Hot Rods Flex City: Can your car do this?

I was broswing the pics that our fantastic Jim Marlett posted from the last drags, looking for my roadster in action. I got more than I bargained for.
In the hunt for the Yahoo cup, Porknbeaner and I have constatly made modifications to my roadster and it has paid off well, but we're not there yet.
We have dropped my E.T.'s by 2 full seconds and 2 more to go, but that's not the point. I noticed something that we knew would be an issue and planned on attending to this year, but I didn't know how close to the danger zone we had come.
Take a look and see if you can spot it.
http://jimmarlett.zenfolio.com/p888501656/h480d5514#h480d5514
and
http://jimmarlett.zenfolio.com/p888501656/h480d57d4#h480d57d4

Here's a shot 'at rest'. It may need some lightening to see the difference.
http://www.jalopyjournal.com/forum/album.php?albumid=766&pictureid=100658

Now, detectives, see if you can find the evidence of looming trouble.
Oh, by the way, these types of reviews are something everyone should be conducting on their car periodically, for saftey's sake.
Know your car. Know your car better then your lover...
r

 

are you talking about the rear bones flexing?

 

Yep and that is without traction. 5 wide 900 year old bias ply truck tires. Can you imagine what traction would do to it?

Well I have slept on my driveway a couple of nights.

 

Anybody ever tell you, the lawn is more comfortable?

 

"are you talking about the rear bones flexing? "
Bingo.
See how much flex that bone is providing ahead of the short ladder I put on top of it?
Needless to say, we will be building another, stronger set before the next drags, oh an a few other things, too.

It boils down to this, how many of you know exactly what your car is doing while you drive it? Are there any bugs that need to be fixed? Is there anything you don't know about that could cause you heartache if left unattended?
This is serious stuff to think about when you build a car.
We all should take a good look at what's going on with our cars periodically.
You just might save a life.
r

 

it is widely known that the driveway is much warmer...

 

There was a newby that ran a thread earlier this year doubting any flex in Ford rear bones. (torque tube or open drive, they were 'engineered' to resist flexure from any torque applied)

Just like a lover, one might suspect trouble looming when the 'U' joint starts shuddering: Either she's real turned on, or something's getting ready for an explosive climax!

 

I thought it was common knowledge that original bones flex when torque was applied to them.
Sure its been debated.
They were designed to provide triangulation placement and a torque tube provided the torque support against a sub 100 HP engine. In their original application they never see any significant torque load if any.

Converting to open drive shaft without replacing the function of the torque tube is something I wouldn't do & especially if I was upping the output of the engine.

 

Photos are a good idea. So is having a friend watch your car at the drags.
I told my buddy that the rear end on his gasser '55 Chevy was jumping forward and backward at launch. He broke a trans mount on the next run and didn't know why until I told him.
It's also a good idea to get photos at the end of the track - sometimes the wind is doing odd things to the car at speed (like the '55 Chevy at the 2010 HAMB drags with fiberglass front fenders that were flapping out like wings when he got up to speed).

 

Bugs!!!

No one has upped the output of the engine yet. It has made that much torque and HP since the first day I fired it.

I think that countless rods have been built for the last 60 or so years anyway where the bones have been split and no torque stay has been added. The 100 hp or less is probably the golden rule on them, well that and no modern tires that are going to bite.

I don't think that the raven regognized how much stress that the radius rods were taking. With those tires the roadster was like driving on oil, and he was peddling it just to get it to 3rd gear.

I don't think that most of the fellas realize what is happening to their suspension components either. Now I look at things differently than most but I think the point is that one should have some idea before their rod leaves them in the ditch. I am probably completely off base here but that is what I come away from this with.

 

This is very important in a street car too.

A friend has a 27 roadster that if he gets on it hard,it will break one of the attachments at the rear hairpin rods....upper one I think, and if I recall, it uses like a tie rod end.

I haven't seen this car since late 80's,so it's hard to remember

 

So what exactly is the force applied to the bones and their attachment points....


Engine out put times 1st gear ratio times rear end ratio don't forget your torque multiplication for automatic converter if you have it.

Tire diameter and stickynes play into it too.
With no tire spin and 100 % hook up it lifts the entire car by those attachment points and with some awful leverage.

 

I don't know about the new mentality but they used to say if you can't spin the tires you have too much tire.

I think that something should be made public here, the bones in question are re-enforced. How many do we see running around with just the stock bones split. No beefing whatsoever.

Funny most split bones use a tie rod end for an attachment point, with a pair of ladder bars normally a heim joint is used, I prefer a 3/4" molly joint but you are correct that is still a little flimsy if you are hoisting the wheels on a very heavy car.

