79 k10 Newbie issues. Stressed out Mom, please help!

[Julie79k-10]

Apologies, Super long QUESTION! I just bought a 79 Chevy k10 np203 short wide 350/th350. It initially had the rear drive shaft out. The guy I bought it from supplied replacement, we installed it. Truck won't drive in any gear. If given lots of gas it will some what crawl forward, when it wants to. (doesn't happen everytime) watching, while in miserable crawl mode, The rear drive shaft barely turns and no movement in the front in any gear, hubs locked or unlocked. This is pretty much my final confusion before it goes to the shop. Any advice would be greatly appreciated as I bought it for son's 1st project. Troubleshooting so far- checked trany, fluid/filter changed. Trany vacuum line/modulator changed. Hubs lock/ unlock fine. Shifter and linkage complete disassemble, cleaned/oiled/adjusted in neutral position. T-case oil changed. Trans column gear checked for play, seems to be ok. I did a battery system restart, also steps for transmission reboot, idk if it works on later models but did anyways. No idea if t-case is converted. Have tried different gear potions just with no luck. That's it so far, I'm curious about driveshaft issues or maybe governor stuck shut or chewed up, I can't get the housing off, might try banging it lose? also vac, modulator screw not adjusted right? Shifter sucks, not in right gears, a twin stick conversion possibly? Torque converter, shot transmission, broke t-case? Idk maybe we just have no idea how to operate it, definitely first time 4x4 full time 203. Please help!!! Thanks

 

[AyWoSch Motors]

Apologies, Super long QUESTION! I just bought a 79 Chevy k10 np203 short wide 350/th350. It initially had the rear drive shaft out. The guy I bought it from supplied replacement, we installed it. Truck won't drive in any gear. If given lots of gas it will some what crawl forward, when it wants to. (doesn't happen everytime) watching, while in miserable crawl mode, The rear drive shaft barely turns and no movement in the front in any gear, hubs locked or unlocked. This is pretty much my final confusion before it goes to the shop. Any advice would be greatly appreciated as I bought it for son's 1st project. Troubleshooting so far- checked trany, fluid/filter changed. Trany vacuum line/modulator changed. Hubs lock/ unlock fine. Shifter and linkage complete disassemble, cleaned/oiled/adjusted in neutral position. T-case oil changed. Trans column gear checked for play, seems to be ok. I did a battery system restart, also steps for transmission reboot, idk if it works on later models but did anyways. No idea if t-case is converted. Have tried different gear potions just with no luck. That's it so far, I'm curious about driveshaft issues or maybe governor stuck shut or chewed up, I can't get the housing off, might try banging it lose? also vac, modulator screw not adjusted right? Shifter sucks, not in right gears, a twin stick conversion possibly? Torque converter, shot transmission, broke t-case? Idk maybe we just have no idea how to operate it, definitely first time 4x4 full time 203. Please help!!! Thanks

Well a 203 is chain driven instead of gear drive, so maybe the chain broke, and is jamming everything up, and is just loading the converter.

This may sound very silly and obvious, but could the emergency brake be stuck on or a brake shoe welded itself to the drum? Does it roll at all when pushed or towed? That would eliminate it being a brake being stuck, or one or both of the diffs seized.

A very similar thing happened to my best friend's unlce's truck. After putting the transfer case back in, it wouldnt move at all.
I don't know what they did to fix it, I'll have to ask him.

Also, you could try removing the front drive shaft, and try it again. I think that's what my friend did. Not sure if it helped him or not.

 

[77 K20]

Did this truck supposedly run and drive before the rear driveshaft was removed?

So far I'd think the transmission is slipping/transmission is bad. Especially how sometimes it would move a bit with lots of gas. Was the trans fluid dark/burned when it was changed?

The 203 transfer case is a chain drive- but when the chain breaks then you lose 4wd, but rear wheel drive still works. I just had that happen to me last year. I'd doubt the chain broke.

