Is my transmission going kaput?

Discussion in 'Transmissions' started by Calamus, Jan 13, 2021.

  1. Calamus

    Calamus Newbie

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    Hey folks,

    I've got a 1997 Z71, which I believe has a 4l60e automatic transmission.

    I've been working on restoring it for hunting and hauling, and I recently replaced the wheel hub assemblies, rotors, and drums, along with some rather cheap winter tires to get me through the winter (Norman 7's by Nokian).

    I replaced all of those things at the same time, and around that time I started to hear a hum once I hit about 40kph (24mph). It increases in pitch until about 90kph (55mph) when I start to stop hearing it - possibly cause there are so many other noises at that point, lol!

    At first it was just chocked up to having cheap winter tires, and I figured it was road noise. However, over the last several drives I've noticed the following:

    - the hum is the same whether driving on wet pavement, dry pavement, gravel, or snow covered pavement. The sound doesn't change based on type of road I'm on.
    - The hum goes away completely when I let off the throttle and coast in gear (slow down)

    I'm starting to get concerned that this is some early signs of transmission trouble. It does seem to shift ok, while driving it shift smoothly up and down at the moment.

    Is what I'm describing ringing any bells?

    Possibly unrelated, but I'll mention it in case:

    - I've been getting intermittent engine code error P0719. I've figured its the brake switch itself - and have one on order to swap it out - but I'm also aware that this error can stem from a faulty Torque Converter? I've got no idea if this could even possibly be related to the hum or not?

    I don't expect people to diagnose on the net, but any insight to the mechanical workings, or advice anyone can provide is appreciated before I take it to a shop for boucoup monies.

    thanks!
     
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  2. HotWheelsBurban

    HotWheelsBurban Burbs are great!

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    Have you checked the fluid levels? And what does it look like? Burnt look and smell, or still red?
     
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  3. Pinger

    Pinger I'm Awesome

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    I'd check rear wheel bearings before digging into the trans.
     
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  4. Calamus

    Calamus Newbie

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    Thanks for the replies guys, both good suggestions.

    @HotWheelsBurban : Just rechecked it. It was a little bit low, but not significantly. I topped it up and went for a drive. Hasn't made a difference. Also, it's a bit dark red, but not too bad - and it doesn't smell burnt to me.

    @Pinger : I replaced the front wheel hub assemblies when I did the rotors, and we also replaced the rear axle seals. When we did the seals we checked the axle bearings and they looked fine.

    lol, any other thoughts?
     
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  5. stutaeng

    stutaeng I'm Awesome

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    Um, possibly related to the CEL code. That probably needs to get fixed first.

    Read here: https://www.gm-trucks.com/forums/topic/241487-trouble-code-p0719/

    Did the code come on after you started hearing the noise? And what's the history of the truck? Has the transmission be serviced before?

    I suppose you can jack the rear and put it in gear and see if the noise is still here and go from there? But step one will be correcting the CEL code since it involves the TC. Possibly dropping the pan and hopefully not finding glitter and fresh fluid step 2?
     
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  6. Calamus

    Calamus Newbie

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    @stutaeng : Unfortunately I don't know a lot about the service and maintenance history of the truck. It's a recent purchase for me. I do know the trans is original. I also know that the sound appeared after doing a tremendous amount of work in different areas, including the rear axle seals, and the output shaft seal on the trans. Of course, we also put the new tires on at that time.

    The brake switch should be arriving soon, and I'll swap it out to narrow that down. I can't say if that code had come up before, as I hadn't checked it. When it went in for intial inspection I was told the ABS code was on - that turned out to be linked to a faulty drivers hub assembly which was replaced.

    Is it possible that the tech wiped all the codes and didn't mention the p0179 code? Yes. Can I say that with any certainty? No.

    In any case, I'll def get that brake switch swapped out asap and report back.
     
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  7. SUBURBAN5

    SUBURBAN5 I'm Awesome

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    Real quick I'm just chiming in. Definitely get the codes off and repairs done. Second try to make sure your humming is from the front. I know you said the rear got new seals. Did you do the pinion or check the bearing. Quick story one day we drove the suburban and it starting humming. Btw real humming cant mistaken the noise. Went away with pressing the gas or faster speeds but cruising or taking you foot off the gas at lower speeds you would hear it. Drove it forever like that until I got owner ship of it. One day driving to work the diff blew. Guy rebuilt it and noise went away. So point of story that humming was the bearings in the diff not the axles. Keep that in mind. Also does your tran slip or have hard shifts. Normally with trans you'll notice something with trying to maintain speed or accelerate. Also your positive it's not your ujoints?
     
  8. Nad_Yvalhosert

    Nad_Yvalhosert I'm Awesome

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    Classic rear pinion noise. On the gas acceleration noise from slow to nearly highway speed? Goes away on coast?

    Try this: go driving, at the speed that the noise is most noticable. Push the gas pedal softly, only accel an extra 1-2 mph. Let off the gas pedal, only to slow down a couple mph.
    On the gas, off the gas.
    On the gas, off the gas.
    On the gas, off the gas.

    Does the sound come and go with accel only? If so, I'd guess pinion bearing is bad. Likely oil starved... you did say you replaced rear axle seals.
     
  9. Supercharged111

    Supercharged111 I'm Awesome

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    Damn you beat me to it. This. ^^^^^
     
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  10. Pinger

    Pinger I'm Awesome

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    The difference between on and off the gas is a sign that it's transmission related and rear axle is definitely a possibility.

    Couple more points on wheel bearings. They can be deceptive - noisy in running but nothing obvious when checking them. The noise will sometimes change when the brakes are applied. Worth checking but as above post, diff also a suspect.
     
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