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Discussion Starter #1
2017 Colorado Diesel 4WD

Got rained and mudded in way out on dirt road in Utah

Barely escaped after 3 hours in 4WD low range, 2nd gear (maybe 20% in 3rd), chains on rear tires, pulling 2,500# trailer. Diesel, chains and auto-locking diff were awesome, would not have made it without all three.

That evening, next time I started engine, we heard a significant pop/thunk from the transmission area (we were in 2WD at the time). The pop occurred immediately after the engine fired up.

This pop/clunk occurred several times over the next couple of days pretty much each time the engine started then quit doing it and everything was normal.

After a few days and several hundred miles (all in 2WD) with no issues, at the end of a long day on curvy, paved roads, we started hearing a low thrumming noise when turning and I could feel a subtle pull in the steering wheel toward the side making the noise. It felt and sounded similar to driving over gentle rumble strips. The pull and sound occurred mostly to the left. Felt normal when traveling in straight line.

Above issue came and went over a 20-30 minute drive home but got worse to the point that when we got back to our camp spot I was very concerned. I tried putting it in 4WD low and high range and driving short distances and also turning it off and on several times but that didn’t really seem to help. Parked truck and the next time I started it, there were two loud pop/thunks, just like the ones it had made days earlier. After that, it was perfect and it has not exhibited any problems since, in about 1,000 miles.

We shortened our vacation and got into Flagstaff GMC/Buick dealer to look at it. They complained about the mud underneath and couldn’t find anything wrong. Service supervisor tried to tell me it was just mud from the tires rubbing on something and that the steering wheel pull and thrumming noise were because the tires were out of balance from the mud. Give me a break, we had driven hundreds of miles between the initial popping and when the pulling, etc. started and there was no shimmy or problem at 65 mph.

Today, I was under truck and I noticed that the shaft that connects the transfer case that gets power to the front end to the front differential can move fore/aft a few inches and if I push it as hard as I can back and forth, it makes a clunk at the end of its travel that I believe is in the location we were hearing the pop/clunk from and would be very similar to the pop/clunk if it were pushed with more force.

The best I can come up with and I'm looking for thoughtful feedback, is that, even though the dash rotary switch was in 2WD, the truck was, at times, partially engaging 4WD and that was causing the hubs to act as though they were partially engaged. Is that even possible? Is it possible that the switch that engages/disengages the 4WD or a sensor is faulty and causing the truck to try to go into 4WD on its own? If so, could it be that when the truck is turned back on, the sensor/switch/motor resets and the clunk is the shaft reacting somewhat violently to the system self correcting to 2WD mode?

I would like to go to dealer with some specific things for them to check rather than have them just tell me everything checks out and there’s nothing they can do unless/until it exhibits symptoms.

I posted on the chevycoloradofans forum and there were some helpful comments that informed me that only the passenger's side shaft disengages when in 2WD. I'm trying to understand that and how it could explain the tendency of the noise and drag to occur mainly on left turns.

Any help appreciated!
 

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Glad you didn’t end up stuck. Here are a few thoughts I have.

With the switch in 2wd you should be able to spin the front shaft freely from under the truck by hand. If it was stuck engaged at either end, you wouldn’t be able to turn it.

There is a motor on the end of the shift fork that operates the 4wd. It moves the shift rod. Check to see if you damaged it or if it is loose.

If you can’t spin the driveshaft by hand then you can see if the front wheels are engaged by jacking up the front end and turning the tires. This could help determine if the axle or if the tcase are the culprit.

Also check to see if you punched a hole in the tcase or axle housing. No fluid = lots of noise.

I’ll poke around in my brain. I know tons about drivelines, axles and t-cases. Had plenty of them apart. No longer have a colorado so I’m plucking info as I remember it.
 

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Discussion Starter #3
Glad you didn’t end up stuck. Here are a few thoughts I have.

With the switch in 2wd you should be able to spin the front shaft freely from under the truck by hand. If it was stuck engaged at either end, you wouldn’t be able to turn it.