If the 203 is a full time (no part time conversion kit installed) and you try to move it with the front hubs unlocked there is typically a bad grinding noise coming from the transfer case. So I think that can be ruled out.

The trans vacuum modulator thing just controls when it shifts. Mine has come unplugged in the past and it would still drive. It just didn't want to shift at a "normal" lower RPM. So it's not that.

No electric trans reboot/reset on these old trucks. Zero electronics in them.

Did you try moving the truck with the 203 lever in all the different positions? The two positions the way forward is low range (doesn't matter if the 203 is converted) the middle one in neutral, and both positions back towards the seat will be high range. Could be the transfer case is in neutral, but doubt it...


Know anything else about the history of the truck? Why was the driveshaft out to begin with? A history might shed some light and provide some clues.

 

[ali_c20]

Welcome from Austria.
Maybe the rear driveshaft was removed for towing by the po, so the truck was in a no driving condition when you bought it.
Remove both driveshafts and look if the output shafts are rotating on the t case when the truck is in gear in all possible shift positions on the transfer case.
Try the same procedure with reverse and first/second/drive.
If the output shafts of the tcase move the problem is lower in the drivtrain, if not you have to find out if it's the tcase or the transmission or the torque converter.
Good luck.

 

[Strick]

Good morning. The NP203 is chain driven with a gear range box up front. In the rear of the case is a planetary set up. I have had some of these with the similar symptom. The chains get worn and it is very difficult to keep them engaged in any position, especially 4LO. The shifter is external on these and can be adjusted but probably to no avail. I've experienced some of these cases that would not pull if there were aftermarket hubs on the front axle; if there were then they'd need to be in the "lock" position for the case to operate.
I have also installed the part-time kit from Milemarker in the rear of the case that modifies the planetary setup. This alleviated the last issue that I had with a NP203 not pulling. The last one was truly the last one as I have replaced all the NP203 cases with the NP205 gear drive cases in my trucks. You may look into doing this conversion as well, you will be very pleased with the operation and results.
Good luck and welcome to the site.

Strickland

 

[WFO]

Welcome from the Texas Panhandle, Ma'am.
Sounds like the transmission is gone to me too.

 

[mtbadbob]

Welcome to the site! I agree with 77 K20, sounds like a bad tranny to me. TH350's are not my fav, I've seen many go bad on 1/2 ton chassis when put to work, most could be related to people not knowing how to rebuild them.

 

[Babs]

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[dvdswan]

welcome to the site.

 

[bthomas]

Front driveshaft installed?

 

[Doppleganger]

Sounds like a pre-existing condition before you got it. I agree with the rest....bad trans.

And btw.....

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[Bextreme04]

You need to do some fault isolation. Does the engine free rev and doesn't move, or does it seem loaded up and binding? Get it up on jack stands and pull the rear driveshaft. See if you can turn the rear tires by hand freely. See if you can turn the front wheels freely by hand. Start it up and put it in gear. Does the yoke spin on the front/rear outputs from the T-case? Change the T-case shift position, check the outputs again. If the engine sounds loaded up and the outputs on the t-case don't spin in any shifter position(except N), then you have a T-case issue. If the engine sounds unloaded even when shifted into gear, you have a trans or T-case issue. If it sounds loaded up UNTIL you remove the driveshaft and you can't spin tires by hand, you have a stuck brake or problem in the diff.

 

[dbush]

Welcome, from Wyoming!

 

[Julie79k-10]

Thanks for all the info guys!! We are definitely going to try a few things this weekend. Also contacted a transmission repair shop last night and we're out to weeks.

 

[Julie79k-10]

Thanks for all the welcomes!! Plan on pulling the drive shafts first thing tomorrow, I'll post how it goes after... Hopefully we see movement!! If it turns out to be the t-case, any suggestions where we could get a 205 for a decent price or what's some options on the twins shifter conversion? I keep reading, that pretty much everyone switches. According to the vins and and numbers on the Engine,trans and other things I've found on it, its all original. Pretty cool I'd like to keep it that way if we can.. Thanks again!!