Rearend links- 4 link, 3 link, parellel, angled???

When I engineered the independent front suspension for the T, I had a door board with a big clunky German-made drafting machine bolted to the top of the door. I picked up the machine with broken scales for cheap at a yard sale, but you could still buy scales for it. Could have done the same thing with a good 4-ft steel scale, 1-ft scale and a T-square. I had some stuff left over from earlier times like a clear plastic degree wheel and some good compasses, but it was nothing expensive.

After I got the frame, crossmember and rack located on the paper, I cut out some "paper doll" tie rods, spindles and control arms from thick, solid cardboard and stick-pinned 'em together. I kept changing lengths and angles until I got what I wanted. I had all the geometry figured out and knew exactly what the instant center, bump steer, camber gain, etc. would be before I ever bought the first stick of chromoly.

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Originally Posted by maddddog

No, I mean the holes on the rear end.

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Depends on which configuration you're goin' with. Are you gonna use short links (13" like you figured) or longer links like the 24" jobs I showed or a rear arrangement like Jerry Clayton suggested?

Great thread guys! Informative and understandable! Subscribed!

My next project I'm going to stay away from the IRS and keep it simpler. I think I'll like the IRS but I've lost too much hair over the ordeal. :LOL: :LOL:

Dave G

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Originally Posted by techinspector1

Depends on which configuration you're goin' with. Are you gonna use short links (13" like you figured) or longer links like the 24" jobs I showed or a rear arrangement like Jerry Clayton suggested?

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I want to run them forward but they will be short. In one of your drawings, you have the bars going back past the rear axle. Is this to keep the bars longer to minimize the arc they travel in?

Thanks again Techinspector for helping out here. When its done, and I need an inspection, do I have to pay for your plane ticket or do you pay for that as part of your service to CHR ?:D

Quote:

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Originally Posted by maddddog

I want to run them forward but they will be short. In one of your drawings, you have the bars going back past the rear axle. Is this to keep the bars longer to minimize the arc they travel in?

Thanks again Techinspector for helping out here. When its done, and I need an inspection, do I have to pay for your plane ticket or do you pay for that as part of your service to CHR ?:D

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Sorry for the delay getting back to you dog, have had trouble getting into the site.
Yes, the longer the bars, the less severe the change in instant center location. Also, the closer the bars are together at the rearend mount as viewed from the side, the less severe the change as the diff goes through bump and droop.

Let's say for instance that you made your diff bar mounts 2" above the diff tube and 2" below the diff tube. The pivot points would be 7" apart viewed from the side when including 3" for the diff tube diameter. This would provide a minimum of instant center change as compared to making mounts, say, 12" above and below the diff tube. When confronted with a question of where to mount something, I usually take it to the extreme one way and the other and try to figure out what the results would be. Visualize the drastic instant center change with the pivot points 27" apart as compared to having them 7" apart. Draw it out and run some bump and droop lines and you'll see it for yourself.

Ok boys, here is what I got so far.
Its gonna take 2 posts to get all the pics uploaded.

One question, any reason the shocks couldnt go in front of the rearend. There is more room there than in the back with the radiator and panhard or watts (not drawn yet)

Tell me what you think.

Here are the rest of the pics.

Thanks for your help.

Looks good so far maddddog. The only suggestions I would make is to be sure the adjustment holes in the 4 link brackets are in an arch that follows the same arch the link would make if you removed the bolt though the hiem & moved it up and down from the top to bottom adjustment holes. That way when you make adjustments from one hole to the other the holes will line up without changing the link length. ''Hope that all made sense''.

Also, I would box in, or in some way reinforce the 4 link brackets on the rear end housing. It looks like you have the brackets on the frame boxed in nicely, but the rear end brackets may bend if not braced better.

I made aluminum spacers for mine in several places to hold everything rigid, only because being modular it's all a bolt together deal.

http://img.photobucket.com/albums/v2...8/RearEndZ.jpg

As far as the shocks going in front of the rear end, shouldn't be a problem. Spring load will change of course.

Thanks Pro-
The rearend brackets are not done yet. They will be boxed and have the shock bracket built off the bottom some how.

That should be a nice compact rear suspension. Should look Cool. :cool:

Thanks Pro.
Question for you.

You said "I would make is to be sure the adjustment holes in the 4 link brackets are in an arch that follows the same arch the link would make if you removed the bolt though the hiem & moved it up and down from the top to bottom adjustment holes. That way when you make adjustments from one hole to the other the holes will line up without changing the link length. ''Hope that all made sense''.

I was trying to figure out exactly what arch was used on a number of other brackets I looked at. They didnt match the swing of the link.

For instance- pick a link, any link. Lets say the top link. The rear bolt is installed, say in the middle hole. Remove the forward bolt and swing the link up, hole matches, swing the link down and the hole matches. Now move the rear bolt to the bottom hole and none of the holes will line up in the forward bracket. If that makes any sense.

