4H Clunking

So I’m in 4H, snowy surfaces, and upon slow acceleration from stopped there’s a clunking/clicking/clanking sound and a slight jerk as it “engages”. Usually while turning slightly, I think, or on a hill. It might only be happening when it’s really slippery. Is this normal? I just had the front differential replaced due to a bad actuator (4000 miles), but it made the noise and was jerky before. My Tacoma gen 1’s, gen 2’s, or Tundra gen 1 never do this. ‘22 Platinum

 

Mine clunks and jerks slightly going into 4h/4l, and back, sometimes while stopped. Even with wheels straight and on flat ground. Unless truck is moving just a bit while switching, then it engages quickly and quietly.

 

Mine is silent when engaging/disengaging 4H/2H. When I’m already in 4H it clunks and jerks when accelerating.

 

So 4h light is steady on and not flashing, then when accelerating it clunks? A little bit of bind is expected while turning in 4wd. But this doesn't sound like that.

 

Yes 4H light is steady on, for example I’ve been in 4 all day. It’s not binding.

 

It’s like the tire might be slipping but then power is suddenly sent to it and it engages. Like a delayed reaction, and a clicking, clanking sound. Not like the clunking I get on my 2nd gen tacomas when switching between 2 and 4.

 

Yeah I’m in 4wd most of the time here in Montana. It seems to work well except for this weird clanking.

 

So after looking through wiring and parts diagrams it would appear we do indeed have a front locking diff. Which is a huge surprise. Why toyota hasnt added that info into sales literature i dont know. I will verify on my truck later but it looks like everyone with 4wd gets it. If it is there I'll do some testing to see when it kicks on and off. Would definitely explain what you've described.

 

Here's some screenshots of what gets me thinking this way. The front diff looks a whole lot like what the rear diff with locker looks like. Every version of diagram I've seen has it wired in as well. I encourage anyone to prove me wrong or right.

 

First, just practically, there is no way Toyota wouldn’t market the fact that the Tundra had a front locking diff if, in actual fact, it did have a front locking diff.

Second, looking at the schematic of the front differential carrier (not the housing), itself, it looks like a standard open diff with spider gears.

I’ve seen the wires that go into the front diff and do not know what they are for. Does the front axle, perhaps, have an electronic disconnect, like all Jeep Wranglers (not just those with factory lockers), to save gas mileage when not in 4wd?

If there is a Toyota engineer or tech on this forum, perhaps, they can answer?

 

Also, as a safety matter, I can’t imagine Toyota would put on a front locker without making it driver-controlled. If it engaged at the wrong time and didn’t allow you to disengage, it could severely limit your ability to turn in a tricky situation, besides putting substantially more stress on the front axle components, which are definitely not as beefy as those in the rear.

 

It's not a front locker. Traditionally Toyota has engaged/disengaged 4wd in two ways, 1 in the transfer case to lock the front and rear driveshafts together, and 2 in the front axle/differential to decouple the front driveshaft and differential from turning all the time for fuel economy purposes when in 2wd. It's called the Toyota ADD system, you can look it up. It also keeps the system from having/needing to use locking hubs as the axles are locked to the hubs.
https://www.off-road.com/trucks-4x4/tech/the-automatic-disconnecting-differential-system-19259.html

 

OP here checking in. Took it to a Toyota mechanic, not the dealership, and did a test drive. We think it’s the ABS disengaging. It sounds pretty similar to when you disengage the ebrake. The ABS must be sensing slippage when I’m pulling out of little steep spots.

 

That does look like a locker but remember the Landcruiser and LX may have the option of front and rear lockers and they all share this platform with the Tundra. The parts break down is probably showing all part’s associated with the housing. The old school 80 series Landcruisers were able to be configured as triple locked. Front, Rear and the center diff locked. That would be unstoppable on these new Tundra’s.

 

Is the traction light coming on when this happens?

 

I’m 95% sure the traction light isn’t coming on, but it’s happening so quickly it’s hard to look at the dashboard fast enough. I’ve seen the traction light come on many other times though when rallying around in the snow, but that’s in higher speed situations.

 

If the light isn’t coming on, then I’d be reluctant to believe it’s the abs system activating as part of the traction control. Is your foot on the brake when it happen? If not, why is the abs activating then?

 

Foots not on the brake, it’s happening when I’m accelerating. The abs system works in conjunction with traction control possibly? Or “stability” control? And power getting sent to, not sent to, or taken from in the form of braking? to one or another wheel? Seems like the computer and electronic systems are doing lots of instantaneous stuff we aren’t capable of feeling. This was my take from the mechanics explanation.

 

Only uphill? Like a hill hold assist feature?

 

Have you tried disabling the nannies with the double 3-second hold on the traction button? What you're describing sounds like assist, but I'd imagine this sound is new...

 

I've noticed clunking when engaging 4h, occasionally. It's definitely not every time, and I've always just attributed it to some binding. No warning flashes on the dash, 4h light stays lit, and everything seems to function as it should.

 

just to be clear, you’re already in 4H right? You’re not actually switching from 2 to 4 when you hear the clunking?

 

the mechanic said the abs system can do stuff even when you don’t touch the brake pedal. My foots not on the pedal when the clunking occurs, it happens when I’m accelerating so my foot is on the gas pedal. Apparently the abs system is tied in with traction control, pre-collision braking, stability control, etc.

 

I think this is it! I’ll experiment today. I tried reading about hill assist and e-brake functionality in the manual, it’s like 4 pages long!

 

He’s in a third Gen. Not sure if the process is the same?

 

Oh whoops, I gotta pay better attention

 

No, I hear the clunk when engaging 4h from 2h. Didn't hear it today.

 

got it. My clunking is happening when I’m already in 4 and accelerating from a full stop up inclines.

 

I believe (and have understood by The Yota Guy on YT I'm thinking is who said it), front and rear differentials are "limited slip". This is a step down from a locker, it is similar to what you know as posi-traction.


Mike