4x4 Issues - Mechanical Help

2005 TRD Off Road 4x4 5 speed automatic.

Lately I get some grinding when switching from 2wd to 4H. It has happened maybe 3-4 times in the past 10 times I've engaged the system. It seems that it happens after the 4wd system hasn't been used in awhile. Its winter up here now so when I say "in awhile", I mean after a day or two. I always engage 4wd while coasting in drive, as I found taking the load off the drive train always produced a smoother shift.

After the initial grind, I can switch back and forth from 4H - 2wd - 4H endlessly at various speeds up to 90 kmh (~55 mph) without any issues. Fluid in the diffs / T case have been changed regularly as per the maintenance schedule with

$30 75w 90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w 90 synthetic gear oil. Currently only half way through the service interval, so spent fluid is not the problem. Gonna put the truck on a lift tomorrow and sample the fluids for any cuttings. I can't pinpoint the noise but it seems to be forward of the drivers position.

Just looking for some ideas on where the grinding is coming from, and possible reasons why. The hubs are always engaged so the only "engaging" parts when throwing the switch would be either the T case or the front diff. Either the actuator isn't shifting fast enough, or the syncro (where is it located?) that matches the front diff and T case speed is getting lazy.

Any help, ideas welcomed...

 

Why are your hubs 'always engaged'??? Did you remove the ADD? I had an '05 before... no shifting issues.

 

I believe he is just stating that to rule out the posibility of the hubs not locking up properly. OP, correct me if I'm wrong. The ADD system does the equivalent, engaging the front wheels as part of the driveline.

 

I guess I phrased that wrong. Imagine the front of the Tacoma lifted off the ground. I assumed that since when you spin the front wheel and the CV shaft will also spin (even in 2wd) that there were no disengaging hubs per se at the wheels? I just assumed that ADD (Automatic Disengaging Differential) did its thing inside the front diff versus at the hubs like the days of old and manual hubs.

Anyways I know little about the system and am looking for some mechanical minded people to help me out.

 

I don't know a whole lot about this either, but I think you're on the right track with the actuator not shifting fast enough. Actually, the computer should not try to shift the transfer case until it sees that the ADD is completely engaged. Maybe there is an issue with the electrical contacts in the ADD? Once the ADD is engaged there should be minimal difference in speed between the front and rear driveshafts.....is there even a syncro inside the transfercase? Seems like there shouldn't be a need for one.

Sorry I can't be more help, I would probably swap out the ADD actuator if it was my vehicle.

 

What king of grinding sound is it. like something skipping tooths or cracking loose? The only thing grinding in front would be the actuator on the front diff. Any posibility some sand salt got into it ?

 

I had a 5 speed Mazda once that lost the syncro in second gear - sounds just like that. Two gears mashing together at different speeds.

Have you ever been in a semi truck or other HD truck that grinds going into gear? Same thing. Its just a quick grind, then the gears seem to mesh and do their thing.

Its not impossible that sand got into something as it is winter here - but I doubt very much its the problem.

 

Part Time 4WD vehicles went from no (always locked) hubs (all front drive parts moved) to

Manual locking hubs to

Automatic locking hubs (had to drive in reverse to unlock) to

Automatic Disconnecting Differential (shift on-the-fly).

 

The first thing you need to do...is start looking at the Service manuals and find out exactly what parts could be involved.

 

This might sound a little odd but are your sure the tire pressure is the same left to right? I had a low tire (really low like 15psi) on my last 05 leaving a friends place once and it crunched pretty good when I went to put it in 4wd to make it up a hill out of his place. It sounded like the nasty beat second gear synchro gone crunch my last mustang made. Fixed the tire the next day and never heard it again.

 

I know nothing about this stuff, but I will give you my experience. I had a growling noise, when its really cold, from the front end when I shifted to 4H. This, in my experience went away after I changed out wheel bearing hub assembly. They were really bad. Not sure if it is related to your problem. The noise sounded like splines not aligning properly. It came from front wheel area and only happened in extreme cold. I knew bearing was bad, and was trying to push them a little further.

 

I was reviewing all that last night. There is a syncro in the T case that would be very $$$ to replace. The actuator on the T case is selling for around $400 from auto recyclers, so I imagine a new one from Toyota is at least double that. The front differential actuator I wouldn't imagine to be any cheaper. It runs from a vacuum apparently. I checked all lines this morning and nothing looks out of the ordinary.

Just installed my winter studded tires so I'll be sure to check them all over to ensure they are equal.

Checked out both wheel bearings this morning and nothing out of the ordinary. No play in either and no rough noise when spun.

Drained both the front diff and T case gear oils this morning and nothing of any significance there either.

My thoughts is the syncro in the T case. Unfortunately this is also the most $$$ problem as both the T case and transmission has to be pulled to service - and recycled T cases run around $1500. Add labor and the bill is pretty significant.

At this point I'm just going to continue to use it. At least when it breaks for good, I'll know what to replace. Maybe in the spring I will pursue it a little further, or maybe just buy something else...

 

this might explain why that happened...
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

 

Well Fortech, my "new" front diff starting doing this today...