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4wd Grinding problem

garydan

garydan

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Port Saint Lucie, Fl.
So I have 700r4/np208/Dana 60 front. I've owned this truck for about a year and a half. I've never really put it in 4wd until recently since I got my axles done. When I have the truck in 4wd, in either 4-Lo or 4-Hi I get this intermittent grinding noise when I hit the gas. I can cruise at a slow pace... say 10mph and get no grinding noise... but if I get on the gas a little bit the grinding comes back. It sounds like something is slipping... because the grinding isn't constant. The sound really does sound like its coming from the Tcase.

So I began thinking whether or not it was the transfer case or the hubs, so I ran a few tests.


Test 1) Hubs Locked, transfer case in 4-Hi or 4-Lo = Intermittent Grinding on acceleration.
Test 2) Hubs Locked, transfer case in 2wd. No Grind.
Test 3) Hubs UNLOCKED, transfer case in 4-Lo or 4-Hi, No Grind

So, I guess I haven't really eliminated the transfer case or hubs. When load is on the front drivetrain, something is causing the grind. Dang... just thought of another test. I could unlock one hub at a time to eliminate the hubs.

So... say it is the transfer case... could that chain actually slip when the front drivetrain is under load? Seems quite impossible to me. I've recently had the transfer case opened up and everything checked out ok.

Is there a chance that the driveshaft is tapping the crossmember when the front end is under load in 4wd (remember.. no grinding if hubs unlocked)
 
If the driveshaft is hitting something, it will leave a mark on the shaft. Easy to see. The chain can certainly slip when it gets worn and loose enough.
But, its normally not a grinding noise.
Since its a cog chain, it "jumps" from cog to cog when it slips.

Quick test, climb under with it in 2wd, grab the drive shaft and push it up and down and side to side hard.
Investigate what moves.
If the input shaft to the front end wobbles, bad pinion bearings.
If the output shaft to the transfer case moves, bad bearing there.
If a U-joint moves.....you get the idea....

Also, check the fluid level in the front end.
 
Check the splines on the front driveshaft,they could be sloppy --and the CV joint in the driveshaft for looseness at the centering ball...those can cause that noise,along with everything else listed above..a badly worn needle bearing in thespindle might let the axle shaft rub against the inside of the axle tube or the spindle end ,the u-joint yoke can rub on the axle "C" too--..
 
Is the grinding similar to the one you get when its hard to put the t-case in 4hi or 4low???? i would take the hubs out of the equation you can manipulate them so they are no factor.IMO



Also how the heck do you rebuild the CV joints on the front shaft i suspect my front d-shaft is bad might as well go to pick and pull and another one.
 
bot0611 said:
Is the grinding similar to the one you get when its hard to put the t-case in 4hi or 4low???? i would take the hubs out of the equation you can manipulate them so they are no factor.IMO



Also how the heck do you rebuild the CV joints on the front shaft i suspect my front d-shaft is bad might as well go to pick and pull and another one.
Click to expand...

It's not the same grind as that. Just thinking about it... it really does sound to me like the splines are slipping on the shaft because its an intermittent grinding.
 
garydan said:
It's not the same grind as that. Just thinking about it... it really does sound to me like the splines are slipping on the shaft because its an intermittent grinding.
Click to expand...

Might be a good time to take if off and see..what speeds do you experience this???
 
Definitely a loud grinding noise, not a gear whine noise? Cause a gear whine is normal for an NP208 in 4hi/4lo. I mostly hear mine in 4hi during accel or under load and 4lo it's more pronounced.
 
496truck said:
Definitely a loud grinding noise, not a gear whine noise? Cause a gear whine is normal for an NP208 in 4hi/4lo. I mostly hear mine in 4hi during accel or under load and 4lo it's more pronounced.
Click to expand...

Yeah... I hear the whine too... definitely not that. I'm going to put some alignment marks on my driveshaft and take it for a spin. Then I'll see if the splines are slipping.
 
Don't really need to do that. First of all, the only time I ever saw a spline slip, it only did it once.
After that, it just freewheeled.
Plus, if it slips the front and rear joints will no longer line up, and you would start having massive vibration.

Just look at the bearing caps to see if they still line up.
 
Fordum said:
Don't really need to do that. First of all, the only time I ever saw a spline slip, it only did it once.
After that, it just freewheeled.
Plus, if it slips the front and rear joints will no longer line up, and you would start having massive vibration.

Just look at the bearing caps to see if they still line up.
Click to expand...

You are right on man. Now that I think of it... its painfully obvious. I found something tonight though. I really didn't think this could be the problem since when I was in 4wd (hubs unlocked) I didn't get the noise.

Check it out... looks like crossmember is getting hit. Does the t-case get tweaked enough when under load to hit there? I'm about to go back outside and do a little grinding on the cross member.

small_DSC00050.JPG


small_DSC00045.JPG


small_DSC00051.JPG
 
Check it out... looks like crossmember is getting hit. Does the t-case get tweaked enough when under load to hit there?
Click to expand...

Oh yeah. Even a new truck would move that much under load.
I've seen the shift lever of a transfer case rise up a couple of inches when you put a load on it.
Everything on the drive train, engine, transmission, transfer case, is mounted on rubber mounts.
So, yeah you got flex.

Of course, its not normal for it to hit there.
So why is it?
Hard to say from here. You are going to have to do some more investigating. Could be something the PO did, or just wear on components. Broken or soft transmission or engine mount, Spring problems, or a combination of the above.

Someone else here may have seen that problem and know what causes it.

BTW, its hard to tell, but I swear those look like the original joints. Don't see how they could be from 85, but maybe the PO bought a factory driveshaft....
 
Mmmm.. oili crossmember yummy...ha

Are they mount nuts torqued??? i mean do they need any torquing??? what can happen if you over tighten them?
 
Fordum said:
Oh yeah. Even a new truck would move that much under load.
I've seen the shift lever of a transfer case rise up a couple of inches when you put a load on it.
Everything on the drive train, engine, transmission, transfer case, is mounted on rubber mounts.
So, yeah you got flex.

Of course, its not normal for it to hit there.
So why is it?
Hard to say from here. You are going to have to do some more investigating. Could be something the PO did, or just wear on components. Broken or soft transmission or engine mount, Spring problems, or a combination of the above.

Someone else here may have seen that problem and know what causes it.

BTW, its hard to tell, but I swear those look like the original joints. Don't see how they could be from 85, but maybe the PO bought a factory driveshaft....
Click to expand...


I did put a 6" lift in. Maybe that is part of the problem. I'm also picking up a new transmission mount. It does look a little worn. I'll use this opportunity to also change the front seal on my t-case since it seems to be leaking in that area. I don't think I have any bearing issues... Just a bad seal. There is no slop in the shaft, I grabbed it and moved it like you suggested to check for bearing problems.
 
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