Is this supposed to happen with a transfer case?

[Old_iron]

I am trying to get the front drive shaft to rotate freely.

Here's what I did. I jacked up the front end so both wheels are off the ground, and locked both hubs. I put the trans AND the transfer case in neutral. When I rotate one of the wheels, or try to rotate the front drive shaft, it moves a little then stops. Like its engaged in the transfer case.

It has a np205 behind a sm465, truck 4 speed manual trans.
The truck is not yet running, and I am trying to test the transfer case. As far as I know it worked before.


Am I misunderstanding how it is supposed to work? What am I missing?

[57taskforce]

Originally Posted by Old_iron

I am trying to get the front drive shaft to rotate freely.

Here's what I did. I jacked up the front end so both wheels are off the ground, and locked both hubs. I put the trans AND the transfer case in neutral. When I rotate one of the wheels, or try to rotate the front drive shaft, it moves a little then stops. Like its engaged in the transfer case.

It has a np205 behind a sm465, truck 4 speed manual trans.
The truck is not yet running, and I am trying to test the transfer case. As far as I know it worked before.


Am I misunderstanding how it is supposed to work? What am I missing?

In nuetral I believe the 205 is still locked in 4x4 correct me if I’m wrong.
*edit I was wrong!
I rebuilt my 205 last year and if I remember right All neutral does is unlock the input shaft from the rear output shaft but the front output shaft stays locked to the rear output shaft AKA 4x4 so with the rear tires still on the ground the fronts won’t turn. Put it into 2 high and your front shaft should unlock inside the case. Clear as mud???


It’s been a minute since I messed with mine sorry I got you pointed in the wrong direction.

[kwmech]

It should spin freely even in 2wd, sure it's a 205?

[Old_iron]

Originally Posted by kwmech

It should spin freely even in 2wd, sure it's a 205?

Pretty sure. Here is a picture.

[Old_iron]

Originally Posted by 57taskforce

Put it into 2 high and your front shaft should unlock inside the case. Clear as mud???

I'll give that a try after work today.

[kwmech]

Yup, 205. front shaft is neutral until it goes into 4lo or 4hi. 2wd, front shaft is still neutral and should be able to spin front shaft with hubs unlocked.

[MJN]

Originally Posted by Old_iron

I am trying to get the front drive shaft to rotate freely.

Here's what I did. I jacked up the front end so both wheels are off the ground, and locked both hubs. I put the trans AND the transfer case in neutral. When I rotate one of the wheels, or try to rotate the front drive shaft, it moves a little then stops. Like its engaged in the transfer case.

It has a np205 behind a sm465, truck 4 speed manual trans.
The truck is not yet running, and I am trying to test the transfer case. As far as I know it worked before.


Am I misunderstanding how it is supposed to work? What am I missing?

So you locked both hubs and the t-case is in neutral, are you sure there isn't anything wrong inside the front differential? Does it have a locker/posi front diff? The driveshaft will be free to spin with the t-case in neutral or 2-hi as long as the hubs are unlocked. If you want to rule out the t-case then unlock your hubs and try to spin the driveshaft in neutral and 2-hi. If you haven't already- pop the differential cover off and check things out. If it all checks out, you're only out your time and a few bucks for fresh gear oil.

In your picture you have a NP205.

[LagunaGlide]

I would put in 2hi and then remove the front drive shaft. With front wheels off the ground they should spin with hubs locked or unlocked; I Would try it both ways. The front shaft should be able to be spun as well.

[Old_iron]

I just went out and jacked the front up and tried all the combinations. Hubs locked, unlocked. Tcase in neutral, 2h, etc. The front diff is good, I checked it out thoroughly before installing it.
Any ideas?

[El Dorado Jim]

sub'd

[El Dorado Jim]

Originally Posted by Old_iron

I just went out and jacked the front up and tried all the combinations. Hubs locked, unlocked. Tcase in neutral, 2h, etc. The front diff is good, I checked it out thoroughly before installing it.
Any ideas?

I have no idea what could be wrong, it should spin free if you have the hubs unlocked and its in neutral

[57taskforce]

Make sure the front output shift rail is moving back and forth when you operate the shifter, there’s two rails that shifter handle controls, on is low/high and the other engages and disengages the front output shaft. If the rail isn’t moving it could be as simple as the fork or rail being gummed up or something could be broke too. The linkage bar that controls the rails could be worn too. Mine was, I had to weld the holes up and re-drill them.
This link should help you understand what’s going on in there.
http://67-72chevytrucks.com/vboard/s...d.php?t=469726

[jkeady]

So is this an open diff (as was asked already)? Because if the front diff is doing it’s job, you should be able to turn one front wheel and the opposite side will counter rotate with both tires off the ground. With only one wheel off the ground, turning that wheel will transfer motion back to the front drive shaft.

With hubs locked, both front wheels off the ground and free to spin (no seized brakes, bearings, etc), open differential, the state of the transfer case does not matter at all: you should be able to spin one front wheel if the differential is doing its job.

