Front driveshaft vibration is in the front diff?

I have a first-gen Tundra, same diff at the first-gen Tacoma. I'm tiding up all the odds and ends on the truck before I find a new owner. The big thing is the vibration with the front driveshaft in. I need some help so let me tell the story...


With 3.91, 4.10, and 4.56 gears, I ran 90 mph on the highway all the time. I did the long travel and swapped diffs to 4.88s and ARBs F/R simultaneously. My front diff has the had the shift fork "locked in 4wd" with both the 4.56 and the 4.88 gears. This makes the front end constantly turn and created no issue whatsoever with the 4.56 gears.

Now that I installed long travel and 4.88s, there is a vibration that starts about 40 mph and increases with speed. It starts as a mellow vibration that I can feel in the pedal. As you get to 60 the dash starts rattling and as you get to 80 it feels like the truck is going to eventually shake apart and I slow down.

I pulled the front driveshaft and there is absolutely no vibration from the front end at any speed whatsoever. I have been driving this way since the long travel was installed. The truck drove this smooth with the 4.56 gears installed.

I have tried installing the driveshaft in different positions, and with the slip joint on the t-case side and on the diff side. I have checked the pinion preload and it was good. I have checked the torque on the transfer case flange nut and the pinion nut and they are both good. I checked the torque on the bolts the secure the diff to the frame. I had the driveline professionally balanced. The shop guy said the u-joints were good and it had runout, but it balanced well. After I put it back in the truck the vibration is slightly better since it now starts at 50 mph, but it still intensifies with speed and is not OK at highway speed.

I believe I can eliminate the source of the problem from any component of the long travel suspension, the CV axles, the gears, and the tires as a source of vibration. If they were a source, they should cause a vibration with the front driveshaft removed. They do not.

The driveline/diff guy believes that there is nothing in the front diff that would cause this vibration. I asked about the pinion flange and he said it would be a super strange occurrence. I asked about a bad pinion bearing and he said it will howl and make noise but not vibrate.

This diff was supposedly set up by ECGS 5,000 miles ago and supposedly came out of a rolled Tacoma.

I was wondering if the pinion flange could be bent. The diffs were shipped to me in a 5 gallon bucket- perhaps the UPS guy dropped it? I jacked the front of the truck up and spun a tire to watch the flange spin without the driveshaft installed. Nothing looks abnormal to my naked eye, but since the vibration is starting at 40 or 50 mph, the flange would be spinning much faster than what I observed.

Any ideas of where to look? I am at the point where I am about to have a different gear shop tear the front diff apart but I don't know what they would be looking for.

 

Why are you running locked in 4wd all the time on the front axle? ARB in the front. I see that now

 

Manual transfer case swap, eliminating all electronics.

 

My tacoma started vibrating like yours last week. I have had a new front diff put in lately. I took a process of elimination guess and decided to replace the 387 u joints in the front shaft. I drove the truck with the front shaft out and no vibrations at all. Did the u joint job and put the shaft back in and no vibrations.
Just because the u joints look and feel ok doesnt mean that are. IMO.

 

? You did that or ? Are you sure your transfer case is in 2wd?

 

Your diff is turning the same regardless of driveshaft in or out. If it was going to vibrate it would vibrate. I did the same with a jeep that had a bad vacuum actuator. It also vibrated at speed because the front driveshaft was not balanced and not intended to be free spinning all the time. The dshaft was never pulled so it never moved, just doing something it wasn't designed to do. Tbh if it wasn't vibrating before the gear swap and it is now I think you just got lucky the first time. Put it back to stock before the sale and you'll probably be done.

 

Slapped a dial gauge on the front pinion flange, .020" runout. Currently looking for what it's allowed to be on this truck, but this seems excessive.

 

According to the FSM, maximum runout is .0039". Got a "new" used one, going to throw it in tonight and check the runout.

 

Used flange was better with .010" runout, but still 3x worse than it's allowed to be. Pinion is bad, so the front diff is getting regeared.

 

Thinking the pinion is bent?

 

Looks like it.

 

WoW!

 

the rolled taco i got some parts off had a broken front pinion. the transfer case bottomed out driveshaft slip and forced the diff forward

 

That makes sense- something like that could have happened.