four link rear end?

[Sick5]

i have 65 GMC that has airbags and a 4 link. ive been driving it and watching the rear end. does the rear pinion angle change when driving lowerd and raised?
having it raised it look more level. lowerd the rearend is facing more up.
i just got trailing arms thinking it would fix it. but im waiting to gets some money for the drop crossmember.

[Sick5]

add to thids i notice that it raise aqs i step on the gas... is my fourlink installed wrong?

[jmedero]

dude call Justin at Scotts hot rods and he can help you out. I just got his rear super slam 4 link and he walked me through it. He knows his stuff and hes in Oxnard CA so kind of a local guy.
805-485-0382
justin@scottshotrods.com

[Scottshotrods]

Post some pictures of what you have now on yoyr truck if it is possible to do so.If you can e-mail me some pics of it to at justin@scottshotrods.com and you call me at the shop if you would like to ask me some questions at 805 485-0382

Justin
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[andrewmp6]

Yeah we need pictures because there is a ton of 4 link styles and it could have been put on wrong.The pinion angle does change a tiny bit when the suspension travels up and down.The idea way is to set the pinion angle at whatever ride height you want.

[Sick5]

I'm sure I have a pic. If not ill take on tomorrow
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[Sick5]

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[Sick5]

if you guys need a better picture ill try later on and post few more

[Cue-Ball]

Hard to see from the pics, but it looks like the frame attachment points for both upper and lower arms are completely vertical, and that the arms run nearly parallel. Can't see how they're attached to the rear end itself, but if they're also in the same plane then there would be no pinion angle change as the rear end moves through its range of motion. The further out of line the attaching points are at either end (in comparison to the other end), and the further from parallel the bars themselves are to each other, the more pinion angle there will be as the rear end moves.

having it raised it look more level. lowerd the rearend is facing more up.

Some four link designs are setup to keep the pinion angle constant, some are designed to introduce some angle change to lower the stress on the u-joints.

It'll be easier to tell how your particular setup works if you can see it directly from the side. Or, you could just measure the pinion angle with an angle gauge at the lowest and highest settings. Cheap and easy.

[Sick5]

frustated with this four link not working for me. my question should the pinion angle change as you accelarate.

[andrewmp6]

If you mean the rear end is twisting up or down under accelarate that shouldn't be happening.Who unbolted the shocks on it ?

[Sick5]

this is not a recent picture its a picture i had on my phone. the shock have been moved and mounted.

[lolife99]

It's hard to tell in your pics.
You have an issue with the upper link bars "rotating" the pinion thru the suspension travel.
I don't know if it's your upper bar mounts on the rearend or not.

Got some clearer pics?
The idea of a 4-link is to keep the pinion angle correct, throughout the suspension travel.

[PBFAB.COM]

What's happening is that due to the triangulation of the upper bars, the distance (length) between the pivots of the upper bars and lower bars are not the same. This will cause the pinion angle to change through suspension travel. This is a common symptom of triangulated four-links. It can be corrected by making the upper bars longer, but that can sometimes make it more difficult to get proper triangulation and have drive-shaft hoop clearance.

How much does it change? Is it causing any vibration problems? Or is it more of a "doesn't look right"?

[Sick5]

Originally Posted by porterbuilt

What's happening is that due to the triangulation of the upper bars, the distance (length) between the pivots of the upper bars and lower bars are not the same. This will cause the pinion angle to change through suspension travel. This is a common symptom of triangulated four-links. It can be corrected by making the upper bars longer, but that can sometimes make it more difficult to get proper triangulation and have drive-shaft hoop clearance.

How much does it change? Is it causing any vibration problems? Or is it more of a "doesn't look right"?

now im starting to understand. reason why im getting the shift in angle as the accelaration is being given is because of my mounted wrong.
i do have the shorter one on top and the longer ones on the bottom.
does anyone have something fAB for the outer bars to hook up. meaning not to the axle but to the frame

[Sick5]

my 4link is mounted wrong i would have to redo my four link!
or maybe just buy a drop kit from PB

[Cue-Ball]

Do you just have the bars swapped? In other words, do you have the top bars on bottom and the bottom bars on top? Because your pinion angle is definitely way off, and bars of the wrong length would explain why it would change the angle drastically as it moves through range of motion.

[Sick5]

If I would switch. I would have to some how fab tabs on the outside of the frame. Wait I just had an idea. At the moment I'm mounting the bar ends to the old leaf spring holders I should grind the rivets down and rebolt with grade 8 bolts. I'm going to start Saturday. Take some picture.
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[Sick5]

here are some more pictures

[Sick5]

sorry here they are

[Cue-Ball]

Who designed this four link system? It's very hard to tell from the pictures because there are none directly from the side, but it looks like it's designed all wrong. The upper arms look like they go up as they go from the rear to the frame, while the lower arms go parallel or down. If that's the case, it's all wrong. The arms should be nearly parallel to each other, getting slightly closer as they extend from the rear end towards the front of the vehicle. Like this:


If your bars get farther apart as they extend from the rear end it's going to throw the geometry off, cause pinion angle changes, and generally make a mess of things.

Can you remove one wheel/tire and take a picture directly from the side? We really need to be able to see the horizontal angle of the upper and lower bars to get a better idea of what's going on.

[andrewmp6]

Yeah I'm with you i would cut that off and start over,Its more money but you will be happier in the end once its been done right.The welds on it don't look that bad it was more they didn't know what they was doing.

[Sick5]

Originally Posted by Cue-Ball

Who designed this four link system? It's very hard to tell from the pictures because there are none directly from the side, but it looks like it's designed all wrong. The upper arms look like they go up as they go from the rear to the frame, while the lower arms go parallel or down. If that's the case, it's all wrong. The arms should be nearly parallel to each other, getting slightly closer as they extend from the rear end towards the front of the vehicle. Like this:


If your bars get farther apart as they extend from the rear end it's going to throw the geometry off, cause pinion angle changes, and generally make a mess of things.

Can you remove one wheel/tire and take a picture directly from the side? We really need to be able to see the horizontal angle of the upper and lower bars to get a better idea of what's going on.

sound like i good idea. i will take the bed off for better view of thing. and start looking into another design.

would it just be better to run the trailing arms i just got? would i still be able to get the rear as low with them on?
trying to fig my best option at the moment. i can do a lil fab here and there but my welding skill are not the best. and the welder i have is not the strongestr either.

take a look at picture the first picture the middle bars if i would lower them they would hit the driveline!

[Cue-Ball]

Originally Posted by Sick5

i can do a lil fab here and there but my welding skill are not the best. and the welder i have is not the strongestr either.

Your entire truck is being held up by this system while you're barreling down the highway at 70 mph. You had better make sure you have GOOD welds on those trailing arms and mounting points! Even without anything in the bed you're looking at nearly 4,000 lbs of mass that is completely out of control in the case of a weld failure.

take a look at picture the first picture the middle bars if i would lower them they would hit the driveline!

That's why most times the arms are either mounted straight back (relying on a watts link for centering) or the upper arms run wide at the frame and narrow at the axle like this:


You can't just throw four bars on there in any old fashion and expect it to work well. It might technically hold the rear end in place, but the geometry needs to be correct or things will be moving in all the wrong ways as the suspension moves through its range of motion. This stuff needs to be carefully designed, not just thrown together.

[Sick5]

Lol I don't mean to laugh butt I've been driving this truck like this for about 5 years. Thinking it was done right.what would give me the lower strands.trailing arms or four link