High speed rumble

[bigtendude]

When I go 70mph. in my truck, I hear and feel a pulsating rumble coming from the back of the truck. Is this my 3.73 telling me it don't like going that fast? Or is something ready to fly apart ? It does not do it at 60 or 65mph, only at 70 and beyond. Also I am only getting about 11 miles to the gallon on the E-Way, gotta get rid of that 3.73.......QUICKLY!

[Pontiac1976]

Well 3.73 do not like to drive at higher speed for( rpm) for long times and will grow a little, but it could be outer bearing to hopefully not the inner bearing, Maybe the pig front bearing. Now ones I had the nut back off on the pig at the drive shaft it made a bit of a rumble I did not hear it until it got louder & could feel the vibration quit a bit, this was because of the exhaust could not here it at first till it got louder made more noise.
First thing I would do is check the diff oil.
where & what to use:
There is squared plug on the diff take it out with a 3/8 ratchet the ha of the ratchet fits that ( you might need a small 3" extension to give you room to turn the handle or not) once out take your finger (at this point thin rubber gloves "latex" will keep the oil off your skin) stick in the hole should be oil up to the edge of the bottom thread smell it. It should smell bad diff fluid is got bad smell, but it should not smell burnt nasty smell.
should not feel like metal shaving in it or look milky gray, black hole black.
:Milky gray old & has some water in it. Change hope it not did to much damage. (change oil)
:Black hole black old. Change hope it not did to much damage.(change oil)
if there lot of metal shaving stuff is wearing bad, but very fine to all most nothing is normal.(change oil) should be changed at the normal times.

Does it look like it sweeting any where around the drive shaft, diff cover or the wheel backing plates.
this might be a good time to take a look in side the diff cover see what your looks like it it OK put new gasket oil after you check the #'s on the gear it will tell you what is.

If it low this is bad for bearing and gears at high speed it will wine a lot the diff gets really hot back there & will get hotter with out the proper oil and or level in it. Now if you have posi( limited slip ) there is a additive you have leave room for when filling oil.
Oh if you have a book this will help you with this it's not to hard ( the hard part is trying not to make a mess on you or the floor getting up enough for you to move around that you maneuver good. Because once diff oil is put in it smell bad, so once it used or the older( or used) it is the more it smells if it gets on you, you got it all day maybe two days ;D

[bigtendude]

I know what it smells like already. I have had this crap on me when I had one in the shop that was rear-ended pretty bad. There was a bit of seepage from the plug, but I snugged it up, it slowed a bit more. But also noticed there is some coming out a bit around driveshaft spline and slinging up on bottom of box. There is a standard pipe nipple for a plug, it has a male square fitting on it, about 1/2 to 9/16" Have to use open end wrench on it, to remove it. Will teflon pipe tape help stop any seepage from the fill plug? I read somewhere that my diff. holds 2 1/9th. quarts? Does this sound right? Thanks for the reply, will have to check it out.....Larry

[Pontiac1976]

Will teflon pipe tape help stop any seepage from the fill plug?

yes that will help if over tighten or still a little loses.