A few years ago I bought a 75 GMC Jimmy for 500 bucks and sank 300 into for
misc parts inlcuding floor pans that I welded in. Everything is rusted on
it and pretty much everything needs replaced. The one thing I really like
about this one is that it's full convirtable.
Recently I got a 85 GMC Jimmy Diesel with the 6.2L. The price was free but
the Motor needs re-built. The body is straight, there is no rust. It needs
a new air compressor for the A/C and batteries (since the owner wanted those
when he gave it to me.)
I can fix up the 85 and dump the 75.
I can fix up the 75 by using the 85 for parts.
Money wise fixing up the 85 makes the most sence. I like the idea of
re-building the NP 203 transfer case from the 75 and putting it on the 85.
After having seen all the full electronic innovations on 4x4 I've decided
that the 203 was ahead of it's time.
The full convertible is a beautiful thing. Bastard year, that - a square
body with the full 'vert. '69-'73.... ah the first gen beauty. *big starry
How sure are you that there is no rust? I just find it hard to believe you
live somewhere where you have a rotted out 75 you fixed up and it roted out
agian in a few years, and you found this jem for free? Just HOW rust free is
Yes it do. I would take the top portion of the 1975' wind sheild and graft
it onto the 1985. Hopefully the doors on the 1975 are OK enough to throw on
the 1985? I believe you can chop off the top frame of the door and get
satisfactory results as well. Then box off the top of the rear pillars where
you cut off the roof and you have a convertible with the nice striaght body
line on the front fender and those goofy over-under square headlights.
Better than that weirdo straight-down-backwards body line on the '75 though!
Why? Total bastard of a transfer case!
1: Heavy: Basically the same cast iron case as the venerable NP205 (they are
direct swaps for each other)
2: Chain Drive: The gear box portion is quite stout, but the front drive
shaft is run by a chain where as the NP205 justifies it's weight by
consisting entirely of massive helical cut gears.
3: Full time 4WD: Wastes gas, tires, and power to the rears. Allows the
truck to get stuck in a situation where 1 wheel is spinning just like it's a
2x4. This t-case acts as a differential allowing the front and rear drive
shafts to spin at different speeds. No true t-case does this, they are
locked and turn at the same speed.
3A: Part time 4WD kits exist: Whopty frikken do, every other T-case already
is! So your going to spend a hundred bucks or whatever on an inferior t-case
to bastardize it, and cause it to not properly oil it's self? Uhm, why?
You can go too www.offroaddesign.com and using your NP203 attach it to an
NP205 and create a "doubler". *grin* - only really usefull if you have at
least 1 locker. And like to get it dirty.
Eh... ya... that's about it. Paper weight?
It's not that hard to put spider gears in a T-case. Does "electronic
innovations" mean "made for lazy yupies" or "guaranteed to break when used"?
Get a real T-case, the only thing that makes them fail for the *most* part
is abuse, like drive line wind-up - or they eventually need to be rebuilt.
No clutches, computers, encoders, motors, solenoids, aliens, etc. Just
NP205/NP203/Doubler: Probably over the top in your instance. But you can
sure get allot of options with this bastard. Front wheel drive only, rear
wheel drive only, four wheel drive, independent ratios front/rear (hi front,
low rear) even!
NP205: You don't have one, doesn't sound like you really (ab)use this truck,
so why find one?
NP203: You seem to like it. Is it a slip-yoke version (retarded design) or
is it a fixed yoke version? Even if it's a slip yoke, if you like it throw
it in the '85. It doesn't have as low a range as the 85's t-case though.
NP208: T-case in your 1985. Another bastard year. Lightweight, aluminum,
chain driven, slip yoke, and nothing you can do to it to change it.
NP241: Basically like the NP208- lightweight, aluminum, chain driven, slip
yoke - but you can put in a SYE (slip yoke eliminator) kit and turn it into
a fixed yoke. Don't have one, why find one?
