Toyota Nation Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
I clicked my dash button to lock the differentials. "Testing" my system and it seems to be locked, the light doesn't turn off on the dash and I'm still chirping around all corners... still locked... any ideas?
 

·
3s-gte in a Camry?!?
'89 Camry Alltrac
Joined
·
8,488 Posts
I got your PMs... I was off-grid for a while, just got back.

The center diff lock system on the manual trans Alltrac Camry is vacuum actuated. The best picture I have is below:



Same trans you have (though different motor). The actuator is the vacuum canister on the right with 4 vacuum lines going to it. Those lines run up to the two VSV (vacuum switching valves) on the top of the firewall:



The vacuum lines run like this:
Vacuum line from intake manifold -> check valve on vacuum canister -> vacuum canister -> vacuum line up to Y that leads to both VSVs -> 1 vacuum line to each side of the vacuum actuator (2 total). The vacuum canister is integrated into the actuator and looks like one unit externally.

One VSV is 'normally open" and one is 'normally closed'. This should leave a constant 'pulling' force to hold the center diff lock open during normal operation, and reverse it for locked operation. The actual locking happens inside the transfer case portion of the transmission and the light on the dash is turned on by the position switch on the top of the transfer case (white connector, in line with the prop shaft output).

The actuator arm itself is covered by a rubber boot (below the 4-bolt mounting plate in the top pic), so it would be fairly hard to mess with that in the car or see if it is moving with switch actuation.

So, there's the system overview... not sure where to start with debugging it though!

The only problem I had with that when I had the car was I hooked up the vacuum source to the wrong port on the engine (non-stock engine...). That's not a problem you should be having.

Maybe check the following:
- 12V between the two connections on each VSV when button pressed, ~0V when button not pressed
- Vacuum always on 'input' connections to each VSV (from the Y)
- Switching (and opposite) vacuum on each VSV output to the actuator

If the locking sleeve is stuck, it make just take some time and maybe manual operation to get it unstuck. Let's hope the actuator is not leaking...

-Charlie
 

·
Registered
Joined
·
8 Posts
Discussion Starter #3
I got your PMs... I was off-grid for a while, just got back.

The center diff lock system on the manual trans Alltrac Camry is vacuum actuated. The best picture I have is below:



Same trans you have (though different motor). The actuator is the vacuum canister on the right with 4 vacuum lines going to it. Those lines run up to the two VSV (vacuum switching valves) on the top of the firewall:



The vacuum lines run like this:
Vacuum line from intake manifold -> check valve on vacuum canister -> vacuum canister -> vacuum line up to Y that leads to both VSVs -> 1 vacuum line to each side of the vacuum actuator (2 total). The vacuum canister is integrated into the actuator and looks like one unit externally.

One VSV is 'normally open" and one is 'normally closed'. This should leave a constant 'pulling' force to hold the center diff lock open during normal operation, and reverse it for locked operation. The actual locking happens inside the transfer case portion of the transmission and the light on the dash is turned on by the position switch on the top of the transfer case (white connector, in line with the prop shaft output).

The actuator arm itself is covered by a rubber boot (below the 4-bolt mounting plate in the top pic), so it would be fairly hard to mess with that in the car or see if it is moving with switch actuation.

So, there's the system overview... not sure where to start with debugging it though!

The only problem I had with that when I had the car was I hooked up the vacuum source to the wrong port on the engine (non-stock engine...). That's not a problem you should be having.

Maybe check the following:
  • 12V between the two connections on each VSV when button pressed, ~0V when button not pressed
  • Vacuum always on 'input' connections to each VSV (from the Y)
  • Switching (and opposite) vacuum on each VSV output to the actuator
If the locking sleeve is stuck, it make just take some time and maybe manual operation to get it unstuck. Let's hope the actuator is not leaking...

-Charlie
So I’ve been trying to still diagnose this, I had pulled the motor and was doing the 3sgte swap and decided to sell it and now the stock engine is back in and I was hoping while it was out and then back In the diff would have been unlocked. No go, vacumm lines seem to be all correct.. I’m so lost
 

·
Registered
92 Corolla, 90 Camry
Joined
·
790 Posts
What’s the default fail safe position should there be no vacuum? Maybe disconnect both vacuum lines to the diff device to see if it goes to the default unlock position.

Then disconnect one and move the one with vacuum to the lock connector and then manually move to the unlock connector to see if diff device working vs. Vsv valving. If it work Diagnose vsv system.

note I don’t have this locking in my car!
 

·
3s-gte in a Camry?!?
'89 Camry Alltrac
Joined
·
8,488 Posts
So I’ve been trying to still diagnose this, I had pulled the motor and was doing the 3sgte swap and decided to sell it and now the stock engine is back in and I was hoping while it was out and then back In the diff would have been unlocked. No go, vacumm lines seem to be all correct.. I’m so lost
I'm assuming you have driven it and it still 'chirps' around corners...

Verify a few things for me (check in this order):
  • The VSV connectors have 12V across them when the diff lock switch is pressed and 0V across them when the switch is not depressed. The dash switch 'switches' ground to the VSVs. The Red-Blue wire should always have 12V compared to ground. The Blue-Black wire should go from open circuit to ground when not pressed to shorted to ground when pressed (check with 'resistance' mode, engine off).
  • You have strong vacuum on the VSV vacuum feed lines (each output of the Y hose to them)
  • You have vacuum one one and no vacuum on the other VSV output lines (that switch when you press the diff lock switch)
  • Swap the 'output' vacuum lines that go back down to the actuator.
If those are all good, it might be a physical issue with the actuator (vacuum leak, stuck shift fork, who knows what else). You may need to pull off the actuator and make sure you can freely move things by hand... I don't know if that is going to be possible with the engine/trans in the car.

-Charlie

What’s the default fail safe position should there be no vacuum?
It stays in an 'unknown' state. Basically, whatever it has been in previously. When mine was missing vacuum after the engine swap (put vacuum feed on a non-vacuum source) it was sometimes locked and sometimes unlocked.

-Charlie
 
1 - 5 of 5 Posts
Top