Mike, I am in a serious bind, and need to call upon your expertise to hopefully figure this out. I've got a 2000 model ZR2 Blazer, that came equipped from the factory with the 4L60 automatic transmission, and the Autotrac transfer case. Wanting a manual means of engaging the transfer case, I made the decision to install a cable shifted NP-231, that originally came from a 1995 GMC Jimmy. That vehicle had the 4L60 as well.

Installing the transfer case floor shifter assembly, shifter cable & 231 transfer case took some work, but it is all now installed in its' factory location, as it was on the 1995 model. The transfer case functions perfectly.

The problem that I am having is that the transmission will NOT shift when I select 4LO. It DOES shift perfectly fine when I select 2HI or 4HI. The speedometer DOES work in all three ranges, 2HI, 4HI & 4LO.

Here is what I have done so far. My factory Autotrac transfer case has two sensors in the tail shaft, and one additional sensor located in the housing just above the front output shaft. I do not know what each of these sensors exact function is, but I do know that one of them is the VSS. It also has two electrical plugs that snap into the Encoder Motor. The 1995 NP-231 has one VSS sensor on the drivers side of the tail shaft. Knowing that the VSS in the 231 would need to be wired in to my factory wiring harness for the transmission & speedometer to work correctly, I retained the original electrical plug that was connected to the VSS on the 231, from the 1995 GMC Jimmy. The wires colors are purple with a white stripe, and lime green with a white stripe. I found that the wires in my factory harness that ran to the sensor that is located on the drivers side of the Autotrac tail shaft, were an exact color match to the ones that fit the 231's VSS plug. So, I simply spliced them together, and plugged it in. I believe that this is what is allowing the transmission to shift at all in 2HI & 4HI.

On my first test drive, I left the other two Autotrac sensors disconnected from anything. The transmission shifted perfect in 2HI & 4HI, but not 4LO. A friend that runs an off-road shop told me that the other two sensors from the Autotrac would need to be plugged in to their original electrical plugs, to "complete the circuit", for the transmission to shift correctly. So, I removed those same two sensors from the Autotrac, and plugged them back into their exact same wiring plugs on my Blazer. I took it for a test drive.....and still, nothing changed. He explained that the two electrical plugs that run to the encoder motor would NOT need to be plugged into it, because it was on a totally separate circuit from the transmission. So, I left them unplugged from anything.

I have also unplugged the factory 4 button 4WD switch that was on my dash, and just popped a "blank" into its' spot, that came from a 2000 2WD pickup.

I do not know where to go from here, and am literally at my wits end after finally completing this much anticipated conversion......just to find that I cannot get the tranny to shift in 4LO. With our National ZR2 off-road meet in Hot Springs just a few days away, I am in a serious bind to get this figured out very quickly, or I may not be able to attend this event that we have been planning for almost a year now. If you can help with any advice, I sure would appreciate it! Thank you in advance!

Jeremy what do you mean you "can't get the transmission to shift" when in 4LO...will it not move from park, or are you saying it will stay in 3rd regardless of RPM/speed when in D?

If it's the latter, will it stay in 3 if you leave it in D, stay in 2 if you put it in 2, will it stay in 1 if you shift it to 1?

If that's the case, I'd say you leave it and have a selectable 4LO transmission sequence.

If not (and I guess either way now), I'd call over to Advance Adapters. I know Dave had a similar but different issue with his Atlas when he installed it, and they helped him out.

What do those other 2 sensors look like on the Auto-Trac? May have to swap parts from the Auto-Trac into the 231 and tap the housing so all the sensors can remain hooked up, but I'd have to see it to know more.

Good luck man!

Jeremy, if you really want some help from Mike, I suggest calling him at the shop - I think he's there after 4:00. Whether he gets online or not is sketchy, depending on what is going on. I know there are times he doesn't see this site for weeks at a time.

Also Jeremy, as a matter of "trying stuff until something works", plug in your dash switch again and try all the combinations underneath.

The problem is that when in drive or 3rd the transmission will not shift out of first and into second or third. You can manually shift the tranny into second, but it will not do this on it's own. I've run into the same problem too.

Jeremy, my Atlas did the same thing when I first put it in. Ended up being the Reluctor (sp) sensor. After I put that in it started shifting from 1st to 2nd like it's supposed to. I still don't have 3rd or Drive in low. Advance adapters say it's something computer related?



Dw

With the transmission selector in 1st gear, 3rd gear or 4th gear, it remains locked in first gear, when it is in 4LO. If you run the RPM's up until about 4200 RPM, and hold it there...the transmission will finally slam in 2nd gear. If you select 2nd gear , the transmission will remain in 2nd gear.

The other weird thing is that when it is in 1st gear/4LO, when you let off the gas after you are moving, the transmission feels like it goes into neutral, rather than feeling like it is still in 1st gear LO range. If you start in 2ng gear, it does not do this! The gear reduction does its' thing just like normal.

Anyone got a link to Mike's shop? Thanks for the input guys!

