Curios tranny issue

[Erock80]

'98 k1500 5.7 4L60E 3:42 gears(?) 72,000miles

So this strange little trans issue has come up, and I'm trying to pinpoint the problem to the best of my ability before I seek any "professional" help... I use the term loosely there. Since I don't want to pay $400 for a shift module, you know...

Basically, when I'm accelerating, under any conditions (ie, hard, easy, unloaded, loaded, etc.) the first shift, is very short and a bit rigid. As if the tranny is shifting too soon into second gear. The first shift usually takes place at about 900-1000 rpm (seems awful early to me). Second gear winds out nicely, and though the shift between 2nd and 3rd is smooth, there is a "clunk" sound that the only way I can describe it sounds something like a sloppy U-joint. Everything else is fine, including the downshifts on decel/braking. Btw, all the U-joints are tight, or at least seem tight, so I suppose there is some noise coming from within the tranny. Scarry...

So any ideas what could be going on here? I know that with these electronic shift modules etc the thing could have a pinhole exhuast leak or something stupid (which I just discovered one in the muffler btw) and be shifting funny because of it.

So, My main question is (to those of you with a similar rig), where is your first shift taking place on the tach? My next question is, am I saving up for a tranny swap or just adding some lucas to the next fluid and filter change?

Thanks

[z07]

1000 does seem low but I don't have a 4l60e in my truck, my wife has one in her car though but it isn't a valid comparison but it shifts at higher RPMs and varies with the way it is driven.

Can you put the gear selector in 1 and build up to 3000 rpms without any strange noises?

It's my understanding that the 700r4, 4l60 and 4l60e have the third gear clutch pack as their most common first point of failure. If yours is failing this could be the early signs of it. What color is the ATF and is there anything on the magnet?

[Erock80]

Thanks z07...

To elaborate, the atf is nice and red, just like it should be, and has no "burnt" odor to it. Actually, it really seems quite fresh, despite the last fluid and filter change being done about 35k (and 5 years) ago.

As far as leaving the shifter in #1 and letting it wind out.... I'll have to report that back later. I'm heading out soon to run a few errands. I've only ever used 1 when I'm in 4wd and putting around the yard or something, not letting it wind out.

[Erock80]

Update:

I took it out and wound it out with the shifter down in 1. It shifted into second at about 3 grand.

Then I just put the selector into OD and gunned it from a dead stop. She wound out first gear to 5,500rpm and did a smooth shift into second. Still floored, second gear wound out and shifted smoothly (no clunk) into third at about 5 grand and I let off... I ran out of road and I was already doing 80 (in a 40).

Cruising normally with normal take off and acceleration, it still wants to shift out of first at 1000rpm, it did shift at 1500rpm on a slight grade. This translates to appx. 7-8mph.

I probably wouldn't think anything of this, other than the fact that it just "feels" funny shifting so early.

Maybe it's nothing, but that "clunk" I get going into third has got me worried.

[case84258]

idk really im thinkin that it seems a bit early to me too. has it shifted that low since youve had the truck

[Erock80]

It's always shifted a bit "soon" on that first shift.... But I never really paid any attention to it before. Maybe only since the "clunk" has started has my curiosity been piqued about that first shift.

I had a '94 Z71 a few years ago, with the same setup, though I can't recall the gear ratio, but it never shifted like this one. Never the less, I'm still wondering here what's going on.

[hotrodpc]

You may not like this response, but for what its worth, here is bulletin from GM on the clunk you are talking about. If I understand it right, I would interpret it as transmission is experiencing normal wear and tolerances are getting looser. The early shift may very well have always been there and you just have not noticed it. A great sign that your fluid is of proper color. The #1 failure in a 700r4 and 4l60e is the good old broken sun gear. When it goes, it goes, you will know it. Sonnax makes an upgraded one for about $70 so I always tell everyone to get it and be sure your local trans rebuilder is putting it in. Most GOOD trans shops are aware of this and do the upgrade anyway and it built into the cost of their rebuild. But it appears your trans may be just fine according the bulletin below.

Some vehicles may exhibit a clunk noise that can be heard on a 2-3 upshift or a 3-2 downshift.
During a 2-3 upshift, the 2-4 band is released and the 3-4 clutch is applied. The timing of this shift can cause a momentary torque reversal of the output shaft that results in a clunk noise. This same torque reversal can also occur on a 3-2 downshift when the 3-4 clutch is released and the 2-4 band applied. This condition may be worse on a 4-wheel drive vehicle due to the additional tolerances in the transfer case.
This is a normal condition. No repairs should be attempted.

[leolkfrm]

It gets stranger as they get newer, I'm driving a 2009 silverado on a teat track this week with auto control 4wd. found that if the switch is not in 2wd it has a real strange shift pattern under heavy accelation.

[Erock80]

hotrod... what are you talking about, "I may not like this response" that's great news! I mean, assuming that is the issue, but it sure sounds like what that article described. I have blown up a sun gear before in an old 700R4, so I know what to expect if that ever happened again.

Anyway, I've been poking all over the web looking for any info like that, but I must've been turning over the wrong rocks because all I was finding was tech specs and rebuild kits... Anyway, You've been very helpful. Thank you. We'll see if anyone else has two cents they'd like to put in, but for now, I'll take that as gold.

God I love this forum.

[hotrodpc]

Yes, its great news that its normal, but I am picky, I don't like wierd noises and being told they are normal and have to learn to live with the them. Kinda like the early 5.3 engines and the rattle they made at start up. Again, GM says its normal, learn to live with it. That noise was due to skirtless pistons. They had so many complaints about that noise and unhappy people, I think they went to skirted pistons in about 03, maybe 02. I just wonder if a shift kit may correct your clunk issue. I understand totallly how the clunk is being made. It has to do with the time it takes for a band to come off and a clutch pack to be compressed, so if a shift kit would speed up that process, then maybe the clunk would not exist. It would also appear to me, that this clunk should only be happening at low to lower mid throttle take offs. I would think at any thing above a mid throttle take off, the timing would be quicker therefore the clunk should not exist if I understand it right. Glad that helped.