4-link geometry

[elwood]

hi all,
ive been working on 4-linking my 29 model A frame,
first i built a 2x3 square tube rear cross member, off set to center my 9-inch, and replaced my stock one.
now im trying to find out how to triangulate the 4-link.
i cant seem to find any pictures of model A,s 4-linked.
you know the differential housing sits directly under the cross member, and i built my cross member hugging the differential housing for maximum snug fit when compressed.
its looking to me like i haft to set the top bar even with the top of the differential housing and drop the bottom bar a distance from the top bar and triangulate the point to the front spindle.
i need a link please, ive tried googleing for this with no luck, maybe im looking in the wrong places.
thanks.
elwood

[enjenjo]

You can angle the top links in from the rear end to a frame crossmember, opposite what is normally done, but it works good too.

[SKR8PN]

Go here   www.picturetrail.com/SKR8PN  Daytona and Daytona II albums, and look at the suspension shots of my four link. You want the lower bar as near level to the chassis as you can get it. The UPPER bar will angle down in the front,and will determine where your instant center is located.  The large brown poster on the wall is my plot of the wheelbase,the center of gravity,the neutral line and MOST of the instant centers available to me. I am going to be moving my IC forward and down to try to eliminate most,if not all of the wheelstand this car does now.  Any questions,please feel free to ask and I will try to help as much as I can.


I guess I should ask......are you using a four LINK or a four BAR system?? There IS a difference

[Flipper]

You act like wheelstanding is a bad thing.

As long as there is plenty of VHT down, I love it.

.....although it does kinda suck when stuff is in a different place when the front end comes back down.

[sirstude]

Hey skr8pn, nice lookin Golden,  The training pictures look really familiar.  We are on our 3rd over the years,  great dogs.

Doug

[SKR8PN]

You act like wheelstanding is a bad thing.

As long as there is plenty of VHT down, I love it.

.....although it does kinda suck when stuff is in a different place when the front end comes back down.

It REALLY sucks when ya leave the rear bumper on the track!  I refuse to install wheelie bars on this car  

[SKR8PN]

Hey skr8pn, nice lookin Golden,  The training pictures look really familiar.  We are on our 3rd over the years,  great dogs.

Doug

Gracie Sue is our second Golden,and I just can't see us ever being without one. And I love my Labs to........ Ginger,the Lab, is a the hard headed one and bit of a PITA!!! Just kidding!! The real problem with Ginger is her energy level. She can flat wear my butt out when it comes to playing. She refuses to stop!! She will go until she absolutely drops over, get up,go get her ball,bring it me and have a look in here eye that says: "OK Dad,I'm ready,throw it again!!"
Gracie Sue,AKA "The Swamp Collie", was a breeze to train,and still is a real joy to have around. She is everybodys buddy!!

[Crosley.In.AZ]

It REALLY sucks when ya leave the rear bumper on the track!  I refuse to install wheelie bars on this car  

LOL.... wheelie bars are now on the Hughes Performance race cars.... The crew chief / driver had the Corvette's electronic box 'blank out' on him at the launch. So the throttle stop did not activate

the car stood up on the back end high enough the battery kill switch handle hit the asphalt. It then got real quiet ........... till the front end came back down on the ground. Bent wheels , chassis, oil pan........

Data recorder worked great......

[PeterR]

I am going to be moving my IC forward and down to try to eliminate most,if not all of the wheelstand this car does now.

It is so hot here my brain is almost ready to melt and run out my ears, so if what I say is completely mixed up just tell me to put my head in cooler.

The effective thrust force runs up a line drawn from tyre contact patch though the instant centre.  If the thrust line passes in front of the vehicle CoG there will be a tipping moment that tends to rotate the body nose up, and if it passes behind the CoG, then the tipping moment tends to make the body rotate nose down.

If it passes exactly through the CoG then there is no tipping moment and the body will tend to rise evenly.  

From the image of the wall poster it would appear as though the grey coloured line runs from the tyre contact patch to the vehicle CoG, and if that is so, any instant centre in front of the line will cause nose up behaviour, and IC behind the line will cause nose down behaviour.

Moving the IC forward, or downwards tilts the thrust line forwards and increases the wheel stand, if you wish to reduce wheel stand it should be moved in the opposite direction.

A secondary effect often overlooked is the difference in front and rear spring rates.   If the rears are very stiff to reduce torque roll, then even if the lifting force acts directly through the CoG, the front of the car will still lift much more than the rear.  

I have the cooler standing by.

[SKR8PN]

Peter,thank you very much for responding to this thread!!!
I am still trying to gather as much info as possible on this,and ANY input will be greatly appreciated!!

The way it was explained to me sounds to be about the opposite,unless I am not understanding you........That line(string) you see on my chart is what they are calling a "neutral line"  that runs from the rear tire contact patch to a point level with the center of gravity(CG) but also directly above the front axle center line. The actual CG of the car can be seen in the second picture of the plot,left hand side,near the top of the plot. It is the big cross with a circle around it. In that same photo,you will see two silver circles,the one farther to the rear(to the right and above the neutral line) is where the IC is set now. The other circle is one of the other IC's that I am considering.......
The way it was explained to me was like this........think of your elbow as the rear axle and your arm as the four link. Pick a spot on your arm close to your elbow and put 50lbs on it. Now raise your hand by just bending your elbow. It is pretty easy to lift. Take that same 50lbs and put it way out on your finger tips and the force required to raise it increases greatly..........

Using that idea,is what makes me think that I want the IC farther forward to stop the front end rise,and to get the rear to rise a bit. I have no idea what keeping the same LENGTH of the IC,but changing just the HEIGHT of the IC does to chassis reaction....YET!!
As far as spring rates,I have no idea what they are. I just got the car up on jack stands yesterday so I can begin removing the engine for a quick looky-see inside and I plan on pulling all four coilovers and checking them out.

[elwood]

hi guys thanks for the interest here,
im trying to post a pic.
test test

[dragrcr50]

Am I missing something here?  is it a street rod or race car you are building sir???  on most model a street rods the rear bars are even not to a point in front, that way the pinion doesnt change in its  travel and a smooth ride is likely.. if you are doing a race type 4 link then it is a diff story...

[Crosley.In.AZ]

As I understand it , the bottom links are level to the ground  at ride height and parallel  to each other.

the upper links are level / parallel  to the bottom links..... BUT at a 45 degree angle from the diff to the chassis /  frame.  this locates the rear end in the chassis & prevents side to side movement.

No panhard bar needed

[elwood]

hey guys,
thanks for the interest in my post.
im building a street rod.
im setting up a 4 bar, not 4 link.
wish i could post a pic here.

[Crosley.In.AZ]

hey guys,
thanks for the interest in my post.
im building a street rod.
im setting up a 4 bar, not 4 link.
wish i could post a pic here.

Dirt simple to add a photo if you have it on your computer HD or something hooked to the computer..

Under the reply box you type into  is an "add an Attachment " box...... clik on "browse" to find the photo.

Must a photo of acceptable size and the system here will tell if it is TOO big .