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Pop or bang from underneath truck when put into gear

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Old 02-08-2011, 09:01 PM   #1
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Pop or bang from underneath truck when put into gear

Hey everyone. This totally confuses me in several ways, so here it goes. It is around 10F here in upstate NY with 40mph winds. When I put my car into reverse after moving forward and sometimes into drive after moving backwards, I hear a pop or soft bang coming from under the car. I can hear it if the window is open and yes, I do feel it going into gear. The car seems to be driving normally with no other sounds. This has been happening over the past couple days, especially when it is cold. I just had the transmission fluid changed with a deep pan installed plus a 1/2 qt of Lucas put in (full quart was used last fluid flush). I also had a transmission cooler installed last year. Just recently, I also had to have the rear diff pinion seal replaced and I just changed the fluids in both diffs and the transfer case (and there are no leaks). A few months ago I changed the throttle position sensor and it improved shifts a bit.

The real confusing part is that after driving it around for 10-15 minutes, I tried shifting it again between R-pause in N-D and back and it was 90% quieter but with the same jolt going into gear. What could this be?
Old 02-08-2011, 09:07 PM   #2
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Re: Pop or bang from underneath truck when put into gear

Quote: Originally Posted by ComputernerdBD
Hey everyone. This totally confuses me in several ways, so here it goes. It is around 10F here in upstate NY with 40mph winds. When I put my car into reverse after moving forward and sometimes into drive after moving backwards, I hear a pop or soft bang coming from under the car. I can hear it if the window is open and yes, I do feel it going into gear. The car seems to be driving normally with no other sounds. This has been happening over the past couple days, especially when it is cold. I just had the transmission fluid changed with a deep pan installed plus a 1/2 qt of Lucas put in (full quart was used last fluid flush). I also had a transmission cooler installed last year. Just recently, I also had to have the rear diff pinion seal replaced and I just changed the fluids in both diffs and the transfer case (and there are no leaks). A few months ago I changed the throttle position sensor and it improved shifts a bit.

The real confusing part is that after driving it around for 10-15 minutes, I tried shifting it again between R-pause in N-D and back and it was 90% quieter but with the same jolt going into gear. What could this be?
I just checked a diagnosis chart for the 4L60E and I am guessing it may be a high line pressure issue. I had a line pressure control solenoid replaced 11/07. Could this just be a case of cold weather thickening the fluid because the deep pan and transmission cooler are doing too good a job at keeping the fluid temps down? It is a B&M cooler mounted upside down behind the grille. The pan is a Dorman deep pan with a drain plug.
Old 02-08-2011, 10:22 PM   #3
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Re: Pop or bang from underneath truck when put into gear

It seems to be a semi common problem. my rear end had a "clunk" when I put the truck into drive, it was the rear end, not the transmission. Never did figure out what it was, I learned to live with it. It helped making sure I had the brake all the way pressed it before putting it into gear.
Old 02-09-2011, 08:27 AM   #4
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Re: Pop or bang from underneath truck when put into gear

Quote: Originally Posted by Wrkn prgs
It seems to be a semi common problem. my rear end had a "clunk" when I put the truck into drive, it was the rear end, not the transmission. Never did figure out what it was, I learned to live with it. It helped making sure I had the brake all the way pressed it before putting it into gear.
I am always careful about that. I not only make sure the brakes are pressed as far as I can, but what I normally do when I shift gears (R to D and D to R) is wait a second after the car completely stops, shift into neutral, pause a second and then into gear. I never allow the car to roll while I am changing gears. I notice alot of people shift gears with the car still moving (like the mechanics that work on my car), but I don't do that.

If it is the rear end, is this something where some other problem would have been found during a fluid change (with the cover off)? Also, the shop that did the fluid change (before the pinion seal replacement) used posi additive. Could that have anything to do with it?

Also, I did notice that the noise is worse when the truck is in 4LO and the jolt that the car makes when it goes into gear is more intense.
Old 02-10-2011, 09:46 PM   #5
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Re: Pop or bang from underneath truck when put into gear

Okay, I think I figured it out. It is only doing it after the car has been sitting for a couple hours. The first few shifts into reverse (or sometimes drive if I was moving in reverse) are hard and louder than usual. After driving a few miles, it doesn't do it. Still a problem?
Old 02-13-2011, 12:10 AM   #6
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Re: Pop or bang from underneath truck when put into gear

Could I somehow be low on rear diff fluid even though there are no leaks and they refilled it with Lucas 80W-90 after replacing the pinion seal? My NEW rear diff cover is RUSTED already. It only seems to be making the sound when the car is cold. The "jolt" is happening regardless of temperature within 1-2 seconds of the shifter hitting R or D. Wouldn't the shop that did my pinion seal notice that I had a bad U-joint when they dropped the driveshaft? I don't think they could have missed that. They would have told me.
Old 02-15-2011, 07:34 AM   #7
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Re: Pop or bang from underneath truck when put into gear

it could also be a bad TPS sensor. have it scanned for free at autozone and check for a linear reading. also scan it when the engine is fully hot and also fully cold.....
Old 02-15-2011, 09:05 PM   #8
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Re: Pop or bang from underneath truck when put into gear

Quote: Originally Posted by bigdaddykane93
it could also be a bad TPS sensor. have it scanned for free at autozone and check for a linear reading. also scan it when the engine is fully hot and also fully cold.....
TPS is new. I just replaced it a couple months ago with a NAPA sensor. How could that be affecting it? It shifts fine when the car is cold and warm (maybe slightly delayed when cold because I have a cooler). Replacing the sensor actually softened the shifts when it is cold. Before replacing the sensor, it shifted funny soon after starting the truck.
Old 02-15-2011, 09:28 PM   #9
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Re: Pop or bang from underneath truck when put into gear

Does this noise mean that there is damage anywhere? If there was, wouldn't the noise be continuous? No leaks and it only happens for the first couple shifts (reverse to drive and vice versa) and only when cold. There is Lucas 80W-90 in both diffs and MAXLIFE ATF in the transfer case (all new fluids). It is quiet once everything is warm from a few miles of driving. I drove it 5 miles earlier and I could not reproduce the problem that was happening after idling it for 7 minutes to warm the engine after class this evening.
Old 02-18-2011, 03:39 PM   #10
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Re: Pop or bang from underneath truck when put into gear

It was definitely the cold weather. It is 58 degrees today and the shifting is not only not nearly as violent, but it is for the most part silent. I shifted it into drive earlier to go to class after idling it for just 3 minutes (normally I let it run for 5-8 minutes in the morning before driving to class) and I didn't feel it shift. I thought for a second that I blew the trans up somehow, but then I slowly put my foot on the gas and the car moved as usual.
Old 02-21-2011, 05:56 PM   #11
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Re: Pop or bang from underneath truck when put into gear

Quote: Originally Posted by ComputernerdBD
It was definitely the cold weather.
Cold weather certainly makes things act funny, that's for sure. Hopefully, once it warms up to 70 or so it'll completely go away.

What kind of car is it?
Old 02-22-2011, 12:32 AM   #12
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Re: Pop or bang from underneath truck when put into gear

It went away completely. I don't know why or how, but the temperatures are down again and I am not hearing the noise at all and it is engaging alot softer, even if it is cold. It is driving normally, so I don't think anything is broken. It is a 1998 GMC Jimmy with a 4L60E trans.
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