dntsdad

HI from the newest newbie. Just bought a 92 extra cab 4x4 for my son for Christmas. It has the V6 and a 5 speed with the autohubs and the add system. Problem is the 4x4 engagement.

First of on this system, when i shift to 4h or 4l, how far should it take to be fully engaged? Instantly, a few feet to let everything mesh, 20 yards???

When I shift to 4H it doesnt seem to engage at all and I just get a bit of knocking like it is trying to. After a while( few 100 yards) it will slip in, especially if I pop the throttle a bit. When going to 4L sometimes it will engage but pull severely hard to the right, almost like the right wheel is locking up but not the left although i am not sure thats the case.

Either way, when it is engaged i get a knocking that syncs with the speed of the truck. It sounds like a driveline that would be knocking on something speeding up and down with an increase or decrease in movement of the truck. I am thinking of putting it on stands and putting it in 4x4 and trying to find the knock location this way instead of running down the street trying to listen too.

I know this is a crappy explanation but I could really use some help on where to start. I have little 4x4 experience but have overall experience with cars but hot rods instead. Any help that could get me started on the right path would be great.

I know that most of you will say to change the hubs to locking ones but I dont want to get into all that right now. This is my sons first vehicle and I am not ready to start doing stuff like that yet.

Thanks in advance for any thoughts.

Marc

With my ADD hubs, 4 hi or 4 lo engages as soon as the truck moves an inch.

thook

I'm going to go against the overall grain a little here, but I like the ADD system in my wife's '92. As long as you understand how it works, what components are involved....(which aren't many, relatively speaking), and aren't using the vehicle in more than moderate offroad situations, it's actually rather cush and convenient. And, pretty stinkin' reliable, in my experience.

The ADD system should engage instantly when you shift the t-case into 4wd H or L. It operates by electronic vacuum switching valves (VSV). There is an electronic switch on the t-case that is activated by the shifter that in turn activates the VSV's for the ADD actuator on the front diff. Those twoVSV's are located on the pass side wheel well up top of it. From there, two vacuum lines run down to the actuator. The vacuum source for these lines is, of course, from the engine, but the VSV's are what regulates the flow of it and therefore the "pulling" of the actuator fork to slide the sleeve that locks the axle to the diff gears. Probably would make more sense if you knew what it all looked like.....

http://personal.utulsa.edu/~nathan-b...26addcontr.pdf

http://personal.utulsa.edu/~nathan-b...le/24disas.pdf

It's possible that you have a small enough leak in the vac lines that the actuator fork can't fully operate the sleeve inside the axle housing. So, it kinda hangs up until it will finally fully engage by movement of the axle itself.

On the other hand, it also all needs to be lubricated by the differential gear oil. Have you checked the fluid level there?

Cyberman

Not sure about the knock, but it could be anything between the front driveshaft and the hubs. The ADD system is vacuum controlled. You might want to check those vacuum lines to make sure it is engaging properly.

RobD

http://www.off-road.com/trucks4x4/ar....jsp?id=399612

One of the best articles on how it works and troubleshooting your ADD/4x4.

dntsdad

thanks all for the replies....yes the oil levels are fine. I checked that first of all.

I dont really know where to start on this. Very frustrating!

As I read thye manual, it seems that i can be driving at any speed under 50 and pull the thing into 4H and vice versa. Is that correct?

thook

Hmmm......I don't remember the allowances for speed being quite that fast. But, if your manual says so, then I suppose it is correct. I remember it being at 25mph or less.

A good place to start would be by following the vacuum lines from the actuator right next to the front diff. Follow them up to the VSV's and note how they assemble. Then, pull them off and see if there are any holes in them. It's a good idea to label them, though, so you know where they reattach.

If you don't find any issues there, I'd pull the actuator off and see if anything's buggered up. If you find you aren't sure of what you're looking at, maybe you could take a couple of pics once you have it apart. Once you get in there, you'll see it's not really all that complicated or a major deal. Just a few simple parts, really. Now, if something's damaged, that's kinda major....

91diesel

put manual hubs on anyway! :-)

Maybe the knocking sound is something in the front drive shaft knocking around? Bad CV joint?

the_ocho

yes that is correct for shifting to and from 4hi and 2hi. i would say below 25 to be safe but yes the manual says 50 it also says if its cold out or shifting is hard to slow down or stop.

it says for 4hi to 4low that you press the clutch and be going less than 5mph. i ALWAYS stop when going to and from low. there is just so much of a difference in gear ratio that its just logical

all this info is from the lil card thats in the slot on my drivers side visor. yea i still got that

dntsdad

If I went to manual hubs the way I understand it is that I would change the VSV feeder vacuum to a constant feed from the motor so it would always be engaged but getting out and locking the hubs would be my way of locking things up. Wouldnt this keep the front end locked all the time? Or would having the shifter in 2H keep it mechanically unlocked/free until i shigt into 4h or 4l? I guess i need to understand this a bit better!!!!

From this is assess that the only thing i lose is the "on the fly" ability and possibly a more reliable system?

