Jump to content

Engaging 4WD High


spddm0n

Recommended Posts

I have an '85 720 KC manual trans with divorced transfer case.  Does anyone know if you have to put this set up in 4WD LOW and then go back into 4WD High, to engage 4WD High?  It sounds odd, but this is my experience.

 

If I go from 2WD to 4WD High, it no longer engages the transmission even.  It's like it's in neutral. 

 

Then, I can pull the lever further into neutral - and it appears to be the same, like it's in neutral.

 

Then, if I go into 4WD Low, it does engage both the transmission and all 4 wheels will turn.  

 

Then, if I go back through neutral to 4WD High, it engages the transmission and all 4 wheels will turn.  

 

I don't remember if I verified the gear ratios (while driving) to determine if I am actually experiencing both High and Low gears in the transfer case.

 

Anyone ever experienced this before?

Link to post
  • Replies 16
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

2 hours ago, datzenmike said:

You should have auto locking hubs???? Jan '83 and on build dates?? Not sure how these engage, vacuum?

I have auto locking hubs.  I don't know the actual science of these hubs, but they simply engage when the xfer case is in 4WD and the vehicle begins to move forward.  Problem is...when I go to 4WD High, it's like the transmission is in neutral.  You let out the clutch, while in any gear, and the vehicle doesn't begin to drive forward.  The engine just revs up when you try to start driving the vehicle.

  • Like 1
Link to post
1 minute ago, datzenmike said:

Well hold on. The truck should still move forward on the rear wheels even if the front's are not working.

Yep.  That's the problem.  It doesn't. 🙂  It will once I'm going back to 2WD from 4WD Low, and stop in 4WD High.  I don't get it. 🙂  Something messed up in the xfer case I wonder??

  • Like 1
Link to post

Has to be. Well what you can do is check the oil level... not that this will fix it but it's one of the few things you can do with a trans case from the outside and finger's Xed... it might work. Next is the trans case shifter loose or awkward to shift?

  • Like 1
Link to post
3 minutes ago, datzenmike said:

Has to be. Well what you can do is check the oil level... not that this will fix it but it's one of the few things you can do with a trans case from the outside and finger's Xed... it might work. Next is the trans case shifter loose or awkward to shift?

I did check the oil level.  It's good.  The shifter is also nice and tight.  That is what is so weird.  No noise coming from it either while in 4WD (when it is engaged in 4WD Low).  I'll have to verify of the gear ratio is actually in Low when the shifter is in Low, and then what gears are being utilized when I put it 4WD High after it's been in Low.  It might be staying in Low.

  • Like 1
Link to post
13 hours ago, datzenmike said:

The T-100 is almost exactly 2:1 in low range, so you should easily be able to feel the night and day difference.

Ok.  Is the 2:1 ratio the ration from 4WD Low to 4WD High, or 4WD Low to 2WD?  I imagine the ratio from 2WD to 4WD High is not 1:1, correct?

  • Like 1
Link to post

I don't know about the T-100 transfer case. But with other 4wd pickup transfer cases the change from 2wd to 4wd did not involve any change in gear ratio's until you went into low  axle, instead just adding the extra drive axle. The gear ratio did not change. I've had two different Chevy 4wd pickups and one Ford 4wd pickup. They were all the same, Ford, Chevy, GMC, International, Dodge and through all other years also.

 

Don

Edited by 620slodat
  • Like 2
Link to post

No change in ratio 4 high just engages front driveshaft. If manual hubs and they are locked in you can engage 4 high while driving. You have to stop for 4 low so you don't grind. I don't know the procedure for auto hubs.

  • Like 2
Link to post

I did some testing yesterday...It's super finicky!  Three things are consistent....

{NOTE:  I just figured out there is a lamp in the dash for the 4X4 system.  It was burned out.  No wonder I couldn't tell where the heck I was in the system}!

 

1. If I'm sitting with the vehicle running, transmission in neutral, in 2WD...when I move the 4X4 selector into 4WD Low (also using the clutch), and then all the way back to 4WD High, it engages 4WD High immediately and allows you to put it in gear (trans) and bewgin driving.  Evident with the lamp in the dash too.

 

2.  If I'm sitting with the vehicle running, transmission in neutral, in 2WD...when I move the X4 selector into 4WD High, it does NOT engage the xfer case and allow you to drive forward (or backwards).  It just revs the engine as though the transfer case is in neutral.

 

3. If I'm just sitting with the vehicle running, transmission in neutral, in 2WD...when I put the transmission in 1st gear and begin to drive forward, once I'm moving forward (this also works in reverse)...I can put in the clutch and move the 4X4 selector into 4WD High and let out the clutch and it will engage 4WD High and continue driving.

 

Could there be a shifter adjustment that could be performed?  It's almost like its skipping 4WD High and going into neutral.  The FSM doesn't say anything about it.

 

Could the transfer case have some worn components or a bent for or something?  What are the symptoms of these scenarios?

Edited by spddm0n
  • Like 1
Link to post

The one consistent thing I'm reading that you say is that when you push the clutch in it works properly.....

any chance you have to push the clutch lever regardless in order to activate the 4wd?

  • Like 1
Link to post

These auto hubs are centrifugal locking.  Engage tcase, which spins the half shaft, which free spins in the hub until they rotate in to locked position.

 

Because of this, you can't rock your way back and forth out of a hole with auto hubs.  They will unlock then relock then unlock then relock every time you change direction. 

  • Like 1
Link to post
On 7/30/2019 at 11:57 PM, Lockleaf said:

These auto hubs are centrifugal locking.  Engage tcase, which spins the half shaft, which free spins in the hub until they rotate in to locked position.

 

Because of this, you can't rock your way back and forth out of a hole with auto hubs.  They will unlock then relock then unlock then relock every time you change direction. 

Suck.  Yeah, I remember those days.  I had manual hubs for that reason.  Good reason enough to swap these for manual at some point. 🙂  I 

  • Like 1
Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.