M998 Transfer Case in "H" Slips out of Gear

[Phoenix77]

It turned out my rear differential was toast. Dropped $1,100 and swapped it out myself. Haven't had the problem since.

 

[Mogman]

OK, this thread is a little old but perhaps will get a response, thanks.

My 1987 m998 does exactly what has been described here. I was driving it one day and it just slipped out of gear. I had to go to L in order to get it to move. Drove it home at 10mph before I started messing with it. Of course I stopped engine to shift.

Prior to this happening I replaced both front half axles, all the steering components i.e Pinon, tie rod ends and follower arm (six pieces). everything torqued and lubed per spec.

With vehicle on the rack I can see both rear half axles look good. they both turn when wheels are turned.

When the thing pops into neutral You can hear what sounds like a penny bouncing around just between the seats.

My question is how can I test the half shafts or differential or transfer case to see what is causing this?

Interesting note: I was originally told that trans fluid was leaking into the transfer case thus overfilling it. So I did a Trans filter change and transfer case oil change. When I took the filter out I noticed that the O ring was on the filter side of the plastic tube that feeds the case. The diagram shows that the O ring should be placed on the case side (top) of the plastic tube. After doing this she ran for a month without a problem them bam it just started up again.

Any suggestions would be greatly appreciated.
ooops almost forgot. I have a very small slow leak from engine rear oil seal if that matters at all.

That oil leak is pretty much normal for the two piece rear seal, don't bother with it until it gets to be a problem as it will happen again in time.
The pinion is in the differentials are you sure you meant to say that? careful inspection usually can find the problems.
Put the T case in neutral, BLOCK the wheels and see if you can turn ether of the drive shafts.

 

[AJB777]

That oil leak is pretty much normal for the two piece rear seal, don't bother with it until it gets to be a problem as it will happen again in time.
The pinion is in the differentials are you sure you meant to say that? careful inspection usually can find the problems.
Put the T case in neutral, BLOCK the wheels and see if you can turn ether of the drive shafts.

Sorry for the late response. Its tax season. I meant to say Pitman and Idler arms. the front end steering parts.. all replaced. Ill be puting up on the rack tomorrow and get back to you thanks.

 

[AJB777]

It turned out my rear differential was toast. Dropped $1,100 and swapped it out myself. Haven't had the problem since.

Did it make any noise when it broke or in neutral?

 

[AJB777]

any broken HS will act this way...

could you elaborate on "broken" please. do you mean inside the hub? because visual inspection outside look fine. Thanks.

 

[AJB777]

Sorry for the late response. Its tax season. I meant to say Pitman and Idler arms. the front end steering parts.. all replaced. Ill be puting up on the rack tomorrow and get back to you thanks.

could you elaborate on "broken" please. do you mean inside the hub? because visual inspection outside

Sorry for the late response. Its tax season. I meant to say Pitman and Idler arms. the front end steering parts.. all replaced. Ill be puting up on the rack tomorrow and get back to you thanks.

ok, I got the beast up in the air this morning. This is what I found. First the left rear half axle boot at the inside brake end is torn and grease is leaking. Need to replace both half shafts.

Now, on to the tests. I started by turning the drive shafts with TC in N. Front drive shaft turns both front wheels loosely in the same direction FWD and REV. When I spun the tires the opposite tire barely spun but in opposite direction both front and back. Now with TC in H. Both drive shafts acted exactly the same as in N. With TC in HL, both front and rear Dshafts spun their tires solidly and at the same speed FWD and REV. When I spun a wheel, the other side reacted in the other direction but in proportion to my input indicating a good lock.

Now for the fun part. I lowered it down to about 3 inches off the ground and startred the engine. With TC in H and Trans in D, nothing. I was able to get it in D by going to R and back, but it didnt stay in D long before it slipped out of gear again. When I put it in HL and D, all tires turned solidly together in FWD and REV indicating a good lock.

So all these test still didnt give me a good indication about where the problem lies exactly. Any thoughts, anyone, anyone, Ferris?
Thanks in advance

 

[Mogman]

Well you did not do the test as I described it, I meant for you to BLOCK the wheels and see if you could turn ether drive shaft with the T case in neutral not have the wheels suspended. is there any play in the half shafts with bad boots? It does sound like a T case issue but not being there and seeing how you are testing it I cannot say for sure.

 

[Action]

I would have left it on the ground and you under it with shifters in H and D. Have driver let off brake. Look for either propshaft spinning.

 

[Mogman]

I would have left it on the ground and you under it with shifters in H and D. Have driver let off brake. Look for either propshaft spinning.

BUT if you do be VERY careful, chalk the wheels and or chain it to something, it hurts like hell to be run over by your own vehicle, don't ask me how I know but it took almost 60 stitches just to close up the right leg!!

 

[AJB777]

Well you did not do the test as I described it, I meant for you to BLOCK the wheels and see if you could turn ether drive shaft with the T case in neutral not have the wheels suspended. is there any play in the half shafts with bad boots? It does sound like a T case issue but not being there and seeing how you are testing it I cannot say for sure.

ok, i misunderstood. I was dropped on my head at a very early age. I will do the test correctly and report back. But I am pretty sure all the half shafts are firmly attached. Ill get back to all in the next few days If I dont run over myself. Thanks so much for the input.

 

[Action]

Park it against a sturdy tree.

 

[AJB777]

Park it against a sturdy tree.

OK I found time to check it further this morning. I lowered and blocked the wheels. With engine on, TC in H and Trans in D, I crawled under the vehicle. At this point there was no power to the wheels as it had slipped out of gear. No sign of any HS movement. I tried with all my might to turn Drive shafts. They did turn but only less than one inch from firm stop to the other, I think that's normal. I tried to rattle or turn every HS and not even the slightest movement. They are firmly locked into each wheel.

Now up to the drivers seat I went. As stated the vehicle was still out of gear. I tried D-2-1. Nothing. Then put TC in HL with engine off. turned it back on. Nothing, no power to the wheels. So, once more I cycled the TC from H/L to L and Voila, power to the wheels. Put it back in H and D and there was power for about 2 min and then she slipped out again.

So I think what we have here is a bonified TC problem. Under no circumstance can I detect any abnormal conditions in the half shafts. they all seem firmly attached to their respective hub and disk. Its going to take me about a month to get this fixed but I will post results here. If you have any other ideas let me know...... thanks all.

 

[Action]

you should hear spinning somewhere while under it.

 

[Mogman]

Well it certainly sounds like a TC problem.

 

[AJB777]

you should hear spinning somewhere while under it.

You know, I did hear a very faint spinning sound but it was so faint that if I had not been actually listening I probably would have missed it. The sound also changed in pitch from 1 2 and D but hardly noticable.

 

[Mogman]

You know, I did hear a very faint spinning sound but it was so faint that if I had not been actually listening I probably would have missed it. The sound also changed in pitch from 1 2 and D but hardly noticable.

That is what I would expect if the transfer case was not "in gear" only the transmission output shaft and the TC input shaft would be spinning

 

[Phoenix77]

Did it make any noise when it broke or in neutral?

It would make a gravelly noise and rev up when in neutral or when I put in "H"

 

[Action]

It would make a gravelly noise and rev up when in neutral or when I put in "H"

but where was the noise coming from? and i dont mean "under the truck".

 

[Phoenix77]

Rear differential and thereabouts.

 

[AJB777]

but where was the noise coming from? and i dont mean "under the truck".

From the TC