Do i have this correct?

the_ocho

yes you lose on the fly. you have to get out and lock the hubs. i personally love my add. the on the fly has saved me so many time. i remember a night out wiht my girl where i was in 2wd and got stuck on purpose to scare her then i said"oh wait i got 4wd" shifted and got right out. no getting out and getting muddy

dntsdad

I agree. I like the idea of the add IF I can get it all working. This is by no means a serious rock crawler so the on the fly is something I want to keep. If my son wants to make it a serious crawler, he can address this later. For now, he'd probably be happy being stuck in the mud with his girlfriend!!

91 4Runner

You could also leave the ADD system intact and install the manual hus as I did, then you have the ability to shift on the fly (when hubs are locked), 2Low when hubs are unlocked in 4Low. Also with hubs unlocked it removes some of the wear and tear on the front drivetrain.

But that doesn't really address your issue - I'd say a vacuum leak somewhere. It will knock if the accuator doesn't fully engage the axleshaft. (well more like a grind depending on speed)

SEAIRESCUE

My lesson learned is to NEVER assume the 4WD is properly working on a used vehicle you are considering buying. I did that on a 1999 Taco. I did not have any service manuals and attempted to fix the ADD system. What I initially knew nothing about was the electrical controller under the instrument panel area and the vacuum reservoir under the fender well. The link to understanding ADD by another poster is great. Wish it was available when I had problems. The system is not magical and works great when all the components are properly working and properly connected. The engagement device located on the front diff, with the two vacuum lines, is the high maintenace item followed by the vacuum lines themselves.

My $0.02

dntsdad

I was thinking that the "fork" that is actuated by the vacuum was not working properly since the dash light didnt comes indicating the 4x4 was engaged. However, I spent most of yesterday tracing wires and vacuum line only to discover that someone had not reinstalled a harness connecting the ADD indicator sensor on the front diff. I have that all working now and when I move the shifter to 4h or 4l the light in the dash now illuminates.

My understanding, and why i spent so much time worrying about the light, is that if the light comes on, meaning its getting a good signal from the sensor mounted in the diff, that the "fork" did in fact move to where it should. This would tell me that the ADD system, at least the electrical and vacuum parts, are working properly and that I have a mechanical issue i.e. tranfer case, driveline, cv shaft, etc. somewhere causing my problem.

This make sense? Anyway to test/check the CV joint without ripping it apart to do so to rule it an option or rule it out? The boots are all good and i do not see any rips or grease being leaked out.

mrdoug

For my 02 (auto), 4hi can be engaged up to 50mph, the rear elocker 15mph (maybe that's what you're thinking of?). You have to be in neutral for 4lo.

When I did my manual hub conversion, I didn't loose on the fly engagement. I'm basically setup for the best of both worlds.. I lock my hubs, then use the on the fly push button to actually engage the front diff. I can even have my hubs unlocked and engage 4wd to start spinning the diff, but since the hubs are unlocked, I'm not acutally in 4wd.

The way I use it for winter on the road driving is, if it looks like snow, then I lock my hubs before I leave the house and leave the push button off. When I hit snow/ice, I simply hit the push button 4wd and I'm set. Turn it off when I get to 'normal' pabement. Works like a charm.

I think that it's a common misconception that manual hub conversion rules out shift on the fly 4wd engagement.

DC Hoerunner

the rattling in 4wd could be the skid plate that goes around the lower front driveshaft it broke off on mine. and for the 4wd late shifting try pulling out the add actuator and making sure it doesnt have rust on the sleeve.

leebee

did reconnecting the plug correct your issues with the 4x4 engaging properly? thook posted a couple of links for you to check out, the full version can be located in the stickied posts at the top of the page, look for 'fsm' or 'factory service manual' and you are golden.

usually, there are simple fixes, check out the fsm's trouble shooting section for hints on your unique situations.

lee

dntsdad

hi leebee...

no i didnt. i have the light now working but still clunking when trying to engage.

thook

Yeah, that light only tells you if the actuator fork has moved across the little ball bearing type switch that is the indicator. It does nothing in terms of engaging 4wd. If it's still clunking when you try to engage, I'd still have to say the problem is somewhere in the axle/diff/actuator assembly. Something is just binding.

As for CV's, with ADD, the CV axles continue to spin while in 2wd. In which case, it's reasonably safe to say it's not the CV.....otherwise it would be noticeable in 2wd, as well. Still, you can check them for excessive play by grabbing hold and tugging on them. There should be no play at the joints themselves. You will find some play at the spindle (where the CV shaft slides into the back of the wheel hub), but that should only be in and out.....not up and down or all around. I mean, you may find there is a little play in that area, but that would normal for typical wear.

Considering that you don't know much about what was done with the vehicle before you bought it, it's possible someone has tinkered with front end beforehand. I know in my case, when I was correcting some post-accident problems I was having with ADD 4wd, I'd installed the actuator fork incorrectly. I had not mated it properly to the engagement sleeve. However, I just didn't have 4wd at all. Which was probably due more to the fact I had a RAGING HOLE!!! in one of the vac lines, but that's not the point.

It's also possible the actuator fork is broken in yours. Or, the splined shaft of the side axle from the diff that the sleeve mates to is damaged. A remote possibility, I guess, but not impossible. I'd have a look.