4 link setup question

[Bluecrush]

I am installing a Poly Performance universal 4 link kit on my truck. The upper and lower links attach to the same frame bracket so the uppers are triangulated and the lower are almost straight ( 10 degree angle). I thought the upper links should be around 75% the lenght of the lower links, but this will be impossible to acheive. The upper links will actually be longer than the lower links, so do I need to point the pinion angle slightly above the t-case output flange? Any input would be appreciated

 

[LT.]

Uppers need to be as close to 70% of the length of the lowers as you can get. Do you have them upside down?

LT.

 

[Bluecrush]

They are not upside down, but I can't figure out how to make them shorter when just the upper links are triangulated. What is the drawback of this setup?

 

[I Lean]

They do not need to be 70% of the length. That number is essentially meaningless.

I personally like the uppers to be longer than the lowers, it makes the pinion track just a bit better than the other way, if your antisquat numbers are where they should be.

 

[ChestonScout]

The uppers need to be at least 70% of the legnth of the lowers. Any shorter and thats what will twist your pinion angle under articulation.

So the rule is 70% or better.

I have never made uppers longer than lowers but I mine are basically the same length and work great!.

Just tack everything in place and cyle the suspension with no springs and see what it looks like. My guess is you will be fine

 

[Bluecrush]

So I just went for it today, the upper links are 46", and the lowers are 40". I pointed the pinion right at the t-case, and with everything tacked together cycled the suspension. I was surprised that the pinion angle did not really change at all! I could see how you could make the uppers shorter in a double triangulated 4 link, or if you used two different frame brackets on a single triangulated setup, but when both links mount to the same bracket and location on the frame with a single triangulated setup, the uppers will always be longer. But the lower links are pretty level, and the upper link brackets have plenty of adjustment, so hopefully I will have neutral anti squat.

 

[UNSTUCK]

Also depends on where you place your truss. You can gain or lose a few inches bases on your angle.

 

[Bluecrush]

So now I'm on to the the front 4 link setup. It will pretty much be the same design as the rear with triangulated uppers and straighter lowers, but the frame is much narrower if the front, so I won't have 45 degrees on the uppers. Any suggestions or tips would be appreciated!

 

[Mope]

Could you post up some pics? I'd like to see what you've got going.

Thanks

 

[Bluecrush]

I always have trouble posting pics on this site because they're either to big, or it tells me a security token is missing? But I will try again later.

 

[ChestonScout]

yup....hard to give advice without seeing what your working with. On my front 4 link when I had the uppers trianglulated I actually brought the upper links out past the outside of the frame and made brackets to work. Of course I have 9 miles of lift to make that work.

40 degrees is the standard. If your close to it you should be ok.


With my current 4 link up front I have the lowers triangulated and the uppers straight. It works perfect.

Are you going to have enough room under your oilpan to have triangulated uppers? Speaking from experience its not fun to put links through an oil pan. That is why I changed my 4 link design up front

 

[jswainthug]

I have always liked the 3 link with panhard setup!

 

[RockMonkey]

So I just went for it today, the upper links are 46", and the lowers are 40". I pointed the pinion right at the t-case, and with everything tacked together cycled the suspension. I was surprised that the pinion angle did not really change at all! I could see how you could make the uppers shorter in a double triangulated 4 link, or if you used two different frame brackets on a single triangulated setup, but when both links mount to the same bracket and location on the frame with a single triangulated setup, the uppers will always be longer. But the lower links are pretty level, and the upper link brackets have plenty of adjustment, so hopefully I will have neutral anti squat.

With straightish lowers you'll really want to be careful with that antisquat number. It sounds like your links are mostly flat, which is good. How much vertical seperation do you have between the upper and lower links at the axle end, and at the frame end?

 

[Bluecrush]

yup....hard to give advice without seeing what your working with. On my front 4 link when I had the uppers trianglulated I actually brought the upper links out past the outside of the frame and made brackets to work. Of course I have 9 miles of lift to make that work.

40 degrees is the standard. If your close to it you should be ok.


With my current 4 link up front I have the lowers triangulated and the uppers straight. It works perfect.

Are you going to have enough room under your oilpan to have triangulated uppers? Speaking from experience its not fun to put links through an oil pan. That is why I changed my 4 link design up front

Good things to consider. I figure there might be 6" between oilpan and link mounts. I think bumpstops might prevent damage during flex, but a hard hit or a slight jump could send it straight into the oilpan?

 

[Bluecrush]

Here are some pics of the rear. This is a Toyota frame and a 14 bolt. The lowers probably won't be as level as I thought after establishing a higher ride hieght. Vertical seperation at the axles is 9" and 4.5" at the frame. There is 3-4" of adjustment at either end.

 

[Bluecrush]

This is what I have to work with on the front. Dana 60 with SFW truss system and integrated ram mount. I have 46" or less links to work with. I was thinking triangulated uppers inside the frame rails, and slightly angled lowers outside the frame rail. Shorter uppers should get me closer to a 40 degree angle.

 

[RockMonkey]

I predict you'll have your upper control arms in the highest frame-side holes, and wish there was one higher.

 

[Bluecrush]

I predict you'll have your upper control arms in the highest frame-side holes, and wish there was one higher.

Why? Should the vertical seperation be more equal at each end? Or does it have something to do with the uppers being longer than the lowers?

 

[Herzog]

You will want more than 4.5" of separation at the frame. I just got done re-doing my upper links mounts, I had pretty much the same separation: 4" at frame & 8" at axle. My rear suspension sucked on medium plus throttle vertical climbs.

 

[RockMonkey]

Why? Should the vertical seperation be more equal at each end? Or does it have something to do with the uppers being longer than the lowers?

It will behave better on steep climbs. With more anti-squat and straight lower control arms, steep climbs will tend to cause the driver rear tire to jack down, which lifts the driver front tire into the air. You reduce this negative effect by reducing antisquat.

Antisquat is calculated by the intersection of an imaginary line drawn from the bottom of the tire through the instant center of the suspension (imaginary point where the control arms would meet if they were extended forward), and a vertical line drawn through the vehicle's center of gravity. The higher up the convergience of these points is, the more antisquat you have (more weight is being transferred through the control arms to support the weight of the vehicle during acceleration). So if your control arms are closer to the same vertical seperation at the front as they are at the back, the instant center will be further forward (it could even be well in front of the vehicle), and the antisquat will be lower.

Sorry for the technical explanation, I may not be good enough of a writer to explain this so it makes sense...