Hi everyone,

We're on vacation with our 2004 Chevy Suburban, 1500 LT, 4wd. I drove it from Indiana to Florida virtually non-stop yesterday. Somewhere in Tennessee, when I stopped for fuel, I had something weird happen....

I was coming off the interstate and while slowing, around 20 mph, the car heaved just a bit and we heard a noise as if we had driven through a major pothole. (loud thunk) and felt the car shake from it.

After I refueled, as I was backing out of a tight parking spot, with the wheel hard over to the right, I felt the suspension heave just a little, and the resistance cause the truck to almost come to a stop. I gave it a touch of throttle to keep it moving, and then when I put it in forward gear, had the same very loud thump and felt it again in the cabin. (shook the truck)

Later in the trip, it happened again when I backed out of a parking spot and engaged drive, only this time, there was a noticeable, rhythmic thump as I accelerated which you could hear as well as feel. I had a semi bearing down on me, or I would have stopped to investigate. The vibration eventually disappeared.

I had no warning lights or indications of anything wrong. I'm going to change the trans-axel fluid and differential fluid. I don't know much about the service history of this truck as I have only owned it for a year, but I have put a new transmission in it at 108K. (It is at 120K now) The transmission failed the day after I bought it, so I am not super convinced the previous owner took very good care of this vehicle.

Parting thoughts: I leave the truck in 2wd mode, always unless needed. It does switch into 4WD mode normally, but does make a clunk when it does so. When I climbed underneath and felt the transfer case, it was hot to the touch, I don't know if that is normal. The truck has no fluid leaks, and other than what I described above, performed normally for the trip. I have not been able to duplicate it since, which makes me wonder if heat might have caused the issue.

Any thoughts as to what might be going on? Thanks in advance

Scott

 

Motor mounts??
Also, try switching in & out of 4wd to see if it replicates the problem. Please keep us posted, an interesting problem - Good luck btw!

 

I would say you had it in 4 wheel drive, either you put in in unknowingly or it went in on its own. The clunk you are hearing and feeling are the front half shafts trying to power the front wheels. I would suspect this only due to the heat in the transfer case,that long of a drive the drive line should be warm not hot to the touch! I would get to a mechanic or dealer and find out why or how it went into all wheel drive. Front servo motor may have abandoned you!

 

Thanks for the responses. The servo motor is an interesting thought. The sensation that I experienced when I was in reverse is similar to turning when in 4WD. At no time, did the lights indicate I was in anything but 2WD mode, but I imagine it's possible to fail at the transfercase and not send a signal.

I've only been getting about 15.5 mpg at highway speeds (70 mph, 3.73 differential). Is that a little low? My previous suburbans, it seemed I was around 18, but it has been a while since I had them, so I can't remember. If that figure is low, then it would seem to support that I am in 4WD.

I'm going to try to get it into the dealer later today.

 

I also believe it's the 4WD system engaging when it's not supposed it.

Yes, spinning more mass in 4WD will cause more fuel to be burnt.

 

Can't comment on the other stuff, but my '07 tahoe gets 16 mpg, pretty much all the time, mixed driving. On a longer highway trip it might go up a tick or two more, but not much.

When looking for mpg online, seems right to me for both my truck and yours. But I have no idea the accuracy of fueleconomy.gov lol.

 

Well, back from the dealer, $888 magically disappeared from my wallet. Naturally, they could not duplicate the problem, but found some other things. I had a light clunk in the steering wheel, which you could feel more than hear, so they replaced the steering shaft.

I had the truck aligned in March, but apparently it was out of alignment again, so now it's all better. (I didn't notice anything prior, but the paper says it was out and now it is back in) Seems to drive the same...

I did have them change the differential fluid (front and back) and the transfer case fluid. Also found that the air conditioner belt was cracking, so replaced both belts, which they were probably due for. I declined the obligatory "Your air filter is filthy" complaint, I think I can handle that myself, as well as checking my blinker fluid levels.


So, the bottom line, got some stuff fixed, but never addressed the symptoms of what I experienced on the way down. I guess I'll have to wait until the thing blows up completely in order to get it fixed. On a side note, it sucks when the truck breaks down away from home, I have the tools to do the fluids and belts there. Shame on me for not thinking to do it prior to the trip, but at least I did sign up for AAAplus just in case.

 

400 miles into our 1100 mile trip home, we are dead on the road, having blown a transmission line. Actually, blown isn't right word, apparently a hose clamp came loose. But at 3 am, and 700 miles from home, it's more exciting to say "blown".

 

if its like most gm trans line its probably been seeping/leaking for years. who services your vehicle?

 

I had the dealer in Florida service it a few days ago. Turns out the oil cooler line (not OEM) had a rubber hose that the clamp came loose and allowed all the fluid to exit the system in spectacular fashion. Easy fix, after getting towed to a repair shop. (Thank God for AAA at 3 am on a weekend after a major holiday, they actually found a place that was open to do the repair.)

The transmission was rebuilt by a highly respected shop in my home town about 18 months ago. I find it ironic that the clamp magically "loosened" after service was performed by the dealer in that specific area. I don't have proof, but I am suspicious of the timing.

Prior to this, the truck has never leaked a drop and has always been dry underneath. I do all my oil changes and routine maintenance, so I am very familiar with the underside of the truck.

Interestingly enough, the thump and heave issue has not recurred, knock on wood. We are holed up in Lexington for the night, after being awake for 24 hours. Only 5 hours to go tomorrow and we'll be back home.