Front Axle 4WD Disconnect

[Trail X]

(Picture credits go to The Roadie)

It seems my front-end disconnect is acting up on me. I don't know how long it hasn't been working, but I assume it's fairly recently. I actually first noticed it when rotating my tires, as I normally throw it into 4WD to hold the front wheels still while I tighten the lugs.

This is the splined disconnect housing. The actuator is the strange-shaped black plastic part.


So, my symptoms are as follows, no 4WD light, yet no front connection at the splined disconnect. So this leads me to beleive that the front actuator/plunger is working properly. From my searching, it seems that the actuator does not provide positive traction to the syncro-shift fork, but it provides a spring force. This is done because the syncro will not always align properly with the splines of the intermediate shaft. So the actuator can apply pressure so the syncro will snap into place as soon as the splines align.

The internals of the actuator. Notice the spring in the plunger.


So because my actuator is operating properly, I have some sort of mechanical problem in my disconnect. I'm assuming I have one of these three issues... misalignment of the input and output splines, so that the syncro will not snap over the intermediate shaft splines... not enough grease, and the syncro has gotten stuck... or a broken shift fork.

Click the following picture for a detailed view:


I notice there are a A4WD and S4WD front axle actuator option. The A4WD option having no disconnect, and only a solid connector. I wonder if it would be possible to just replace the front spline and shift fork with a single solid connector. We can still stick the actuator in the housing so we don't receive and error codes at the computer.

Anyways... this is my start to looking into this issue... I haven't even had time to take a real good look at the actuator yet. Is there any insight from anyone? Anything to be careful of, or to take special note of?

Thanks guys!

[The Roadie]

Oh, James. I wondered when the first one of us would have this problem. No substitute for just going in there and looking. GM really blew the design of this unit. I've heard of broken forks, but more often it's horrible wear on the splines and the collar. GM currently can't supply any of the collars IIRC, so maybe there's a redesign in the works. A major aftermarket supplier is looking for broken parts now to evaluate whether or not they should get into the market. I would REJOICE if they did. So if you take this apart, stay in touch with me to send off your busted bits for analysis.

I think it would be safe to engage the collar all the time, with the downside of more wear on the rotating bits of the front diff and shaft back to the transfer case. And potentially some clutch wear in the TC, except the AWD folks stay engaged all the time and it's no big deal for them. My contact at the major aftermarket company says even the AWD vehicles have problems with the lubrication and bearings in that assembly, though.

Nasty to discover a problem like this that can destroy our ability to offroad the trucks. But it's better than the Tacomas with cracking frames and composite beds.

[Trail X]

Here's a picture of the internals. (these are not my pictures... just found them so I can shed more light on this topic)



Here's the shift fork on the syncro.



Apparently the small nub under the spring can also shear off. I guess this happens if the engagement is too hard and the shift fork somehow gets bound up on the syncro. Evidence below.



I honestly don't see any down-side to engaging the syncro all the time. It wouldn't induce any more wear on the trans clutches, because as is, they have relative motion between the clutches whenever 4wd is not engaged, as the front prop-shaft does not turn. The only element in the TC that would see more wear would be the front drive chains, as they would constantly be moving. The front diff wouldn't wear any more than it currently does, but it would wear in a different part, currently the diff housing does not spin with 2HI engaged. All motion is therefore transferred through the spider gears... interestingly, spider gears aren't really designed to constantly spin anyways. You would however make the front diff spin all the time, but it wouldn't be any different than a standard rear diff that spins all the time.

So really, by constantly engaging the front disconnect, I only see slightly more wear on the TC front drive chains... nothing else that I can imagine.

[The Roadie]

I can see a welded disconnect in somebody's future.

[OregTrailBlazin]

Dang James, that sucks!! At the start of the season too!!



How about making it cable actuated, like the OX lockers?? That way you can still disconnect it but it's more fail safe, shouldn't be too hard to machine something to take place of the electronic actuator... Though it's sounding like you have something worse wrong then just the actuator..

