I have a 1990 4Runner SR5 4X4 that I just bought. After driving it for about 20 minutes in 2wd mode I can hear an electrical sound like something is turning on and at times a vacuum sound from behind the dash or under the hood. This coincides with a whirrring sound from the front axle and then I hear a loud thump from the front when I slow down almost like something bottomed out. This only happens in 2wd mode. I think there is an electrical problem causing the 4x4 to engage by itself? I think its clearly something electrical because if it was just mechanical, it would happen all the time? Has anyone else experienced this?

 

I have never experienced the problem with my '91 Runner 4x4 but I do know that the 4WD is engaged using vacuum. Look in your passenger side wheel well and notice a vacuum canister. It has lines funning from it to your front differential. Check those for leaks. When you shift into 4WD, solenoids activate to direct the vacuum to activate the front diff. It sounds like you might have a vacuum leak and it is only partially engaging.

David

 

The problem is that I am experiencing this in 2wd mode. I think something is acuating the 4wd?

 

Can anyone out there please help?

 

Well what I would do to text the idea is change out you ADD hubs to Mannual and then get ride of the vacc system for the 4X4 system. there is a write somewhere around here if if someone else dosen't know what it is I will find it and post it for you. you are looking at around $50-$200 depending on what type of hud and where you get it. I just did Warns ($118 at woodys off-road) on mine and its working out great



Matthew :alien:

 

Try disconnecting the vacuum lines from the ADD on the front axle housing. You can plug these temporarily using a golf tee. If this solves the problem, then you likely have a short somewhere that is trying to engage the ADD on the front end. If this doesn't solve it, plug them back in and take ti to Toyota :o(

 

It ended up being a bad relay underneath the dash. Thanks for all the help. I will probably end up looking for manual hubs so that this can never happen again.

 

How did you determine that it was a bad relay? As far as changing to manual hubs, are you sure you want to do that? Think of the convience that you are going to lose. I prefer the ADD in my Runner....because I hated getting out of my Jeep CJ to lock in the hubs. It's highly unlikely that your relay will fail again....if it does, you now know the symptoms and how to fix it......it's cheaper than the cost of manual hubs.

David

 

dhammeraudio,

I would definitely recommend switching to Manual Hubs. I noticed a slight increase in fuel mileage after changing mine. It wasn't that difficult at all to do (if I can do it, then anybody can)! You can pick up a set of new premium Warn hubs just about any where for around $120. If you're lucky, you can get some AISIN hubs from a junk yard. Corey has a good write up on his home page on how to refurbish them.

Check out the tech section on the home page--go to the Maintenance and Repair section and you'll see how to do it. Some really great guy wrote the article on changing to manual hubs

If you have any questions, you can also PM or e-mail me.

Matt