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New owner, confused about case, crossmembers

D

dbozman

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'74 K5 Cheyenne with a swapped-in 454. Has T350 auto and what I've found out now to be an NP203. Truck has 4-inch RC lift and the front has been converted to locking hubs. Little disappointed to find out about the 203, but this will be a mostly street rig on 35s and open diffs.

I'm getting a lot of gear oil blowback somewhere beneath the truck and am trying to track it down. Both diffs are drained and I'm rebuilding the vents. The case does not appear to have a vent tube. The 203 runs gear oil, correct?

Next, there are two crossmembers connected by a skid plate. Is this normal? The rear crossmember doesn't appear to actually support anything, other than the rear of the skid. And both crossmembers have been dropped, assuming to compensate for angles from the lift. Is this necessary? I'm used to Jeeps and Toys and don't have a clear understanding of how this system works.

I'll attach a photo of what I'm talking about:

For street use, will the 203 be acceptable?

cross.jpg
 
dbozman said:
'74 K5 Cheyenne with a swapped-in 454. Has T350 auto and what I've found out now to be an NP203. Truck has 4-inch RC lift and the front has been converted to locking hubs. Little disappointed to find out about the 203, but this will be a mostly street rig on 35s and open diffs.

I'm getting a lot of gear oil blowback somewhere beneath the truck and am trying to track it down. Both diffs are drained and I'm rebuilding the vents. The case does not appear to have a vent tube. The 203 runs gear oil, correct?

Next, there are two crossmembers connected by a skid plate. Is this normal? The rear crossmember doesn't appear to actually support anything, other than the rear of the skid. And both crossmembers have been dropped, assuming to compensate for angles from the lift. Is this necessary? I'm used to Jeeps and Toys and don't have a clear understanding of how this system works.

I'll attach a photo of what I'm talking about:

For street use, will the 203 be acceptable?

cross.jpg
Click to expand...


TH350/203=not good for street use only:mad: . I would think of a using the 700r4 for the tranny and then the 203w/part time kit would probably be OK, but I'm sure others can tell u more.
 
Clarify. Why not good for street use (not talking daily driver here)? Lack of OD I'm assuming.
d
 
dbozman said:
Clarify. Why not good for street use (not talking daily driver here)? Lack of OD I'm assuming.
d
Click to expand...
OD depends on you. If you do a lot of highway driving, then it would benefit more. If you do city driving, I'd leave the 350 in there.

The 203 can be a good thing and bad. The good, if its still full-time status and hasn't been converted, can give you the benefits of all wheel drive. But its also harder on parts especially the front end. It also robs gas economy, too. If it has been converted to part-time, its no different than any other t-case but still is heavier and bulkier than all the others out there. Chains stretch and cause slack in the rotation assembly. Just several little things add up with the 203 that makes them less than desirable.
If it were me, and the case is working fine, I'd leave it alone and focus on other areas that may need more attention than the case.
 
a 350/203 was good enough for street use 30 years ago why wouldn't it be good now. there are definately better choices now a days but that combo is fine. to save some gas get the part-time kit for the 203 and hubs for the front axle. ive seen crossmembers like that before so im sure its factory.
 
As I said, the front has hubs. The case seems to work fine.

Questions:

-- Does it take gear oil?

-- Is the current drop on the crossmember necessary?

-- Where's the vent tube on the case?
 
Yes, that's factory setup, two x-members, one for the tranny/t-case foot (adapter), one for the skid only.

http://www.slosh.com/ck5/tankie-stock-crossmembers-1.JPG

The spacers are not factory -- the fact that they're pipe should be a giveaway =)) -- and look suspiciously like they're tilting the t-case down, so yep, for angles.

Which is all fine.

When I did my Doubler, I ended up with three x-members, one for the foot, one for the Doubler, and one for the back end of the skid plates. The middle one has an odd angle for the Doubler ... as I don't have a tubing bender, I didn't fab a custom one and made my extra factory one do :)

http://www.slosh.com/ck5/xmembers-mounted-1.JPG


As for the drivetrain, a '203 can work just fine ... the chain is the weak point. I'd be more worried about a TH350 behind a big block.