Diversified Creations

Advance Adapters (800-350-2223) does not open for another hour & 15 minutes! Shiot.

Dave, what do you mean, "Reluctor Sensor"? I've heard of a reluctor ring, but not a reluctor sensor. I know that it has something to do with the Vehicle Speed Sensor. What exactly did you change on the Atlas, to make it begin working? Did you just swap out a sensor of some sort? How did you install it?

EDIT: Is it this $241.50 4L60E Trans Reluctor Kit from Advance Adapters? It has no product description...

Here is some interesting info on the subject: CLICK

I talked to Advance Adapters, and after they got all their engineers together & scratched their heads on it........they basically did not have any answers!

huh. i put the NP231 into my blazer (but i didnt have the autotrac) wonder if mine has the same issues.

when in lo range i always manually select the gears anyhow...

I've never noticed anything odd driving wise after the swap in any range... I do still have the dash pushbuttons hooked up, although it's been on my list to remove them one of these days...

Jeremy, maybe I already missed it, but are you saying it won't shift automatically, or won't shift at all, regardless of where you put your shifter?

I agree with JD, I always manually shift when offroad. I don't agree with how the computer shifts it most of the time.

Yes it will shift manually.

Mine wouldn't. I wouldn't blow off the trip if it'll shift manually, jmo.



Dw

then ride out!!!

I didn't like anything shifting automatically, so I'm pulling the auto once and for all.

I never did like how it would slam from 1st to 2nd when I was in LOW range, so I used to do the same as JD

Yep....I'm an idiot.

Sometimes ya get so bogged down in the little details, that you forget that you're thinking "inside" the box, rather than outside.

Before I re-wired the other two sensors back in yesterday, the transmission operated just fine in 1st gear, but just would not shift out on its' own. It just stayed in 1st gear. After we re-wired those other two sensors harnesses back in & plugged the sensors back into them, the transmission would go into a *neutral* state as soon as you let off of the gas. It also still would not shift.

After reading you guys responses in this thread a little while ago I too realized that I ALWAYS shift my transmission manually off-road, and I rarely ever actually shift into 3rd gear when in LO range. Duh! I always stay in 1st gear for control, and manually shift to 2nd when I need it.

So, I went out just a few minutes ago, removed the other two sensors from their plugs, and drove it. Lo Range, 1st gear, foot to the frickin floor. As soon as I let off the gas, that tranny nearly threw me through the windshield it slowed me down so fast! Next, I stomped on it again in 1st gear, then manually popped it up into 2nd, and laid rubber for a few feet! (front shaft is removed). So, YES....I can drive this thing exactly as I always do off-road, just as it is now! It would still be very nice for the transmission to shift as it should though, when in 4LO.

The install is fully complete. Even got the pristine 1996 floor shifter console that Brule found me, installed as well. Aluminum skids are trimmed to fit & installed. Looks like the ol Blazer got a massive "tummy-tuck"! The ol' fat belly Autotrac is gone!!!


Dave, HELL NO....I ain't missin the trip fer nuthin! Thank you guys for opening my eyes!

The transmission shift is controlled by the PCM (powertrain control module). There are 2 shift tables in the PCM, one for high range and another for low. The PCM get's the information required to control this off the Class II communication buss, and other inputs from the vehicle. One of the main inputs is the VSS signal. When is high range, the PCM looks for a specific vehicle speed before it will shift. When in low range it looks for a much lower vehicle speed. Other critical inputs include TPS (throttle position) and engine RPM.

THe PCM switches between low range and high range shift tables based on a input from the transfer case switch. When you push the low range button the PCM get's a input to change the shift table.

You should be able to plug your original encoder motor in, and the original switch. When you push the low range button the shift table should change to low range calibrations. It will think the original transfer case is there and will change the shift table. This should make it possible for you to make the "Great Off Road Adventure" next week.

I believe a switch can be wired in to eliminate the need for the original switch and encoder motor. I would need to research this some, and I don't have time right now.

By the way, this same shift table is the reason a 4 to 1 t/case is not a easy option for a S-Series. This same issue will result, because the VSS does not match the other inputs required for transmission shifting.

One way around a part of this problem is to install a reluctor ring on the output shaft of the trans, before the transfer case. Then, if you never tell the PCM to switch to low range, it will always think it is driving at normal vehicle speeds. Your speedo would read really fast in low range, but who cares. A major problem with this is early transmission failure. It is not as big a issue with stock motors, but if you make more power the trans will slip under heavy load. The PCM controls the line pressure in the trans (this is what makes the trans shift) and when in low range it raises the pressure to make the shifts faster. This is why the trans shifts so much harder in low range. If it thinks it is in high range, additional pressure will not be applied to the clutches and bands in the transmission. This will allow additional slippage, and can cause trans failure. There are ways to work around this, but none of them are real easy.

Mike, could you essentially change those shift tables with something like EFI live?

Good information!

It is possible the encoder motor could over travel, and could possible damage it. If you are not using it anyway, who cares.

