huskinhano about the merits of convertible inner rockers and related parts. If there will ever be a resolution to this argument it is because of the math stated here.

 

Patrickstapler:

Alright...lets do this again. Read the whole thread or just these parts below...up to you. Chassis stiffening

Quote- originally posted by Huskinhano

 

Originally Posted by patrickstapler Tom, you Shaun has a very detailed page on his site about lowering the 'vert seat pan. It does remove "some" of the structural support but not all. If you are considering a partial cage already, another addition is to remove the seat pans altogether and tie the 'vert inner rockers across the mid section with formed tubing to the floor and then add stringers front to rear for attaching the seats.

Pat, I saw Shaun's post on that. Shaun made note of possible losses of the modified seat pan IIRC. Let's say one foregoes the seat pan due to their height. Just how effective are the inner rockers now? This is something you could probably answer, the stamped steel inner rockers have a larger CSA (cross sectional area) then the steel 2x2 tubing. Would the stamped sheet metal rockers with their larger CSA be stiffer then the 2x2x.125 tubing with it's smaller CSA even though the wall is thicker?

The reason I have given thought to a 6 point cage, I'm not really crazy about the idea but it would solve a few issues. It would make the body a lot stiffer. The main reason is I would like to try the standing mile with the ECTA at Wilmington OH. One of the guys on Bangshift who I'm friendly with not only races a S10 with a Mercedes 4 cylinder diesel but is on the tech committee. He said 3 point belts is all that's require to run up to 135 MPH but on older cars they really like to see a 6 point cage. There is some safety on the street with the cage but having the cage would require different seats and 5 point belts. The old snow ball effect. Then again do you want to be climbing over side bars to get in and out? I know they make swing away kits and you could just keep the side bars out on the street but then you're taking away from the structural rigidity defeating a main purpose of the cage.

End quote by Huskinhano

 

patrickstapler continues:

The difference between the two are pretty drastic. You have to consider the section modulus (generally the resistance of a shape to bending) and the inertial moment (generally the resistance of a shape to twisting) between the two shapes. Comparing a 2"x2"x.125" square tube to a 3"x6"x.06" (guessing at rough size here) 'vert inner rocker it looks like this:

Square Tube
Section Modulus = .55 in all directions
Inertial Moment = .55 in all directions

'Vert Inner Rocker
S(x) = 1.81 S(y) = 1.24
I(x) = 5.42 I(y) = 1.87

In reality, the differences may be more substantial than this with the 'vert inner rockers as they are essentially the mirror opposite of the outer rockers all welded together. I believe (and I may be wrong) the factory install of the 'vert inners was a only a outer and inner section welded together with one vertical divider wall. What I did on my car is weld in the full inner rocker with its own vertical wall to the already existing outer rocker with its own vertical wall in place. My car effectively has complete rocker assemblies welded back to back with spot welds top and bottom and full stitch weld along the top edge of where the two rockers meet.


So from the above, I imagine the reason Ford added inner rockers is to keep the car from breaking in half length wise...since there is no roof structure to perform that function. From the numbers above, you can clearly see that simply adding a pseudo full frame via sub-frame connectors would most likely not prevent this type of failure. Second, I imagine the reason Ford added the inner one piece seat pan AND the outer seat pan boxes WITH solid plate tying the two together at the hump is to alleviate twisting...again, no roof to perform that function.


Now apply these principles or thoughts if you will to hardtops or fastbacks. Yes they have a roof to perform the functions of alleviating longitudinal bending and twisting. However, only enough to keep the car from failing. Ok, so lets add some sub-frame connectors. Again, using the numbers above, you can clearly see they do not and will not perform the same task as adding inner rockers. Now lets add cross bars between the sub-frame connectors. Ok, we have maybe eliminated some small amount of twisting. Visually if you will, now imagine instead of cross bars of say 1 3/4" x 1/8" wall (guessing here) which has a section modulus of .24, we add all of the 'vert inner and outer seat pans and 'vert inner rockers. We have already proven via math, the sub-frame connectors pale in comparison to 'vert inner rockers. So compare the cross sectional area (more cross sectional area...higher section modulus...less movement) of the inner and outer seat pans that span the entire width of the floor and weld to the entire width of the floor top and bottom and weld to the 'vert inner rockers. You can see you have effectively created a huge boxed in inner and outer structure that is welded side to side, top to bottom, and inner and outer versus simply tying the front and rear frame rails together which do very little to prevent twisting or adding two small tubes side to side which also do very little to prevent twisting.


I'm not saying the sub-frame connectors or cross bars do nothing. I am saying they do very little in comparison to other methods. I will also admit that adding the 'vert parts with torque boxes may not be for everyone. It is a very invasive and time consuming project. Not to mention you do have to deal with the hump over the hump and use some of the 'vert interior pieces. This may also not be for everyone.


These are just my thoughts...they may not be considered accurate by some or all. However, I also believe if Ford could have gotten away with simply adding sub-frame connectors and cross bars, they probably would have because it is a hell of lot faster and less expensive.

[Vicfreg 771]

Good stuff!

I am a Mechanical Engineer as well. 

I have the full inner and outer rockers, subframe connectors, and built up shock towers.  

More is better, especially on the Convertibles.  

 

[Mach1 Driver 560]

15 hours ago, Vicfreg said:

Good stuff!

I am a Mechanical Engineer as well. 

I have the full inner and outer rockers, subframe connectors, and built up shock towers.  

More is better, especially on the Convertibles.  

 

Agreed, I plan on both rockers and SFCs. I know the upper seat platform and lower boxes prevent twist, but dang both cause problems. The seat platform will mess with the console and the lower boxes are in the way of the exhaust. What did you do in these areas? I guess the question for a fastback is how much is enough?

[RPM 1,190]

17 minutes ago, Mach1 Driver said:

Agreed, I plan on both rockers and SFCs. I guess the question for a fastback is how much is enough?

I too have sfc.The answer to your question I give credit to my oldest brother: too much is not enough :)

[Mach1 Driver 560]

4 hours ago, RPM said:

I too have sfc.The answer to your question I give credit to my oldest brother: too much is not enough :)

I say it a little differently: too much is never enough