Np241 grinding noise please look

[hcenteno21]

I have a 1990 gmc jimmy, and have had it for a few years. It always has had this noise, but just noticed how loud it was when when jacked up rear end. It is coming from transfer case and it happens when i go over 25 mph and let go of gas or in nuetral. If i touch gas pedal noise goes away. My truck has an 8" lift on 35s. Mechanic without really looking at it said its chain, i have been reading a lot and it seems like the least likely to be the problem. Anyone have any idea? Ujoints seemed good when i checked them.

 

[hcenteno21]

So to clarify it makes a really loud grinding noise when driving over 25 30 miles and letting go of gas pedal. I noticed if I put truck in 4x4 there is a slight sound all the time but it does not grind. it also does it when i put it in neutral while coasting. It is an extremely loud grind, which is the reason i haven't moved the truck much the last 2 years. It sounds like something in there is really bad. Any help is appreciated!

 

[Rugger187]

My 89 does the same thing. I've rebuilt the NP241 and the driveshafts and it still makes the same noise. I just ignore it. Been ignoring it for the last 12 years.

 

[4X4HIGH]

From your description it sounds like a bad gear set-up in the rear diff. Try pulling the rear driveshaft and then putting a plastic bottle over the tailhousing of the t-case and zip tying it on then put the rig in 4x4 and drive it and see if the noise is still there.

 

[hcenteno21]

From your description it sounds like a bad gear set-up in the rear diff. Try pulling the rear driveshaft and then putting a plastic bottle over the tailhousing of the t-case and zip tying it on then put the rig in 4x4 and drive it and see if the noise is still there.

Ok well i removed rear driveshaft ujoirnts are gopd removed tail housing bearing is good unfortunately i put it back together but oil seems really thin also had some shavings not too much on bell housing but i am going to drain and fill and go from there

 

[goochieman83]

Not sure if this helps but I had the same issue with my 86 K5, 700r4 and np208, the rear bearing and chain are shot in it. Going to have to be rebuilt. I had the exact noise you are talking about. Mine was due to driveline angle. Also getting a cv shaft from Tom Woods built to help with the issue. Hope that helps.

 

[diesel4me]

I think the chain only is used when it is in 4wd...in 2wd I am pretty sure the power goes right from the input shaft to the rear output...

I agree it sounds like excess backlash in the rear end gears or driveshaft angle issues..maybe a rubber mount has failed and is letting the bolts transmit vibrations during coast also..does the T-case have a support brace from the case itself to the bellhousing or frame ?..if so,is all the bolts tight?..

 

[Kay86K5]

What type of rear shaft do you have? Is it a normal 2-joint shaft or a CV? If it's a 2-joint shaft, I will put $100 on it's your shaft, especially with that tall of a lift. This is a very common issue and everyone always jumps on the "bad gears" or "bad chain" wagon even though it's not that at all