Back story & Symptom:
About 2 months ago I installed a rebuilt front prop shaft and noticed this past weekend on a highway trip a vibration at 115km/hr (roughly 65-70mph) and at 2750rpm.
This rumble seems to go away when I increase the speed or go under the stated speed and it also occurs at the same speed if I slip it in neutral until it coasts below speed.

***When I leave the transmission in 3rd gear and drive up to the same rpm range 2750RPM the vibration is not evident.....

Main question:
In 3rd gear at 2750RPm would the driveshaft be spinning at the same rate of speed as the same rpm but in 4th gear?
Thank you in advance,
Paul

 

At 115 Km/h, the driveshaft spins at a certain fixed rate no matter if in 2nd, 3rd, 4th, 4th+TCC, neutral, or engine off. The driveshaft speed reflects wheel speed, unrelated to engine rpm or gear selected.

 

If the drive shaft is a possibility, remove it and drive in H lock to see if the problem is gone.

 

Thank you for the replies gentlemen.
Both responses were exactly what I was hoping for.
I'll fill you in on the results.
Cheers.

 

Answer is no. In 4th gear & 2750rpm , you will be going much faster than
In 3rd gear & 2750rpm..
So driveshaft will spin faster, in 4th 2750rpm.
Than in 3rd at 2750rpm.

 

I pulled the front driveshaft and it is perfect at all rpm's.
Now the debate between rebuilding the factory one, tom woods or GB.
I don't want to re-open the debate but why is the GB so much more than the Tom Woods double cardan one from lucky8?

The truck is stock height now but will receive a 2" lift within the next 2 years....

 

Before you do anything, check your wheel bearings.

I have had a similar vibration since I got my truck three years ago, and changing driveshafts didn't help. I also swapped diffs and it didn't help (my diff was definitely pretty worn out, though). After letting my problem continue for a few years, it has gradually morphed into symptoms that indicate a bad wheel bearing. I haven't swapped the hubs yet, so it isn't certain, but I'm confident my problem is wheel bearings.

Yes, it's weird that pulling the front shaft fixes it. But that is exactly how my problem works. I'm guessing the power delivered by the front drive shaft aggravates the symptoms so they are more easily perceived.

So if I were you I'd certainly pull the front drive shaft and rebuild it if it hasn't been rebuilt, but don't expect the rebuild to completely fix your issues.

 

Ok everyone.
I had a rebuilt drive shaft on my truck that I got off of a parts truck that I picked up a few months ago but was unsure of how old it was and as I mentioned I had this vibration. I removed it and the vibration was gone in my mind nixing the possibility of a wheel bearing.... Got my new Tom Woods shaft, installed it and I still have this vibration..... I now have a new drive shaft that I have confidence in but I seem to be back to square one.....

I can't get over the fact that with th front drive shaft out and the diff lock engaged there is no vibration at 120kms....

 

Dr. Mordo seems to be bang on.....

 

you would not be the first to receive a new shaft with a balance problem,
but if you are going to do hubs do a search for taylor # 100060 that is the ALL MAKES number for a replacement hub and ABS sensor you can get them on ebay for under $100 no need to pay $300 for the exact same hub.