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

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I am building the frame for my 38 Fiat Topolino.
I have looked at pictures, read tech stuff, looked for pictures I saw once but cant find now etc, etc.

I am frustrated and at the point of hanging the rear end and I havnt made up my mind as to which way to go. So before I make that final decision as to what I am going to do, I though I would give you guys a shot at blowing the cob webs out of my head and giving me a direction that makes sense to me.

Here are the issues-
The car is short and the drive shaft will only be about 14" long from center of u-joint to u-joint.
The seats are shoved back quite a ways and legnth of links (or should I say shortness of legnths) is critical just to fit in the car.
Long angled ladder bars is out of the question, no room.
Long parellel ladder bars is not my first choice so I have eliminated that for the moment.
Given the room I have to work with a 4 link would be the best.
I have seen some 3 link setups, if thats what you call them, and that is interesting to me, here is why.
The upper links (in a 4 link) to be 15-16" long ends up into the back of the seats. (no problem with bottom links, enough room down there) and angled is out of the question (yes I can use a panhard bar)
The 3 link systems I have seen puts the upper link slightly into the seats but its in between the seats and that would work.

How important is the legnth of the upper links or link?
Can I make it work with something like 13-14"?

I guess the discussion can start here. I know its a dynamic and complex question but I just had to ask to see what you guys have to say.

Any pictures would be helpfull.
Thanks

I was going to say mine are 13''-14'' long but after measuring them that's the tube length. the complete bars with rod ends are more like 20''

When we were building the rear suspension for my Dodge truck, we needed a very short locating system, and came up with a custom made set from Suicide Doors. It is a triangulated 3 bar setup, and uses a wishbone shaped upper bar to locate it fore and aft and sideways too. Mine is set up with an S10 rear, and uses their adapter plate to mount the rear of the upper bar, but if you use another rear, like a 9 inch Ford, you can weld mounts right to the housing.

Here are a few shots of mine.

Don

I was hoping you would see this Don, thats the setup I wanted to take another look at.
Does that 3 link work well?

Oh yeah, when I push the truck around the shop it goes nice and straight. I haven't had it on the road yet, but Dan is familiar with this setup from the bagged S10 world, and says it works great. I can't see any reason it wouldn't work ok, and it takes up very little length. Suicide Doors makes some very nice stuff, and they will custom make them to your dimensions.

Don

Oh Yeah, I forgot its not on the road yet. I dont know why, you seem to pop them out like they're easy.

Please tell me this, when one rear wheel comes up (twisting the rear relative to the frame) is it the bushings that squish to allow it to do that?

Thanks
Jim

[QUOTE=maddddog]I am building the frame for my 38 Fiat Topolino.
I have looked at pictures, read tech stuff, looked for pictures I saw once but cant find now etc, etc.

What kind of power are you going to be throwing at this Topolino? And what is the endgoal as to where you want it to work best, like street, strip, or both?

[QUOTE=mooneye777]

Originally Posted by maddddog

I am building the frame for my 38 Fiat Topolino.
I have looked at pictures, read tech stuff, looked for pictures I saw once but cant find now etc, etc.

What kind of power are you going to be throwing at this Topolino? And what is the endgoal as to where you want it to work best, like street, strip, or both?

Slightly built 454. Maybe it will make a pass down a drag strip but I doubt it. Its for friday nights and full moons only.

It will be just a cruiser with a ridiculous engine and looks. Just for fun.

As I slowly move forward I am getting pretty comfortable with a triangulated 4 bar. I have been messing around with the mock-up and I think I can make that work the best. Not exactly sure how to establish the 8 points of contact on the 4 bars, but I am getting closer with my understanding of what does what. At this point the lower bars are 18" center of pivot to center of pivot. The upper triangulated bars will be maybe a little shorter 16 or 17". That seems to fit in the room I have but final attachment points have not been established in my mind. So, in the absense of knowing exactly what to do, I am just making all the bar components with the bars a little long, hoping I close in on the answer by the time they are ready to finish. That should be sometime tomorrow.
Do you have some suggestions? Love to hear anything you have to say.

Johny joints are cool. Thanks for that 383.

Billy Shope was one of the original Ramchargers, a group of engineers at Chrysler Corporation. I have learned much from reading his writings. Here is some of it.....

"I would also add that, when it comes to the angles (as viewed from the side), pay attention to the OEM setups and NOT to the aftermarket pieces. I saw pictures of one aftermarket arrangement which appeared to have the IC behind the axle, which would mean SEVERE squat on launch. You don't want that. If you want to eliminate squat or rise entirely, arrange the links so that lines through them, as viewed from the side, intersect on a line which passes through the rear tire patch and has a slope equal to the CG height divided by the wheelbase. If the intersection is above this line, the car will rise on launch; if below, squat. It's not necessary for either pair (top or bottom) to be level."

he explains further......

"In the side view, visualize a horizontal line through the center of gravity and a vertical line through the front tire patch. Then, a line...called the "no squat/no rise line"...passing through the intersection of these two lines and the rear tire patch.

Finally, visualize lines passing through the centerlines of your links. There will be an upper line (through the upper two links) and a lower line (through the lower two links). If you don't want the car to squat or rise, arrange the links so that the intersection of the upper line and the lower line falls on the no squat/no rise line. If you want it to rise, put the intersection above the line; squat, below the line."

Editors note: Without knowing exactly where the center of gravity is, a fairly close approximation can be made by using the camshaft height as viewed from the side of the car. Sitting down with pencil and paper and drawing the arrangement out to scale will get you in the ballpark.

Thanks Techinspector.

I wish I knew how to find some of those lines he talks about. I read that exact piece yesterday.

A picture is worth 10,000 words. Any idea where to find that kind of stuff sketched up?

What techinspecter has said is very very true, But on an equal note you are looking for a cruiser. Even though what he has said is crucial you are not starting with a race car or even a daily driver car in the end. I know you will have to work with what room has been given to you. What he said would be great to start with if you didnt have anything started and wanted to design a great handeling car from the start. Take your bar lengths you have start with some mounting (where you think they can go) and move the rearend assy to see what happens, with your pinion angle, and shock movments. After all said and you think is done. I dont know what fabrication or design skills you might have but I think you might have a rough time with what He has given you to do. Now I hope you best of luck. There is alot of great information here. You will be the guy that will have to decifer all the info. Oh and a triangulated 4 link isnt a bad setup. Just watch your upper bar angles not enough and there rear will move side to side.

best of luck.

we call those super pivots.

See this is why I like this site. I can even learn quit a bit more. This is a great site. Thanks

We use the delron bushings all the time. They deflect enough for a decent ride.But rubber is the best riding material, But they dont last for a long time. I like the delron myself, Good ride quality.

Techinspector. I know what those are. I went to that auto parts site and looked at those bushings. How would I find the dimensions on those? I do have an auto store that lets me go through the boxes Should I do that? It takes a little time, but I usually find something that will work.

Don, I have the quarter eliptical springs and was going to do that but I came up with a nice pair of QA1 adjustable coilovers. Being the cheapskate I am with time and money (mostly time in this case) I have chosen the coilovers.
Are your bushings Poly or rubber?

Thanks guys