Solved! Trying to Identify a Possible Drive Train Issue, Looking For Advice...

[atomicshawn]

Here's the issue: Yesterday I stopped at a stop sign at the top of a small hill, ready to make a right hand turn. Clear to go, I let off the brake, moderate pressure on the accelerator, wheel turned but not cranked, I moved a couple of inches, a foot at the most, then heard and felt a loud pop or clunk with a corresponding moment of hesitation. Felt like a gear slipped. Then the truck accelerates normally. I've put 30 miles on it since the noise/hesitation happened and hasn't come up again. No other abnormal noises or symptoms.

Related or not, I've had a relatively consistent subtle knock or clunk when I accelerate from a stop for over a year now. A friend with an identically built 80 had the exact same noise and found rear DL slip yoke wear, replaced the DL, and the noise went away, so I have assumed that I have a slip yoke wearing as well.

So I guess my question is this; is there anyone who has had a similar problem? Has anyone ever seen a slip yoke wear to the point it jumps a tooth but keeps hanging on? Any other ideas or thread references?

Obviously I need to lift the truck and do a thorough inspection, especially the slip yoke. I'm just having a hard time getting my head around a symptom that feels like a slipping gear that's intermittent with no other significant symptoms. Viscous coupling maybe? I don't know. Any feedback would be appreciated. Thanks.

 

[greentruck]

The first thing I'd look at is the U-joints. Is there a reason you're going straight to the yoke as the cause?

 

[CJF]

Here's the issue: Yesterday I stopped at a stop sign at the top of a small hill, ready to make a right hand turn. Clear to go, I let off the brake, moderate pressure on the accelerator, wheel turned but not cranked, I moved a couple of inches, a foot at the most, then heard and felt a loud pop or clunk with a corresponding moment of hesitation. Felt like a gear slipped. Then the truck accelerates normally. I've put 30 miles on it since the noise/hesitation happened and hasn't come up again. No other abnormal noises or symptoms.

I usually won't chime in when what I've got is just a hunch, but here's one: Worn drive flange that's almost stripped.

 

[95ToyCruiser]

I've had the same thing happen to me, my solenoids are going in my tranny, happened a while back, then went away and then kept happening more frequently..

It will try to start in second or third and just slip, sometimes it would just slam back into 1st...lately I've been having to put it manually in 1st...

Have a new tranny sitting for a year, just need to throw it in (like improving, not fixing lol)

It could also be the drive flanges stripped, but the later drive flanges have more spline contact and I've had no problems with them despite breaking 5 oe birfs before going with longs...

 

[atomicshawn]

Update: Something that I failed to mention because I didn't think it was related is I had what I thought was a misfire at speeds 45 mph to freeway speed, pushing a hill; Pop! and then a split second shudder multiple times per minute, relatively consistent but didn't always happen. Only at speed under a load. Again, didn't think the two problems were related...

I don't know why I didn't think of it before, but I have manual locking front hubs, so the other day I unlocked them and locked the center diff. The subtle subtle knock or clunk when I accelerate from a stop is totally gone.... and so is my "misfire".

TC? I don't think so. I'll be tearing down the front axle in the next few days. I'm thinking the problem has to be obvious... Guesses anyone?

 

[atomicshawn]

...actually the first thing I'm going to do is remove the manual hubs and make sure their not the problem, but I doubt I could be so lucky.

 

[Kernal]

Please post up some photos if the problem turns out to be in the manual hubs.

 

[atomicshawn]

Please post up some photos if the problem turns out to be in the manual hubs.

Ya nope! Knew I couldn't be so lucky; took my AVM hubs off tonight, inspected all splines, everything looks very healthy. Sonofa! guess I'll be tearing down the axle this weekend unless someone else has a better idea? I had my TC torn down 3 years ago when I installed lower gears and trying to remember that set up and what could fail and produce the symptoms I'm having. I suppose I'll look Closely at the slip yoke on the front DL next. Any other guesses?

 

[greentruck]

Drop the front DS before you tear into the axle. I assume you can lock your TC to get going. See if that changes things.

One thought I had back at the beginning but didn't mention is that the issue from the stop sounded like possibly a birf? But you've connected it to the other symptoms, so probably not. But there's still the possibility that there are two issues at play here, pick two out of three: driveline, engine and birf?

 

[atomicshawn]

Drop the front DS before you tear into the axle. I assume you can lock your TC to get going. See if that changes things.

One thought I had back at the beginning but didn't mention is that the issue from the stop sounded like possibly a birf? But you've connected it to the other symptoms, so probably not. But there's still the possibility that there are two issues at play here, pick two out of three: driveline, engine and birf?

So your saying removing the DL, locking the center diff and hubs might produce some symptoms that make it more clear the problem is in the front axle assembly. That's a good idea. As much as I hate to think about it, the idea that there is more than one problem is a very real possibility. But there were several symptoms that were eliminated by simply locking the center diff and unlocking the hubs that make me think the whole thing is somewhere between the center diff and the hubs: No more clunk off the line, no more "misfire", also I never mentioned that there was a type of growl that would happen at speed at that sweet spot between acceleration and decel, and that was eliminated as well.

The symptoms remind me of a problem I used to see when I was a Mits tech; on the AWD 3000GT VR-4 the trans output shaft had a dry connection to the female splines in the transfer case. Water would penetrate it and the splines would rust. Eventually the shaft would jump teeth, make a popping sound/sensation. Eventually the teeth would sheer, the shaft would spin freely, and burn up the viscous.

But who knows. Hopefully I can get to it this weekend and the mystery will be over.

 

[greentruck]

With the front DS out, I'd try things both with and without the hubs locked. If you still have an issue with the DS out, I'd say it is a front axle problem. If there's still a difference between locked and unlocked hubs, that will point toward what it might be in the axle.

If removing the DS seems to solve part or all of the issue, then I'd return to where we started, thinking there's an issue with it, rather than the axle.

One more thing about the DS. Any chance it was recently lubed? Too much grease in the slip joint can cause internal pressure resisting the compression of the DS and definitely make a racket. This will also exacerbate any existing issues with U-joints or yoke. I did that the first time I lubed the rear DS on my FJ55. Thought I had a major problem, but finally figured out I needed to loosen the zerk and get some of the grease out.

 

[atomicshawn]

Disassembled and inspected the front axle assembly. The only problem I found was it appears the copper tube for the air locker has been rubbing on the smooth side of the ring gear for the last 3 years, and it was just about worn through. Glad I caught that, but nothing related to the symptoms I'm having.

Putting it back together I swapped my Slee double cardan DS for a newer one I borrowed from member KSJ85. which DID NOT take care of the problem.

Using KSJ85's asymptomatic 80 to compare I noted we have about the same backlash in the TC, but I noticed significantly more clatter in my TC gearbox when rotating the drive flanges back and forth by hand. On the road the symptoms are similar to some of those described in: https://forum.ih8mud.com/80-series-tech/606027-transfer-case-noise.html

I suppose that's where I go next...

 

[atomicshawn]

Should have looked closer at the hubs!

(More info here: Solved! Slipping Drivetrain: Possible Causes? Order of Operations ?)