Front End Darts At Speeds Above 40 Mph

I have a 1954 Willys CJ3B with an LS1 style motor and turbo 350 transmission. The front end is a custom built Dana 44 with 4:56 gears and an Eaton e locker with stock CJ5 disc brakes. The caster was set at 7 degrees positive, all front end parts are new, the steering gear (saginaw) is new, the tie rod ends are new as well as the ball joints are all new. The shocks are new rancho. The tires are 315xr70x17 BF Goodrich and are like new and have been balanced within the last month. I run 30 pounds of air in the tires.

The springs are 2 1/2 lift BDS springs with a slightly longer shackle. The springs are under axle.

Yesterday I went for a short drive and at about 40 mph it began darting from side to side and became very scary to drive.

Any suggestions as what might be done to improve this problem?

 

Maybe not the issue, but 30 psi seems really high to me. Also, I don't see anyplace that you have aligned the steering. ??? Incorrect toe-in (and etc.) can cause this. Do you have a track-bar and is it loose? Spring shackles tight?

When and how did this first happen - was it okay before and what changed?

 

Is toe-in set to spec?

 

Toe- in is set to 1/8 inch, all shackles are tight, there is no track bar on this unit. It worked well when I had a Dana 30 under it, but it had smaller tires and 15 inch wheels on it at that time.

 

Can you post some pics?

 

I’d start by lowering the air pressure. You can use sidewalk chalk to cover a section of tread and then drive a little to see if it wears off evenly. I’d guess that somewhere near 20 psi will be more appropriate, unless your rig is really heavy.

also, you say the tires were balanced within the last month... did the Jeep ever drive smooth with these newly balanced tires? Is it possible one or more were balanced incorrectly?

 

ITLKSEZ- what would you like pictures of? As for balancing it was done by discount tire on their latest equipment.

 

Did the Jeep ever drive properly after the balancing? If yes, then you can likely rule that out (unless some weight fell off). If no, then I would swap tires front and rear and see if the problem persists.

 

I making the 2 front tires in today to get rebalanced to see if that makes any difference

 

Steering components, stance, front end in general. Sometimes it’s easy for someone else to see something that others have missed. The “big picture” type of thing.

 

'Discount' alignment? Mmmm.

And 1/8" toe ain't much. More toe increases centering force. Lack of toe causes wander.

 

1/8” toe in is too much.
Shoot for 1/32 to maybe 1/16” max.
Or shoot for perfect straight then tighten/shorten the tie rod by 1/2 of a turn.
To set perfect straight toe adjust, first set Jeep on a flat spot and run a string line up along each side of the tires. Align front and back tires simultaneously.
Then tighten the tie rod 1/2 turn for proper toe.

 

are you sure the steering box isn't rocking . just asking

 

Toe in is at 1/16", steering box is tight on the mount, The tires have been re balanced today, I replaced the extended shackles with stock CJ5 style with new bolts and bushings. I will lower the air pressure on the tires and take it for a test day in the morning.
Warloch- is that true even if you set the toe in, perhaps I need to replace the 34.7 outside diameter tires with 33 inch.

 

I've had tires that were worn uneven cause steering issues. Check your Ubolts. I've had loose Ubolts cause very poor steering.

 

You said you had the axle built with 7° of caster but between the higher arch and longer shackles I will bet that you do not actually have that much caster effectively. I would check the actual caster sitting on vehicle weight. I agree with the tire pressure comments above as well, these vehicles are so light that 30psi seems high.

 

A quick update. I rechecked the caster and it was at 7.25 degrees positive. Replaced the shackles with stock early CJ5 style, set toe in to 1/16 inch, and lowered the air pressure to 25 lbs.
Went on a test drive and it handles much better, almost no wander at 60 m,ph.

Thanks for the advice