Subframe connectors

[Dino]

Yeah with all this talk of upgrading steering and suspension, I'm ashamed to say that my car still does not have subframe connectors. So that needs to change. I initially planned on installing the US Cartool set that contours to the floor, but I stepped away from that idea because the floors would need a lot of prep, and I have a lot of insulation stuck to the floorboards that I don't want to disturb. So what are my other options? Hotchkiss seems pricey for what it is. There's these from Chassis Engineering. Or I could make them myself. The Chassis Engineering ones look like a good deal though. With the connectors welded in place, do I really need anything else for a street driven car?

[b5blue]

The classic Mopar B body connectors. 

[b5blue]

https://poormanmotorsports.com/competition-engineering-3117-1966-1974-mopar-b-body-subframe-connectors-bolt-on-2-x-1-12-tubing-stee

[Kern Dog]

For a fraction of the cost, you can go to a metal supply store and just get two lengths of 3 x 3 x .90 thick square tubing.
You could use 2 x 3 tubing too. I've never bought actual pre cut connectors, I've always made my own. I've done 3 B body cars and 2 A bodies.





You can do this yourself. You just need a Sawzall, grinder and welder.
Good luck, man!

[metallicareload99]

If I recall correctly, you have excellent metal working skills? I imagine you could probably save money and end up with nicer results fabricating with square tubing 

[Mike DC]

 
IMO subframe connectors are helpful but it's not the whole story on stiffening the chassis. 


We have two examples of the factory trying to stiffen the B-body chassis - the ragtop convertibles (and Hemi 4spd cars), and the 1973 redesign. 

On the convert/Hemi cars they did torque boxing at both ends of the rocker panels.  For the 1973 redesign they did torque boxing on the front subframe + they braced the shock towers to the firewall + they boxed the lower radiator brace between the front subframe rail. 

The boxed radiator support has an asterisk. The 1973 redesign also switched the K-frame over to rubber mounts at the same time, so they lost any stiffening gains they were getting from the rigid K-frame.  On the other hand, XV motorsports also saw gains from rad support boxing even on rigid K-frame cars.   

[Dino]

Yeah I suppose I could just make some myself. And even if it doesn't improve the overall ride by much, it won't hurt it either. Alright so subframe connectors, Borgeson steering, and QA1 UCAs, that hopefully are an improvement on the stock UCAs with offset bushings.
I already have a welded and gusseted K member, and reinforced LCAs

[Mike DC]

Subframe connectors have a pretty much 100% approval rating from people who install them, whether it's a race or street car.  You never hear anybody saying it wasn't worth the trouble.   

I will say there's no need to cut the floor up for them.  Nor to use very thick tubing.  You only need to add stiffness between the subframes until that area of the chassis stops being one of the weakest links in the chain. 

The factory subframe rails and T-bar crossmember were stamped out of 13-guage steel IIRC.   
14-guage is a common option for steel square tubing, which is the next size thinner than 13. 
11-guage is 1/8" thick.     

[metallicareload99]

I didn't realize you didn't have any frame stiffing. Not trying to plant the idea, but it might ride better after doing it  at the very least it should allow the springs do what they are supposed to do and let the shocks do their job without the unibody interfering.

This operation hook thread has some ideas on how and what to fabricate, especially the second page:

http://www.dodgecharger.com/forum/index.php/topic,41726.25.html

[Mike DC]

The purpose of connectors/stiffening gets easier to understand if you think of the car like a skateboard. 

With the sway bars, you are trying to fine-tune the stiffness at each axle.  But it won't help if the board deck itself is made of flexible plastic.   

[Kern Dog]

Another way to look at it is that the more flexible an unreinforced chassis is, the more it acts like a spring of its own, sort of like building a house on sand where the ground beneath you moves and shifts around even if the house itself is well constructed.
I welded mine in on my back with no car lift in 2014. I did the work before I installed the car lift. I also painted them to blend in like a factory effort.
None of that is necessary nor does it affect performance. I just did it for appearances.

[matrout76]

Chris Birdsong has some good info in this video starting around the 5:20 mark:

https://www.youtube.com/watch?v=E40xqkkT6Ts

i wish i would have seen this before installing my US Car Tools subframe connectors.  His comments about extending a piece up to the front frame rail make a lot of sense.

[Mike DC]

I wish i would have seen this before installing my US Car Tools subframe connectors.  His comments about extending a piece up to the front frame rail make a lot of sense.

