New dif shudder/vibration?

[Racer-X]

New front dif installed late last week. I'm feeling a little vibration (best i can descibe it) 20-30 feet after taking off from a stop. Then it goes away when you get up to speed. It also does it when you come to a stop in the same speed range.

So it's obvious something has been done wrong but any ideas what? I want to sound edumucated when I take it back in.

More info: They changed both sides of the case due to the crack, but used the old insides.

Not 100% positive its not the new tires (BFG MT) I'm feeling since both the tires were put on and the front dif changed within 20 miles. But since it's only a very low speed that I feel anything I doubt it.

[Racer-X]

New front dif installed late last week. I'm feeling a little vibration (best i can descibe it) 20-30 feet after taking off from a stop. Then it goes away when you get up to speed. It also does it when you come to a stop in the same speed range.

So it's obvious something has been done wrong but any ideas what? I want to sound edumucated when I take it back in.

More info: They changed both sides of the case due to the crack, but used the old insides.

Not 100% positive its not the new tires (BFG MT) I'm feeling since both the tires were put on and the front dif changed within 20 miles. But since it's only a very low speed that I feel anything I doubt it.

[KenP]

They may have screwed up a shim or something. But I bet it's not the diff, but some related part they had to deal with. Then again, diffs are difficult.

Damn, that was such a precise, technical answer. Aren't you glad you asked in the "nerdy section"?

[rodster]

Is this the Nerds Anonymous meeting?

Hello, my name is Rod and I'm a nerd.

But I don't know squat about trannies, diffs or for that matter, why trannies want to be diff. Sorry.

[rodster]

PhilD will probably see this in the morning and have something useful to offer.

But I'm not calling him a nerd.

[Dan]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rodster:
PhilD will probably see this in the morning and have something useful to offer.

But I'm not calling him a nerd. </div></BLOCKQUOTE>

How about a geek?

[KenP]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dan:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by rodster:
PhilD will probably see this in the morning and have something useful to offer.

But I'm not calling him a nerd. </div></BLOCKQUOTE>

How about a geek? </div></BLOCKQUOTE>See, that's why he didn't respond. Yous guyz skeered 'im awayz.

[Racer-X]

after driving my PU truck to work this morning I'm thinking it may just be the new tires. My PU has aggressive tires and I'm feeling the same thing. funny I never noticed it before.

If there was a problem with the dif it would show soon in the fluid right? I was planning to drain it anyway because to be honest I don't trust the dealership to have put in the synthetic fluid that the hummer requires.

[NoMoGMPG]

The vibration could be the tires, or the driveshaft out of phase slightly. Best way to tell is remove the front driveshaft and drive it in high lock, if it doesn't go away, look to the tires, if it does go away, take the driveshaft to a driveline specialist for balancing.

How's that for a "nerdy" answer?

Dave

[Racer-X]

Thanks GMPartsGuy. I'll try that this weekend.
My original plan was to keep the old tires and mount them on the original rims - just incase I ever needed them. Then I couldn't figure out a scenario that that could happen. How nice would it be to have them now! Live and learn.

[OrangeCrush]

Under normal circumstances, I'd say your pinion angle is off...

HOWEVER, if you're getting a vibration accelerating AND deaccelerating, it can't be pinion angle since it can't be off both ways.

You'll either get a vibration stepping on the gas or letting off the gas.

(not to mention that though our trucks are AWD and the frt driveshaft is turning all the time, pinion angles are not quite as impactive on the front driveshaft as it is on the rear)

Before I did anything, I'd swap the driveshaft 180 degrees. If that doesn't help, I'd say check the Ujoints and have the driveshaft rebalanced.

I doubt that your vibration has anything to do with tires for a couple of reasons.

First, unless you didn't recognize the vibration before, the tires haven't changed so the vibration shouldn't have just started... if your tires are the cause, it should have felt the vibration before you had the diff replaced.

and second, tires out of balance really won't show a vibration at 20-30 mph (under most circumstances for tires these sizes) Vibrations from out of balance tires usually start 50 mph and up (normally)


Last but not least, there is a minute chance that if the gears are setup incorrectly, it could cause a small vibration (too much backlash, wrong depth, etc, etc).. but like I said, possible but highly improbable.


My .02 worth.

Mark

[OrangeCrush]

Okay, all that and I didn't notice the part about putting new tires on. If you have the stock tires and wheels, I'd put those on first... though I said that normally out of balance tires don't show up at lower speeds, that is apparently the newest change so I'd start there.

Sorry for not reading the entire problem before.

Mark

[NoMoGMPG]

The new tires could exacerbate a hub bearing problem that was under the radar with the old tires.

[Texas Red]

If it was first noticed with front diff replacement, it's a front diff problem. Take it back ASAP. Do you notice any whinning?

[Racer-X]

Mark, I'm not thinking they are out of balance. I'm thinking I'm feeling the lugs on the tires. I went straight from 4 wheel parts (where I had tires put on) to the dealership maybe 15-20 miles away. I may not have noticed it in that times because all I could think about was how I was spewing dif fluid everywhere and waiting for it to totally go.

My buddy is telling me that if it's a dif issue I could drain the fluid within 200 miles or so and I would show metal in the fluid. Would you guys agree?

I can definately feel this both coming and going from a stop. Infact I can even hold it in the speed range (about 3-5 MPH) and maintain the vibration. My bro had a good idea - he said he gets the same vibe in his Ram after lifting and putting on MT's. He asked me to turn in that speed range and see if it gets worse - the idea being that you can feel the tires lugs much more if your in a turn. What do you guys think? Would turning also put more stress on the hubs causing increased vibration if it wasn't the tires?

[Racer-X]

Red, please note tires changed at virtually the same time. Whining? I can't hear anything over those tires...LOL

[OrangeCrush]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> My buddy is telling me that if it's a dif issue I could drain the fluid within 200 miles or so and I would show metal in the fluid. Would you guys agree? </div></BLOCKQUOTE>

Regardless if something is wrong, if you drain the fluid in 200 miles, you're gonna get metal shavings... it doesn't necessarily mean something is wrong, you've got new parts... they're gonna leave a fine metallically look.

Now, if you drain it a couple of thousand miles after the first drain and you still have it, then I'd say you're on the way to having a problem.

Judging from what you've described, I'm agreeing with the lug theory. Tires with big lugs will definitely make a noise/vibration at 10 mph'ish speeds.

Like we said, the easiest way to test that theory is to put the stock tires and wheels on.

HTH's,

Mark

[rodster]

This thread is mechanically way over my head but FWIW, when I put the Toyos on my truck there was a very noticable vibe/rumble at very low speed. It's still there and I kinda like it.