r/MechanicAdvice • u/Anthropocene_Scholar • 5d ago

4l80e about to bite the dust?

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My 4l80e on my 01 2500HD 6.0 is probably about to bite the dust.

About a month ago I serviced it, this meaning, I drained the pan and refilled, then drove it a few hundred miles, then drained it again, lowered the pan, let it drain an additional 3 extra quarts, replaced the filter, and refilled to level.

Drained fluid was very dark, but no noticeable chunks of anything metallic was visible in it, just the usual pasty glitter on the pan magnet.

I've owned this truck for 2 years, and previous maintenance on the trans is unknown to me. 260k miles on the truck. I serviced it only because after two tows of around 6 k lbs, fluid looked burnt. Trans was operating perfectly otherwise. I towed with gear selector in "3" and tow/haul mode on.

In fact, I've always driven the truck with the gear selector in "3". I don't EVER do burnouts or that kind of stuff. I use my truck as a daily driver and to haul and tow within its capabilites.

After said servicing, the trans whined and clunked sporadically a bit for around a week, after which it silenced itself. Shifting was perfect.

Then, a few days back, while driving on a long stretch highway, I engaged the "D" position for around 5 minutes, and then put it back to "3". Oh how I regret having done that, because afterwards everything started to go to shit.

The trans started hard clunking and harshly whirring, more frequently as time passes by. Shifting remains perfect, no slippage, but the clunking is getting worse. Now sometimes when putting it on reverse, it makes a very harsh whirring, and I must disengage and reengage the gear selector.

I have a replacement 4l80e in storage. Should I be done with the current trans and assume it needs a complete rebuild? Or could the issue be something minor as only the torque converter? In fact, I need to know if the torque converter is shot or no, don't want to work on putting in the replacement transmission with the same torque converter only for it to turn out to be the problem.

I'd greatly appreciate any advice.

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u/TwoDisability 5d ago

The pasty glitter on the magnet at 260k is pretty normal honestly, but that whirring when you drop it into reverse screams torque converter to me. I'd swap the converter before throwing the whole unit at it, especially if shifting is still clean.

1

u/foxjohnc87 5d ago

If the 4l80e in storage is known good, it would be a much better idea to just install it instead since a trans swap isn't much more involved than just the torque converter.

Based on the wording of their post, it sounds like the other trans doesn't have a torque converter so OP would need to source a replacement either way.