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4l80e / controller questions

4

4L80e

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Colorado, United States of America
Sorry in advance for the noob questions. I'm trying to get accurate info for my engine/4l80e swap into my 1978 4x4.

1) I have a 1991 4L80e that came out of a diesel with the NP205. I also have a computer and harness from a 1995 2500 with the 7.4L/4L80e/NP241.

--Will the 1995 computer work properly with the 1991 trans?

2) The seller of the 1991 trans said it was working well (came out of a wrecked truck), but I don't really know. I guess I also need a different torque convertor since I have a gas engine, not diesel. So I'm not sure what would be the wise (best value/lowest risk) move:

--Try the 1991 and see how it does?
--Have it rebuilt from the get go?
--Get a newer used trans with the factory upgrades?
--Buy a rebuilt from GM so I have the nationwide warranty?

FYI, I'm leary of ordering a rebuilt 4l80e online since the buyer ends up eating the shipping cost if something goes wrong. Still I'm open to all suggestions. Thanks!
 
The problem with the 91-93 4L80E is it uses a different control strategy for the pressure control solenoid. The aftermarket controllers do not support the 91-93 pressure control solenoid strategy since it was only a short run that it was used. That being said, you can swap out the early style for a later style, and run it. As to a gear indicator, the 95+ trans has a nuetral safety switch mounted on it that also provides outputs for a gear indicator. It can be fitted to the earlier trans, but requires making a bracket to hold it, and swapping out the manual shift shaft for it to work.
 
Thank you. I read up on the pressure solenoid and understand that now. Different frequencies.

Thinking this over a little more I'm leaning towards just seeing if the 1991 4l80 works as is. If it's bad all the latest and greatest parts from the later models will drop in, correct? Really no good reason to get a later model?

One thing I'm not clear on is how the speed sensors work. My trans has two sensors, plus one in the NP205 tailhousing. Do the aftermarket controllers need/use all 3?
 
the 91-93 4x4 trannies were unique as they used 2 speed sensors whereas later models used only 1. all 2 wheel drive 4l80es used 2 though. the one near the converter is an input, and rear one is an output. 94+ trannies only used the input, and the sensor in the transfer case for the output(they appear to have an output sensor, but it is a dummy plug with no pickup inside. the 91-93 4x4 is the easiest to use as a standalone as it has a dedicated output speed sensor. 94 on requires a controller that can figure in the gear reduction in 4 low since it uses the sensor in the back of the transfer case. 97+ with the larger cooler lines spaced out seen quite a few improvements, and mid 99 up had quite a few more.
 
That was very helpful. Thanks.

So the last few days I've done a lot of reading. What I've found is most aftermarket controllers don't have the capability to input your transfer case ratio. One that does is the MSD Atomic; when you shift into low range it accounts for whatever ratio you have saved in the software. However, I have a crawler box (2.7-1) in addition to the NP205 (1.98-1) and of course the Atomic doesn't let you have two low ranges.

I called TCI about their EZ TCU and they said to connect their speed sensor wires to the rear trans sensor. I don't see how that could work well when I'm in low range. USShift (very friendly) first said to connect to the transfer case speed sensor, but then said to hold off as he's coming out with a more advanced controller later this month.
 
Burning oil said:
OptiShift uses Tcase sensor.
Click to expand...
The question is, what happens when you put it in low range? Does it have settings and a 4 low input so it can recalculate the ratios? If you're running a double reduction, then the earlier style 91-93 trans with it's own output speed sensor is the way to go.
 
OptiShift input would plug into the rear sensor on 4L80E if the tone ring is there then you can program the shift points you want.
Or use tcase sensor and again program the shift points for each gear.
 
You know I may have missed something obvious. All these controllers have manual tap shifting. All I have to do is put it in manual mode when in low range and use momentary switches to shift. That way I have full control when off roading and will never get blind sided by unexpected auto shifting. What do you guys think?
 
There isn't a drawback that I can see, plus it'll let me save the B program for tow/haul mode. Tap shifting is going be extremely nice to have in the mountain driving here as well.

Now I need to figure out how to do the momentary switches. I have a floor shifter so your column lever trick is out.
 
If you use a 91-93 style trans with its own output speed sensor in it, then the controller won't care if it's in direct, low, or crawler. The TCM just needs to know how fast the output shaft speed is so it knows the actual gear ratio, and when to shift. The 91-93 trans was great for swaps as it used a dedicated output speed sensor for the 4X4 trans. So that means it doesn't matter what ratio your transfer case is, it has it's own output speed sensor in the trans already. If you go with a 94+, it is reccomended to go back to the 91-93 style with a speed sensor in the rear of the trans because if the TCM doesn't know the correct output shaft speed, it can throw gear ratio errors, and go into limp mode even in tap shift mode. I'm sure you can set the TCM up so it will work, but if you still have your 91 trans, swap out the pressure control solenoid, and run it in your swap.
 
I'm trying to get my head around this. Say the transfer case is in double low (5-1) and the shift tables say to shift at 20 mph. With only a sensor in the rear of the trans won't it shift super early, like 4mph (20/5)? What did the 1991 OEM TCM use the transfer case speed signal for? Thanks for your help.
 
Isn't the tow/haul button just a momentary on? It would have to be on / off for TC lockup. The TC lock up mod requires constant ground not a momentary.

Meaning it would only lock up the converter while you hold the button and the instant you let go the TC will unlock.

I could be wrong, but I'm 99% sure.
 
Will L. said:
Isn't the tow/haul button just a momentary on? It would have to be on / off for TC lockup. The TC lock up mod requires constant ground not a momentary.

Meaning it would only lock up the converter while you hold the button and the instant you let go the TC will unlock.

I could be wrong, but I'm 99% sure.
Click to expand...

I don't know about the factory controllers, but with the Optishift, it's a second program ("B") which you can set up however you want. Tow/haul, performance, economy, etc. There's a wire on the controller that you connect to a regular switch. Ground that wire via the switch and the TCM uses Program B until you switch back.

The tap shifting is 3 completely different wires. 1 for up shifts, 1 for down shifts, and 1 for auto/manual mode. They are all ground type circuits also.
 
4L80e said:
I'm trying to get my head around this. Say the transfer case is in double low (5-1) and the shift tables say to shift at 20 mph. With only a sensor in the rear of the trans won't it shift super early, like 4mph (20/5)? What did the 1991 OEM TCM use the transfer case speed signal for? Thanks for your help.
Click to expand...
The TCM will shift at a preset output shaft speed. So if your in double low of say 5:1 doing 4 MPH, the output shaft of the trans will be turning 5 times fast at 20MPH. Thats the beauty of the 91-93 4X4 trans as it has it's own output shaft speed sensor in it. So the TCm will shift at teh same speed regardless of what low range you are in. People who have used the ALLISON with double under drives put the output speed sensor i nthe tail section of the trans for this very reason. Then it doesn't care wether it is in direct, low, or crawler, it shifts at the same transmission output shaft speed regardless as that is teh ONLY speed it reads since it reads it BEFORE any of the gear reductions of the transfer case or crawler box.
 
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