Does that make any sense?

Sorta' like these brackets.
Whether they line up in the real world. :confused: But the adjustment holes have a slight curve in the row.


http://img.photobucket.com/albums/v2...nkbrackets.jpg

Well it looks like that pic. post upside down. **)

While messing around trying to find a comfy spot for the coil over shock, I came up with this. Plenty of room there.
The bell crank drawn is a simple one for concept purposes but it seems to work great. These 2 pics show it in 2 positions. A simple link coming up off the rear end tube should work.
I can increase or decrese the ratio of shock/spring action by adjusting the holes in the bell crank. Kind of like laying the shock over at an angle.

What do you thing about this setup?

I have been messing with this all day. I think I have it.
Some fine tuning is still required, but all in all, I think it will work.
I still need to add the watts link and develop a pivot for the shock bell crank.
A couple cross members and some gussets get added next.

It seems like there is a lot going on, but I dont see how to simplify it much.
Good thing I have a pattern following flame cutter (poormans laser):eek: and a good drill press.:D

Any ideas what would make a good bearing or bushing in the shock bell crank? The weight of the rear of the car is pivoting on this point and I am not sure how to bush that pivot.

And why are my pics so big? I am not doing that on purpose.:confused:

How about Johnny Joints. They were mentioned by 27tee and linked by ceh383 and would seem to be a viable mechanism to use in this application. Here are different sizes....
2" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1167
2 1/2" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1166
3" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1081

It may be the angle or the way I'm looking at it, but visualize a line through the shock centerline and another line extending through the shock eye and the pivot point of the rocker arm. These would appear to be somewhere close to a 90* angle and that's how I would do it too, although I'd figure the angle so that the rocker was halfway through its arc at half suspension movement, the same way you set up valve spring rocker arms in a motor.

Now, visualize a line from the c/l of the diff up through the mount on the rocker arm and another line extending through the upper rocker arm mount and the rocker pivot point. The angle would appear to be somewhere around 110* and will increase as the diff goes into bump. With this arrangement, as the diff goes further and further into bump, it appears to me that the spring movement gets less and less, so you have a decreasing amount of spring as the bump gets longer.

I'm no guru on this stuff, I just parrot what I have learned from others. But in this case, I think I would rather have the progression of the spring rate at least linear, if not increasing a little as the suspension increases in bump.

Then again, I may be looking at it all wrong because I have not seen a side view of the geometry.

Quote:

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Originally Posted by techinspector1

How about Johnny Joints. They were mentioned by 27tee and linked by ceh383 and would seem to be a viable mechanism to use in this application. Here are different sizes....
2" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1167
2 1/2" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1166
3" with grease zerk...
http://www.currieenterprises.com/ces...t.aspx?id=1081

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Are you suggesting using them for the bell crank on the shock linkages?

I would think that something like the roller camshaft bearings could be used in and fabbed pivot----they are available in various sizes

They will be carrying the weight of the vehicle so will need to be pretty robust

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Originally Posted by jerry clayton

I would think that something like the roller camshaft bearings could be used in and fabbed pivot----they are available in various sizes

They will be carrying the weight of the vehicle so will need to be pretty robust

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I looked at some roller bearings (not for a cam though) and they need a hardened surface to roll on. Do cam bearings have an inner race?

There is a watts linkage on the market that uses tapered roller bearings, like wheel bearings. A little big but might be a solution, what do you think?

Here is a side view at ride height.

The shock is compressed 1/3 of its travel.
4 inches of bump from this picture and the rear end hits the frame ( I am planning on 3" of travel and a rubber bumper)
1.5" of droop from this picture and the shocks are fully extended.

Techinspector, I did struggle with the geometry of the shock/bell crank thing and fully admit I am just guessing. Love to hear more.

Should I keep the bellcrank working at a 1 to 1 ratio or increase one side or the other?

Any unusual forces on the bellcrank pivot or just the weight of one corner of the vehicle?

Thanks all for contributing.:D

Quote:

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Originally Posted by maddddog

Are you suggesting using them for the bell crank on the shock linkages?

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Yes, the rocker arm pivot. You call it a bellcrank, I prefer to see it as a rocker arm. :)

Your pictures are so large because you're uploading them at 940 x 637 pixels. You need to resize them before you post them. Cut them down to 640 x whatever before posting.

How about using the same bushing GM used on the trailing links on the 60s - 70s GTOs, Chevelles, etc.?

I would use a 1:1 ratio. Then you're not fiddling with your shock rates.

Also, you'll have to mount your shocks upside-down, won't you?

Quote:

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Originally Posted by Henry Rifle

Your pictures are so large because you're uploading them at 940 x 637 pixels. You need to resize them before you post them. Cut them down to 640 x whatever before posting.