203's run gear oil of some variety; I think GM told us 80wish Back In The Day, but they're down to 30w now.

There should be a pipe elbow or something up top to act as a breather... I forget, as my '203 was torn down to just the range box and the PTO cover now has the breather.

-- A
 
dbozman said:
As I said, the front has hubs. The case seems to work fine.

Questions:

-- Does it take gear oil?

-- Is the current drop on the crossmember necessary?

-- Where's the vent tube on the case?
Click to expand...

For #1 and 2, see above ... for #3:

http://www.slosh.com/ck5/np203-breather.JPG

it's on top, due north of the rear axle u-joint, and is serious clogged in this pic =))

-- A
 
Looking at the way that the second cross member is attached I would have to say that it is certainly not a stock installation. It looks like someones attempt to create a beafier and longer skid plate which is not a bad idea but in this case looks poorly executed. If you are using it as a daily driver I would ditch the second member to clean up the underside and also loose the uneeded weight. I cant help you with the vent tube question but for lubrication I know people do use gear oil in their 203's but I believe that ATF was also put in to them in the 80's. The belief being that the lighter weight of atf would increase mileage. Of course with a 454 and a th350 the mpg on this rig might more closely be measured in GPM!
 
454k30 said:
Looking at the way that the second cross member is attached I would have to say that it is certainly not a stock installation. It looks like someones attempt to create a beafier and longer skid plate which is not a bad idea but in this case looks poorly executed. If you are using it as a daily driver I would ditch the second member to clean up the underside and also loose the uneeded weight. I cant help you with the vent tube question but for lubrication I know people do use gear oil in their 203's but I believe that ATF was also put in to them in the 80's. The belief being that the lighter weight of atf would increase mileage. Of course with a 454 and a th350 the mpg on this rig might more closely be measured in GPM!
Click to expand...

That's the stock skid plate ... there are at least two types, one longer than the other, and that looks to be the long one.

But yeah, pipe? :rolleyes: At least cut the threads off :haha:

-- A
 
NP 203 uses MOTOR oil!..

A stock NP203 uses 10W-30 or 10W-40 MOTOR OIL !.
According to GM,many got damaged when owners put 90W gear oil in them assuming that is what they take!..supposedly the gear oil was too heavy and couldn't lubricate some tight fitting parts in the case,and they wore out prematurely..however,I have seen many NP203's that had 90W gear lube in them,and had zero trouble too..I'd think the "EP" gear lube would be more protective than plain motor oil,but I guess GM disagrees..I tend to stick with what the factory reccomends..(until its out of warranty at least!)..:rolleyes:

Im not sure about Dextron being used in the NP203,but they did use it in many other cases and manual tranny's,so I guess one would live if you used that instead..
 
diesel4me is correct. my manual says 10w-30 or 10w-40 for a 203. I actually just put some in mine about a week ago.
 
I don't see why the x-fer case needs to be dropped. My 76 has 6" of lift and it is still in the stock location. Same basic drive train 350/350/203.
 
jfaulk said:
diesel4me is correct. my manual says 10w-30 or 10w-40 for a 203.
Click to expand...
I concur. Everything I've ever torn apart had the same.

The crossmembers/skidplate are factory items. The pipes serving use as a drop is not.

There are two different skidplates for the dual crossmember types. As said above, one is longer than the other. The longer one uses 8 bolts to fasten to the crossmembers and the shorter one uses 4. I have these plates in my shed and can snap some pics if anyones interested.
 
Worked a bit today. Dropped the rear crossmember and the skid, and drained the case. Most definitely had gear oil in it, but it was pink. Being a talented investigator, I figure that means I've got some fluid exchange between the t-case and T-350.

This is a new truck for me. I noticed a substantial amount of dried fluid on the underside of the tub above the case. There's what I assume to be a vent fitting on the tailcone, but no vent line. Figuring the fluid transfer is causing an overfill situation in the case, which is venting under pressure.

Correct diagnosis? I really didn't want to drop the case, but I will if necessary to prevent/cure the situation. Would a proper vent line solve the problem?

Thoughts?
 
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