4WD problems after servicing

[Nelsonmd]

So I had been having trouble getting my 4WD to engage so I took the actuator off saturday, cleaned it out and tested it, it flipped back and forth just fine using the vacuum line. I sealed it up and put it back on, and replaced the vacuum lines from the VSV's to the actuator. I appeared to work perfectly at first, but now tonight after getting home, I couldn't get it into 4wd again. The vacuum is definitely switching properly, I checked. Any ideas what could be going on here?

It seems the next thing is to either drop the diff and see if there is anything wrong/dirty in the diff, or to try to take the actuator itself apart completely to try to get it working a bit smoother if that's even possible. I couldn't get the actuator apart when I had it off.

 

[Grenvilleter]

Sticky vacuum check valve in the vacuum supply line?
Perhaps there is a shortage of vacuum due to a stuck check valve or lack of vacuum rather than a lubrication issue in your front diff?

 

[LittleCaesar]

Take a read, it could be the solenoid:
4WD won't disengage on 99 4Runner LTD - YotaTech Forums

 

[Nelsonmd]

Sticky vacuum check valve in the vacuum supply line?
Perhaps there is a shortage of vacuum due to a stuck check valve or lack of vacuum rather than a lubrication issue in your front diff?

That's not a bad thought, I will try that. I'll be surprised if this is my problem since I can feel a pretty healthy vacuum on the VSV's.

Take a read, it could be the solenoid:
4WD won't disengage on 99 4Runner LTD - YotaTech Forums

He is describing something different I think, my light isn't intermittent, it indicates properly, and his 4wd engages, mine doesn't. That is a good read though, I certainly hope I don't have to go pulling all that stuff off the TC.

 

[TheDurk]

Matt, it sounds to me as though the problem is in the actuator, perhaps in the clutch. There is very little on the actuator in the FSM, but I am attaching what there is.

If you have a healthy vacuum and it switches sides as it should, I don't see how the problem could be anywhere but the actuator or possibly the diff itself.

This is from my paper '99 FSM which covers the vacuum actuator, unlike the on-line FSM which only has the electric '01-'02 version.

 

[Nelsonmd]

I bought a brake vacuum pump kit from HF and tested out my actuator and got some interesting results.

My vacuum from the intake is sitting right around 10psi as is spec'd, and on the far side of the check valve, it's sitting at about 7.5-8 psi, so jsut a little lower.

On the tube to disengage 4wd, the actuator works fine, holds pressure and changes just right.

On the engage tube, it doesn't hold a vacuum and I had to pump furiously to get it up to the 10psi spec'd for the vacuum line. I'm guessing this is my problem. I can think of only 2 places it could be leaking from, the joint in the middle of the actuator (held together by the 2 bolts seen here)

and the other point is an internal leak around the shaft, so it would be leaking into the diff. I suspect it is the first point because I would think that if it was leaking into the diff, then it would be sucking gear oil into the vacuum chamber and it really wouldn't work at all.

To fix the flange joint, I could theoretically separate it a bit, and put some gasket sealant in there and close it back up, though I couldn't get it to separate very much at all when I had it off.

If it's the internal shaft seal, I will probably just have to replace it.

Has anyone ever disassembled the 4wd actuator before? Any tips?

 

[Grenvilleter]

Sorry I can't help but you could put a little positive pressure to the leaky side and put it into a pail of water to see where the bubbles come out.Plug up the working nipple to keep water out.

As it works in one direction, it obviously is not the diaphram but I am curious as to where the leak is.

 

[TheDurk]

Did you try plugging the disengage tube while you evacuate the engage tube? If it then holds vacuum (even though I would expect it not to actuate as it can't get any air) then it could be leaking to the other tube. The size of that bellows created by the hose back to the VSV could be why it is so weak.

That might be a tough fix. I admit I have no idea how it could do this in only one direction, but that's why I suggest the test.

Are you using Port A and B as shown in the FSM page I posted or the actual hose tubes?

 

[Nelsonmd]

I used the tubes, but I replaced both tubes with brand new ones when I did the service.

I am starting to think I need to be calling some scrap yards to find a replacement.

 

[the great him]

let me know if you can not find one, i think i have one sitting around in my garage, and if not im sure my father inlaw has one... or could get one

 

[Nelsonmd]

Another question, is the check valve going to the intake really needed? I can't really think why it would be. I am thinking of just bypassing the check valve to get back the 2.5psi and see if that will be just enough to help actuate more consistently.

As for an update, our snow is gone, so I have not worked on this anymore. One it warms up properly, I will try to figure out where my vacuum leak is coming from and fix it.

 

[TheDurk]

Another question, is the check valve going to the intake really needed? I can't really think why it would be. I am thinking of just bypassing the check valve to get back the 2.5psi and see if that will be just enough to help actuate more consistently.

As for an update, our snow is gone, so I have not worked on this anymore. One it warms up properly, I will try to figure out where my vacuum leak is coming from and fix it.

You will lose vacuum every time you take your foot off the accelerator. I don't know if that will cause you to slip out of 4wd while driving. I can tell you my BMW e23 735i had a vacuum powered A/C valve control system with a bum check valve. Every time I got to the top of a hill and took my foot off the gas, I'd lose the A/C.