[bartonmd]

I honestly don't see any down-side to engaging the syncro all the time. It wouldn't induce any more wear on the trans clutches, because as is, they have relative motion between the clutches whenever 4wd is not engaged, as the front prop-shaft does not turn. The only element in the TC that would see more wear would be the front drive chains, as they would constantly be moving. The front diff wouldn't wear any more than it currently does, but it would wear in a different part, currently the diff housing does not spin with 2HI engaged. All motion is therefore transferred through the spider gears... interestingly, spider gears aren't really designed to constantly spin anyways. You would however make the front diff spin all the time, but it wouldn't be any different than a standard rear diff that spins all the time.

So really, by constantly engaging the front disconnect, I only see slightly more wear on the TC front drive chains... nothing else that I can imagine.

Seals (front pinion and T-case output) and front prop shaft U-joints, maybe... I know the D60 front diff leaks at the pinion seal, on my Cummins, when you drive around with the hubs locked in, whether the T-case is in 2WD or not... Doesn't leak a drop when the drive shaft isn't moving..

I would say that it would be putting more wear on the bearings (carrier and pinion) in the front end, that it may or may not be made for, but I gather it's exactly the same diff on the AWD models, so that should be fine...

You will notice a drop in mileage, though... I know on the CTD, mileage drops from 20-21 empty (4.10 gears) to 18 with the hubs locked in... though we (TB) spin the half shafts and spider gears all the time, anyway, so just spinning the carrier and front prop shafter probably won't kill us as much as if we were able to cut if off at the hubs...

Mike

[Trail X]

I had a few hours of daylight today to play with the disconnect. I wanted to practice a "trail repair" scenario so I didn't pull out the jack stands.



Anyways, here's the actuator. The front plunger is in fact spring loaded, but has more spring force than I had imagined.



2 wheel mode (plunger in):



4 Wheel mode (plunger out):



Not much plunger throw, but enough, so it seemed the actuator was working properly. So I focused my attention to the little greasy hole. Hard to get too much information from this:



It seemed that the shifter fork was in place, and I noticed no metal chips in the immediate area, although the grease seemed slightly dirty. I attempted pushing on the plunger engagement area with a ratchet extension, and was unable to get the fork to move more than a millimeter or so. So either the spring force in there is just extremely high, or there's something keeping it from pushing in.

It also seemed interesting to me that the tripod joint of the CV shaft seemed somewhat 'loose.' Meaning it could wiggle a bit up and down when in place. I'm wondering if the inner CV shaft bearing is bad... or if maybe this is common?

I attempted to wiggle the tripod joint around with 4wd engaged, thinking maybe there was an alignment issue with the collar... no avail.

So it sounds like I'm going to have to tear it apart if I can ever find the time. I'm not looking forward to having to remove the CV shaft. Anyone know what size the nut is on the CV shaft?

FOR CONTINUED PICTURES OF THIS PROJECT, GO TO PAGE 3, OR CLICK HERE: viewtopic.php?p=9181#p9181

[The Roadie]

Excellent idea on the practice repair. The nut is 35mm, unless you've replaced them with Cardones and used the Cardone nut, which is inexplicably 36mm.

I change tie rods and CV shafts on the trail.

Or remove the driver's side one altogether if I have a Gatorade cap and forget to carry the spare wheel hub bearing.

Oh, the pressure needed to push on the fork is exceedingly high. Look at the exposed gear train here, and there is yet another stage hidden inside the plunger.

[teebes]

Sorry to hear about the front end annoyance


Before you tear your front end apart, have you validated your encoder motor is working properly and fully engaging your front drive shaft? Mine was misbehaving in a way that wasn't triggering the 4wd service light as well.

Also, why are you using 4wd to remove your tires

[Trail X]

I find it easier to have it engaged... that way you stick the tire on, and tighten down the lug nut without having to wrestle the tire with that first lug. Remember, the hi-lift isn't as adjustable as a jack, so you can't really set the tire down with light weight to merely keep the tire from spinning.

I dunno... that's my thinking at least.

[foosh]

Well you could just get them tight all the way, then let the truck down and tighten them when they're under load of the truck...

[intimadatorsquizz]

James did you fix your 4wd ?or did you find out what's wrong with it yet?i'd be interested in seeing what parts broke and seeing what i could do to help you get it fixed again.

