2005 Silverado 3500 popping in 4wd

[D60]

I'm facing an '05 GMT800 with LLY, about 230k miles. It's a dually and tows hard with large ag tractors.

It has a completely random pop from the front end and it occurs only in 4wd. It typically occurs when you bind up the system in a turn, but sometimes it happens in gentle turns, sometimes in tight turns, and occasionally going straight.

Trying to gently "launch" in 4wd does not seem to cause it.

I've pored over crossmembers, steering linkages, ball joints, torsion bar mounts, diff mounts, pinion bearings and everything else.

I've satisfied myself it's either in the t-case or maybe whatever the actuator in the front diff drives. Does this drive a shift FORK, or is it just sliding a SPLINED GEAR? Trying to find info on the inner workings of the CAD is difficult.

Has anyone ever seen the front CAD cause a "popping" under load due to wear? If there's a fork I'm wondering if that wears/has pads that wear?

I don't want to reco a t-case rebuild if it's really the CAD which would be less expensive and less work.

@clinebarger @BrendanC

 

[CapitalTruck]

You sure its not just a blown CV joint/half-shaft? Sure sounds like that to me, unless that gen 3500 used solid front axles.

 

[Phishin]

My bet is you have a bad CV half shaft.

 

[D60]

The owner fired the parts cannon before bringing it to me and installed new half shafts.

 

[BrendanC]

I'm facing an '05 GMT800 with LLY, about 230k miles. It's a dually and tows hard with large ag tractors.

It has a completely random pop from the front end and it occurs only in 4wd. It typically occurs when you bind up the system in a turn, but sometimes it happens in gentle turns, sometimes in tight turns, and occasionally going straight.

Trying to gently "launch" in 4wd does not seem to cause it.

I've pored over crossmembers, steering linkages, ball joints, torsion bar mounts, diff mounts, pinion bearings and everything else.

I've satisfied myself it's either in the t-case or maybe whatever the actuator in the front diff drives. Does this drive a shift FORK, or is it just sliding a SPLINED GEAR? Trying to find info on the inner workings of the CAD is difficult.

Has anyone ever seen the front CAD cause a "popping" under load due to wear? If there's a fork I'm wondering if that wears/has pads that wear?

I don't want to reco a t-case rebuild if it's really the CAD which would be less expensive and less work.

@clinebarger @BrendanC

the front differential actuator pushes a fork that slides a splined collar onto the passenger side output shaft. would be very difficult for that to be making noise. most likely if it’s the front end it will be coming from worn out business. check the bushing in the passenger side of the frame rail very well. the upper bushing/mount is also something to inspect.

transfer case has two forks. one engages the chain (mode) and the other engages 4low (range). the forks in the transfer case have wear pads on them. The rear case half is notorious for snap ring groove wear allowing for excessive end play. this will eat up the mode and range fork causing the transfer case to end up in neutral or like mine blow up. the pump will also end up rubbing through the rear case half. my recommendation is a new aluminum rear case half and new mode and range forks.

i refill with 0w-20 motor oil from the speed sensor hole and run it over filled (roughly 3 quarts). i change this annually.

 

[BrendanC]

I don't want to reco a t-case rebuild if it's really the CAD which would be less expensive and less work.

pulling the Tcase apart is miles easier than the front differential. i can tear down and rebuild a NPxxx unit in an hour or two. just need a very good set of snap ring pliers.

 

[D60]

pulling the Tcase apart is miles easier than the front differential. i can tear down and rebuild a NPxxx unit in an hour or two. just need a very good set of snap ring pliers.

Nah, I wasn't talking whole rebuild. It looks like that extension housing can come off without even dropping the diff?

I was just hoping to get eyes on the CAD as I've seen bubble bodies trash the fork and do all manner of weird things. Dodge, too, for that matter.

Plus parts cost is significantly greater on a t-case -- I'm sure it could afford a chain and synchro and I'd do a pump rub plate.

No externally visible signs of pump rub yet.

I pulled the CAD actuator and moved the plunger with my finger. Everything seems to feel good and engage readily so I'm thinking this is a t-case issue. Likely either main shaft end play or a trashed mode fork.

 

[BrendanC]

Nah, I wasn't talking whole rebuild. It looks like that extension housing can come off without even dropping the diff?
View attachment 267692
I was just hoping to get eyes on the CAD as I've seen bubble bodies trash the fork and do all manner of weird things. Dodge, too, for that matter.

Plus parts cost is significantly greater on a t-case -- I'm sure it could afford a chain and synchro and I'd do a pump rub plate.

No externally visible signs of pump rub yet.

