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79 Jimmy 4x4 help

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MavsJimmy

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Hi all, im new to this site and new to 4x4's. Have a 79 Jimmy that I am fixing up and haven't driven it much cause I'm confused about the full time 4x4. It has a 350 engine and a np203 (not converted to part time as far as i know). My question is where/how should i have it for normal street driving? (gear on N, Hi loc, Hi, Low loc, or Low). It also has locking hubs which are unlocked.
when i got it it was left on N with hubs unlocked but im not sure if thats how I should be driving it.
Thanks for the help
 
Shouldn't move if it's in Neutral. If it has been converted, Hi is where you want it for street driving.
 
If its not converted, and you are daily driving it , with the wheel hubs locked in, you can drive it in " HI "
If you have the wheel hubs unlocked, you will need to have it in " HILOC "

If its converted and you are daily driving it, you can have it in " 2HI or 4HI "
and have the wheel hubs unlocked all the time till you need 4WD.
 
If it has manual hubs and a 203, my guess is that it has a part-time conversion kit in it. IIRC, all auto/203 K5s came with "automatic" hubs; they were in 4WD all the time. The other option is that the PO installed just the hubs instead of a full part-time kit.

If there is a kit in the transfer case, then your shift pattern (seated in the truck, with the shift lever all the way forward), which was...

Low Lock
Low
Neutral
High (normal driving)
High Lock

would now be...

4x4 Low (with hubs locked)
2x4 Low
Neutral
2x4 High (normal driving, with hubs unlocked)
4x4 High (with hubs locked)

Either way, with kit or without, if the TC is in neutral, the truck shouldn't move under power.

Just FYI, you might find this interesting: 1979 Blazer Sales Brochure
 
Thanks for all the help. You were right it does not move when in N. My mistake, it was on H. Now as far as the hubs go, I am pretty sure its not converted because I can shift into all gears (5 with N). Here is a helpful GMC Jimmy link tocmp.com
 
MavsJimmy said:
Thanks for all the help. You were right it does not move when in N. My mistake, it was on H. Now as far as the hubs go, I am pretty sure its not converted because I can shift into all gears (5 with N).
Click to expand...

If you have an automatic transmission, NP203 and manual hubs, something was swapped out. From the factory, '79s with that combo (auto/203) did not come with manual hubs as they were full-time 4WD. It's possible the previous owner installed the manual hubs with a part-time kit, or perhaps he just installed the hubs alone so he could unlock the front wheels without the hassle of taking the t-case apart.

You will still be able to shift into all modes regardless of what's in the case - the only thing that will change is what happens with the driveline if there's a part-time kit installed.

Until you can put the K5 up on jackstands and test it, I would unlock the hubs and leave the t-case in the High position (one position towards the driver from Neutral).
 
Thanks Meanboyjr
Is there any quick and easy way to figure out if I have the np203 part time kit or if previous owner did only put in manual hubs without the kit?
 
photo.jpg
 
MavsJimmy said:
Thanks Meanboyjr
Is there any quick and easy way to figure out if I have the np203 part time kit or if previous owner did only put in manual hubs without the kit?
Click to expand...

Not exactly quick and easy, but relatively painless...

You will need to put the truck up on jackstands with all 4 wheels completely off the ground. For safety's sake, don't do this with two floor jacks and some firewood. Use jackstands on relatively level ground. Don't ask how I know.

Also, it helps if you have someone with you, so one person can stay in the truck and the other can watch the wheels.

Lock the front hubs. Put the t-case in either High or Low (btw, I think these are marked HI and LO on the shifter plate) - either one notch up or one notch down from neutral. Start the truck and let it settle into a low idle. Apply the brakes and put the transmission in Drive. Slowly release the brakes.

If there is a part time kit in the case, the front wheels will not rotate, as the transfer case should be in either 2 Low or 2 High. If the hubs are locked and the wheels turn, there is no part-time kit in the case.

Be sure to lock the hubs. If you do not lock the hubs when you test this, the front driveshaft will still be able to turn, but the wheels will not follow. If you can't get a good look at the front driveshaft, you can be fooled into thinking there is a part-time kit in the case when there isn't.

One other thing. If you do have a part-time kit, it's a good thing to lock the hubs and drive around in 4WD once a week or so for a few dozen miles. This allows the tail shaft bearings to get proper lubrication.

HTH.

BTW, sweet looking rig.
 
Your transfer has been converted to part time. If it were not converted and your hubs are unlocked the truck will not roll in any gear position. The 203 has spider gears like a rear end,and the power is transfered to the shaft with least resinstance. The conversion kit locks up the spider gears so you can lock/unlock the front shaft.
 
Even without PT kits a lot of people will put manual hubs on it anyways and just run them locked all the time (like I did)

Manual hubs were cheaper, more easily found from reputable brands, and have about half the working parts, so they are much more trail friendly. That is why I went manual on my full time truck (it is now a part time 205 though)
 
77 casa grande said:
Your transfer has been converted to part time. If it were not converted and your hubs are unlocked the truck will not roll in any gear position. The 203 has spider gears like a rear end,and the power is transfered to the shaft with least resinstance. The conversion kit locks up the spider gears so you can lock/unlock the front shaft.
Click to expand...


Not true. The NP203 will run with unlocked hubs (or missing front driveshaft) if it is in H-Loc or L-Loc.

I didn't think about it before, but you bring up another way to test the t-case to see if a part time kit was installed...and this one doesn't involve jackstands. If you unlock the hubs and try to drive it in High or Low, it will not move if it has not been converted. If the truck drives with unlocked hubs in High or Low, then it is converted.
 
Ok so I tested it out tonight and with the hubs unlocked the truck will drive in H, L, L loc, and H loc. The "4x4 Loc" dash light turns on when in Hi loc only (dont know if thats what it should be doing).
 
MavsJimmy said:
Ok so I tested it out tonight and with the hubs unlocked the truck will drive in H, L, L loc, and H loc. The "4x4 Loc" dash light turns on when in Hi loc only (dont know if thats what it should be doing).
Click to expand...

Sounds to me like a part-time kit has been installed.

Don't forget to lock the front hubs and drive it around in 4WD for a few miles out of every 150 or so.
 
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