Subframe Connectors and unibodies

[66 Sat]

I've just fitted bolt-in subframe connectors to my car and confirm they make a HUGE difference, just in normal driving.

I fitted them this past weekend and drove the car this afternoon. It felt immediately better, much tighter, and cornering is a revelation, it stays so much flatter, but it's better in every way, acceleration, braking, the lot.

I went with the Competition Engineering ones from Sunmit. Very well made, black powder coated finish. Total weight of both connectors, bolts and plates is 12kg.

One thing I will say - they are a pain in the *** to install. They are made to very tight tolerances (with regards to the bolts and the holes in the connectors and the support plates) but unless the holes you drill are as perfect in terms of tolerance, then getting the bolts through will be painful, and will require some enlarging of holes, which defeats the purpose of the tight tolerance...
Welding them in would be easier and quicker. I used a magnet and vacuum to clean up the thousands of metal shavings left behind in the box sections after drilling.

Mine are in, and tight, but I'm going to weld them as well to prevent any future potential loosening.

Also consider access - you physically can't get a drill at the correct angle for the rear outside top hole as the sill is in the way, so you need to drill through from the centre of the car outwards, but then your muffler might be in the way. I used a 90° drill adapter to drill a pilot hole from the outside so the main hole didn't wander when going through the outer wall of the box section, and luckily I had enough room as I have cylindrical glasspack mufflers.

I'm amazed that what I've always perceived as the flex in the suspension components, steering, tires etc was mostly in the chassis itself. I'm sure the welded through the floor connectors would add something extra again, but just tying the 2 halves of the car together must surely achieve most of the same effect. I'm super happy with the result.

 

[AMX364]

On a 70 Barracuda convertible, I had a rattle that I could NOT find, even with everything out of the car. Driving down the road I noticed movement in in the side mirror. Moved hand by door seam and felt the door moving around. Found it. Installed weld on subframe connectors. This was about 1980, so choices were few. It did fix the rattle. This was a stock type 383, so no real high power issues. I now install frame connectors on any RWD car that I own. None on Omni Turbo FWD.

 

[Dennis H]

Welding seems best. The USCartool’s in mine were welded in by Joe Sanderson (RIP). He ended up in the ER with a horrible rash due to scraping off the undercoating in summer with inadequate clothing. They took a number of rattles and jitters out.

Transformation.

Between the radial tires (bought with Bias and G70’s) and the USCartool, the previous owner would not know the car.

 

[fesser]

The difference with mine is I used tubular instead of rectangular connectors. The tubulars resist twist better (by how much I'm not sure).

Interesting. I am planning on building my own, and hadn't considered using cylindrical tubing until I read your post. A very shallow google search brought up results that were consistent with what you posted about strength (I also didn't see anything showing by how much). I sort of like the idea of no flat surface hanging just below the floor as it seems a radius would be less likely to accumulate junk and debris. Although, using something to seal it to the floor (like Kern did) would mostly alleviate that concern. I wonder if there is a downside.

 

[68 Sport Satellite]

Interesting. I am planning on building my own, and hadn't considered using cylindrical tubing until I read your post. A very shallow google search brought up results that were consistent with what you posted about strength (I also didn't see anything showing by how much). I sort of like the idea of no flat surface hanging just below the floor as it seems a radius would be less likely to accumulate junk and debris. Although, using something to seal it to the floor (like Kern did) would mostly alleviate that concern. I wonder if there is a downside.

the only downside with mine is that by design (Global West brand), to accommodate the cylindrical shape and welded end brackets they are not tucked in as tight to the floor as some of the square channel type, so they are partially (maybe 15%) visible when standing back and looking at the car at ground level. Unibody stiffness and handling improvement is amazing.

 

[71Beeper]

These connectors were bolt in ones and were on the car when I bought it. Problem was that the rear portion sat under the rear frame rail and was visible when looking at the side of the car.
So I had them tucked into the rear frame rail before adding the rear torque boxes.

 

[MoparJW]

I've just fitted bolt-in subframe connectors to my car and confirm they make a HUGE difference, just in normal driving.

I fitted them this past weekend and drove the car this afternoon. It felt immediately better, much tighter, and cornering is a revelation, it stays so much flatter, but it's better in every way, acceleration, braking, the lot.

I went with the Competition Engineering ones from Sunmit. Very well made, black powder coated finish. Total weight of both connectors, bolts and plates is 12kg.

One thing I will say - they are a pain in the *** to install. They are made to very tight tolerances (with regards to the bolts and the holes in the connectors and the support plates) but unless the holes you drill are as perfect in terms of tolerance, then getting the bolts through will be painful, and will require some enlarging of holes, which defeats the purpose of the tight tolerance...
Welding them in would be easier and quicker. I used a magnet and vacuum to clean up the thousands of metal shavings left behind in the box sections after drilling.

Mine are in, and tight, but I'm going to weld them as well to prevent any future potential loosening.

Also consider access - you physically can't get a drill at the correct angle for the rear outside top hole as the sill is in the way, so you need to drill through from the centre of the car outwards, but then your muffler might be in the way. I used a 90° drill adapter to drill a pilot hole from the outside so the main hole didn't wander when going through the outer wall of the box section, and luckily I had enough room as I have cylindrical glasspack mufflers.

I'm amazed that what I've always perceived as the flex in the suspension components, steering, tires etc was mostly in the chassis itself. I'm sure the welded through the floor connectors would add something extra again, but just tying the 2 halves of the car together must surely achieve most of the same effect. I'm super happy with the result.

