Need help with ADD issues

[Black798]

So within the past two days, I have started having an issue with my 4wd. The other day I pushed the 4wd button to go into 4wd moving at about 10mph and rather than engaging the 4wd there was an awful grinding noise. I stopped the truck and cycled the 4wd button and then it engaged just fine. This happened a couple more times throughout the next day.

Today I went to engage the 4wd going about 50 and it wouldn't engage at all so I pulled over and after a few tries got the 4wd to engage. I jumped back on the highway and all was good for about 50 miles until I started hearing a really fast clunking the immediately went away when I turned 4wd
for the 4gnoff. Now I cant get 4wd to work at all.

I dont know much about the ADD system on these trucks but I am certain this is where my issue is. All cv joints and boots are good and functional.

My truck is a 98 v6 auto with the push button 4wd.
[MENTION=10169]TheDurk[/MENTION] maybe you have a diagram of the vacuum routing or anyone else that may have an idea as to what I need to be looking at for the culprit. Any advice is appreciated.

 

[phattyduck]

Doesn't sound like ADD to me. It sounds like your 4WD actuator is going bad or your transfer case itself is having problems.

The ADD system only tries to engage after the transfer case is locked in 4WD, and at that point the driveshaft and CV shafts should all be spinning the 'correct' speed to be able to mesh without drama.

Trying to actuate 4WD at high speed, on the other hand, requires the front driveshaft to be spun up to full speed by the synchro on the 2-4 shifting mechanism. You probably have a busted synchro on there now...

-Charlie

 

[Black798]

[MENTION=139000]phattyduck[/MENTION] I am pretty certain it isn't in the transfer case. When I push the 4wd button I can feel the transfer case spinning the front driveshaft up to speed and right when I would expect the green 4wd light to come on from the front locking up it just grinds. I messed with it some more and it eventually locked into 4wd for a pretty long time.

I think it has to be something with the vacuum system that controls the front because it was locked in for a really long time and then all of a sudden started grinding. I can also feel the grinding is in the front.

 

[phattyduck]

Maybe its time for a fluid change for the transfer case and front diff? If there was enough grinding, there might be some metal chunks to find - and that will definitely tell you where the problem is.

-Charlie

 

[Black798]

I'll check the fluid in both and see if either has metal shavings. Its probably unrelated but a month ago my front diff breather kept burping out a decent amount of fluid but I checked the fluid level and it was good. I picked up some vacuum line today and am planning on replacing all the lines that run the ADD. I'm also going to pull the ADD actuator in the morning to test it and inspect the internal components to make sure nothing is really damaged

 

[19963.4lsr5]

Everytime my diff breathers burped gear oil condensation was in the oil and clogging the vent line.


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[HiluxSurf SSR-G]

Does the 1998 Limited have the multi-mode TC? Iirc, the multi-mode TC first came in 1999 Limited models.

So if you've been driving your truck on the highway in 4WD with a non-multi-mode TC, chances are the TC could be damaged due to binding.

 

[Acorn22]

If your actuator is bad, I have a spare from my 98 that I can get to you for cheap, just shoot me a PM.

 

[Black798]

Everytime my diff breathers burped gear oil condensation was in the oil and clogging the vent line.

Im hoping thats what it was causing it. When I checked the fluid there was no evidence of water contamination but temperatures have been going from very cold to very hot lately which could contribute. I just extended the breather and added an inline filter to catch any more oil.

Does the 1998 Limited have the multi-mode TC? Iirc, the multi-mode TC first came in 1999 Limited models.

So if you've been driving your truck on the highway in 4WD with a non-multi-mode TC, chances are the TC could be damaged due to binding.

You are correct, the pre 99 models did not have multimode. I only use 4wd on the highway when there is snow or ice present so the binding is very minimal. Driving without 4wd on the highway where I live is not an option 7 months out of the year. So I am confident the TC isn't damaged, listening to the times it was grinding It was very apparent that it was in the front passenger area, right where the ADD tube is. But I don't really understand how that can grind if the transfer case and cv are spinning the same unless the vacuum isn't pulling the collar over fast enough?

If your actuator is bad, I have a spare from my 98 that I can get to you for cheap, just shoot me a PM.