[Trail X]

With the new wife, rain, no garage, and dwindling sunlight... I still haven't had a chance to pull it apart. I'm hoping to this weekend.

My biggest dellema still is the intermediate shaft... I'm afraid if I just leave it in there it will have a tendency to rattle around inside the oil pan tube. So the truck may be out of commission if I remove the disconnect.

Edit: Now I'm curious though... if you don't have a TB... what interest do you have in this issue?

Edit X2: Did a little IP lookup... should I make you a Vendor?

RB Distribution Inc
Products:
Manufactures motor vehicle parts & accessories; manufactures motor vehicle mirrors Vehicle stability control systems, Vehicle traction control systems, Wheel clamps, Airbags, Seatbelts, Collision avoidance systems, Impact sensing systems, Head restraints, Air bag propellant canisters, Vehicle horns

Doesn't look like you're too far away either!

[The Roadie]

I can totally vouch for Jim here. He's posted the same request on the OS, and I've been discussing issues like this with his colleagues in other product lines. His company's fan clutch and many other aftermarket parts for high failure rate items saves the user community BUNCHO BUCKS.

They don't sell direct though. Sigh....

But we LOVE to evaluate prototypes.

[Trail X]

The nut is 35mm,

This is a lame question... but I checked around my local hardware stores today and none of them had a 35mm deep socket. Any suggestions as to where to find one of these elusive creatures?

[teebes]

Local sears has them here. Same with a decent auto store (Kragens/Checkers, Auto Zone).

A couple tips when you're pulling the cv's:

-Use your brakes to lock up the axles in order to loosen the axle nut. I usually stuff a breaker bar between the brake pedal and the driver seat, then use the power seat to adjust.

-Remove tie rods from the knuckle side along with all the other goodies. This will allow the knuckle to lean away from the vehicle enough to pull the CV through without too much effort.

Good luck!!

[intimadatorsquizz]

With the new wife, rain, no garage, and dwindling sunlight... I still haven't had a chance to pull it apart. I'm hoping to this weekend.

My biggest dellema still is the intermediate shaft... I'm afraid if I just leave it in there it will have a tendency to rattle around inside the oil pan tube. So the truck may be out of commission if I remove the disconnect.

Edit: Now I'm curious though... if you don't have a TB... what interest do you have in this issue?

Edit X2: Did a little IP lookup... should I make you a Vendor?

RB Distribution Inc
Products:
Manufactures motor vehicle parts & accessories; manufactures motor vehicle mirrors Vehicle stability control systems, Vehicle traction control systems, Wheel clamps, Airbags, Seatbelts, Collision avoidance systems, Impact sensing systems, Head restraints, Air bag propellant canisters, Vehicle horns

Doesn't look like you're too far away either!

yes i am interested in getting the old parts and possibly getting you new parts to fix it.i didn't want to come out and say where i worked some people get a touchy about that stuff.but i work for Dorman Products here in Colmar PA.and we're looking into the 4WD and the AWD TB and Envoy 4x4 problems.so whatever parts i can get as samples helps us try to improve it to be better and cheaper for you guys.i've just received a broken shift fork and and realy trying to get some of the defective intermediate shaft stuff.the cheasy GM fork list for $64.77 which is a joke so we're looking at that right now.

Thanks in advance and thanks again Roadie

[Trail X]

I understand about trying to go under the radar sometimes... some sites aren't so friendly to companies that want to help them. Since we want all the aftermarket support that we can get, we try to be as friendly as possible here.

I'm hoping the weather will hold out long enough this weekend to take the disconnect out.

[intimadatorsquizz]

Cool let me know what you find.I have 1 piece of all the new parts sitting here on my desk that I ordered in to look at and just at our cost it was almost 600.00 for all the pieces and that doesn't include any of the housings.So you can see why we'd like to make these parts at a better price and quality.

[The Roadie]

.. thanks again Roadie..

Glad to help. I KNOW my disconnect is going to break someday if I'm not always careful with engagement, and I need you guys to be ready with the replacement parts. Control arms, too.