In ´80 Aspen? There is no electronics that I could find. Is there a way to adjust when it locks? Now it feels like it is killing the acceleration It locks at ~35mph like it should...

The early ones had a lockup circuit in the valve body and locked up hydraulically.

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Official Cookie and Mater Tormentor.

It's hydraulically controlled, just like all the other shifting action in that transmission. Once the pressure in a certain fluid circuit reaches high enough to move a piston backed up by a particular spring (which happens once a particular road speed is reached), the piston moves and allows fluid to flow to the lockup clutch actuator in the torque converter, and the converter locks.

There was a TSB for the first few years of lockup-equipped cars ('78-'80ish) for just the complaint you raise (early lockup). It involves installing a stiffer lockup control spring in the valve body, to raise the lockup speed. Most of these have been done over the years, but one occasionally still encounters a pre-TSB lockup control spring — or just a weak one that's allowing lockup at too low of a road speed. You can pick up the spring you need at the dealer for under $4, part number 4202 672.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan, you have information for everything

Do you have pic of which spring is it? I´ll do something to it when I chance the oil. The problem is that if I go to local Chrysler dealer, they´ll ask "what the hell is Dodge Aspen" But I´ll find stiffer spring.

It´s pretty difficult to drive at slippery road now

And problems

Last week I noticed that lockup is not engaging. Yesterday, I changed new filter and oil, and cleaned the valvebody. Olf filter was very dirty and there was dirt in magnet too. I decided to try luck, and try it with new oil. And the result is that lockup now engages only with reverse. Took the oil pan out and there is something mojo in the magnet again. Could it be from the converter, can it broke like that, or is it something else? Tranny itself works fine.

Very dirty fluid + shavings on magnet + improper trans operation = your transmission is toast.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Yeah, already picked up another tranny. It´s non lockup

It could be the lock-up converter clutch has failed.
This failure happens suddenly and sends lots of junk into the transmission.
DD

80-up trans had the better lock-up module and spring(orange colored).I agree with Doug your trans is toast.When the TC fails, it starts plugging up your trans cooler first,this causes fluid backpressure to build up in the TC, activating the lockup clutch at the wrong time.Between the TC draging,and the cooler plugged up,it,s a 1-2 KO punch for your trans.Also be sure to replace,or flush your trans lines,and buy a new trans cooler.I would NOT reuse your present cooler no matter what.

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V8?? We don't need no stink'n V8!!

Problems continue

Before I installed the "new" tranny, I took it apart and checked it. Clutch plates and bands were ok, showing only minor wear. Now it works right, exept it doesn't want to shift 3rd gear at cold. First 1-2 miles with 2nd and then it shifts 3rd and works normally after that. I've cleaned the valvebody a couple times, no change. Fluid is Mobil ATF220.
Also I couldn't find right band adjustments for it (1976), now front 2 and rear 5 turns.

Edit: I left work and let it run in neutral a little before leaving, works fine. Something wrong with converter oiling?