So... my Buck$Zooka may not be ready for shrink-wrap just yet. I have a vibration (or shudder) in 3rd gear. I know bupkis about transmissions and I have no plans to be a guru in there. I will instead share my observations, seek input, and let the transmission folk slap me around and make me write checks. Injectors have sucked all the fun out of turning wrenches on Stinky until spring. Chipping may void the warranty, so I pulled the chip the last time I had the stealership look at it in October of 2011. I'm pretty sure I can't hide the recently-added sizable single-shot sticks and custom tune to make them run, so that warranty paperwork might have a "remit payment" line at the bottom.

• HD4R100 installed in August 2011
• All gears have a solid (but not slamming) shift.
• My transmission runs real cold - just 70 degrees above ambient, so it's 100 degrees in there this time of year.
• 3rd gear vibrates under cruise to moderate load, but the vibration disappears when I let off the accelerator or push deeper in the accelerator.
• I notice it more when I'm in four-wheel drive.
• All other gears are baby-butt smooth.

At first, I thought I was driving over tire-chain ruts because the vibration feels the same... but it kept doing it on pavement without compact snow. The transmission has been doing this in 3rd gear for a while, but the issues with the engine were masking the problem... until now.

Thoughts?

 

Are you absolutely sure your not losing a U-joint on the drive-line. That is kinda what it sounds like to me. Maybe the center carrier bearing..
I would investigate that area first.

 

I'm pretty sure they all need attention... soon. It was already planned as soon as the engine was squared away (minor wrench-turning is still OK). I'm just wondering why the problem would single out 3rd gear.

 

maybe the rpm of the drive-line match's up with the rpm of the trans output in third and the rpms sinked together is the rpm that you notice it at ?? I don't know ?? but it sure sounds good.. LOL

 

I had a "noise" once upon a time. and I started with brakes drive train etc.

turned out to be the carrier barring. but it took a while to narrow it down.

was frustrating

 

I will go with driveline issues too. One thing you should do first is rotate the tires. See if the problem goes away. Tire wear can cause some unique sounds and vibrations.

 

I too say check U joints and carrier bearing....1, because it sounds like a RPM related issue/load issue, and 2, because they are all easy to deal with. What RPM does it occur at? I'm guessing its more when you are cruising than when you are getting on it at all, so I would guess between 1500-1900...If thats the case I would put more money on u joint or carrier bearing...only thing that is throwing this off is the fact that it is more noticeable in 4x4...

 

The gear ratio in 3rd is 1:1... if my memory is hangin' in there.

Maybe the vibration is augmented by the imbalance with the front drive in 4X4 and the two drives start dukin' it out in 3rd. After all, the rear now has to argue about the speed... rather than just be in charge.

 

Check your u joints and carrier bearing before you start coming up with drive ratios causing boxing matches... If its time to change out your u joints do them all at once.... they are fairly cheap and easy to do...as well as the carrier bearing...

 

If 3rd in an auto is indeed 1:1 then there might be a vibration that you feel in the driveline at a certain driveline RPM...the reason for it showing up in 3rd would be that the engine is turning the same RPM as the drive shaft allowing you to actually notice the vibration. My bet is on carrier bearing or a driveline came unbalanced.

 

Results:

• Bent driveshaft (that ought to cause issues). It was out by 20 thousandths, near the carrier bearing.
• Front U-joint had a little "burling" (I think that was the term) on three ends (side, tangs... whatever they're called), but the other two U-joints were in excellent condition. All three were destroyed while trying to remove them to inspect them. I watched the process and those buggers were stuck in there pretty good... I could never remove them with the tools and skills at my disposal.
• The old weights on one shaft made it out of balance, and removing them solved the problem. The other shaft had weights 160 degrees out from where they now need to be.
• Dry splines... but I already knew that.
• Carrier bearing is in excellent condition.

Shop guy pulled front and rear drive lines to inspect, completely rebuilt, straightened and balanced the rear drive line, and re-installed both drive lines. $318. I owe that guy some business. Anybody need their drive lines gone through?

 

Wow...resultant to your accident maybe? If the shop does fabrication I might be in the market for a one piece unit...

Id talk to your insurance company...might be able to get it all covered as a result of that insta lift you had earlier this year. Either way its worth a shot.

 

Fairly confident I have the same problem. I was reading through your symptoms and have everything but the 4x4 worse. Did yours feel like a "thump thump thump" vibration right under driver floorboard around 35 to 50?

 

$318.oo parts and labor was great. Where I live it would of been $1500.oo. Great to see it fixed.

 

Hmmm... I looked right over that... good point. The problem has been there a while, but far more subtle. I noticed it more since my 3rd-gear scratch during a WOT test in 80e (now omitted from my tuner). It has grown worse as my injector issues may have exacerbated the problem with the incessant torque romps. It wasn't until the engine was smooth that I could isolate the vibration to the drive. There are just too many things on the list that could have been the root cause, or more likely... everything added up.

The torque converter can cause this as well. This is one of those buggers that's a process of elimination. Depending on miles and treatment, your driveline may need to be looked at... but the transmissions on these are not that robust and are a tall blip on the suspect-o-meter.