It may be possible to reprogram the PCM with some of the aftermarket systems out there. But, be aware very few people ever open the shift control part of the PCM, and if you make a mistake you are screwed.

jeremy, i had the same issue when i made my 233 into a manual shift. i tried hooking the tccm and

encoder back up but that didnt work because my encoder switch was faulty to begin with. besides,

the whole reason i wanted to go manual is to get rid of all that crap. its been a while but i think i

concluded that the pcm gets the signal to change shift tables from the tccm. if this is tru then it

might just be as simple as figuring out which wire in the tccm harness caries the signal to the pcm. i

began looking over wiring diagrams to figure out which wire it was. i also tinkered around a little bit

to figure out what voltage the signal needs to be (maybe even a ground signal). after i while i

convinced myself that i was satisfied shifting manually in 4lo so i never messed with it. however i

didnt think about line pressure as mike mentioned, i only considered shifting. after seein what he

said i think im gonna go mess with it some this weekend. im hoping it will need a 12v signal or ground so i can

just wire it into a switch and be done but nothing ever seems to be that simple. i was also a little

curious about what would happen if such a switch was flipped accidentally at higher speeds. i still

have all the wiring diagrams with colored marker scribbled all over em so i should be able to figure something out. i'll let u guys

know if i discover something usefull. time to go tinker

just an update... after going over many many wiring diagrams i have found the signal wire from the tccm to the pcm. its the wire on the top right of the tccm harness. it is greywith black. i think this is the only wire used by the pcm to determine that the truck is in 4lo. the switch on the encoder tells the tccm when the t case is in 4lo, the tccm in turn signals the pcm through the wire connected to pin c1. so voltage on that wire should change the shift tables and line pressure in the tranny. im gonna go mess with it tomorow. the only problem is i cant find correct voltage. alot of the signal wires only carry like 3 or 5 volts. i no longer have a tccm so i cant tell how many volts are present on the wire when in 4lo. i will attempt to signal with 12v tomorow but in the mean time if anyone on this site sees this and wants to go out and probe the grey and black wire on the corner of the tccm harness for voltage in 4lo, i would really appreciate it!

i can't figure it out either anymore, but HIGHLY interested in the answer!

Brule, I'm going to try it, just as soon as I get a little time to tinker with the truck...

Good news guys, grounding the wire works like a charm! The tranny shifts just like it did from the factory and no longer has the "neutral" feel when coasting. very simple fix for those who have switched to a manual t case. What I found out.....

The grey/black wire carries 12v from the pcm to the tccm harness any time the key is on.

Grounding this wire at any time causes an instant change in shift points.

You do no have to stop or even be in low range, however its probably not a good idea to hit the switch while moving and probably a bad idea altogether to do it while in high range. after all, you would have to stop anyway to shift the t case so the best idea would be to only switch then...which is when it would change if it was still in factory configuration.

Removing the wire instantly changes shift points back to normal.

If the switch is flipped while in high range the tranny upshifts at like 1000 rpm and really lugs. while this can't be good at all for the tranny it probably wont break anything if accidentally flipped.

Thats really about it. Nothing very complicated at all. I shot this VIDEO in the process of messin around with the truck tonight. I dont have a fan or fan shroud on the motor right now...truck has been parked for about a week. so if you want a good laugh, keep an eye on my temp guage towards the end of the run. I was only gonna take it out for a sec so i wasnt worried...i didnt realize how hot it got till i saw the guage in the vid.

Anyway hope this helps yall!

Yet another advantage to my manual tranny.....

Excellent job on figuring this out guys.

sweet! looks like i've got 1 more electrical thing to fix in the upcoming weeks!

Any chance this would help out w/ my Atlas as well? Being I virtually have the same exact issues.


Dw

i expect it would dave!

although really i've never noticed it since i select my own gears while in 4 lo.... always good to have a fix though!

That is absolutely awesome man! Outstanding! Thank you for videotaping that too. You are the man!

Thank you Brule for showing us how to do this! I have hardly had time to pay attention since the HS trip, much less time to dedicate to messing with my TC anymore. Gotta get my fuel isue worked out first....

Same thread on TXZR2.com

Thanks Brule for posting that, I meant to last night and forgot.

No problem. I just wanted to make sure all sides were following the same information.

thats one hell of an amazing find guys. congrats!

Finally got around to doing this tonight, works awesome!!


Dw

I'll definetly have to keep that little great/black wire in mind, just because I like having my speedo read accurately, lol... At least that's how I understand it...

Thankfully I have a 5 speed, so that's about the only issue I'd have going to a manually shifted t-case (which I can do fairly easilly, apparently, since I've got the NP233... Yay 3 buttons!)

vacuum solenoid my friend!

or a posi-lok cable.

Just thought of something...

Bravada axle.

No more pesky vacuum to deal with

Now, to start hunting for a 231...

What year bravada axle should I look for (2ooo blazr2). I won't have tranny shift issues with the 231 conversion got a 5 speed and cast iron front dif

Any 98+ S-Series Bravada should be good to go...

Actually any AWD S-series should have it... I know there's a couple AWD Blazers running around...