Rumble @55-65 mph

[WaltZ]

between 55-65 mph there's a rumble with no noticeable vibration.
below and above those speeds it's gone or unnoticeable.
wheels are balanced.
put in neutral at those speeds and idle down motor and still there.
at a loss for this one,
any ideas
thanks in advance

[maroman]

Might help to know what you are working on? But sounds like driveshaft, has it been off?

[adjudimo]

My brother in law had a slightly bent axle do that several years ago, but I would check the driveshaft first.

[roadster]

Pinion angle vibrations tend to be most noticeable around 60 mph as I recall. Might try to change trans angle at crossmember with washers , see if it gets better or worse .

[firstgenaddict]

tail shaft bushing? I had one of these play me the idiot on a drive line vibration once...
U joint?
Pinion angle as previously stated.

IF it's in the rear end... My Opinion is --- you should be able to "feel" something in the, if you had the trans in neutral and jacked the car up and rotated the axle shaft without the tires on ideally without the brake drum on -- slowly rotate each axle and feel for anything slowly feel for any notchiness if you remove the drive shaft you can really get a feel for the rear end by slowly rotating in a quiet shop. 

As a safety reminder to anyone reading this thread:
If your driveshaft tube has any dents or other damage it should be replaced and rebalanced - the structural integrity of the drive shaft is greatly diminished upon any damage/deformation to the tubular structure.

[MO]

Have you checked to see if the vibration is noticeable if you run the rpm's up while parked, matching those speeds? Clutch engaged and disengaged? I've seen worn pilot bushings and trans main shaft issues cause vibrations too. 
What type of wheel balance? I once had a tire that was so bad it needed to be trued to properly balance it.
Checked for bent wheel?
Checked motor and trans mounts?
U-joint?

 

[dutch]

Be interested to know when you hear the sound, if you accelerate or decelerate if the sound goes away   if so I'd bet on it being a U joint starting to go.. 
They don't always vibrate early in the process of going out - but they will give off some varying degrees of sound vibrations often when the needles are subjected to loads being taken off of them one direction or another..

[BillOhio]

I have a buddy that had the nubs worn enough on his pinion flange that it had to be replaced. The u joint was not staying centered. 

[crossboss]

Don't overlook the basics here. Engine/frame mounts tight? Trans mount tight? IF any of those are loose and or broke/worn out it can cause the issues your experiencing. Second, wheels torqued correctly? Exhaust/mufflers rubbing on the chassis? Lastly, any chassis components loose, driveshaft and rear end issues? Keep us informed.

[maroman]

I am thinking this guy disappeared.

[x55cam]

Does your rear view mirror vibrate during the rumble?

[WaltZ]

 things for me to look at here, and the rear view mirror does not vibrate when the rumble is noticable.
thanks so far and will keep you all posted.

[WaltZ]

cruised tonight and noticed when I pushed clutch pedal to take out that 1 to 1.25" play, with just a little bit of pressure on it when the play is gone , the rumble all but disappears.
next step would be?
thanks in advance

[Kelley W King]

I would pull the trans. Could be pilot bushing, release bearing, transmission, or you could luck up  and the transmission bolts be loose. Have you checked the trans oil level?

[MO]

I agree, pulling the trans will allow you to check a lot of potential problems.