Quick Question: Time for 4x4 to engage

Just need some insight so I can pretend to know what I'm talking about to my wife...

Last night we finally used the 4x4 in our new 2012 Tacoma (auto tran) and she asked a question that I couldn't answer. She noticed that when we engaged 4x4 while traveling ~40mph it took about 8 secs to engage; when we engaged 4x4 while traveling between 10-20mph it only took about 3 seconds to engage. Then I noticed that if I engage it while completely stopped - it won't engage at all until I start moving forward...

Why does the time for 4x4 to engage vary depending on the speed of travel? So in my experience if I'm rolling at 40 mph it takes 8 seconds for it to engage, less than 20 mph it takes 3 seconds, and if at a stop it won't engage at all until you move forward. Why is that?

Everyone should remember from my previous thread that I'm mechanically retarded so I have to ask basic questions. But this is how I learn. Thanks everyone for any insights.

 

Whats the question?

 

Sorry about that - edited.

 

It takes a slight delay for the synchros to mesh together. When you're stopped completely, they're not moving at all, so if they're not lined up properly, they won't line up at all until you start rolling ahead. And it takes longer the faster you go (generally speaking) because the gears are spinning faster.

The best case that I have found to engage it, it when rolling slowly (1st gear since I'm a manual) without having my foot on the gas pedal. You may notice when you engage 4wd with your foot on the gas, that the truck lurches a bit. Taking your foot off the gas minimizes this.

This delay is why you need to be thinking well ahead of what you're actually doing. Observing the road well ahead, and thinking "Okay, in 500m, 1 km, 1 mile, whatever, I will probably need my 4wd. I should engage it now."

 

Exactly. The solenoid that pushes the gear over to engage the front axle is waiting for a "no load" or "Light load" Situation. I don't believe there is any synchronizer on that gear (There wasn't when I swapped my front axle gear for 4.88's) Take your foot off the gas while the truck is rolling forward and wait for the 4WD light to stop blinking. It's the least stressful, and fastest way of engaging 4wd on our trucks.

 

My terminology might be a bit off

 

Thanks for asking a question that i've been wondering too. good stuff to know!

 

This is great detail - thanks! Why in some cases can it take almost 10 seconds when traveling at a constant speed (40)? It seems a little long; but again, I know nothing about mechanics and am just speaking out of my @$$.

 

The front diff disconnect has to lock, and the xfer case has to shift. When travelling, you have to be going straight for the front diff to lock faster. It also becomes quicker the more often you use it.
Make sure you use it for 10 miles per month, off pavement, to keep is working properly.

 

Awesome. I was always a little worried about engaging it at speeds around 40 didn't know if it was good for the components and what not. Now I know that and then some thanks for the advice and for asking the question.