Let me start with; at this point, this is for the sake of conversation, as I have not made an attempt to confirm a cause.

My truck has 196k on it.

Symptoms:
Light braking the truck pulls up straight.
Moderate braking, the truck drifts left... no steering wheel pull, but opposite steering is needed to maintain a straight line.
Heavy braking the front ducks to the left and more/quicker correction is needed.
There is a perceivable yaw of the body when this happens.

My initial thought is worn right rear leaf spring bushings, allowing the axle to move aft on the right side, changing its angle to the chassis, and causing the rear to swing out to the right, pointing the front to the left whereby making it drive/drift left, and account for the need of right steering to correct it.

Has anyone experienced this issue?
Any other theories?

 

I have never really had a problem with brake-steer from the rear axle, it was always something in the front. Either a bad line, or caliper seized on the guide pins. Think I would have a look there first...... just to be sure.

 

Is there any shops in your area that does a 4 wheel alignment? They might be able to find an issue if there is one.

 

Does your truck sit significantly off-level when viewed from the rear? If you've got one clapped out leaf spring (and one not so clapped out), moderate to heavy braking will cause the truck to pull toward that side.

 

No, it all looks level.

The issue has existed before and and after a full brake upgrade.
If I brake "hands off", there is no pull on the steering wheel (the steering wheel doesn't move), but the body yaws left and the truck drifts left.
If the issue was front brakes, I'd expect steering wheel pull.

If it was tie rod ends (allowing the left wheel to toe out under brakes, and lead left), I'd expect some kind of wheel shimmy under power, and I wouldn't expect body yaw.

If the left rear was braking harder than the right rear, and the track bar bushings where shot, I could see the yaw under brakes happening... but I would expect the left rear to lock before the right under extreme braking (not the case).

 

Not that I know of, but I'm sure there's one around... just have to find one.
One of these weekends, I'll get it on a hoist and give it a look over.

I'm just beating the bushes for some valid theories, to hone in on where to start looking when I get under there.

 

Verify that both rear brakes are working, and adjusted properly.

 

What is not stock on the truck related to this?

I recall rear axle is from 3rd gen 1500?

Any other brake related mods?

Proportioning valve may be suspect.

Sway bar

Track bar bushings cracked.

Leaf spring bushings cracked.

Overload in leaf pack might be cracked.

Brake pad condition comparison bt both sides.

Don't understand drift part. Reads as though passenger side grabbing more.

 

Stock unchanged suspension and axle setup... new Rancho shocks at ~85k (I guess they're due again, but seem to be doing their job still).

Just recently upgraded to 2500LD brakes all round (all brake components are new at the wheels).
This issue started before the brake upgrade.

I'll report back when I get some hoist time to inspect all the bushings.

"Drift" was used to describe the vehicle moving left without steering input.
Passenger side rear bushings shot, allowing that wheel to fall back, changing the axle angle and inducing rear steer to the right, pointing the front to the left, hence the direction of travel (my theory).
Though it could be, I don't think it is dependent on differential braking in this case.

Closing in on 200k, I'm sure there are plenty of bits coming due for replacement.

 

Have someone follow you down the road, that KNOWS what you are going to be doing. Have them check to see if your 'tail is wagging'. does the truck change its 'angle of attack' when applying the brakes? Does it dog-track when not on the brakes??

I could see bad bushings doing that...... but, I would think it would make some noise too. But, not like I have never been wrong before.