Diff. Vibration

[VA_GMC]

Back in Sept. I changed the diff. fluid. My truck has a locker, so I added the friction modifier. Since that time, I've noticed that the truck has a vibration if I take off from a start w/ a moderate amount of throttle or more -- if I ease away from the throttle it continues to vibrate noticably but if I let off all the way then get back on the throttle, it goes away. It almost seems like the locker is locked until I give the driveline some slack.

Anyone have a similar exp.? Could this be normal?

Any help would be appreciated.

[DmaxMaverick]

Unless you have installed an aftermarket limited slip, you don't need/don't want a friction modifier. The modifier can actually change the formulation and interfere with the lube's original additive package. That rear end was not designed to be used with any additional friction modifiers. Synthetic lubes that claim to not need a friction modifier, do not have a friction modifier in it. The lube is formulated to operate without one.

Adding a fricion modifier could cause problems with the locker. It could cause the locker to engage, or stay engaged when it is not designed to.

The additive could also cause problems with seals.

[Petrella]

hmmm i dont know if that would be a diff problem, but check your U Joints, and if equipped, your driveshaft hanger bearing make sure there is no play. Also make sure the inside of your wheels are clean from dirt or mud, because that can cause the wheel to go off balance and vibrate.

[VA_GMC]

I checked my u-joints a couple times. They seem o.k. but I haven't always been able to tell with weight on them - plus, I do have a carrier bearing and it moves enough (the rubber mount has probably 1/4" of play in it) that I can't tell what's happening with the u-joint at the front.

When I am on the interstate and hit a dip that causes the truck to "lighten up" when coming out of it, I can feel some vibration as well. Could be related to a driveline. - ??

The joints have 95K on them. Maybe I should go ahead and replace them.

Does the amount of play in the carrier bearing mount sound excessive? This is the first truck I've had that has one of these.

Wheels are clean.

I thought my owners manual called for an additive - I'll look again. I used Mobile 1 synthetic when I replaced the fluid.

Thanks.

[rjwest]

Why Wait for the Universals to fail, You got your money's worth, Time for new " greeseable ones.

Might as well do carrier also.

If you plan on keeping vehicle, Replace parts
that are life limited, No sense waiting for fails,


Lastly, The Locker's are Hard to fill, Need to
run a few miles and check level again....

[Dennis22]

Replace the Universals! I waited to long a couple of weeks ago.... front drive shaft let go, took out the wiring harness to the tranny and a piece on the front cover. $100 dollar job turned into a $500 job.
Dennis

[Robyn]

I just replaced the joints and the carrier bearing in my 86 dually crew cab 4x4 and the joints were starting to brinell some and the carrier was full of grass and junk from letting the local girls use it to haul hay and they got it in tall grass. YUKKKKKK.
Really made a difference with new Brg and joints
Definately not worth waiting till they go bang and take something out.

[rjwest]

If you see anything around the joints, like rust, cooperish cooler, THERE BAD.

[VA_GMC]

I haven't been able to find any reference to an oil additive/modifier. I'm going to dump the fluid and replace it again at the same time I run through the d-shaft.

Thanks for all the replies.

[VA_GMC]

...also wanted to ask if anyone has identified a u-joint brand that is "better" than another for these trucks. A couple of our local parts stores carry the Neapco joints. I haven't been happy with them on another truck but it may have just been the application - not a typical d-shaft. I'm hoping to find Spicers somewhere in town.

Thanks.

[DmaxMaverick]

Go to Autozone, and when they look up the part for you, ask for the "Brute Force" brand. Excellent heavy duty joint, and came highly recommended by a well respected GM HD tech.