Unpredictable cornering

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Jul 18, 2018
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Seattle
Finally driving my 76 fj40 after 4 years of rebuilding. I've found cornering a little unpredictable. Usually on broader sweeping corners, anywhere from 20 to 35 mph, I start into the corner in a consistent arc. Right after the rig rolls into the bank, I'll get a second 'pitch' where it feels unstable and 'finds a new line'.

This obviously makes me really lose trust for higher speed corners, like freeway driving.

Current state of my cruiser is, 2 inch lift by OME with new leaf springs, shocks and shackles. I added 4 or 6 degree casters (cant remember which). It tracks very straight, maybe even a little heavy. I havent aligned for toe.

My current philosophy is that my shackles are pivoting throwing my axel into a different arc after the turn starts. The reason I'm thinking this, is I installed rock lights right on the rear shackle perch. The drivers side shackle was nearly vertical while the passenger side was leaned way back. I jack up the back on the frame, which straightened the passenger side.

Any other ideas on what could be causing this? It my therory is true, do the shackles need to be tightened?
 

EWheeler

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Finally driving my 76 fj40 after 4 years of rebuilding. I've found cornering a little unpredictable. Usually on broader sweeping corners, anywhere from 20 to 35 mph, I start into the corner in a consistent arc. Right after the rig rolls into the bank, I'll get a second 'pitch' where it feels unstable and 'finds a new line'.

This obviously makes me really lose trust for higher speed corners, like freeway driving.

Current state of my cruiser is, 2 inch lift by OME with new leaf springs, shocks and shackles. I added 4 or 6 degree casters (cant remember which). It tracks very straight, maybe even a little heavy. I havent aligned for toe.

My current philosophy is that my shackles are pivoting throwing my axel into a different arc after the turn starts. The reason I'm thinking this, is I installed rock lights right on the rear shackle perch. The drivers side shackle was nearly vertical while the passenger side was leaned way back. I jack up the back on the frame, which straightened the passenger side.

Any other ideas on what could be causing this? It my therory is true, do the shackles need to be tightened?
Did you try tightening the shackles to test your theory? If thats what you think, then do it and see if it helps???

Did you spend much time driving the FJ40 before the rebuild?

Do you have a lunchbox locker in the rear differential?

What you describe makes me think of roll steer which can happen on linked suspensions that are not properly setup geometry wise. But i do not think it can happen in the same way with a leaf sprung truck so i dont think thats your problem.

Stock steering setup? Is the centerlink in good shape? How much play do you have in the steering wheel at rest?
 

3_puppies

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which way are the shims facing?
how about some pics of the front end and rear end set ups?
the shackles should be nearly the same angle on the same axle
 
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I’d align your toe in. I suspect as the weight shifts the path the outer wheel is travelling is different from the inner wheel.

Google search pushpin alignment an you’ll find how easy it is to do it yourself.
 
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I also have OME 2" lift on my 40. I did set the toe-in to 1/8" and I didn't add any shims. Vehicle runs straight and true without any issues while turning.

I know you already did the work to install the shims so leave them for now. Set the toe-in to 1/8" and test your cornering again. If it still has issues I would remove the shims and test again. If you take it to an alignment shop they will tell you whether or not the shims are helping or hurting your alignment.
 
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Tires?

My FJ40 had some over 20 year old 12.5" wide mud tires, and it behaved like that.
Put new 10.5" KO2s on with no other changes and it was like a whole new truck.

Of course, then I added a rear lock-rite and it's back to being like that, but at least I expect it and am not worried about tires exploding for no reason
 
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Did you try tightening the shackles to test your theory? If thats what you think, then do it and see if it helps???
Haven't tried tightening shackles, look like an easy test.

Did you spend much time driving the FJ40 before the rebuild?

Do you have a lunchbox locker in the rear differential?
Spent very little time before the rebuild, but did drive 60 for 2.5 hours and this problem did not stand out.

I have no lockers install.

Stock steering setup? Is the centerlink in good shape? How much play do you have in the steering wheel at rest?
Steering is a saginaw steering box freshly rebuilt at red hat. So I really dont have any play.

Honestly, I have to research the center link as I don't know if I have one in my setup.

which way are the shims facing?
how about some pics of the front end and rear end set ups?
the shackles should be nearly the same angle on the same axle
Shims on the front axle are thick to the front. I'll send pics right after this mega post. The shackles are not at the same angle. Back to @EWheeler Post, I'll straighten and tighten.

U bolts tight?
Tightened to 180 ft.lbs

I’d align your toe in. I suspect as the weight shifts the path the outer wheel is travelling is different from the inner wheel.

Google search pushpin alignment an you’ll find how easy it is to do it yourself.
I have the plates to install on my lug nuts, I get to it this week.

295/70 r17 KM3
Super heavy tires but new and balanced.
 

cruisermatt

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How did you miss that!?
 

cruisermatt

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it looks like you have a front spring on the rear and a rear spring on the front?
 
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Haven't tried tightening shackles, look like an easy test.


Spent very little time before the rebuild, but did drive 60 for 2.5 hours and this problem did not stand out.

I have no lockers install.


Steering is a saginaw steering box freshly rebuilt at red hat. So I really dont have any play.

Honestly, I have to research the center link as I don't know if I have one in my setup.


Shims on the front axle are thick to the front. I'll send pics right after this mega post. The shackles are not at the same angle. Back to @EWheeler Post, I'll straighten and tighten.


Tightened to 180 ft.lbs


I have the plates to install on my lug nuts, I get to it this week.


295/70 r17 KM3
Super heavy tires but new and balanced.

Shims thick to the front would reduce caster which would increase wander and dartiness. I believe thick should go to the back if they are needed at all.

FYI, your centre arm was removed with a Saginaw P/S conversion.
 

pb4ugo

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Shims thick to the front would reduce caster which would increase wander and dartiness. I believe thick should go to the back if they are needed at all.

FYI, your centre arm was removed with a Saginaw P/S conversion.
Shims installed with the thick part forward will increase positive caster and typically track better. Thick part to the back will increase negative caster and will increase wander and twitchiness. I agree with crusiermatt, looks like there's 1 frt spring and 1 rear sping on the frt and the same on back.
 
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How do I tell?

Look at the number and length of the leaves that make up each pack. From the pics we can see 3 full length leaves on one side, and 4 full length on the other...
 
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Ok, I have the numbers:
Front left 2e18
Front right 8b17
Rear Left 12ac17
Rear right 2e18

Area both fronts suppose to be 2e18?
 
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Minnesota
Wouldn't both axles be cocked? As in not 90º to the center line of the vehicle?

That would make things a dumpster fire to drive.
 

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