View attachment 1788765

I also installed these, I think they work very well.

Drilling the holes perfectly for the bushings in the rear to be able to fit was a pain indeed.
I found that after some months of driving, the holes for the bushings in the rear started to elongate, so I welded them, and the connectors worked better after that.

You could also fill up the area in the torsion bar crossmember, where the bolts pass through, with bushings/washers, so you can get those bolts really tight without compressing the crossmember walls.

 

[68-500]

The area that is circled is my problem with traditional SFC’s. Where the front rail connects to torsion support there is an internal support connecting front of TS to rear TS. Where the SFC connects to the TS its empty, nothing connects rear and front of TS. Your just welding to a piece of sheet metal. Even if you where to open up the TS and weld to both front and rear of TS you just created a hinge between FR and SFC. To remedy this you either need to do Chris Bird song method or angle SFC out to where the FR meets the TS thus eliminating the hinge between FR and SFC. I’m not a structural engineer but life experience tells me traditional way is a compromise.

 

[j-c-c-62]

The area that is circled is my problem with traditional SFC’s. Where the front rail connects to torsion support there is an internal support connecting front of TS to rear TS. Where the SFC connects to the TS its empty, nothing connects rear and front of TS. Your just welding to a piece of sheet metal. Even if you where to open up the TS and weld to both front and rear of TS you just created a hinge between FR and SFC. To remedy this you either need to do Chris Bird song method or angle SFC out to where the FR meets the TS thus eliminating the hinge between FR and SFC. I’m not a structural engineer but life experience tells me traditional way is a compromise.

View attachment 1789263

The only thing you're thinking IMO is slightly overlooking here is, the forces input into the TB crossmember basically/mainly flow thru the rear fitting of the TB, into the crossmember, and continues over to the FR to support the front of the chassis/engine. So, connecting the SFC somewhat midpoint between the TB and the FR connection IMO has merit, vs favoring one side or the other. Now improving that midpoint connection is worthy and it is possible. In my attached pic of an A body I had the luxury? of removing the floor pan in that area and allowed me to add internal bracing as needed. It may be difficult to spot but I also added a welded plate with plug welds to the OEM crossmember before welding in the SFC as reinforcement.
Your concern about this important "sheet metal" connection is valid and rather rare.
On the topic of round vs other shapes for SFC, I believe is misguided. If the SFC was a complete standalone structural member, torsional stiffness of round would be useful. But in this case, it is part of a system that appreciates the torsional stiffness of the complete design, and torsional stiffness of individual pieces are not the key to that goal, roll bars are a different animal and not a good analogy in this discussion. SFC connectors have a number of other forces to deal with besides torsional stiffness. I will admit round SFC makes for good marketing.

You can see more pics here starting around pic #26
72 Swinger Track day/ProTour practice car

 

[Crackedback]

I've just fitted bolt-in subframe connectors to my car and confirm they make a HUGE difference, just in normal driving.

I fitted them this past weekend and drove the car this afternoon. It felt immediately better, much tighter, and cornering is a revelation, it stays so much flatter, but it's better in every way, acceleration, braking, the lot.

I went with the Competition Engineering ones from Sunmit. Very well made, black powder coated finish. Total weight of both connectors, bolts and plates is 12kg.

One thing I will say - they are a pain in the *** to install. They are made to very tight tolerances (with regards to the bolts and the holes in the connectors and the support plates) but unless the holes you drill are as perfect in terms of tolerance, then getting the bolts through will be painful, and will require some enlarging of holes, which defeats the purpose of the tight tolerance...
Welding them in would be easier and quicker. I used a magnet and vacuum to clean up the thousands of metal shavings left behind in the box sections after drilling.

Mine are in, and tight, but I'm going to weld them as well to prevent any future potential loosening.

Also consider access - you physically can't get a drill at the correct angle for the rear outside top hole as the sill is in the way, so you need to drill through from the centre of the car outwards, but then your muffler might be in the way. I used a 90° drill adapter to drill a pilot hole from the outside so the main hole didn't wander when going through the outer wall of the box section, and luckily I had enough room as I have cylindrical glasspack mufflers.

I'm amazed that what I've always perceived as the flex in the suspension components, steering, tires etc was mostly in the chassis itself. I'm sure the welded through the floor connectors would add something extra again, but just tying the 2 halves of the car together must surely achieve most of the same effect. I'm super happy with the result.

View attachment 1788765View attachment 1788767View attachment 1788768

Weld them in, if you can. AS others have mentioned, the bolt holes/bushings will elongate over time

 

[DeltaV]

He ended up in the ER with a horrible rash due to scraping off the undercoating in summer with inadequate clothing

Asbestos or some type of chemical reaction from the "tar"?

 

[RemCharger]

And that right there tells you they work.

 

[j-c-c-62]

Asbestos or some type of chemical reaction from the "tar"?

Because of the hazards and extreme costs to rectify, shared knowledge of the use of asbestos in the undercoating of older cars is seldom mentioned.
Asbestos hazards can be severe if not life threatening but likely occur many years after initial exposure. Meaning the crap you might scrape off your car in your garage onto the floor will affect your kids long after you are long gone and they have discovered a cure or lung transplants have become perfected, we hope.

 

[ckessel]

And one of the reasons you should be wearing at least an N95 rated mask when removing old undercoating. Or a lot of other stuff that creates dust. Keep that stuff out of your lungs.