Steering lunge problem (1 Viewer)

[Armenoonanian]

Okay everybody I need your help I have 1983 FJ40 with 78K original miles, and I'm noticing a problem, I think in the steering, occasionally while shifting gears, sometimes 1st to 2nd other times 2nd to 3rd and usually, during accelerating, I feel it slightly lunge to the right and goes back straight. I have already replaced all my leaf springs because they were old as well as all the shocks, I noticed a little bit of play in the steering wheel so I had the steering box rebuilt, I had a front end alignment done, and replace the steering dampener, the tie rods are also in good condition... I just got it back today and I feel the same thing. Will appreciate any help

 

[snaggletto]

Those shackles do not look stock, what is the bolt to bolt dimension on your swing shackles? I want to say stock is ~2.75" or ~70mm (not sure on this). If the shackles are longer and/or your aftermarket springs are not quite formed right, then your caster (angle of front steering knuckle rotation) may be out on the front and back axle (pinion angle) a bit. More positive camber creates twitchy steering, more negative makes it really want to track straight. A 2 degree STEEL (do not use aluminum) caster correction shim with the fat part facing forward on the front axle would give you 2 degree more negative caster and would likely help. If the pinion angle in the rear is out a bit, it would manifest itself as driveshaft vibrations, which may not be an issue for you. Otherwise, you may have to look into your wheel and steering knuckle bearings, maybe even motor mounts and such to see if something moves, or torques when you shift/accelerate.

 

[B y r o n]

Have you ever watched a drag race? Then you probably notice from time to time that some cars pull to the right or left when they leave the line. It has to do with traction and suspension movement. I think you may be experiencing the same type of thing. When you accelerate you load your suspension momentarily and that pulls you to one side. As the force of your acceleration settles you go back to driving straight ahead. It could be the slightly longer shackles, worn spring or shackle bushings or loose bolts or any combination.

 

[bj461a]

Do you have a locker installed? After installed a lockrite my 40, it does the same thing under hard acceleration. Most notible when turning slightly to the left.

 

[Armenoonanian]

Those shackles do not look stock, what is the bolt to bolt dimension on your swing shackles? I want to say stock is ~2.75" or ~70mm (not sure on this). If the shackles are longer and/or your aftermarket springs are not quite formed right, then your caster (angle of front steering knuckle rotation) may be out on the front and back axle (pinion angle) a bit. More positive camber creates twitchy steering, more negative makes it really want to track straight. A 2 degree STEEL (do not use aluminum) caster correction shim with the fat part facing forward on the front axle would give you 2 degree more negative caster and would likely help. If the pinion angle in the rear is out a bit, it would manifest itself as driveshaft vibrations, which may not be an issue for you. Otherwise, you may have to look into your wheel and steering knuckle bearings, maybe even motor mounts and such to see if something moves, or torques when you shift/accelerate.

Thanks for responding. That picture was taken before I replaced everything. Now I have new leaf springs and new shocks from OME. The shackles are also replaced and now the dimension from center to center is 85mm. I also have the shims with the fat side facing forward. From the beginning, I thought its the gearbox because I noticed that the previous owner did a lot of offroading but after rebuilding the gearbox and changing all those don't know what else to do. Before the play of the steering wheel was a lot. I tried to adjust but since the lunge problem didn't go away decided to rebuild. Honestly don't know where to start. Let me know your thoughts.

 

[Armenoonanian]

Have you ever watched a drag race? Then you probably notice from time to time that some cars pull to the right or left when they leave the line. It has to do with traction and suspension movement. I think you may be experiencing the same type of thing. When you accelerate you load your suspension momentarily and that pulls you to one side. As the force of your acceleration settles you go back to driving straight ahead. It could be the slightly longer shackles, worn spring or shackle bushings or loose bolts or any combination.

Thanks for your help. Probably I have to find some good specialist who can check the rear differential because I hear some knocking when I turn.

 

[Armenoonanian]

Do you have a locker installed? After installed a lockrite my 40, it does the same thing under hard acceleration. Most notible when turning slightly to the left.

The previous owner said that the truck has lockers. Can you please tell me how I can check that?

 

[greenbeasty]

If it pulls a little, and knocks when you turn, you have an LA locker type in the rear. It is working properly.

 

[76 PTO]

You probably have a lunch box locker. They will click when turning. They will cause a lurch under acell. Jack up the rear end and turn a wheel. If you here click click click.

 

[Armenoonanian]

If it pulls a little, and knocks when you turn, you have an LA locker type in the rear. It is working properly.

Yes, it knocked today when I was doing a U-turn to the left. Thanks for your help!

 

[Armenoonanian]

You probably have a lunch box locker. They will click when turning. They will cause a lurch under acell. Jack up the rear end and turn a wheel. If you here click click click.

Today when I was doing a U-turn I clearly heard knocking from the rear end. Tomorrow I will do that test. Thanks!

 

[greenbeasty]

I love mine, DD for a while , wheeled it HARD with 38 Super Swampers for a while, rebuilt it once in 20 years. One of the best mods I ever made.

 

[Shark56]

As stated above. A locker will click or knock while turning. I have found on mine that if the tire pressure is not even, side to side in the rear, I will get a noticable pull when accelerating. Even when then rears are the same pressure I get a slight pull if I accelerate hard or shift hard.

 

[snaggletto]

Jack up the rear end and spin one wheel. If they both move the same direction, you have an auto locker in your differential. If they spin in opposite directions, then you would have an open differential. An open differential is preferred for street driving, and is still very capable for light off road use.

 

[Armenoonanian]

Jack up the rear end and spin one wheel. If they both move the same direction, you have an auto locker in your differential. If they spin in opposite directions, then you would have an open differential. An open differential is preferred for street driving, and is still very capable for light off road use.

Both tiers moved in the same direction and I hear knocking when was spinning a little faster.

 

[Armenoonanian]

You probably have a lunch box locker. They will click when turning. They will cause a lurch under acell. Jack up the rear end and turn a wheel. If you here click click click.

I just lifted the rear of the truck and spin one of the tiers. Both tiers moved in the same direction and I hear knocking when was spinning a little faster.

 

[Steamer]

With a lunch box locker there should be no clicking when both wheels are rotating the same direction and same speed. It is when one wheel goes faster than the other, that the clicking or ratcheting will occur as does happen in a turn. Unless of course you are accelerating heavily in a turn and the locker locks up (as it should) and both wheels will be forced to turn the same speed and the tires are forced to skip or chirp and the vehicle will try to go straight.

With it jacked up and you chock or hold one rear wheel and turn the other, you should get maximum ratcheting/clicking.

 

[greenbeasty]

It's fine, don't worry about it. Tough little critters.

 

[MostlyNuts]

My '78 FJ40 has a lunchbox, a spring shackle reversal with a Saginaw PS upgrade. Also has the 'surge' in the same way you describe. I am also doing the same things you are. Replacing the old PS box just for good measure, replacing all the bushings and I suspect I'll need to add a Deckers Traction bar also, FJ40 Traction Bar - https://www.deckersonline.com/fj40_traction_bar

Will let you know where I end up with that.

 

[1969FJ]

Are your motor mounts and/or other mounts OK ?