center diff locked at highway speeds???

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sweet trav

sweet trav

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my friend just called and asked if its bad to drive at highway speeds with center diff locked??.

I would assume so but wanted to check first.

it's an 02 lx and he was also having issues with his auto lights not working as well as the diff being locked.

he said he recently washed the vehicle and sprayed water under the hood but I find it hard to believe that would cause your diff to stay locked although possibly cause lights issues.

thanks for any info!
t
 
Trunk - I thought I read somewhere in the owners manual (maybe 'Mud - don't remember) that the center diff lock should not be used above 50 or 55 MPH.

Is that incorrect? Thanks in advance for clarifying.
 
Just bumping to be sure.... the button in my '03 LC gut bumped and there were some 75mph miles driven. Not sure how many but we pulled over and unlocked it.

Would it be obvious if something had broken? WHY iIN THE WORLD did they choose to put that button there? Has anyone protected it in a suitable and aesthetic manner? It seriously needs some kind of a guard so it can't be accidentally engaged.
 
I bomb down washboard roads at 60mph with it locked but don't lock it on pavement.

I don't think it will harm anything short term.
 
The problem with running a locked differential on pavement would be binding in the transfer case gears. This really isn't much of a problem because even a small bump is most likely enough to allow the binding to unload. (Driving down a washboard gravel road is no problem at all, the gravel allows enough slip to keep things happy in T-case land.)
Overall it's probably not a great thing for the life of the T-case but I wouldn't worry about an occasional incident.

The center differential is there to allow the front and rear axles to rotate at different speeds. The same way the axle differential allows the wheels to rotate at different speeds. In the case of an axle there is a large difference between the rotation speed in a corner. In the case of the center differential the speed difference is a lot smaller.

This is the best explanation of how a differential works I've found
 
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I think you put far far more stress on the drivetrain when you're actually wheeling. I say no way it could break anything.
Not that it's a good idea to cruise down the highway with the center diff locked. I think the consequences are more about unsafe lack of axle differentiation and tire wear.
 
Hayes said:
I think you put far far more stress on the drivetrain when you're actually wheeling. I say no way it could break anything.
Not that it's a good idea to cruise down the highway with the center diff locked. I think the consequences are more about unsafe lack of axle differentiation and tire wear.
Click to expand...
It would probably handle a little squirrely in corners too.
 
The 99 LC I've been rehabbing was driven with the center differential locked for at least a year, including highway speeds. Not a ton of miles as it sat in the driveway a good share of the time, but the po didn't understand how the system all worked and didn't know the front right cv had popped out of the front diff. Was nervous I was going to find some serious shredding of the center diff gears but when I drained the oil it was in good condition and really no shavings in the oil or on the magnetic drain plug. Fresh oil and hasn't missed a beat since. Wouldn't recommend it all the time but also wouldn't be to worried if got bumped for a few miles, especially neither front or rear diff locked.
 
I've bumped mine on also. At the time I had just bought it and, I didn't exactly understand it had to be moving to engage/disengage. It just felt a touch "grippy" on the road when I cornered. I don't know if it does damage, but their are some situations when switching from H to L that you can truly damage things. I think I did something bad with mine switching it around my first week (crunch!). No trouble yet, but fingers crossed.

oftpiste, I like your idea of a cover, but that one looks like it would be rough on the knee with that edge. Since you can find the switches, I am thinking someone has a cover that would work better.

On another note, I think it's good that flipping on the Diff Lock flips off VSC (on the 2004). I had a 4Runner previously and there were many threads on the forums talking about how to disable VSC for some years.
 
Thanks for the reassurance and explanations everyone. I'm hyper vigilant about bumping the button with my knee but wasn't driving when this occurred otherwise I would have noticed the difference in the feel of the ride. Fortunately the driving time was pretty much completely in a straight line. Glad to know it isn't so catastrophic.

If anyone has managed some sort of protection for the button I'd love to know about it.
 
@rusty_tlc Those old GM/Internet Archive movies are pretty cool. Lots of 'en to watch. GM and Jam Handy cranked those out until the '60's- they cover an awful lot- and sold cars to folks in the movie theater as well....
 
Something I got to thinking about while I worked yesterday. I can see why speed may not be all that important. With the center diff being a fluid coupling, possibly the diff lock may be in essence a lockup clutch, just as in a an automatic transmission. The AT lockup works over a wide range of speeds- it can kick in when the revs get steady at 35- or 75- MPH. So why can't the basic mechanics and operation of the AT lockup be modified and used to lockup a fluid center diff- just as it is used to 1:1 lockup a torque converter? The only functional difference would be where the TC lockup is automatically mechanically and/or electrically controlled, we push a button for manual diff control.

I don't think any of us take extra precautions when our TC locks up at 55 or 60 MPH- nor do we worry the locked up TC will shatter the tranny gears behind into scrap, right?

Just a thought...
 
The center diff is not a fluid coupling nor does it have a clutch. It's a steel-on-steel geared differential. Locking it works more or less like locking an axle. An electrically driven actuator engages splined connections that physically connect the the outputs to the front and rear drive shafts. Speed does not matter as long as the front and rear drive shafts are turning at close to the same speed (driving in a straight line).

FZJ80s have a fluid coupling on top of the center differential, but this only serves to bias the torque in an unlocked state. The coupling in the center differential itself is still 100% solid and mechanical--not fluid.
 
@Hayes Thanks! I know when I was looking into LC's I did read about the fluid coupling in the 80's. I searched a few times here as well as elsewhere on the net and got descriptions of how the center diff works- but nothing deeply technical, like what the components are and how it all functions together. I'm a bit more enlightened now :)
 
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