Transfer clutch engages with a THUD

[SoCal LS-L]

So now that its snowing here, I have discovered that after about a half-second delay my transfer clutch (and the rear wheels) engage with a thud sound.

I have been having a slight problem with my wheel sensors, my ABS will always kick on when I apply the brakes in reverse.

So is that maybe why the transfer clutch engages so harshly maybe? I admit I dont know much about that part of our drivetrain, so any insight would help, thanks fellas!

[oab_au]

Originally Posted by SoCal LS-L

So now that its snowing here, I have discovered that after about a half-second delay my transfer clutch (and the rear wheels) engage with a thud sound.

I have been having a slight problem with my wheel sensors, my ABS will always kick on when I apply the brakes in reverse.

So is that maybe why the transfer clutch engages so harshly maybe? I admit I dont know much about that part of our drivetrain, so any insight would help, thanks fellas!

The ABS should not have anything to do with it Chris.
The thud is a delay in the action between the TCU signal to the C solenoid and the transfer clutch piston applying pressure to the clutch. It allows the front wheels to start spinning, before the rear is engaged.
It can be caused by the Transfer valve sticking in the valve body, needing more pilot pressure to move it.
An oil pressure leak in the clutch cylinder.
Or the actual clutch plates have worn down too much.

It is this type of delay that breaks the clutch hub off the transfer gear, so I would not let it happen too much.

Harvey.

[SoCal LS-L]

Originally Posted by oab_au

The ABS should not have anything to do with it Chris.
The thud is a delay in the action between the TCU signal to the C solenoid and the transfer clutch piston applying pressure to the clutch. It allows the front wheels to start spinning, before the rear is engaged.
It can be caused by the Transfer valve sticking in the valve body, needing more pilot pressure to move it.
An oil pressure leak in the clutch cylinder.
Or the actual clutch plates have worn down too much.

It is this type of delay that breaks the clutch hub off the transfer gear, so I would not let it happen too much.

Harvey.

Im glad I asked. Thanks Harvey, I guess ill keep it FWD until I really need to use it.

Edit: Question, so how does the TCU detect the front wheels are spinning?

[svxfiles]

Originally Posted by oab_au

The ABS should not have anything to do with it Chris.
The thud is a delay in the action between the TCU signal to the C solenoid and the transfer clutch piston applying pressure to the clutch. It allows the front wheels to start spinning, before the rear is engaged.
It can be caused by the Transfer valve sticking in the valve body, needing more pilot pressure to move it.
An oil pressure leak in the clutch cylinder.
Or the actual clutch plates have worn down too much.

It is this type of delay that breaks the clutch hub off the transfer gear, so I would not let it happen too much.

Harvey.

What He ^ said!

[icingdeath88]

Originally Posted by SoCal LS-L

Edit: Question, so how does the TCU detect the front wheels are spinning?

2 speed sensors. One in the front diff (front wheel speed) and one in the tailshaft (rear wheel speed). TCU compares the speeds and if the front wheels are spinning faster than the rear, it engages the transfer clutch.

[1986nate]

Chris, it's better to not let it be in FWD mode as the transfer clutch is much easier and cheaper to replace than the front diff. Transfer clutch replacement is about a 3 hour job, compared to about 10 or more billed hours for a diff replacement as the entire transmission must come out.
This was happening on my silver SVX before I pulled out the junk stock transmission and put in the 4.44's.
As long as you are easy on the gas in slippery conditions, It will prevent the front diff from getting any abuse and the transfer clutch from getting any more damage. Just take it easy in the slippery conditions and when money allows for it, go ahead and get yourself a new or new to you complete transfer clutch assembly with the drum and replace it.

[SoCal LS-L]

Originally Posted by icingdeath88

2 speed sensors. One in the front diff (front wheel speed) and one in the tailshaft (rear wheel speed). TCU compares the speeds and if the front wheels are spinning faster than the rear, it engages the transfer clutch.

So what I was asking earlier was if these could be causing the delay for my xfer clutch..... they trip my ABS when I brake in reverse, meaning they are falsely detecting wheel lockup maybe? So one or more speed sensors maybe bad, this can be ruled out as a cause?

[oab_au]

Originally Posted by SoCal LS-L

So what I was asking earlier was if these could be causing the delay for my xfer clutch..... they trip my ABS when I brake in reverse, meaning they are falsely detecting wheel lockup maybe? So one or more speed sensors maybe bad, this can be ruled out as a cause?

No the gearbox speed sensors and the ABS wheel sensors are not connected. The ABS problem in reverse is different to the Transfer delay.

You could try some additive in the ATF, to see if it will free up the transfer valve, which is probably the cause of the delay.

Harvey.