99 Tahoe OBS NP246 to 241C Conversion gone awry....

midgainc

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I registered today on the forum mainly to hear some replies on what went wrong.

I purchased the Tahoe in Feb 2020 and it looked like a granny grocery getter and was fairly clean. I immediately put a Rough Country 4" lift on it, removed the running boards, and put some MT wheels and Toyo tires. Since then, I have put a new duel exhaust with turn outs behind the rear tires, flowmaster 40's, welded on rock sliders, and just this week, a new rubber floor mat to replace the worn out, stained and nasty carpet. Along the way, I have grown to not like the push button 4x4 activation. I set out to replace with a 241C that I had lying around the shop. I dropped the front diff and resealed and replaced drive bearings. I had a friend swap the t cases and install new u joints in both driveshafts. I finished the mechanical install, and have been working on the wiring changes so that the floor 4x4 lights would work, and the front diff actuator would work. I had the shift linkage working and the speedometer working. I HAD NOT hooked up the front diff actuator.

This week when I picked up the Tahoe from the upholstery shop, the guy said "hey you might want to make sure it is not in 4WD, I had to move the shifter a few times." I thought I had it in 2WD, and took off. 6 miles in, I heard a thump and then a slam and a few seconds later the engine quit.

Apparently, front driveshaft engaged or something to cause front driveline to resist turning from Tcase. The front tcase output shaft ear sheared off, and the driveline wobbled around under the driver seat grabbing whatver it could. End result: 2 miles of wiring wrapped around DS, hole busted in side of Tcase, shifter for tcase left in the road, trans shifter cable end left in road, bottom side of cab beat to crap, wiring going up front grabbed and broke off distributor cap and bent some of the brackets that keep the wiring organized and secured. Needless to say, I have a mess.

All interior wiring appears to be in tack. Starter wiring appears to be in tack, headlight wiring appears to be in tack. All transmission wiring appears to be completely gone. All tcase wiring is gone. I am not sure about fuel pump wiring.

Today, I unhooked about 90% of the engine bay wiring harnes, removed driveline, and removed all skidplates, etc. Next, I am planning on removing the rear driveline, t-case, and wiring harness, and further investigate the damage. I am also looking for an engineless 99 donor vehicle that will have transmission and engine bay wiring. I have a 99 4 door parts Tahoe that is a 2WD, which is complete. Can I use any wiring off of it?

Do you have any suggestions?
 

midgainc

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I will continue this monologue. I purchased a 1999 Yukon that was barely running. It was 100% and unmolested. Me and a college kid removed the engine and transmission harness in 2 days time. All in all, it was not too terribly difficult. We just have skinned nuckles and a lot of grease to clean off. I believe that the wiring harness off of a 2WD would have worked. There appears to be a complete harness that plugs in near the fuse box that goes to the t case and to the front differential. Looking back, I probably could have taken the 2WD harness, installed a posi-lock, and reinstalled another 241C, and used the speed sensor connection for the 2 wd to get rolling again. There will be a need to send a ground signal to the ECM for 4 lo gear changing, but, that would probably be the only custom wiring to complete. I now have 2 extra 1999 vortec 350's in the stable for future rebuilds. Also, have the two 4L60E's available for a future turbo 350 conversion. Once I get a new distributor, and get the old girl running again, I will the address the mechanical issues, like why the front diff locked up when the electronics were not even connected, and why the t-case grenaded and sheared and ear off of the yoke. I have another 241C with the companion flange front output. I am going to see if I can get the correct output shaft for the driveline that I have, and go ahead a re-seal the entire case, while I am at it. One thing is for sure..... I will test drive in 2 WD until I am certain everything is right about the entire drive system.
 

Doubeleive

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I don't have any information for you but when you get into doing custom stuff on a older rig it's hard to find information and not many people attempt such things but with luck the right person will see your post and chime in may be just a matter of time, keep posting on it every couple days and this will keep your post from getting buried in the thousands of other post's. good luck and it may be even more helpful to post up some pictures of what you are doing so we can have a eyeball view and maybe offer some suggestions/
 

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