I pulled the CAD actuator and moved the plunger with my finger. Everything seems to feel good and engage readily so I'm thinking this is a t-case issue. Likely either main shaft end play or a trashed mode fork.

i highly doubt it needs a chain or a synchro. attached are photos of what you would theoretically need. everything can be done “in place” without even removing the Tcase from the vehicle.


my front differential came out of a 07 truck that was under water in hurricane harvey (summer 2017) and sat full of water until december 2017 when i 4x4 swapped my pickup. it has since been rebuilt when i re geared to 4.88. parts minus the bearings and gear set. the 9.25” is pretty well bulletproof.

 

[D60]

i highly doubt it needs a chain or a synchro. attached are photos of what you would theoretically need. everything can be done “in place” without even removing the Tcase from the vehicle.


my front differential came out of a 07 truck that was under water in hurricane harvey (summer 2017) and sat full of water until december 2017 when i 4x4 swapped my pickup. it has since been rebuilt when i re geared to 4.88. parts minus the bearings and gear set. the 9.25” is pretty well bulletproof.

View attachment 267693

View attachment 267694

View attachment 267695

Have you used that exact case half? That looks super sketchy but then I'm comforted that "WARRANTY GARRENTED"

I have no idea what spec is but when I rotate the front d/s in 4wd I get a heck of a chain rattle clunk from inside the t-case. Maybe that's normal, though. I know the XHDs got the widest chain so maybe they don't readily stretch

 

[BrendanC]

Have you used that exact case half? That looks super sketchy but then I'm comforted that "WARRANTY GARRENTED"

I have no idea what spec is but when I rotate the front d/s in 4wd I get a heck of a chain rattle clunk from inside the t-case. Maybe that's normal, though. I know the XHDs got the widest chain so maybe they don't readily stretch

i’ve installed countless ebay 261/263HD and XHD model case halves. they’re all chinese cast aluminum.

 

[D60]

The adventure continues. Before I began it also had a harsh and near immediate engagement into 4hi. You couldn't really feel it, but it was loud like forcing a manual trans into gear.

I wasn't pursuing the 4hi engagement noise per se, but the good news is that after going through the t-case and replacing the synchro assy, this is solved.

While in the t-case I saw nothing that would cause the random clunk once in 4hi or 4lo. Indeed, this noise persists. It's a clunk or thunk in 4wd and certainly seems to be from the front half of the vehicle. Today it did it to me randomly while driving straight in 4hi on my dirt road.

So, I'm confident the t-case is solid. The front d/s u-joints are great. The front pinion is tight and backlash feels reasonable. Both half shafts are new (not my parts cannon).

So, it's gotta be the CAD or something in the front diff. The truck is now owned by an older guy but he bought it from a kid who had bro-dozer'd it, so the history is unk. Hard launches in 4wd? Maybe.

When I began investigating this the front drain plug looked like so. This isn't great but I did not consider it conclusive of anything. It was all "paste" with no metal chunks to speak of. For all we know the diff has never been serviced for the 230k on the odometer

Cleaned up

The paste doesn't strike me as carrier or pinion bearings breaking down, but perhaps something in the CAD had gone awry. I don't know if the CAD fork is ferrous or aluminum alloy?

 

[mattd]

Could be spider gears.

 

[D60]

Could be spider gears.

I like that! Going from least invasive to most, I plan to look at CAD then make the call if we need to split the front pumpkin.

I sure hope I eventually find a smoking gun because something is not right!

 

[D60]

TL;DR: GMT800 CAD actuators can experience a symptom of partial or weak engagement!!

The long:
FINALLY SOLVED after weeks of way too much work.

I first inspected everything external: frame, bushings, torsion bar xmember, diff mounts, suspension and even removed the CAD actuator and moved the plunger with my finger.

Next I went through the transfer case but found no smoking gun.

Then I went through the front diff but everything -- including the CAD itself -- looked great.

Finally today I was able to get it to pop really badly in 4hi or 4lo. It sure seemed like it was coming from the right front, but it's impossible to say.

Sometimes when it would POP it would actually drop out of 4wd. When this happened I'd hop out and try to spin the front d/s, but the t-case was still locked in.

I used my Otofix to command the CAD actuator and it just didn't seem right. Sometimes I'd get 4wd to come back after POPPING by commanding it. Other times I'd command it off but it wouldn't release. REALLY nice to have a scan tool that allows you to separate t-case engagement from CAD engagement.

All I could get on short notice was a Dorman. I removed the old CAD actuator and left it dangling by the wires then commanded it on. It seemed to move a full stroke but I noticed I could press it back pretty easily. There's a spring in there that allows a "cushion" until everything lines up.

Then I plugged in the new Dorman. It sounded more authoritative when it moved. Hard to explain but you can tell. Also noticeably more difficult to depress the spring when extended.

I threw in the new Dorman confident that I was firing the parts cannon with an educated guess, and it works. No more popping!!

If only I hadn't completely torn open the t-case and front diff in the first place!!