Rear end all over the place??

[Houston Ben]

Hi all,
I have an 86 C10 with a 2011 5.3 W.6L80 behind it. After the install of the 5.3 my rear end is all over the place. I installed some traction leafs to help with the axle wrap and it helped a lot but the side to side motions the rear end does when I get on it still scares me. One time I jammed on it to get around a vehicle and it almost pulled me into the vehicle.

I just installed a 2/4 Belltech drop with their SP shocks and the ride is much improved but still bad side to side movement. What can I do to stop this?

Thanks for any help, I am at a loss on this as I have no expertise in this department or any other for that matter.

[andrewmp6]

Does it have the factory leaf springs under it still ?Stiffer springs and shocks is the way to go,Or you can go aftermarket porterbuilt has a truck arm kit and 4 link kit both can come with air bags or coilovers.

[BR3W CITY]

Barrage of questions to feel out what your describing, you don't have to answer them all, but let me know if any of sparks possibility.

Are you on leaf only, or do you have any other sort of antiroll bars, watts link, anything like that?

Is the axle motion the same every time, or is it situational?

Is the axle shimmying under the truck? (like the axle is "walking" like the fixed axles on a toy car, or like one tire is getting ahead of the other)

Is the axle/suspension shuttering or hopping (like the suspension isn't controlling the axle or like its wiggling/floating on the tires)?

Lets start there, and narrow it down.

[Houston Ben]

Are you on leaf only, or do you have any other sort of antiroll bars, watts link, anything like that?

Yes, leaf only in stock form, 4 leafs a helwig traction leaf on front half of leafs and nothing else.

Is the axle motion the same every time, or is it situational?

It feels the same every time it happens. I have a truetrac in the 10 bolt and it helps when both tires spin. This phenomenon usually happens when the truck is shifting and the rear chirps (1 tire) but does not engage the other tire.

Is the axle shimmying under the truck? (like the axle is "walking" like the fixed axles on a toy car, or like one tire is getting ahead of the other)

I don't think so but not 100% sure.

Is the axle/suspension shuttering or hopping (like the suspension isn't controlling the axle or like its wiggling/floating on the tires)?

I do have a weird vibration at speed (50-68mph). I had the tires balanced and this did not fix the problem. I have had the rear end on jack stands and rand the truck and there is deff a problem with my wheels or tires being out of round but I don't think this would cause the side to side action when thee truck is shifting under pressure.

One thing I thought of was having the tuner replace some of the torque management so the tranny doesn't shift as hard. I am really at a loss when it comes to this stuff.

Thanks for all the help and Br3w, you are a great man who is always here to help with a plethora of info!!

[whitedog76]

Is your rearend hopping?

I would check your driveline angles, since you did say that you swappen the engine and trans.

[Houston Ben]

Hi Whitedog, I will have to go buy an angle finder and check, what angle is considered "in spec"?

[BR3W CITY]

Driveline angle + rear end angle = total pinion angle. Up is +, down is - so the total effective pinion is the sum or remainder of those two figures.

U joints will stand about 4* total max, going either way. Since most LS motors are installed 1-4* DOWN (-), that means that the rear end angle has to complement the driveline angle resulting in a total angle of less than -4*. If the rear end is able to roll enough on its axis, then you can twist way out and snap ujoints.

[Houston Ben]

Ok, I went to the store and bought an angle finder and attached to the bottom of my tranny oil pan and then the bottom of the axle where the drive-shaft connects to it.

The bottom of the tranny was at 5 or 6 going the same direction as pictured above.

The bottom of the axle was at 8 or 9 going the same direction as pictured above.

Br3w, I kind of get what you are saying but not completely so could you tell me if this is good or bad??

Thanks!

[BR3W CITY]

This image is a bit tought to read but does a decent job explaining it. There are many ways it "Will" work, but there is usually only 1-2 ways that it'll be ideal. You'll see there is a slight difference between regular and performance builds. High hp cars and some leafspring cars will rotate the rear axle more and pull the driveline angles out.

If thats 5 down and 8 down, then the total should be 3 which is within reason.

http://www.hotrodlane.cc/trannys/driveshaftangles.jpg

[Houston Ben]

Hi Br3w, great illustrations, thanks. Looking at my tranny and axle I feel like my setup is like the third one down which is the bad one. I went back down and took pictures of the angle of both the tranny and axle. Both pictures and measurements were taken from the same side of the truck. See pics below.





Am i thinking too much into this? It looks like my trans is 5.5 down and the axle is 8 up.

Thanks again for your help.

[BigDan3131]

When you did the swap did you have the driveshaft rebalanced to stock or for a higher performing engine?

Did you have all the bearings replaced in the rearend when you had the truetrac installed?

