2002 Tundra 4WD front differential

filhiol · #1 (**permalink**) 03-10-2003, 01:47 PM

IHave been reading the Haynes manual and in the front differential section, it states that when you have push button 4WD, which mine does and engage it that the front differential gives the power to the left drive shaft only. Is this true? Is there never any power going to the right drive shaft as occurs in the rear differential?

peid · #2 (**permalink**) 03-10-2003, 01:52 PM

I have the same vehicle, I can't imagine that being true, but will patiently wait until somebody knows for sure!

ricqik · #3 (**permalink**) 03-10-2003, 03:12 PM

Power should go to both wheels because its an open diff. I've had the right front extended and it spun along with the left rear while in a angled incline. Maybe they meant power starts with the left then transfer to the right when the right looses traction.
One thing I do noticed in 2WD is that every time I floor it my right rear always spins first or more than the rear left. This may be the case with the front only it's the left that starts first.

filhiol · #4 (**permalink**) 03-10-2003, 03:53 PM

Thanks for the info. One other question. When I was under the vehicle last week greasing my truck I noticed that with the engine off and the vehicle in park I could easily rotate the front drive shaft. I assume that when the 4WD-drive switch is engaged that it also locks the front drive shaft to the transfer case gears. Is this correct? Of course, to rotate the rear drive shaft I needed one wheel off of the ground.

HotRod8 · #5 (**permalink**) 03-10-2003, 08:03 PM

I'm not 100% sure how the A.D.D. (Automatic Disconnecting Differential) on the Tundra works, but I think that the axle shaft on one side, I guess the right in this case, is always connected to the diff. The other side, the left in this case, is only connected when you select 4WD. They do this, I believe, with a vacuum operated sliding yoke in the one side of the axle. So.... your manual is probably right in that when you select 4WD the left side of the front axle is engaged, but the right side is always engaged. This is how it worked on my '89, the Tundra could be different.
And yes, pushing this button also engages the transfer case into 4Hi or 4Lo to turn the front drive shaft. Again I'm not exactly sure how this is done, I think it may be an electric motor that shifts the transfer case.

filhiol · #6 (**permalink**) 03-11-2003, 10:15 AM

Hotrod thanks for the input. I feel sure you are 100% correct as the Haynes book does say that the system is more convenient by not having to manually lock hubs but does cause more wear on certain parts which I would assume to be the right axle if it is always connected (thus turning) inside the front differential.

Herb · #7 (**permalink**) 03-12-2003, 12:24 AM

Guys:

I know how the front differential works. I haven't read anything in this thread that's even close to being right.

This is something that's really hard to explain and understand if you don't have a drawing of the front differential.

The next time you're in the dealer service department, ask to take a look at Volume 2 of the service manual for an 02 Tundra. Turn to page SA-29 and ask them to run a copy of page SA-28 and SA-29 for you. Don't bother asking them how it works because they don't have a clue. I had to explain this to my dealer.

When you have these pages in hand and you've had a chance to study them a bit and become familiar with parts nomenclatures, come back and I'll endeavor to explain how this system works.

Herb

filhiol · #8 (**permalink**) 03-12-2003, 12:10 PM

Herb, I am not really interested in how the differential works as I am sure it would be more technical than I could understand. As far as going to the Toyota dealer where I bought the truck I doubt if the service people there could even find page SA-28 and SA-29 let alone understand what they were looking at. These people do not even realize that the V-8 takes more oil than a V-6 and shorted me one quart when I brought my truck in for it's first (and last there) oil change. I guess the only information I want is a confirmation that the front differential is capable of giving power to either the right or left front drive axle as happens with the rear differential and that the front propeller shaft is supposed to rotate freely when the vehicle is in park and out of 4WH. The only other 4WD vehicle I have owned was a 1976 Chevy Blazer with full time 4-wheel drive. If I remember correctly, in order to get the front drive shaft to rotate when parked was to put the transmission in neutral, jack up and turn one of the front wheels.

moosehead9 · #9 (**permalink**) 03-12-2003, 08:58 PM

Yes, the front diff will deliver power to both the left and right
wheels when the four wheel drive system is engaged. Yes, the
front drive shaft will turn freely when 4wd is not engaged.
When you push the 4wd button the electric motor in the transfer
case shifts to put power to the front drive shaft. The vacuum motor on the front diff locks in the right axle and it then functions
the same as the rear diff. The left axle is always engaged and does turn all the time.

Dude Boy · #10 (**permalink**) 03-13-2003, 02:34 AM

Quote:

The vacuum motor on the front diff locks in the right axle and it then functions

Is that just a guess, or does your truck actually have a vacuum operated A.D.D.?

filhiol · #11 (**permalink**) 03-13-2003, 12:39 PM

Thanks moosehead, that is all I needed to know.

moosehead9 · #12 (**permalink**) 03-13-2003, 09:16 PM

My truck has a vacuum accutator on the A.D.D. I assume yours
does too, but other years may not be the same. Dodge and Chevy use a similar system. If you look under your truck at the
front diff you should see the accutator on the left of the diff (your
left when facing the front of the truck). You should see a vacuum
line connected to it also. There is info on this in section SA of the
factory repair manual. The accutator moves a slip spline that locks
the right axle when 4wd is selected (manual or electric transfer).
The front diff is the same as any other open type diff. The locking
mechanism is not in the diff itself.

arkie6 · #13 (**permalink**) 03-13-2003, 11:21 PM

Quote:

Originally posted by moosehead9
My truck has a vacuum accutator on the A.D.D. I assume yours
does too, ...

Hmmm. Mine doesn't. It has an electric actuator for the front differential ADD. It is shown in the 2000 Tundra Repair Manual in secton "SA". Did they change this for 2003 models?

moosehead9 · #14 (**permalink**) 03-15-2003, 10:35 PM

arkie6,

It does appear that the front axle accutator is electric. I would
still like to know what that hose going to it is for. It sure fooled
me into thinking that is was vacuum. Next oil change when I
have the skid pan off I am going to look this situation over more
closely. I thought that an electric valve switched the vacuum
going to it...guess I was wrong. The shop manual doesn't give
much explanation on how anything works. It doesn't say what
the hose is for either...it does mention the hose though.

Dude Boy · #15 (**permalink**) 03-16-2003, 02:10 AM

The front differential has a vent that extends up near the steering shaft on the LH side of the engine. Maybe you are seeing where the hose hooks to the housing?? See the picture below for the upper location of the vents. They are the two shiny caps that you see just to the right, and below the engine oil dipstick. I think the second one is for the transfer case.