The Stovebolt Site Forums The Shop Area Engine Shop A "Posi Rear end" ?

So i took my '53 3100 in to Les Schwab(tire/alignment shop) to have them look and see if everything was lined up right because when i take corners it starts to shimmy/shake/and sound as if the tires are fighting. Everything came back perfect and the guy asked me if i had a "posi rear end" and that he had an older truck that had a posi rear that went goofy on him. I don't have much knowledge and zero experience with this. Any suggestions for checking/diagnosing? It sounds as if there's some sort of clutch plates in the differential and maybe some springs are shot? Ohhh being a newbie :-)

Yes, I think that is the clutches chattering. Make sure yu have the proper lubricant in the rear end.

If you have a stock rear axle, it will not be a posi.

Something else would be the problem.

I'm near positive that the rear end isn't stock however I'm not sure how to verify (yet). I jacked the end up and spun the driver side tire and the passenger side spun opposite. And vis versus for the other way around. Does this mean an open diff?

Thanks guys!

Your diff is open based on the spin you describe. Do you have an open driveline or closed? How many lug nuts on each side?

You could have a steering problem, yet still be in alignment. If the front axle is not stock and has had parts swapped around, the steering arms could be to short or long causing the front tires to fight going around corners. Do you fell this shake in the steering wheel or in the seat of the pants? Theres a term for this, but I can't think of right now. What it comes down to is the inside tire turns to sharp and it drags the outer tire around the corner with it. Once the corner is made, all is right again. If the alignment shop didn't turn the wheels lock to lock, they might of missed it, I'am not even sure there is a check for this.

One more check to make, set the trans in neutral, and one rear tire on the ground, now try and turn the lifted tire. It will be stiff since you are turning the drive shaft if the axle is non-positrack. If you can't turn it at all, it is a posi with bad clutches.

Joe

So as i drive her more this is what i've noticed and found...

When taking corners with any speed above roughly 10 mph i have zero problems, no fighting, nothing. But when im stopped and go to turn, or making a very slow sharp turn then she fights. it starts to seem that the "fight" is almost coming from the rear rather than the front. I will try in the morning to cock her hind leg and give her a spin and see what happens. the alignment shop did test lock to lock and it was near perfect.

Is there any easy way to figure out what parts came from what? i.e. rear end, front end, etc.

Appreciate it guys

In my experience, bad clutches or wrong lube don't chatter, they slip.
Is it exactly the same left turn vs. right turn?

Joe H, you are thinking of toe-out on turns or the ackerman angle. When turning, the inside and outside wheels travel through different arcs requiring the front wheels to be turned at different angles, or they will scrub or drag. I can't tell from the photo album if the front suspension is still stock or not. If not stock, the alignment shop should be able to verify if the toe-out on turns is correct or not. A quick check is to pull a line from the center of the lower king-pin or ball joint to the centerline (side to side) of the rear axle with the front wheels steered straight ahead. The center of the outer tie-rod end should fall on the same line. If the tie-rod is in front of the lower ball joint (front steer clip or crossmember), extend the line forward of the ball joint, the outer tie-rod should still intersect with the line.

John

I remembered last night before bed its was the ackerman angle.

From what he describes, it could be worn spider gears, they can make a lot of noisy when the teeth are bad or missing.

Joe

It does happen both ways, when I'm making turns that don't require turning close to lock the problem is fine. But when I start getting close to lock the problem begins. The chatter is definitely only first gear. I also have to go to second before first at stops or it has a really loose grind to get in to gear. Transmission slipping or starting to crap out or could that be the spider gears or rear end related?