His view about the connectors in the video is not wrong. 

But when it comes to doing it better, I think you could probably get most of the stiffening benefit without cutting through the T-bar crossmember.  Just make the connector full-height where it meets the back of the T-bar member (like the CarTool connectors are).  Then add a minor extra brace ahead of the T-bar member (between it and the front rail).  That should give you a lot of the stiffening benefit without hacking a square tube right through the T-bar member. 

Stiffening is about rigidity.  It's different from brute strength.  A 5-foot-long cardboard mailing tube is stiffer than a 5-foot-long piece of steel rebar. 

This whole issue (vertical/beam stiffening the subframes, from the front rails to the rear rails) is what the Chrysler's torque box plating was for.  If you connect both subframe rails to the rockers better, then the subframe connectors between the rails are less critical. 

I think there's a tendency in the hobby to focus too much on subframe connectors, at the expense of other areas where the chassis flexes.       



Again, I'm not claiming Chris Birdsong's take is wrong.  I'm just offering some other suggestions.

His sway bar engine mount thing is interesting.  But I would like it better as an addition to the factory engine mount, rather than a replacement for it.  If the sway bar mount is the only mount on the driver side, then you are relying on the passenger side mount to locate the engine in more directions by itself.  (I wonder how well the engine would stay located in a hard crash, for example.)   

[Dino]

What do you think of this?

https://youtu.be/ZjOJveyZn_c?si=8nh3i7ff9l9PFRJi

[Kern Dog]

That guy is half an idiot.
He tries to make the claim that the factory designed the cars to flex? No, they designed a car at a price point that would likely last 5-8 years and be replaced. They were aiming to build a quality car at a competitive price. Factories are capable of building a rock solid car that lasts 40 years but who would pay for it?
Tony has some good points occasionally but many times he comes across as a "Flat Earth" guy wearing a tin foil hat.

[Mike DC]

I also disagree with Tony on this one. 

People have been putting subframe connectors on muscle cars for decades.  There is no inherent problem as long as the design & mounting are done well.  The unibodies are better off with more stiffening.  The factory left the gap between the subframes for bean-counting reasons. 

The Hemi 4spd cars were better off with torque boxes, and yet the factory built most B-bodies without torque boxes.  Bean counting.   Mopar police cars typically had more welds on the body than standard.  I'm not sure about the 1960s ones, but by the 1970s they sometimes had extra torque boxing too.         

Jeep Cherokee XJs (the boxy 1980s-90s ones) have been put through all kinds of chassis twisting & abuses in the last 40 years.  They were unibodies with welded-on subframe rails running the full length underneath.  The stiffness helped them. 

European WRC rally cars are beefed-up production unibodies.  They do "wear out" the bodies but it's only through wild abuses.  They do tons of rollcaging and seam-welding on the bodies to reinforce them.  The mechanics would laugh if you suggested they might be making the body too rigid.     

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

The argument that "frames need to twist" depends on the design.  Trucks are built that way.  The flexing frame is effectively part of the suspension from day one.  The frame & bed & cab are separate pieces, to let things move and spare them damage.   The frames are long pieces of thick un-boxed C-channel with a lot of extra metal.  That gives the frame room to flex safely.  The cabs aren't supposed to be flexing like that. 

A unibody car is more like a rollcaged NASCAR.  The chassis/body is designed to stay basically very rigid, and make the suspension do all the work.
At some point in the 1990s/2000s the NASCAR teams tried adding more stiffening to see how far they could go.  I've heard they eventually stopped because there weren't any more gains from it.  They reached a point where it was eating up the tires quicker with no other benefits.  But it never hurt the body/chassis.     

[Dino]

I was very confused when I saw this. Thank you for clearing that up.

[Kern Dog]

Tony is like the crazy guy at the end of the street that sometimes strikes gold with his "wisdom" but most of the time, he comes across as a kook.

[Mike DC]

 
IMO Tony has a decent understanding of a lot of things.  He's just wrong about this one. 

Subframe connectors have been a regular thing on unibody street cars since at least the 1980s.  There were articles about installing them in car magazines in the 1990s.  It has been done for decades on Mopars, Fords, Chevys, etc.  If there was a problem with "over-stiffening" the unibody then we would know about it by now.  The feedback/evidence all runs the other way.  More stiffening is a benefit as a general rule.