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2007 HD Classic front end drag

gthurgood

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gthurgood New Member

gthurgood

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Good afternoon!

 

I need some help trying to figure out what's going on with my 2007 Classic LBZ Duramax. The best way I can describe my problem is that for the past couple of years, it seems like I have quite a bit of drag or resistance in my front end that is petty much constant all of the time. It feels a lot like how it does when I drive through a little sand or mud or something soft when you can really feel the heavy front end plowing through the soft ground a little bit, but it feels like this all of the time. I have only been putting about 6-7K miles a year on the truck for the past five years, (up until recently that is when we had baby #3 and the car seats won't fit into my wife's car and so now it's her daily driver), so I'd say it's gradually becoming more noticeable over the past 12-15K miles or so.

 

To give you as much inf as I can, here's what I've done on the truck over the past couple of years: I replaced both front wheel bearings about a year ago, and it did seem like the driver's side was bad (had some play in it). That seemed to provide some temporary improvement, but very temporary. I replaced the front (and rear) diff fluids about a year ago as well, and there was nothing alarming in either diff. About two years ago, I had the brake master cylinder replaced as I was having an issue with sticky calipers, and the mechanic told me the internal seals on the MC had failed. That seemed to resolve that issue, but it certainly could be related to what I'm experiencing now. I've also replaced the tranny fluid (the second time), flushed and replaced the coolant, and replaced the engine oil/filter and fuel filter at regular intervals. Also, just FYI, I replaced the shocks about 30K miles ago with Bilstein HDs.

I have not replaced any of the front ball joints, tie rod ends, or other steering components (pitman arm, idler arm, etc.) and I know they are all getting pretty warn out, and I'll deal with those when it warms up around here. I'm just over 100,000 miles on the truck and all the steering equipment is original (with the exception of the intermediate steering shaft that I had replaced early on due to the common clunk issue) so I know all that stuff is due for replacement.

 

Another issue that may be related, or may not be is i'm also suspicious that I may be having some subtle tranny issues showing up, most likely with the TC. The main symptom that is tipping me off there is that when I'm pulling the same trailer up the same grade in the same weather, the tranny is getting about 20-30 degrees hotter than it used to. When the ambient temp is around 90 degrees, I've had the tranny getting up to around 210 or 215 a couple of times (when I soon pulled over and let it idle to cool back down before pushing on) whereas it used to hold around 190 under the same conditions. I know that about 100 degrees above ambient air temp is normal, but again, I'm just comparing my temps under the same load and driving conditions in the past couple of years to those of when the truck was newer.

I've searched high and low on this and other forums and haven't found anything that is really hitting the nail on the head in terms of describing what I'm experiencing here, so that is why I'm starting a new thread to see if you guys can help me out. Any thoughts on what's going on here? Could it be the bearing inside the front diff that supports the short axle on the front end? Is it as simple as one or more hanging calipers? I've checked the heat on the wheels numerous times after driving it a bit and they all seem pretty uniform in temp, and not outrageously hot, so not sure of that.

 

Anyway, any other ideas you guys have for stuff I could look at more closely would be much appreciated. Thanks all,

 

GT

gthurgood New Member

gthurgood

Posted
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with the front diff, correct me if I'm wrong but as I understand it in these trucks with the automatic transfer cases (NP263XHD) and unit-bearing hubs, the front hubs and short axles are turning all the time, but there is an electronic disconnect in the front diff that only engages the ring and pinion and such when in 4-wheel drive, is that right? So you're saying it could be that that mechanism isn't working properly and the front diff is engaged all the time?

 

Or, are you thinking about the transfer case being engaged all the time? In either case, what can I do to test if this is my problem? I'm not sure I can do my own work on it if this is the case, but I at least like to get a pretty good diagnosis figured out before I take it to a shop.

 

As for the front brakes, do you have any suggestions for narrowing it down to whether it's an issue with the MC, the caliper sliders, the wheel cylinders, etc. or is it just a matter of starting with one component in the system and working through them one by one?

 

Thanks for the help!

davester Senior Enthusiast

davester

Posted
Posted

Yes, the actuator in the front diff might not be working right. An easy test is to try to rotate the front driveshaft. It should be able to rotate with both front wheels on the ground. This would indicate that both the front actuator has disengaged and that the transfer case has disengaged 4wd. If you can't rotate it by hand, then you have to figure out if it's the front diff or the transfer case. Raising one front wheel off the ground, then trying to rotate the front driveshaft again, if it rotates (and the wheel as well), then the front diff stuck engaged, if it still doesn't rotate, then the transfer case is stuck in 4wd.

 

As for the brakes, yeah, it's just going through one component at a time. I would suggest starting at the wheels and working towards the MC, as that would be going from where the problems most commonly happen to least common...

gthurgood New Member

gthurgood

Posted
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Posted

Thanks for the great info on figuring out what's going on here. So after I read your first post, but before I saw your second post, I got up under the truck and found the actuator. I wanted to see if I could hear the actuator functioning so I lightly tapped on the front diff actuator with a hammer and had my wife shift back and forth from 2 to 4H a few times, and I could hear it activating each time. The next day we hit the road for a long weekend camping trip and the drag issue seemed to be noticeably better to me on the drive (about 600 miles roundtrip). When we got back I saw your latest post and checked the front driveshaft and at least as of right now it does turn freely, so at the moment the t-case and front diff are disengaged as they should be. I wish I had seen your post and checked it before tinkering with it before our trip, but now I know what to keep an eye on and I'll check it out periodically over the next few weeks as I expect we'll still need four-wheel drive once or twice more before this winter lets go here.

 

As for the brakes, I'm due to replace the fluid so I'll tackle that here in the next few weeks or so and see if anything seems problematic there.

 

Thanks again for the great info on testing the front drivetrain to try to nail this down. I'll provide an update in the future once I have a chance to work over the brakes as well.

 

GT

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