LX won’t move without center diff locked and makes loud clicking noises

Joined
Jul 21, 2022
Messages
13
Location
Denver, CO
So I hit an admittedly harder trail than I should have today, and had some bind in the front while in 4lo, and heard some loud clicking noises while making it up an obstacle. Stayed in 4lo the rest of the trail, then when I went to go home and shifted to 4hi, as soon as I shifted to drive the front of the rig sounded like I had gravel in the driveline and I couldn’t move forward. I shifted back to 4lo and it went away and would move normally. I then went back to 4hi, but locked the center diff and it was quiet and moved forward just fine. I ended up getting a flat tow a mile into town, and am getting a flat bed tow home tomorrow, but I’m not making sense of what the issues could be. It sounded like a destroyed the front diff, but I don’t know why locking the center would make the noise go away and the rig seem fine.

Has anyone experienced anything like this that can give me a start in what to check this week when I can get under it?
 

jLB

May be in need of a 12 step LC/LX program.
SILVER Star
Joined
Dec 2, 2014
Messages
3,206
Since you don’t mention it in your post or in your signature, let me guess that you have a 98 or 99 model year (which automatically locks the center diff, when shifted to 4L)?

A stripped or broken CV axle, a stripped drive flange, a lost snap ring, or a broken front differential?

Because with 3 open differentials, the “power” follows the path of least resistance?
 
Joined
Jul 21, 2022
Messages
13
Location
Denver, CO
Since you don’t mention it in your post or in your signature, let me guess that you have a 98 or 99 model year (which automatically locks the center diff, when shifted to 4L)?

A stripped or broken CV axle, a stripped drive flange, a lost snap ring, or a broken front differential?

Because with 3 open differentials, the “power” follows the path of least resistance?
Sorry, yes it’s a 98 LX, so LSD rear, open front.

This is my first IFS 4WD, I guess what doesn’t make sense to me is why it would be fine when locked and not fine when unlocked if it was front axle related.
 

jLB

May be in need of a 12 step LC/LX program.
SILVER Star
Joined
Dec 2, 2014
Messages
3,206
Sorry, yes it’s a 98 LX, so LSD rear, open front.

This is my first IFS 4WD, I guess what doesn’t make sense to me is why it would be fine when locked and not fine when unlocked if it was front axle related.

Because, when the center diff is locked, power is sent to both F&R axles, when unlocked, power follows the path of least resistance, and “leaks out” the front axle.

Think of a RWD vehicle, with an open differential, with one tire with zero traction.
 
Joined
Jul 21, 2022
Messages
13
Location
Denver, CO
Well, both drive flanges looked good, and snap rings were in place. I didn’t have time to dig into the diff side of the CV axles today, but I’m starting to feel pretty confident it’s the diff seeing as it’s a 220k mile 98 with the 2 pinion. I have an appointment with Slee for ARBs and regearing in a few weeks, so looks like that was good timing at least
 
Joined
Jul 21, 2022
Messages
13
Location
Denver, CO

The link above explains it succinctly. Ignore the fact that it's written for the 80 series, the function is the same for the 100s.
Thanks for this, I get how diffs work, what’s still confusing me is locking the center diff isn’t sending all the power to the axle with traction, it’s just making them both spin at the same speed, right? If that’s the case, then i don’t understand stand why the grinding/gravel noise from the front goes away completely with the CDL? In my head it feels like it should still be making noise, since the front diff would still be sending power to the path of least resistance. Yes it would be able to move with the CDL, since the rear would spin too. Maybe I’m not explaining the problem right though, or just completely missing something.
 

TheForger

GOLD Star
Joined
Jan 4, 2014
Messages
2,935
Location
Little Rock, Arkansas
FYI snap rings can remain in place and appear okay, but splines on the axle or in the flange can still be stripped. It's also possibly you snapped a few teeth off the ring gear.
 

BullElk

SILVER Star
Joined
Jun 19, 2013
Messages
2,818
Location
Saraland, AL
Crank LX, keep CDL unlocked, put in drive on flat surface. If LX will not go forward, get out and look at each wheel hub and see which one is spinning. One is.
 

jLB

May be in need of a 12 step LC/LX program.
SILVER Star
Joined
Dec 2, 2014
Messages
3,206
Thanks for this, I get how diffs work, what’s still confusing me is locking the center diff isn’t sending all the power to the axle with traction, it’s just making them both spin at the same speed, right? If that’s the case, then i don’t understand stand why the grinding/gravel noise from the front goes away completely with the CDL? In my head it feels like it should still be making noise, since the front diff would still be sending power to the path of least resistance. Yes it would be able to move with the CDL, since the rear would spin too. Maybe I’m not explaining the problem right though, or just completely missing something.

Because, with the center diff locked, the front/rear are traveling at approximately the same speed/revolutions, instead of just sitting and grinding.
 

Njck22

SILVER Star
Joined
Sep 24, 2017
Messages
1,027
Location
Texas
When you put it in drive with cdl locked everything is rotating in unison, so no grinding occurs. if the flanges are stripped, then they are being driven by the road surface and matched to the axle being turned by the front diff. Same story if you broke teeth on the ring and pinion. everything is moving in unison so no load is being put on the broken teeth to cause grinding. It is entirely possible you broke your ring and pinion, happens often with shock loading. Could also be the spider gears. You can diagnose this very quickly, turn on truck, unlock cdl, pull parking brake, put in drive. stuff should starting grinding. Look for a cv spinning, if so, it's just a drive flange. if not, then something in diff is bad.
 
Joined
Jul 21, 2022
Messages
13
Location
Denver, CO
When you put it in drive with cdl locked everything is rotating in unison, so no grinding occurs. if the flanges are stripped, then they are being driven by the road surface and matched to the axle being turned by the front diff. Same story if you broke teeth on the ring and pinion. everything is moving in unison so no load is being put on the broken teeth to cause grinding. It is entirely possible you broke your ring and pinion, happens often with shock loading. Could also be the spider gears. You can diagnose this very quickly, turn on truck, unlock cdl, pull parking brake, put in drive. stuff should starting grinding. Look for a cv spinning, if so, it's just a drive flange. if not, then something in diff is bad.
This helps make sense, thanks.
 

Users who are viewing this thread

Top Bottom