No Torque Converter Lockup in 4th?

[1993GMCSierra]

Hi all,

'93 GMC 4L60E, with about 2,500 miles on the rebuild.

Recently I've noticed when cold, I'll start going down the road, and it will shift into OD fine, but the converter won't lockup. (running 2000 RPM's at 55, vs. 1700 or so). If I downshift it manually and then back into OD, it will lock up fine, and it works like it should from then on out.

If I let it be, it will stay in 4th (unlocked) regardless of the temp. It's only when I downshift into D and upshift it will shift and lock, and continue to do so.

What gives?


EDIT: I don't know if it does this every time, but I've just noticed it a few times.

 

[firefighter_2319]

you may wanna try the TCC selinoid. that is what operates O.D it pushes on the band. i had a truck that would do that. thats the only thing i can think of at the moment time. you gotta take the pan off to get to it tho.

 

[1993GMCSierra]

I gotcha. I'll check it when I change my fluid next.


Unfortunately, the shop I took my trans to for a rebuild went out of business.

Looks like the guy got sick awhile back, and closed up shop. I sure hope nothing goes wrong, or that's $2,200 pissed out the window.

 

[blackhawk17]

Did you ever change out that solenoid? My '92 seems to be doing the same thing, but I didn't try downshifting into 3rd to see if it helped. I'll try that this afternoon. My gas mileage is sucking. I'm also worried about the heat since some people have mentioned that.

 

[blackhawk17]

Ok, I tried the tapping the brake thing at highway speed, and it causes the TC to lock and it does ok unless I stop, and then I have to do it over again. The shifting down to 3rd didn't do anything for me. Is this the TCC solenoid or could it be something else too?

 

[thunderstruck]

Ok, I tried the tapping the brake thing at highway speed, and it causes the TC to lock and it does ok unless I stop, and then I have to do it over again. The shifting down to 3rd didn't do anything for me. Is this the TCC solenoid or could it be something else too?

Tapping the brake while cruising should actually cause the TC to unlock. I'd say your brake pedal switch is suspect. The switch housing holds two switches; one for brake lights, the other for the TC unlock. So it's possible the brake lights work fine, but the TCC lockup goes nuts when you mess with the brake.

 

[blackhawk17]

I guess I should have been more specific- I read it on another forum and think I accidentally posted it here, but it's still the same problem. I'm double-tapping forums to get some info While cruising at highway speed, I left foot brake while still giving it gas- not a lot, just enough to feel it. And that's when it locks. But it doesn't work all the time. Plus the shift from 3rd into OD has changed noticeably. It's a lot more gradual than it used to be. It's doesn't feel/sound bad- it's actually a lot smoother. But whatever it is it can't be coincidence. I'm sure it's more than a brake switch. I just hope my transmission isn't going out. The solenoid wouldn't be a big deal.


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[blackhawk17]

I think you're right about the brake switch. Is it just a replacement or does it need adjusting? I thought I read somewhere about adjusting it??

 

[thunderstruck]

I can't recall if it's adjustable, plus I know there were several different designs. I would just replace it either way.

 

[blackhawk17]

Well it seems to be a phantom part. No one seems to have it and I was told that GM doesn't even carry it. I haven't put eyes on it yet myself, but from what I've heard on the phone there is no such thing as a TCC brake switch. There's a brake light switch and a cruise control switch...
Other than that there's the solenoid (which no one has either) or a lockup TC module- which runs about $180. I don't think that's it.


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