Fixed yokes are good for both road and offroad use. If you grenade your rear
diff (burn outs or rock crawling), you can drop the drive shaft and not have
to tape a coke bottle over the end of the t-case to keep fluids inside -
then return in front wheel drive. It also puts the slip joint in the DS
where it belongs, so there is no/little lateral force on the joint that can
cause it to bind. This binding can potentially snap a slip-yoke type
I say the NP208 is already in the truck, and I don't know what it would take
to adapt the NP203 to the TH700R4 that is most likely behind that 6.2 vs.
the TH350 that is likely behind the 5.7 that's probably in the '75.... hmmm
I think if the '85 is really cherry converting it to full 'vert would be
sick - and you wouldn't need to do anything to the AC compressor!
Don't forget the banks super charger for that 6.2!
The 85 Being Cherry is a bit much, but it's nice. The 75 Came with plenty
of rust and served in areas with a brutal winter. The 85 was probably
I forgot about the slip yoke. One more thing to replace. I had a 1980 3/4
Ton with most of the parts I'd need to upgrade except for the trannie. HD
Axles, NP205 etc.
The NP203 does have that 'flaw' where if one wheel spins thats all she
wrote. But having been on very bad roads with a one wheel drive truck, and
a 4x4 with posi the 1x1 was much more stable to drive on ice until I put the
4x4 into 4 wheel drive. Where I was going with the comparison was that
modern electronic system tout a bunch of features that the NP 203 had. I'll
have to look at it and see if it's the bastard version. It probably is. I
should of got a Dana 44 on the 75 but its a 10 bolt instead I suspect
everything else will match the lesser version. The 203 does have a low
range and drving it in snow the little I was able before it quit running I
was impressed that it got around as well as it did in non lock mode. I
fully expected to hit the gas and have one wheel spin immediatly.
Thanks for the input I'm going to print that out and save it.
3/4 ton will have the D44 and probably a 14BSF (semi-float) neither of
which are that great.
I agree and the NP203 does a much better job at it too. But the auto
makers are always looking for "progress".
Why? D44 and corp 10 are "almost" the same axle. The D44 could be
considered MARGINALLY stronger than the corp 10, but the parts are MUCH
more expensive. About the only thing a D44 is good for is the front
hubs so you can turn the cheap and easy to maintain corp 10 bolt into
an 8 lug axle.
Unless you plan to go OVER 35" tires (38 say) AND your a total retard
about (ab)using it, you should be able to beat the snot of out that
axle with no breakages. Examples; turn it to full lock and floor the
Other then that go D60 or go home.
All chevy's t-cases have low ranges son :-)
Low range is fairly well useless unles you have at least 1 locking
differential. Other than that it puts *too much* torque too the wheels
and breaks them free easier, where as you can finesse the power easier
in a higher gear. That's why automagic's suck, unless you modify them
you can't put it in 2nd gear to help control wheel spin in low traction
situations. But once you get 1 or two lockers (of whatever type,
welded, lock-rite, ARB, etc) then your diffy wont transfer power from
the wheels that grip to the wheels that slip, and that low range will
come into play.
That's another thing I like about part-time transfer cases. You can get
1 wheel to spin and the resulting fish tail is quite exilerating....
Or you can put it in 2lo (don't lock front hubs) and produce massive
amounts of smoke - easily. lol
No problem send me pictures when your done!! Hell, send me pictures
They are just some pepboys (i think - didn't buy them) cheapies. Peerless
force 4 A/T. They're OK in the snow, slippery in the mud, and roll pretty
nice on the highway. But they do make allot of hum for how tame the tread
is. Those are 31x10.5x16 (stock).
Got the 3" body lift in the bed, been rattlin around for a few months.
Got the new body bushings too.
Just got a bunch of rot repair parts so I can actually attach the body lift
and I think this one would ride best on a bfg a/t or mud terrain.
Now my future 79/85 hybrid.... hmmm.....
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