Front wheels binding when in 4wd and hubs are locked?!?

[Burbinite]

A few months ago I broke the centering yoke on my front drive shaft. I have since rebuilt it with "super strength" u-joints and a new centering yoke. Now since I reinstalled the drive shaft I think I have found why it broke but don't understand what is going on.
When I shift into 4wd I hear this clunk, clunk as the driveshaft turns. I have watched it turn and it doesn't seem to be the problem. Even after driving a few feet my hubs will not unlock, even rolling front or back to relieve the load. I have to jack up the front to get them unlocked. When I jack it up whichever wheel gets weight off of it first turns backwards about 1/4 turn and with quite a bit of force, enough to chirp 33"x 12.5" tires. I have tried jacking up either right or left tires and both do the same thing. With the hubs unlocked and the x-fer case in "N" I can turn the driveshaft by hand and everything seems to work fine. I have done the same with one then the other hub locked and that seems to work as well (open front diff)
Is the problem in the diff? I didn't have the time to open it up and inspect it today. But just wondered if anyone else has had this happen. Sorry to be so lengthy but I wanted to share everything I have done to get the best answer possible. Thanks for your help in advance!!

[bhoeger70]

might sound like a stuipd question, but are the gears in the front and rear diff's the same? Are the front and rear tires the same manufacture and size and age? even a small amount will make a difference.

[Burbinite]

yes and no. 3.73 front and rear. Buckshot mudders in front and BF goodrich ATs in rear but the same size tire. Would 10-15 feet (that's all it takes) of rolling really make that much difference just because tire mans. are different? I guess I'll measure the circumference tomorrow.

[special-K]

These systems commonly bind up.The hubs won`t turn once you have the transfer case in "N"?Is the shifter hard to get out of 4wd?Do you disengage the transfer case before turning the hub?

[Blazer1970]

Originally Posted by Burbinite

yes and no. 3.73 front and rear. Buckshot mudders in front and BF goodrich ATs in rear but the same size tire. Would 10-15 feet (that's all it takes) of rolling really make that much difference just because tire mans. are different? I guess I'll measure the circumference tomorrow.

Yes, two different manufacturers tires could easily be that far off in diameter.

[woodridge]

Circumfrance of a tire is extremely important on a 4WD. Even tires of the same make and size if one set is worn out and the other not can cause binding.

[Burbinite]

Originally Posted by special-K

These systems commonly bind up.The hubs won`t turn once you have the transfer case in "N"?Is the shifter hard to get out of 4wd?Do you disengage the transfer case before turning the hub?

I can't shift the transfer case out of 4wd unless I jack up the front to relieve the bind. So far I have unlocked to hubs before trying to shift out of 4wd. I plan on measuring the circumference of the two different tire makes and inspecting the front diff tonight when I get home from work. I might be tire shopping soon. $1000+ for new tires is not in the budget right now but what good is a 4wd without 4wd!!!

[sierra4x4]

What year of truck is it? My 85 was acting funny when i got it ,it seened fine in snow with 4wd but I pulled onto the road and I could hardly control it. It was all over the place. So i unlocked the hubs and it was fine. After that I pulled the diff covers and found 3.73 in the front and 4.10 in the rear and the thing shifted in and out of 4wd perfectly and the hubs unlocked easily. So i dont know if that little bit of tire size would make a differance. One thing I have heard is if you have a posi or locker of some sort in the front it can make it hard to unlock the hubs.

[Stocker]

Another dumb question, are you on a surface slippery enough to warrant being in 4WD? If not (that is, if you are on a hard surface), it will normally bind up even with matched tires. 4WD isn't the same as AWD and shouldn't be engaged unless necessary....

[thinair]

if all of your tires are the same "size" 33x12.50x15.....it's not the tires,front ones could be bald and rear ones half tread and would still work fine.your front and rear ratios are not the same exact ratio from the factory for a reason........

[Burbinite]

Originally Posted by Stocker

Another dumb question, are you on a surface slippery enough to warrant being in 4WD? If not (that is, if you are on a hard surface), it will normally bind up even with matched tires. 4WD isn't the same as AWD and shouldn't be engaged unless necessary....

Not a dumb question... No. I have been on the street since replacing the front driveshaft; I just wanted to see if everything worked like it used to. I have gone by the suggestion that you should use the 4wd every now and then to keep everything lubed up. When I first got the truck 5 years ago and had not used 4wd in while and needed to make a quick trip I would put it into 4wd, hubs locked, make the trip, shift out of 4wd before I shut the truck off, unlock the hubs. No big deal. Now I can't do that.

To answer another question; I am working on the '72 Sub in my Sig.

Yesterday the rain quit long enough for me to check a couple more things. I placed the truck in 4wd, locked the hubs, chocked passenger tires front and rear, and raised the driver's side of truck. I placed a piece of tape at the top of each tire, down the sidewall. I rotated the front tire 10, then 20 times forward, tape still lined up. I did the same backwards, tape still lined up. Then I measured the distance I could rotate the tires before I saw any movement of the driveshafts 4.5" in front and 3.5" in rear. This is putting my ruler 0" @ the tape then rotating the tire forward and noting the tape's travel at the top of the tire. There is no play between the front and rear driveshaft. The front tires are 1.25" smaller in circumference than the rear tires. I didn't have time to take the inspection covers off the diffs... It still seems to me that the open diff. and spider gears should allow for such differences. Please tell me if I'm wrong. If so, I would like to know how I used to make those "quick trips" in 4wd on the street without issue?

Thanks for all the help so far!

[shakedown96]

sounds like the spider gears are locked up. crack it open and see whats going on in there.

[Stocker]

Originally Posted by Burbinite

I have gone by the suggestion that you should use the 4wd every now and then to keep everything lubed up.

Yup.... when I have done that, it was always with the hubs locked but still in 2WD.... that way, everything turns & gets lubed, but nothing gets bound up.

The front tires are 1.25" smaller in circumference than the rear tires.

I would guess that might be enough to cause binding...

I would like to know how I used to make those "quick trips" in 4wd on the street without issue?

Couldn't say, unless your tires were more closely matched before. And there may have been more play, or 'slop' in the drivetrain before you rebuilt it?

Over the years, I have gone from dirt/mud/snow onto pavement (locked in 4WD) many times in different trucks, and the drivetrain has bound up every time in a very short distance, from moderate to severe bind -- though I haven't had to jack up the truck to get the t-case back into 2WD.

I think binding on pavement is normal, but yours sounds more serious.

[special-K]

I just used my`72 yesterday in fwd.I turned it out on the street and stopped to unlock the hubs.It was bound in 4H.I pulled forward and popped the transmission into N,it was bound.I backed it up and popped the transmission into N,it was still bound.I think it popped out when I pulled forward again.It`s the nature of the beast.