There is a motor on the end of the shift fork that operates the 4wd. It moves the shift rod. Check to see if you damaged it or if it is loose.

If you can’t spin the driveshaft by hand then you can see if the front wheels are engaged by jacking up the front end and turning the tires. This could help determine if the axle or if the tcase are the culprit.

Also check to see if you punched a hole in the tcase or axle housing. No fluid = lots of noise.

I’ll poke around in my brain. I know tons about drivelines, axles and t-cases. Had plenty of them apart. No longer have a colorado so I’m plucking info as I remember it.
Thanks a lot RCDude. A guy on the other forum suggested checking that the shaft spin freely and it absolutely does not turn (in 2WD) so that is huge info to take to the dealer, where I'm headed on Monday. Thanks for chiming in. You dumped your Colorado?
 

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Thanks a lot RCDude. A guy on the other forum suggested checking that the shaft spin freely and it absolutely does not turn (in 2WD) so that is huge info to take to the dealer, where I'm headed on Monday. Thanks for chiming in. You dumped your Colorado?
No prob. Sounds like it’s still engaged at one end (or both) you can jack up the front tires (both) and try and spin them.

Even if the front axle only disconnects one side the shaft still would spin freely because of the open differential and disconnected shaft.

If the axle is still engaged the tire would either spin the driveshaft or spin the other tire in reverse meaning the tcase is engaged (and in park)

If the tires spin freely independently and the shaft doesn’t spin then the tcase is still in 4wd (and in park)

Driving on pavement in 4wd definitely causes binding.

And, Yessir, I did.
 

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Thanks, I'll do some more checking tomorrow but something isn't right and with your help I think I'm closing in on it and hopefully the dealership can make it right. Did you discuss why you got rid of your Colo here and could you point me to it? Otherwise, you mind saying why you unloaded it? Last posts I saw it sounded like you liked the truck. I love mine but it sure is hard to be confident in its long-term reliability. I'm hearing rumors again about diesels in the toyo lineup for 2020 but nothing solid. My wife would definitely be happier if we were back in a toyota but it's gonna be really hard for me to leave that diesel.
 

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Looks like you may be on the right track.
You should definitely be able to turn the driveshaft by hand in 2wd.
However, it may be the t-case switch not unlocking there as well.
Have you tried to go back and forth between 4 have I, 2wd and 4low and back to 2wd?
If you can get on a hoist or jack stands it would be easy to determine which actuator may have failed.
RCD: Do you recall or know If the solenoids are powered both ways?
May be as simple as a loose connection caused by mud, which would not allow axle or t-case to disengage.
Not sure about the pop noise unless control module is faulty causing actuator movement that you may be hearing.
Mine is quiet. Hmmm.... bears more diagnosing on a hoist.

It is ALWAYS a good idea to thoroughly wash the underside of your rig after off roading especially in mud or salty water. Mechanics HATE encrusted vehicles. May prevent a proper inspection due to disgust with your housekeeping.
 

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@alberta minimax the last gm t case I was in (NP 246 out of a suburban with the same auto 4wd) I seem to remember thinking the shift motor pushed the shift rail and the spring returned the shift rail. Those t-cases had many clutch discs so they can apply torque to the front smoothly by applying pressure to the clutches and full on 4x4 the clutches are just fully engaged. Provides a seamless “auto” 4wd But there isn’t a real “shift” into 4wd either (i think...going from memory). Not sure if the Colorado is the same tcase.

@DeeK there are many reasons. It wasn’t getting enough use to warrant keeping such an expensive truck despite its mpg. When it comes to towing, My new rock crawler toyota build weighs a lot more than my old one (full exo’d truggy now) and the Colorado lost its edge towing it. (Now up to 6500lbs loaded trailer and down to 12mpg and not maintaining speed on hills, trans temps climbing). I never had any problems with the truck and it was a good truck but the platform hasn’t been proven and I decided to let someone else test the long term reliability of it..
 

