Do the under hood braces stiffen up your A-body?

-
Ol'forest

Ol'forest

Well-Known Member
Joined
Apr 6, 2009
Messages
419
Reaction score
78
Location
Hamilton, New Zealand
Does anyone have any knowledge or oppinion, on if the under hood braces that run from the firewall to the fenders on 70's abodies actually stiffen the front end up any, or are they just there as something to tie extra wires and stuff to?
Any of you solo racers got any thoughts on this?
 
They actually reduce the flexing of the inner fenders while in a turn. I dont know how much,but my 74 Duster had em and it was quite happy at 50 mph in a highway offramp.
 
They were added so the front end could take a 5 MPH whack from the cowcatcher bumper without crinkling the inner fenders too badly.
 
Great, I didn't know that, I actually crinkled my right fender up some a while back, and it did fold in at that point, I was going quite a bit faster than 5mph though.
 
they're probably not the best in chassis stiffening solutions, but i'm sure they provide some improvement over an Abody without them.
 
frontmotorshot-1.jpg
 
Better off boxing the area ahead of the trans x member and behind the front wheelwell to the sill plate.Those underhood braces will help a little but not too much compared to the boxing method.
 
They were added so the front end could take a 5 MPH whack from the cowcatcher bumper without crinkling the inner fenders too badly.
Click to expand...
I agree.
Click to expand...

Chrysler doesn't. They think the braces were added as a running change in midyear '73 to eliminate visible fender shake. At least, that's what the TSB (page 1, page 2) says. It also gives part numbers and procedures for adding them to cars made before they were added to production—such as my own '73 Dart, which hasn't got the braces and has got visible fender shake.

There's a guy over on the slant-6 board taking more extreme measures to stiffen his car's front structure.
 
That makes alot of sense as the energy absorbing bumpers of the 73's wouldn't have offered the rigidty the early bumpers did.
Excellent info slantsixdan!
 
Ol'forest said:
That makes alot of sense as the energy absorbing bumpers of the 73's wouldn't have offered the rigidty the early bumpers did.
Click to expand...

Incorrect. The '73+ bumpers offer a great deal more structural strength than the '72 and earlier bumpers.

Guessing and assuming in the face of reliable information is…kinda silly.
 
Ol'forest said:
But as they are on tubular hydraulic mounts they couldn't offer any torsional rigidity to the frame.
Click to expand...



Why not? I took the bumpers and shock mounts off my 75 Duster in one peice. All most killed my self. The rear bumper with mounts was 85 pounds. The later shock mounts and bumpers are way more robust than the earlier ones.
 
Burntorange70 said:
Why not? I took the bumpers and shock mounts off my 75 Duster in one peice. All most killed my self. The rear bumper with mounts was 85 pounds. The later shock mounts and bumpers are way more robust than the earlier ones.
Click to expand...

I agree the front bumper and those beastly mounts would defintely help with tieing the frame rails together. With the rad support member being rather wimpy this is a good thing.

I think those underhood braces would help a lot more if they were tied to the shock mounts.
 
Strength, weight and rigidity are 3 different things, yes a 70's bumper is a stronger, heavier bumper, but the mounting system is designed to isolate impact from the car body. Think of all that weight sticking out of the front mounted on what is essentially two shock absorbers, you can see it wouldn't be very good for chassis rigidity. It is the only real difference between the pre and post 73's, so why the fender shake problem, given that the post 73's even have extra torque boxes added to the underside?
Ask a chrysler engineer.
 
You must log in or register to reply here.
-

Back
Top