How about using the same bushing GM used on the trailing links on the 60s - 70s GTOs, Chevelles, etc.?

I would use a 1:1 ratio. Then you're not fiddling with your shock rates.

Also, you'll have to mount your shocks upside-down, won't you?

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I will look into the GM bushings, thanks.

Upside down? I hadnt thought about that. Why upside down, or are you messing with me?:eek:

Quote:

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Originally Posted by Henry Rifle

Also, you'll have to mount your shocks upside-down, won't you?

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If I'm looking at the drawing right, they should still compress when the rear end housing goes up.
But, then it's Sunday & I just woke up from a nap. :whacked:

pro is correct. I was off somewhere on a walkabout, apparently.

I think that the shocks should be mounted more toward 50/50 on there travel--as they compress the spring gets tighter and the bumper comes into play but on extension they will just go unimpeded to full travel and put pulling stresses on the shock parts that aren't considered----

The roller cam bearings just run on the cam journal---at that size they don't need to be hardened as they roll full 360* where as in rocker arms or U joints they ocillate back and forth

The GM bushings were used in the end of a longer link so they just twisted a few degrees in the rubber----on these rocker arms they will probably rotate 45* or more and that would twist the rubber-

A genuine suspension poly bushing for say a anti roll bar probably could be used around a 1 1/2 bar that was supported on both sides----actually, maybe you could incorporate an anti roll bar as the rocker mounting pivots

dog, you're proposing 3" bump and 3" droop? Nothing wrong with that, but the components you've drawn out won't support it. The rocker is way too short. Angles would be acute at that bump/droop. With a 1/1 ratio on the rocker, that would mean 3" from neutral on the coilover. There may be such animals available, but I don't know who would make them (6" total travel). The shock is installed at the wrong extension. When I bought my Eagles, Aldan recommended leaving 55% for bump, 45% for droop. Others have recommended 50/50.

Please list the shock dimensions so I can play with this.

I want to tell all you how much I am digging this discussion. You all are really helping me work through this. Much thanks. Couldnt have done it without you.

Ok, enough of the mushy stuff.**)

These 5 pictures show the suspension in 3 positions.
Full bump.
Full droop.
Ride height. (which is at 1/3 bump, but sounds like I need to set it up more like 1/2)

I have these shocks. They are QA1 adjustable. 17" eye to eye with 5.5" of travel.

I can change any of this and so far it sounds like I need to change-
1. shocks to be at 50/50 or close
2. The legnth of the rocker????
3.????

The rocker has no collisions or binds.
I am comfortable with 5.5" total wheel travel (full droop to full bump)

Ok, Techinspector, get crackin!:LOL: I want a full report on my desk in the morning...... or the afternoon......... ok, by friday ...... or whenever.:D

"I have these shocks. They are QA1 adjustable. 17" eye to eye with 5.5" of travel."

17" eye to eye what? extended? compressed? halfway?

"I am comfortable with 5.5" total wheel travel (full droop to full bump)"

You can have 5.5" or 6" or whatever you want. You just have to build the proper ratio into your rocker arm and make the arm long enough to prevent acute angles and decreasing spring rates on bump.

17"eye to eye fully extended with 5.5" of travel making them 11.5 eye to eye fully compressed.

I have to think about that " and make the arm long enough to prevent acute angles and decreasing spring rates on bump" part. Not sure what I would change.

"Not sure what I would change."

Ummm, how about the length of the arms. You asked for blue last time, so here's some blue :)

So----wouldn't it be simpler to just mount the shock to the rear axle in a more normal matter????? seems like it would fit

I see. With a longer reach on the rockers, the pushrod and shock stay closer to being inline with the travel of the rear end.

"No acute angles". Duh, now I get it.:D

Jerry, At this point I just might. The reason for moving the shocks to this location and using all this mechanism was to put the shocks in a place that had room for them and then have room for a watts link. Today I will take a look to see if I can impliment Techinspectors revisions, but will also take a look at going back to the shocks in the rear of the axle with a panhard bar.

I am known to make things overly complicated once or twice.:D But its allways cool.:cool:

Is there room to put the shocks in front of the axles and still use a watts? Maybe put the watts link behind the rear end housing? Hard to tell from here without seeing what you have to work with room wise.

I have started the watts link, and I think there is room for the shocks in front. Going to work that out and see what I can come up with. Not a lot of room for the shocks too behind the axle.

I guess a Watts is cool, and limits lateral displacement of the rear axle to virtually nil. However, a 30" Panhard bar would allow only 0.104" displacement at full extension or compression of the suspension (2.5" each way.)

While I believe that Panhards are less than optimal, I'm firmly convinced they're far from an abomination (sorry Tech . . . just had to . . .). :LOL:

They're commonly used and work very well on street driven cars with minimal suspension travel.

Not saying you should use one - just a thought.