Good to hear, I will let you know if I end up needing it Thanks!

 

[Acorn22]

Also I had to mess with my front diff just last week because it was puking out gear oil. It was in fact from the breather, but not because I had a bad breather, but because there is a short little 2 inch rubber line that connects from the diff to the 3 metal lines for the breather and 2 other vacuum lines, and that short rubber line had dislocated itself from where the breather comes out of the diff which was causing oil to be thrown up and out of my diff.

Just thought I would share because I also thought it was condensation. Had to take my actuator off and stick my hand up there to feel around, sure enough the rubber line wasn't connected on the breather

 

[Black798]

[MENTION=150857]Acorn22[/MENTION] thanks for the heads up on that, I have a feeling that might be what I have going on because it sounds like the same symptoms. Because my diff isn't overfilled and the breather is good.

So far Ive replaced all the vacuum lines up top, Ill go out here in a bit and pull the skid and start working on the diff.

 

[Acorn22]

[MENTION=150857]Acorn22[/MENTION] thanks for the heads up on that, I have a feeling that might be what I have going on because it sounds like the same symptoms. Because my diff isn't overfilled and the breather is good.

So far Ive replaced all the vacuum lines up top, Ill go out here in a bit and pull the skid and start working on the diff.

Yeah that short tube was really annoying, i just cut a slightly longer one out of spare vacuum line and used that as a replacement because it was nearly impossible for me to reconnect that short of a rubber tube with the amount of space on top of the diff

 

[Black798]

I just crawled out from under mine and Im probably going to do the same thing, there's barely any room in there. I checked the actuator with a vacuum pump and it appears to be working, probably still gonna pull it to check for internal damage to the collar. But I thought when I crawled under there I heard a faint vacuum leak and the system wouldn't disengage so I may have found the issue.

 

[19963.4lsr5]

Those two actuator valves rust and fail also. It happened to the 96 I had. Found a good non rusty set on a 2nd gen in the junkyard.


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[Black798]

I think this may be a contributor...
<a data-flickr-embed="true" href="https://www.flickr.com/photos/147275993@N05/25531491138/in/album-72157686600194093/" title="IMAG0110"><img src="https://farm5.staticflickr.com/4726/25531491138_557e41cf84_b.jpg" width="768" height="1024" alt="IMAG0110"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>
<a data-flickr-embed="true" href="https://www.flickr.com/photos/147275993@N05/38523499565/in/album-72157686600194093/" title="IMAG0107"><img src="https://farm5.staticflickr.com/4593/38523499565_03bcf2e22a_c.jpg" width="800" height="600" alt="IMAG0107"></a><script async src="//embedr.flickr.com/assets/client-code.js" charset="utf-8"></script>

On the bright side, the actuator and valves are working perfectly and all the vacuum lines have been replaced

 

[Scramble]

teeth from the front?

 

[Black798]

teeth from the front?

Yep, looks like spider gears. I honestly have no idea when they broke but I think it's been that way for a while

 

[calimobber]

Yep, looks like spider gears. I honestly have no idea when they broke but I think it's been that way for a while

Mine broke also. At least you did better than me. My broken pieces got caught and punched a hole in the case draining my oil and locking up the front end. I picked up a used unit from a junk yard for $200 wish bucks.

 

[Black798]

Mine broke also. At least you did better than me. My broken pieces got caught and punched a hole in the case draining my oil and locking up the front end. I picked up a used unit from a junk yard for $200 wish bucks.

I did get pretty lucky in that when it broke it went cleanly, but its also very frustrating that I can't figure out when exactly it happened. I wheel the truck pretty hard but Im running stock size tires and avoid using large amounts of skinny pedal.

I dont understand how I broke this diff so easily when there's plenty of guys running 33s or 35s and dont have this issue.

I was able to track down a diff with 100k on it for 225 a couple hours away. My plan is swap that diff in and rebuild the broken one with an arb sometime in the future to get rid of the weak spider gears

 

[thecole1098]

That is interesting that the internals of the diff blew up so easily. Typically the CVs will be the first thing to break as that is the weakest part of the link, unless you were running some upgraded CVs.