If the bones were not split they would be ridding on a single joint. Granted we don't see many cars lifting the wheels or even spinning them with an unslipt wish bone. But it is still quite a bit of stress on it.

There is a lot to think about when one actually buolds a rod. I say it on a regular basis but I don't sink in with most, hot rods are not bolt together cars.

 

Thanks for those pics
And when you tell some Poorassrockabillypunkidzombie that
they are to weak you start a shit tornado about how traditional
splitbones are ....And yes it is traditional to get killed in a poorly
constructed hotrod happened a lot back in the day

 

i keep saying im gunna buy a go pro camera thing so i can put it under the hood or under the car to see what going on.

 

Now you why ladder bars were made. I'd be looking for cracks on those bones.

 

Wowsers Batman!!!

 

"I don't think that the raven regognized how much stress that the radius rods were taking. With those tires the roadster was like driving on oil, and he was peddling it just to get it to 3rd gear.

I don't think that most of the fellas realize what is happening to their suspension components either. Now I look at things differently than most but I think the point is that one should have some idea before their rod leaves them in the ditch. I am probably completely off base here but that is what I come away from this with."

This is why I shared the pics. How many of you out there know what's going on when you nail the throttle on your hot rod?

I knew they were flexing, that is why I renforced them, but to see how much flex took place ahead of the renforcement made me step back and thank God how lucky I was that they held with that much flex. It appears to be around 4" of flex just ahead of the upper ladder bars.
Remember, I'm running skinny, bias-ply truck tires that are hard as a rock, no mouth-watering hook-up here, just lots of tire spin.

This has been a public safety annoucement.
r

 

Scary shit right there. Glad you are going to improve on it.

 

I think you hit the major players here 31Vicky.
It's not unlike using a logger's peavey hook, over the top of the differential pumpkin, putting an extn. pipe on the handle pointed out the back, and jumping on it. Lots of leverage trying to lift the front axle skyward^.

 

Well think of it this way, the engine in question makes about 440 ft lbs (or pound feet for the rest of you fellas) @ 4800 rpm. Not a lot by todays standards and not enough the hoist the front end on most if the cars that we drive. Some of the fellas are actually putting monster engines in 'em and still running on the radius rods and no re-enforcments. They are not running on skinny bias plys either. It is a recipe for disaster. Not try to be a Ralf Nader here just making a statement.

 

Well said, Benno. It seems that lots of people have been 'getting away' with it since the mid fifties. Doesn't mean they haven't been close to disaster without knowing it.
Makes you think, don't it?
Davo.

 

Benno,
Speaking just fer m'self,
WE are unsafe at any speed!

 

Bump, 'cause everyone should read this.

Jim, can I steal that photo to use in my class? I can't emphasize this point enough...

 

Hey beaner or raven,
Whats in this rig as far as trans converter and rear gear ?
Are those stock length 1936 rear bones ?

440
X Trans gear
___________

^^number^^
X rear ratio
__________

^^number^^
X torque multiplier at stall RPR ( use 1 for manual and 2 of automatic)
______________

We get this far that will be the Torque at the axle flange.

Now tire diameter and traction coefficient play here and I'm not quite sure how to figure those. An accurate rpm and 60' time would be pretty close if we use the circumference of the tire.

Then take the torque at the flange multiply by the traction .
You'd use this number in a few calculations next.

I'm a little confused on if we multiply or divide by the length of the arm.

 

Vicky, depends on what your next term, as a solution, is.
IE, the arm length can be used to deliver a force to the frame...at forward end,
or, it can tranfer (restrain) torque to the axle mount 'ears'.
For the front mount, I believe it would be divided by the arm length.
Einstien not reqd. here, never mind Maxwell!

 

If the axle were rotating, the frame end is moving further than the axle end; so I agree that you'd divide axle torque by number of feet of bone length to get pounds of lift force.

 

Well ....
Its obvious that the frame end of the bone has the weight of the car on it ....
And that the axle is trying to lift that weight thru a cetain (Length) with a (yet to be determined) amount of force on the axle end.

??? Multiply by length to get force on axle end
Divide by length to get force thru bone and on the frame mount ???

 

So true. There is a reason why some things (like suspensions) have evolved..like it or not.

 

I'm thinkin ya maybe need a better roll bar to at least above your helmet at setting up in the car. A well built race car saved my ass more then once. Just sayin along with inprovements to the rear.Safety first will let you at least be able to talk about why you broke. NO BALL BUSTING GUYS JUSTTRYING TO HELP FROM A OLD ROUNDY ROUNDER. getter done Roger