The 4WD VSV help thread...

[Radd Cruisers]

This is in reply to a 'Mud member who is having trouble with their 4WD system.

================

The most common issue is the solenoids (also called VSVs or Vacuum Switching Valves).

If the 4wd mechanism works when you apply vacuum to the lines that go to the transfer case, then you need to figure out the VSVs.

1. check to see that you're getting vacuum to the VSVs. The line I am holding is the common vacuum supply line to the VSVs. The other end of this like goes to a junction near the alternator vacuum pump.

Photo 1 - below

2. The top VSV (white in this picture), allows vacuum to pass when the 4WD switch is OFF or when the transfer case is in high range. In LOW range, the transfer case has a switch that is activated by the shift fork position that engages 4WD via power to the lower VSV (grey) and no power to the upper (white) VSV.

With the switch in 2WD and the transfer case in HIGH range, take the hose off and check to see that there's vacuum at at the fitting on the white (upper) VSV. The line I am holding goes to the vacuum diaphragm on the transfer case to disengage 4WD.

Photo 2 - below

3. Check that the lower VSV is allowing vacuum to pass when the 4WD button is depressed or when the transfer case is in LOW range. The plugs on the VSVs are keyed so that they can not go onto the wrong valve. The lower VSV should have power, and the upper VSV should not have power.

Photo 3 - below

4. Check that vacuum is not passing through both VSVs at the same time! Only one VSV should allow vacuum to pass at any one time.

Typically VSVs will fail to open, but it does happen that one will stick into the open position and allow vacuum to pass all the time. If that happens, the effect of the other VSV will be null.

5. You can also check that you are getting power to the VSVs at the various switching positions.


If you need further help, please post and I'll try to answer as soon as I can. There are a few others here with excellent experience who can add info or correct any mistakes I have made.


~John

PS: if anyone can tell me how to put the photo inline with the text, I would be most grateful

 

[Malahki]

I don't often see a shop/vendor that is so willing to go the extra mile to help out a fellow enthusiast. A lot of places don't even support their customers this good. You can expect to be seeing my business in the future.

 

[surly]

Thanks John,

Very helpful. I was putting a vacuum pump on a few different hoses while trouble shooting my system and could even get it in and out of 4wd with just the pump. Only problem was that I had to pop the hood to do it. Narrowed it down to one hose not being plugged in (since engine swap) but at first could not see where to put the loose end.

All good now but appreciate the post, especially with pics. Keep it up when and if you have time.

Cheers,
Surly

 

[chui]

cheers John..
Thanks a lot.. Gonna try it this evening and see what happens..
You should think about coming down here and starting up a workshop..lots of money to be made.
nearly Every one here owns a 4x4, but not enough good workshops around..
let me know..lol

cheers

 

[crushers]

nice post John,
it should be a sticky.

 

[roscoFJ73]

PS: if anyone can tell me how to put the photo inline with the text, I would be most grateful

One way is to upload the pics from a site like Photobucket or Imageshack,then you can paste the link with the explanation of whats in the pics in between.

I'm not good at explaining it,but I have done it that way

 

[cicak]

john

well done - especially from workshop im impressed

if your workshop were here you would have a customer.

 

[robertcruiser]

This is in reply to a 'Mud member who is having trouble with their 4WD system.

================

The most common issue is the solenoids (also called VSVs or Vacuum Switching Valves).

If the 4wd mechanism works when you apply vacuum to the lines that go to the transfer case, then you need to figure out the VSVs.

1. check to see that you're getting vacuum to the VSVs. The line I am holding is the common vacuum supply line to the VSVs. The other end of this like goes to a junction near the alternator vacuum pump.

Photo 1 - below

2. The top VSV (white in this picture), allows vacuum to pass when the 4WD switch is OFF or when the transfer case is in high range. In LOW range, the transfer case has a switch that is activated by the shift fork position that engages 4WD via power to the lower VSV (grey) and no power to the upper (white) VSV.

With the switch in 2WD and the transfer case in HIGH range, take the hose off and check to see that there's vacuum at at the fitting on the white (upper) VSV. The line I am holding goes to the vacuum diaphragm on the transfer case to disengage 4WD.

Photo 2 - below

3. Check that the lower VSV is allowing vacuum to pass when the 4WD button is depressed or when the transfer case is in LOW range. The plugs on the VSVs are keyed so that they can not go onto the wrong valve. The lower VSV should have power, and the upper VSV should not have power.

Photo 3 - below

4. Check that vacuum is not passing through both VSVs at the same time! Only one VSV should allow vacuum to pass at any one time.

Typically VSVs will fail to open, but it does happen that one will stick into the open position and allow vacuum to pass all the time. If that happens, the effect of the other VSV will be null.

5. You can also check that you are getting power to the VSVs at the various switching positions.


If you need further help, please post and I'll try to answer as soon as I can. There are a few others here with excellent experience who can add info or correct any mistakes I have made.


~John

PS: if anyone can tell me how to put the photo inline with the text, I would be most grateful
View attachment 372986View attachment 372987View attachment 372988

hello; googleing i found your post and read it with pleasure; some things i dont understand or /and i dont know
first i dont understand giving trough the vacuum when the valve is powered bij a voltage; in the test of the solenoids in the manuals of toyota i read/i see that the valve gives a flow from a to c , that is from vacuum to the outside air, when the valve is powered
if not powerd it gives through the vacuum from port a to c
also i am curious to the operation of the transfercase control relay; is it closed or open when its powered; i hope you can help me further; thnx robertcruiser