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Discussion Starter #8
Looks like you may be on the right track.
You should definitely be able to turn the driveshaft by hand in 2wd.
However, it may be the t-case switch not unlocking there as well.
Have you tried to go back and forth between 4 have I, 2wd and 4low and back to 2wd?
If you can get on a hoist or jack stands it would be easy to determine which actuator may have failed.
RCD: Do you recall or know If the solenoids are powered both ways?
May be as simple as a loose connection caused by mud, which would not allow axle or t-case to disengage.
Not sure about the pop noise unless control module is faulty causing actuator movement that you may be hearing.
Mine is quiet. Hmmm.... bears more diagnosing on a hoist.

It is ALWAYS a good idea to thoroughly wash the underside of your rig after off roading especially in mud or salty water. Mechanics HATE encrusted vehicles. May prevent a proper inspection due to disgust with your housekeeping.
Thanks for the hints and thoughts. I agree about getting the mud off but it's not so easy to do when you're middle of vacation and towing a trailer. We had to blast out super early to get to dealer for appt time and there really wasn't time to stop and do a thorough cleaning. If those mechanics thought it was bad, they should have seen it before driving through 3 hours of driving rain, LOL!
 

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@alberta minimax the last gm t case I was in (NP 246 out of a suburban with the same auto 4wd) I seem to remember thinking the shift motor pushed the shift rail and the spring returned the shift rail. Those t-cases had many clutch discs so they can apply torque to the front smoothly by applying pressure to the clutches and full on 4x4 the clutches are just fully engaged. Provides a seamless “auto” 4wd But there isn’t a real “shift” into 4wd either (i think...going from memory). Not sure if the Colorado is the same tcase.

@DeeK there are many reasons. It wasn’t getting enough use to warrant keeping such an expensive truck despite its mpg. When it comes to towing, My new rock crawler toyota build weighs a lot more than my old one (full exo’d truggy now) and the Colorado lost its edge towing it. (Now up to 6500lbs loaded trailer and down to 12mpg and not maintaining speed on hills, trans temps climbing). I never had any problems with the truck and it was a good truck but the platform hasn’t been proven and I decided to let someone else test the long term reliability of it..
Well, thanks for your help along the way on this and other issues. I don't have to wish you good luck with your Toyota, you don't need it.
 

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Well, thanks for your help along the way on this and other issues. I don't have to wish you good luck with your Toyota, you don't need it.
Funny, I killed the motor in the new toyota crawler on the second trip out in it. haha. Got a new motor lined up, though.
 

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Funny, I killed the motor in the new toyota crawler on the second trip out in it. haha. Got a new motor lined up, though.
wow, that's really not so funny, is it? what happened? was also curious if your new toyota was better at hauling and getting better mileage than the colorado, that would be surprising. i'm also surprised it's got a higher towing capacity than the colorado. is it a tundra? i've never thought of a tundra as rock crawler material but i didn't think a taco would have a towing capacity similar to the diesel colo.
 

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The Toyota isn’t the tow rig, it’s the toy on the trailer being towed. Just Built it over the last 8 or 9 months

We were on some trails about two hours away from base camp and something happened to the oil pump. (Haven’t torn down the motor yet to find out what) maybe the pick up got clogged, maybe the oil pump failed but No oil was circulating. It was just sitting in the oil pan. Zero oil pressure. It was wet and the rocks where slick so we were really giving it the ol’ skinny pedal for about four more hours after we lost oil pressure before we got it back on the trailer.

Needless to say, you can’t run a motor without oil for four hours. It no longer has any compression and sounds absolutely terrible. it still idles and hasn’t come apart yet but it’s no longer useable.
 

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Discussion Starter #14
@DeeK did you get your issue diagnosed
/resolved by dealer?
Sorry, I don't check in here often and I never could get the auto notification thing to work. The day I went into the dealer was a pretty good storm with snow on roads so I was in and out of 4WD hi a few times. By the time I got there and was back in 2WD, the front drive shaft was spinning just fine. So, the dealer found nothing wrong. I guess all I can hope for is that the problem doesn't return and that not much damage was done to any components when it was acting up. at least it's on record if it does.
 
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