[Old_iron]

Originally Posted by jkeady

So is this an open diff (as was asked already)? Because if the front diff is doing it’s job, you should be able to turn one front wheel and the opposite side will counter rotate with both tires off the ground. With only one wheel off the ground, turning that wheel will transfer motion back to the front drive shaft.

With hubs locked, both front wheels off the ground and free to spin (no seized brakes, bearings, etc), open differential, the state of the transfer case does not matter at all: you should be able to spin one front wheel if the differential is doing its job.

Yes it is an open diff, and yes performs as you describe.
I am trying to figure out why the transfer case is no ot allowing the front drive shaft to spin as expected. I'll look at the linkage later today.

[Bigdav160]

Are you sure your hubs are unlocked? Just turning the knob doesn't ensure they are unlocked.

Wheels off the ground and spin the front tires? What happens? Front driveshaft should not be spinning.

[jeffahart]

Originally Posted by 57taskforce

Make sure the front output shift rail is moving back and forth when you operate the shifter, there’s two rails that shifter handle controls, on is low/high and the other engages and disengages the front output shaft. If the rail isn’t moving it could be as simple as the fork or rail being gummed up or something could be broke too. The linkage bar that controls the rails could be worn too. Mine was, I had to weld the holes up and re-drill them.
This link should help you understand what’s going on in there.
http://67-72chevytrucks.com/vboard/s...d.php?t=469726

This ^^^ You need to understand what mode you are in, and this is verified by unhooking the shift linkage and pulling the shift rails in and out to proper combinations for neutral, 2H 4H ect... Then you can see if it's the shift mount/linkage or an internal rail problem. Verify this first... else, you're just poking at it!


j

[Old_iron]

I discovered the problem. The front drive shaft is binding due to the 4" spring lift installed last year. Attached are some pictures showing the worst that the problem is with the axle in a certain position. Also showing the impact points at the joints.

As you can see it's not even close. Everyone said that the front axles are fine for a 4 inch lift. Maybe the 68 GMC K20s are different, possibly because it had a very heavy V6 in it stock which made it ride lower??


What do I do? Grind some relief into the yoke parts? Find a different driveline from a later model?

[jeffahart]

Looks like the last photo is the 205 output side. Should be a CV. Can you photo the whole shaft. It should be a slip shaft with a CV to 205 output. I don't think the lift is your problem, I think it's your shaft.

j

[Old_iron]

Here is a picture of the whole thing.
Side note, when I bought the donor front diff, it had this front driveshaft yoke attached to the input. It though it was just a newer style than the shaft on the truck but not functionally different. I didnt have the rest of it anyway. I just bolted it up to the diff and compared the range of motion. It has more than enough.

So... I guess I need to find the rest of that style driveshaft? Anyone know years that will fit?

[MJN]

The lift isn't the issue. Your driveshaft is missing the CV portion that mates to the transfer case. The slip joint should be at the differential not the transfer case. It should look something like this photo.

[jeffahart]

Originally Posted by Old_iron

Here is a picture of the whole thing.
Side note, when I bought the donor front diff, it had this front driveshaft yoke attached to the input. It though it was just a newer style than the shaft on the truck but not functionally different. I didnt have the rest of it anyway. I just bolted it up to the diff and compared the range of motion. It has more than enough.

So... I guess I need to find the rest of that style driveshaft? Anyone know years that will fit?

It's not necessarily a year thing. Call around to junk yards and ask for a - 1310 2" CV slip shaft. 1310 is the ujoint. Measure carefully. if the shaft is too short and you jam on the breaks, you can run out of slip and jam transfer to the front diff. Or you can by new for about $350

j

[El Dorado Jim]

Originally Posted by Old_iron

I discovered the problem. The front drive shaft is binding due to the 4" spring lift installed last year. Attached are some pictures showing the worst that the problem is with the axle in a certain position. Also showing the impact points at the joints.

As you can see it's not even close. Everyone said that the front axles are fine for a 4 inch lift. Maybe the 68 GMC K20s are different, possibly because it had a very heavy V6 in it stock which made it ride lower??


What do I do? Grind some relief into the yoke parts? Find a different driveline from a later model?

try turning the shaft around, slip yoke towards differential, may help, or you may have to go with the cv joint style , that shaft looks bigger in diameter compared to most ive seen on the front

[Old_iron]

Originally Posted by El Dorado Jim

try turning the shaft around, slip yoke towards differential, may help, or you may have to go with the cv joint style , that shaft looks bigger in diameter compared to most ive seen on the front

Bingo. I flipped it around the right way. It turned freely until I just finished snuggling up the u joints. Then it just so slightly bound, at the transfer case yoke. I think if I grind just a little off here that will fix it. Any reason not to do that?

[MJN]

Originally Posted by Old_iron

Bingo. I flipped it around the right way. It turned freely until I just finished snuggling up the u joints. Then it just so slightly bound, at the transfer case yoke. I think if I grind just a little off here that will fix it. Any reason not to do that?

If you had the CV joint portion it wouldn't bind and you wouldn't have to grind the yoke either. Why not fix it correctly with the correct parts?

[57taskforce]

Did these trucks come with a cv from the factory? Mine definitely doesn’t have one. I know square bodies did.