1991 Prado 4WD not engaging (1 Viewer)

[garrettpsu]

My 1991 Prado has the electronic hubs and 4 HI selectors to the right of the steering wheel (RHD truck). I know about the vacuum solenoids under the hood, but is there also one on the T case?

Truck would occasionally go into low, but now it won't go into low and/or 4 wheel drive at all. You can kinda hear the hubs making a little noise when you depress the button.

Will be taking hubs apart and cleaning well first.

Thank you in advance.

 

[clintnz]

Not going in to low range is strange - that is a simple mechanical linkage & they are usually very reliable.

The 2 vac solenoids on the firewall send vac (or not) to either side of a diaphragm on the t-case that engages 4wd. Put the gbox in neutral, run the engine, disengage the hubs. If everything is switching properly you should be able to reach under & spin the front driveshaft by hand in 2wd & it should lock up in 4wd as it connects directly to the rear driveshaft.

You can check hub engagement the same way with t-case in 2wd. Hubs out = front driveshaft can turn by hand, Hubs in = it should lock up as it connects t the front wheels. Most people replace those electric hubs with manual as they are not very reliable.

If it's not shifting into 4wd check the vac solenoid operation. Label all the hoses before you pull anything apart, then it's an easy process to pop the solenoid-t/case hoses off with the engine running & feel for vacuum to swap over as you engage the button. If it seems like there is a problem there try feeding vac directly to either t-case vac hose & see if that shifts it. The little computer that runs this & the hubs etc can crap out, happened to me recently & the t-case was intermittently not shifting out of 4wd properly.

Cheers
Clint

 

[AirheadNut]

Ha, Clint beat me to it. ^ This is exactly what I was typing! I would also add that testing low range can be accomplished without the hubs locked in, just pop the transfer case lever into 4L and drive forward a little.

 

[garrettpsu]

Thanks for the good feedback and info. I'll start digging into it. But sounds like getting manual hubs on that truck is the best upgrade right now. My favorite truck in our training fleet, so I was bummed when it went off-line last week. Thanks again -

 

[emmodg]

Step 1 - Take auto hubs off
Step 2 - Throw auto hubs in garbage
Step 3 - Install AVM hubs
Step 4 - Go drive

It doesn't take too much vac to operate actuator on the t-case - a mightyvac tool is your friend! I've had a hose yanked off and one split before.

 

[fordyota]

I have a 93 Prado and very glad to have manual locking hubs. I recently had to also replace my spindles and opted to get spindles that work directly with manual locking hubs so that I could get rid of adapter. If your existing spindles are damaged, might be worth considering.

The folks replying to your thread will put you in good shape on diagnosing your issue but wanted to suggest one more data point. Even though I have manual locking hubs, I still have to hit the "HUB LOCK" button for the "4H" to engage. Wondering if your electric hubs aren't working, that maybe then 4H won't work either.

Hope to hear results of your issue just to be better informed myself.