Does it need to be broken in like the Cone type posi meaning driving it in a figure eight 6-7 times then cooling it down? The reason I ask is because it should spin both tires and chirp both tires going in a straight line and if it isn't that's a problem.

[BR3W CITY]

Originally Posted by Houston Ben

Am i thinking too much into this? It looks like my trans is 5.5 down and the axle is 8 up.

Ya since the rear is up, you have around 13* total, unloaded. If you got hard on the gas, that probably becomes 15-17*. As your truck is getting under power, your pulling further and further from 0.

You won't have ujoints for a very long time with that much angle.

[Houston Ben]

Any ideas on how to fix this??

[SCOTI]

Originally Posted by Houston Ben

Any ideas on how to fix this??

Pinion shims to bring the pinion angle down. They slip between the leaf pack & rear end causing the angle to change. Or you can opt to re-weld the spring perches on @ a better angle.

Then some Cal Trac bars to help those leaf springs plant the power generated.

[Houston Ben]

BigDan, There is no break-in period for the truetrac and I bought new bearings for the truetrac as well, the drive-shaft is brand new and had to be built for the length difference.

Br3w, well hell, not what I wanted to hear but thought is was going to be that way

Scoti, I didn't know there were such things as pinion shims. Guess I know what I will be buying, what would you all recommend for the degree of shim?

Thanks again guys!

[Houston Ben]

I'm thinking an 8* shim, does this sound correct?

[Keith Seymore]

Originally Posted by Houston Ben

Hi Br3w, great illustrations, thanks. Looking at my tranny and axle I feel like my setup is like the third one down which is the bad one. I went back down and took pictures of the angle of both the tranny and axle. Both pictures and measurements were taken from the same side of the truck. See pics below.

Am i thinking too much into this? It looks like my trans is 5.5 down and the axle is 8 up.

Thanks again for your help.

Not enough data.

We need to know the drive shaft angle, too.

http://67-72chevytrucks.com/vboard/s...d.php?t=522180

K

[SCOTI]

First, I would....

Pull the drive shaft out.
Grab a small piece of scrap metal & drill a hole in it so you can bolt it flush to the pinion flange. Now double check the rear measurement.

I would also add a spacer under the trans mount to reduce the front angle. With that reduced, you wont have to make as drastic of a change @ the rear.

[Houston Ben]

Dang, I didn't know there was so much that went into this. I will check the drive-shaft angle tonight.

[Houston Ben]

Scott, I don't have any scrap metal at home, I will have to try to get something from work.

I put the angle finder on the driveshaft and it sits about 2*. With Keith's math info I am looking at 4 for the front and 6 for the rear measuring the angle off the trnas pan and the tail housing of the pinion. So it sound like I need a 2* shim?? thanks again all.

[Houston Ben]

Br3w, Keith, does this sound right??

[Keith Seymore]

Yes - a 2 deg shim should put you at 4 deg u joint working angle for both ends.

But I'm confused: how did we go from the "rear end all over the place" problem to a driveline problem? Has your original complaint been fixed?

K

[BR3W CITY]

Your original 6 down and 8 up would be; 6-2= 4* and 8-2=6* so a 2* shim would be 4* down and 4* up making your i/o parallel. As long as your not making insane power, that should be enough to eliminate vibrations/weirdness. If your making enough power to pull wayy out, you can set the pinion down further so you "pull up" into alignment.

Keith - we ended up here because its possible that with a drastically effed up d/l angle he could be trying to force the whole suspension to rotate and/or be preloading the heck out of one side or wrapping the axle, especially if it was actually binding at any point. There may still be another suspension problem.

[Houston Ben]

Thanks Keith and Br3w for chiming back in. So my next step will be to order and install shims and report back.

BigDan, I forgot to answer your question on the truetrac and both tires chirping at the same time. I have done a lot of searching and the true track seems to takes a split second to transfer power which seems to be the reason why one tire chirps when I'm not totally gunning it. That is usually when the axle feels like it shifts around. If I mash the throttle from the get go it spins both right away, at least if feels like it to me.

Before I had the truetrac in and only had an open diff the the rear axle would really jerk sideways when I jammed on it scaring the crap out of me!

It seems to me that I may have two issues, the pinion angle and the old worn out springs... I don't know!

[Houston Ben]

UPDATE
I put 6* shims for the pinion angle back in Octoberwhich helped a little but still had a bad vibe. Thinking I had bad axles, I pulled them out and they looked worn so I replaced them and e bearings/seals and no change, boy was I mad! I finally figured it must be the trans angle so I bought a high hump trans cover and new trans crossmember which I installed yesterday at my friends house. On the way home it appeared to be gone which I am totally thrilled about but I need to drive it a little more to be sure.

Check my sig for the install of high hump if ya want.

I'll let you all know when I am sure it fixed it!