Technical How much side flex is normal in a triangulated 4 Link?

Is any side to side movement acceptable/normal of the axle on a triangulated four link?

Now that mine is all bolted in and the truck is on the ground, if I push sideways on the very rear of the frame, the frame moves about 1/4-3/8" right above the axle. Once it binds, I slide the entire truck wheels and all on the epoxy floor.

From what I can tell the movement is taking place at two locations.

1. Is where the rubber bushings are giving and getting squished.

2. Is a little bit of slop where the bolt threads taper down.

I can correct both of those if I get longer bolts so the shoulders take up that slop and use urethane bushings.

JAMB NUTS WILL BE ADDED TO THE LINK, I HAVE TO TURN THEM DOWN TO HAVE ENOUGH ROOM FOR THEM.


What do you guys think...Im going to try to post a video.

 

that doesn't sound excessive to me...most cars can be pushed sideways a bit, no matter the suspension design.

 

is that bushing threaded into that link tube? If so, I imagine a jam nut would be needed. There's usually some play without a jam nut.

As for the bolts, I like to have the shoulder of the bolt go the entire way through the bushing/joint and through the other tab, take up the distance the shoulder sticks through the other side with a thick washer.

 

If you did not have bushing compression, your suspension would be in bind.

So yes, movement is normal.

Red flags:

Nylocks don't work unless there are threads showing past the nylon.

You have no jam nuts on the links. Threads are not intended to be rotational elements. You will destroy them in short order.

 

Those bolts came with the kit. I plan to replace them with bolts with a full shoulder that are a proper length. They are just temporary. The entire thing must come apart for paint.

There is not enough room for the jam nuts at the moment. I have to turn the rods down, so there is enough room for them.

Just haven't gotten that far yet.

 

Rubber bushings have more compliance than urethane. So 1/4-3/8 is probably normal, as several replies have said. I agree on the bolts being longer, the best is to have no threads in the bearing area. The bolt shank should take up the shear load of the bearing area, and then sufficient threads for the nylock nuts to have a couple threads exposed at end of the nut.

 

In regards to polyurethane bushings, if the kit came with rubber ones, I would leave them in.

Bushing deflection is a necessary function for this to work. Overly stiff bushings would fight it.

That could make for a jarring ride.

 

I don't see the parallel bars, which usually run below the frame with the front of the bar attached below the frame rails.
The triangulated bars usually run from the center part of the differential and attach to the frame rails at the front.

http://www.superiorglassworks.com/v/vspfiles/photos/TRI4BARCO-2T.jpg

 

Have run them each way,
Trad ladder bar, vs pumpkin mt.
options. Bushing type & bolt length (shoulder)! Are critical here.

 

You didn't answer the question though. Is some side to aide normal?

 

The answer to that question is unequivocally yes.

If you did not have any bushing deflection in your system it would not work.

 

What Gimpy is trying to tell you is that there is no way you could PERFECTLY align the brackets. If there were no compliance in the bushings, the suspension would bind up, ride rough, probably bend something and definitely wear out prematurely. The "give" in the bushings helps accommodate that misalignment. So, yes some movement is normal.

 

NOTE -

EVERYTHING in the system is moving-flexing. The bracketry (BOTH ends !), the urethane bushings, all of the welds, the cross member in the front, etc.

While I would have gone the other way (like the factories did) with the upper bars, I see no problem in that bracketry. The material might be a little thin, just keep an eye on it !?!
But like others mentioned, I would shorten the bars and add lock nuts on the joints, both ends of all four bars. This will help lower the loads put upon the side to side loading from "working" the threads.

Mike

 

The whole point of a bushing is to incorporate a little give and deflection into a ridged assembly.

I built an O/T car years ago and replaced all bushings with poly bushings it ran so rough it was horrible.

ended up using a mix of rubber and poly bushings on the engine and suspension to get a good balance off stiff snd responsive without rattling my teeth and breaking my back driving around .

 

How does this movement affect drivability?

Would this movement not introduce some rear steer when cornering?

 

If this was a drag car, you would go directly into the grandstands.

 

It enhances ride quality.

Yes, it does introduce some rear steer, but then again, so does your 4-link.

Don't think your way out of finishing the project.

 

You'll probably lose 3 10ths a lap at Le Mans.

 

I was thinking a whole half-second.

 

That much? I didn't realise it was that dramatic.

 

Delrin does not appreciably compress under load. These joints will fight suspension action on his setup.

 

Well, it is a 13.6km course!

 

To be perfectly honest, in my opinion the triangulated four link commonly used on street rods is inherently a crappy design. The action of the non-parallel upper bars is geometrically fighting itself. The only reason it even remotely works is because of compliance in the bushings and the very limited up and down travel most cars require. The only advantage to this suspension design is that it purportedly allows you to delete the Panhard bar. But what you are feeling as excess lateral movement is the result of relying on the upper bars and bushings for lateral control. In my opinion it is just barely passable. I refused to install them when I had my chassis/custom header shop.
With the proper bushings and bolts correctly installed (with tightened jamb nuts), drive it the way you wish to drive and see if you are happy with it. Many people are, many aren’t.

 

I have to agree with this. Having a parallel 4 link with a Panhard bar allows adjustment of the rear roll center height by changing the height that the Panhard bar is mounted. Some bracketry with multiple holes for each end of the Panhard bar and you have some simple handling tuning capability. Too good to lose just for the sake of looks, but that's just me......

 

Haha, you guys are hilarious....

But seriously, 400-500 HP in a 56 F100, on rural mountainous roads in WV, I want something that handles well. Not something that feels like it is going to walk out from under me every turn I go through with some spirited driving.

 

You will not notice that small amount of deflection....but if you are so OCD that it bothers you, change it out. Anything that is streetable will have some amount of deflection, including the 4 link with panhard bar, unless you use him joints in the panhard bar. Not recommended.

 

I always aimed for the car's center of Mass, engine/trans height, (fore & aft).
For the intersection, of the control arms. That way, the influence on rear steer, was minimized. As bodyroll came into play, it helped by lessening the "Effect". I was lugging a PE title, for too long in ME Design.
Now at 70 yrs, just smile.
Would add, with a fourth vette rear install in an A roadster, look carefully at the forces, then build for a max load input force. The cars are light, you can make it all work, often w/o side to side 'sway' bars'.

 

Parallel 4 link + Watts link would be better.

 

This is my first install, so I just really didn't know what was acceptable and what was not. I have also never driven/own a 4 link vehicle. Everything has been leaf (which has considerable side to side movement) or IRS.

These are marketed with "no" movement as compared to a panhard bar.

I also have to be careful with fender/tire clearance. Right now I only have about 3/4". I mainly just don't want to get the thing all together, painted, and have to strip it back down because it doesn't handle worth a damn.

 

I had a Model A with a triangulated four bar setup. Stock frame about 60 per cent boxed, front to back.
R&P steering, first front steer and later converted to rear steer.
Well over a 100k travel miles it rode fine and handled fine, for 103" wheelbase.
I did have to replace the rubber bushings once, not a big deal.