NP243 Won't Go Into 4Lo

Hello,

Back in 2010, I swapped out my junk 4L60E for a NV4500 in my 1999 K1500 ECSB. As I'm sure most of you know, this requires switching the input shaft on the t-case. A buddy and I did this seemingly without issue and finished up the swap. Everything seemed to work fine... except for the 4Lo.

The t-case will work in 2Hi and 4Hi, but when I go to switch it to 4Lo, it makes a noise like it's trying to shift, but just goes into 4Hi. It worked just fine before the input shaft change.

It's never really been a big deal as I've been just fine with 4Hi and granny low, but now I want to fix the thing so it works properly. I've always planned on dropping a crate motor in the truck and always said I would fix this issue when I do the motor, but I don't drive this daily and the motor project is on the back burner.

The time has officially come to pull out the NP243C and address the issue. Any ideas as to what could cause this?

Are you 100% sure that the linkage is adjusted correctly?

There is no linkage on a 243. It is the electronic shift version of the 241. Think it has to be in gear turn into neutral to go into 4 low. Maybe a search will bring it up.

b454rat said:

There is no linkage on a 243. It is the electronic shift version of the 241. Think it has to be in gear turn into neutral to go into 4 low. Maybe a search will bring it up.

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I will have to explore the neutral thing. One of the things we never did was install a clutch safety switch and just ghetto rigged it temporarily. I never got around to buying one to install and kind of forgot about it. Maybe now is the time to buy and install one and see if it helps. Perhaps the PCM never gets a signal that the truck is in neutral and won't sift to 4Lo.

I did have the PCM reprogrammed though, so maybe it never even looks for the neutral signal and this isn't the problem. The t-case does actually try to shift, but can't.

b454rat said:

There is no linkage on a 243. It is the electronic shift version of the 241. Think it has to be in gear turn into neutral to go into 4 low. Maybe a search will bring it up.

Click to expand...

Yea I keep forgetting that the 241 is manual and the 243 is electric

Anyone else have any ideas?

Did you un-ghetto rig the switch? This may require a PCM reflash.

Supercharged111 said:

Did you un-ghetto rig the switch? This may require a PCM reflash.

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Not yet. I'll order that today, but I haven't been able to fine any info on if the PCM actually looks for a clutch safety switch. I know there isn't a neutral switch, so that can't be the issue. I've emailed the LT1 Swaps who did the reprogramming and asked, but haven't heard anything.

The PCM knows what gear the auto trans is in and on a manual it knows whether or not it's in neutral. The only question is whether or not the PCM blocks 4lo if it doesn't see a clutch in or neutral. I could try shifting mine in gear to verify when I get home. I've always only gone in and out of low in neutral though.

Supercharged111 said:

The PCM knows what gear the auto trans is in and on a manual it knows whether or not it's in neutral. The only question is whether or not the PCM blocks 4lo if it doesn't see a clutch in or neutral. I could try shifting mine in gear to verify when I get home. I've always only gone in and out of low in neutral though.

Click to expand...

Did you ever get around to trying this out?