[patooyee]

WOW! I got my Jeep running today and pulled it out of the garage for the first time. As I backed out, the back end started dropping. I thought, "Uh oh."

I got it out and tried to pull forward. Nothing much happened with no throttle since I had to air the 44's all the way down to get it out of the garage. So I put about 2000 rpm to it. MAN did that thing jump! I personally didn't feel it in the driver's seat, but I'm told by observers that my rear end jumped up about 4 feet into the air. I broke the BRAND NEW 1-ton CV that I won, too!

Here's a description of my suspension. I think I have an idea as to what is wrong, but want to clear it with the suspension gurus here first. I have a pic to post but am not at my computer right now and will post it later tonight. My upper and lower arms attach to the frame at the same point. They pivot on the same long-ass 3/4" bolt. The upper wishbone goes down to the axle and attaches above the exact center of the dif. The lowers attach to the axle on the top of the axle toward the outsides.

My theory is that I need to move the lower link brackets to the same location only on the under side of the axle tubes. As it is now, the axle wants to torque and the links provide no counter-acting forces to each other.

So what do ya'll think? Again, there will be a pic in a few hours when I get home. I was hoping for a little anti-squat, but not nearly this much.

J. J.

 

[ROCKSFORBRAINS]

"my rear end jumped up about 4 feet into the air. I broke the BRAND NEW 1-ton CV that I won, too!"

Man, that sux

"My upper and lower arms attach to the frame at the same point. They pivot on the same long-ass 3/4" bolt."

Therein lies your problem. I made the same mistake on my very first four link- it was an easy fix, though. I just made a new upper mount on the frame to separate the converging uppers and lowers. How much separation depends on the amount of vertical separation of the links where they attach to the axle.

"The lowers attach to the axle on the top of the axle toward the outsides"

Yes, it sounds like they are too high/not enough VS. I would shoot for 7"or more (the more the separation, the less the stress that are placed on them from rotation of the axle).
.

"My theory is that I need to move the lower link brackets to the same location only on the under side of the axle tubes."

I don't think you need to go down that far- it's a pain in the ass to have those mounts hanging you up all the time. Put them about level with the center of the tube.

" As it is now, the axle wants to torque and the links provide no counter-acting forces to each other."

Exactly. The lower pushes up/forward and the upper pulls down/rearward nearly the same amount on a well working suspension. Think of a parallelogram.

"I was hoping for a little anti-squat, but not nearly this much."
J. J.

Make your new forward upper mounts with multiple holes for adjusting the anti- squat. Some people like more and some less anti- squat (I prefer 100% AS- no squat and no lift)

 

[TRD]

we need pics with angles/distances on it.

just bacuase your links are both on top of the axel doesn't mean it doesn't have resistance to rotation.

what you need to do is figure out all the forces on your links and how they act about the cg. This will tell you why you have soo much AS.

i am going to shoot for a roll axis // to the ground, and that has a little squat.

 

[Booger Weldz]

drop the lowers to just below axle centerline and drop the frame mount for the lowers to like 75% the verticle sep you get at the axle mounts?????

 

[jelbehai]

File sent to ya

Patooyee - sent you an Excel file that you can input dimensions & it'll calculate your Antisquat. Lemme know if it works/helps.

 

[Booger Weldz]

Re: File sent to ya

Patooyee - sent you an Excel file that you can input dimensions & it'll calculate your Antisquat. Lemme know if it works/helps.

share the wealth my new best friend

 

[jelbehai]

File sent to your e-mail...

Being the *newb*, I don't know how to attach a file (the FAQ indicates that Excel files can't be attached. In any case I sent it to ya Booger.

 

[Whaley Enterprises]

ok i have been searching and reading till i am blue in the face,,,and i am just more confused,, can anti squat be calculated with out knowing your cg height?? how can u figure out what anti squat will be before your rig is complete,, i am in the process of building and would like to get it right .. thanks! i know this was kinda of a thread high jack..but its along the same topic..

 

[TRD]

ok i have been searching and reading till i am blue in the face,,,and i am just more confused,, can anti squat be calculated with out knowing your cg height?? how can u figure out what anti squat will be before your rig is complete,, i am in the process of building and would like to get it right .. thanks! i know this was kinda of a thread high jack..but its along the same topic..

you can't, AS is based on CG.

look at the God of suspension thread by CalpolyStud. lots of good info for you in there

 

[jelbehai]

you can't, AS is based on CG.

look at the God of suspension thread by CalpolyStud. lots of good info for you in there

Agreed, but you can estimate it and your calculation is then as good as your assumption... :smokin: :barf:

 

[patooyee]

Here's the pic.

J. J.

 

[TRD]

how about a side shot?

 

[patooyee]

how about a side shot?

Your wish is my command.

This is an older shot of the vehicle. The links have since been shortened about 2". That's the only difference though.

J. J.

 

[ROCKSFORBRAINS]

can anti squat be calculated with out knowing your cg height?? how can u figure out what anti squat will be before your rig is complete

That's why we make our mounts with multiple holes....if you don't nail it right with the estimations/calculations, no big deal.

 

[TR]

basicly you have a radius arm set up and radius arms dont work to well in the rear, either lower your lower links or raise your upper link.

 

[TRD]

edit:

i fucked up on calcs and on't have time to fix toinight, i have a design midterm tomorrow and a shit load of HW, none of which i have started yet

mamybe tommorrow night if someone else doesn't do it.

inital problems seen, your links are too steep and mounting points (on axel) to close together vertically

 

[TNToy]

basicly you have a radius arm set up and radius arms dont work to well in the rear, either lower your lower links or raise your upper link.

No he doesn't. He has a 3-link.

 

[elf_cruiser]

I think that what TR means is that - because the frame-side mounts all go through the same horizontal axis, the links act like a radius arm.

Patooyee - you seriously need to just lower the frame mounts fro the lower arms. Like about 6 inches... REALLY lower them...

I hate to say it but, you have WAY too much clearance there. Your 1/4 ell. springs are way lower than your link mounts, so what is tehre to gain by having the links mount so high??

 

[TNToy]

Here's a link to a post on a buddies 3-link that I asked for a little help with. Maybe it'll help a little bit:
http://www.pirate4x4.com/forum/showthread.php?s=&threadid=108699&highlight=800hp

You can make that upper link level, for one thing. Make the mount over the diff about 2 inches higher, at least.

Your links are too close together at the axle - the top wishbone is only mounted about 4" higher than the lower links... and the bigger the vertical distance is between your upper and lower links, the better they will control axle wrap. I'd mount the lower links directly in front of the axle, which would be fine once you move the upper link up a couple of inches. The front mount of the lower links definitely needs to come down some.

Basically, you try to get things at less of an angle and increase the vertical seperation of your links at the axle, IMO. Dropping the front of the lower link and/or making them longer will also help.

Can you take a GOOD close-up side view of the rear suspension at ride height?

 

[TNToy]

Your 1/4 ell. springs are way lower than your link mounts, so what is tehre to gain by having the links mount so high??

True, why go to all the trouble to make those neat-looking lowers, when a sraight one would have been higher than the spring packs?

At least, even with dropping the lower link's front mounts, those high-clearance links still won't hang down very much, if at all.