burners

While working on construction of a spreader bar I decided to measure the flex of the frame. I measured between the front A-arm cross shafts. The dimension with the weight on the wheels was 24.44". Then I jacked the car up and put jack stands under the frame just in front of the door and measured again. With the weight off the wheels it was 24.5". That's not much of a difference. Now I just recently welded all the seams on the frame from the firewall forward. I'm sure this added to the stiffness of the frame but I'm wondering how much.


If anyone has similar numbers to compare I would be interested in seeing them. I know that cornering loads will tend to flex the frame more and thus validate the need for a spreader bar, perhaps. I would like to see some more data from other cars to see if there is measurable flex in these two conditions.

redvetracr

As my racer sat on the alignment rack I adjusted the spreader bar and watched the settings change..... ...redvetracr

WESCH

Hi

I installed the VBP bar on my 68 BB with the front centrally jacked, bar adjusted for slip fit.
When lowering it back on the floor, I had to loosen the bar nearly 2 full turns.
This being 4 full thread length. And that's only with the weight of the car + engine. Can you imagine driving over a bump or cornering ect. :eek:

I also saw a friends SB car with a cracked A-arm attachment to the frame.
I hope the spreader bar eliminates this type of flex cracks. :seeya

Gunther

burners

That's is, indeed, interesting. So it seems that the frames are flexing quite a bit. I have no doubt that you can change the dimension between the A-arms by threading the bar. I just wonder how other cars actully compare in terms of flexing. It sounds like both of your cars have a lot of movement in the frame.

Twin_Turbo

burners, what all did you do to your front end? I'm going to install a sort of spreader bar (but not one that bolts to the cross shafts but one that will bolt to seperate ears on the suspension mounts)

I boxed the snot out of my front end, hopefully this will be enough to kee the thing from twisting.



There's gussets on the front, on the rear, on the engine mounts, the frame horns are boxed up and there's a reinforcement plate under it so the sway bar won't twist the whole deal, also all those holes in the frame are plated over, including the large one for the power steering ram bracket.

burners

TT, the surprising thing to me is that I haven't really done any reinforcement or gusseting. I only welded all of the seams and the lower A-arm mounts. I don't have a spreader bar yet and I'm taking some baseline measurements before I start designing reinforcement pieces.

Everything looks pretty good on your frame. Although I would reinforce the lower A-arm bolt block so it ties into the vertical part of the frame.

Twin_Turbo

That was the next step. I was planning on doing that today also but I ran out of the correct gauge steel, I only had the really thick stuff I used for the gussets

WESCH

Hi TWIN TURBO

Looks good,
The Front crossframe is an arc , the wheels are outbd & under the frame and will bend the frame/A-arms under heavy load.
The spreader bar is attached to the top end of the A-arms and will eliminate this crossframe arc bending.

I agree that strengthening up the original frame by rewelding it all etc is also helping.
Spreader bars are widely used on many cars to keep the domes from flexing inwards under load.

Do I misunderstand anything ?

Gunther :seeya


[Modified by WESCH, 3:27 AM 5/22/2004]

Twin_Turbo

I know how the original frame looks and how to reinforce it ;) As I said, I will use a spreader bar, it's called a spring mount bar here, I will mount mine on ears welded to the upper suspension mount because I don't like the fact that the spreader bar bolts over the cross shaft, meaning you have to remove it to do some suspension tuning. It would also be in the way of other things cluttering up that area. The front frame flexing is a serious problem, I've seen many cracked frames and sheared suspension mounts, that's why I welded all those up too (cheap azz factory used the same lower moutn on the left and right, so it doesn't even fit worth anything in stock form)

The things that will help most, apart from the spreader bar is the thicker plate under the crossmember, the boxed up front horns with gussets (large ones) and the fact that i plated over the holes in the frame,. In stock form the frame flexes a lot, especially from the forces the steering box puts on the drivers side. Some frames will noticably flex when yous teer while standing still.