kicks when rear wheels engages
 

There's a lot of snow here in Montreal this year. Every time I push the gas the front wheels slip for 1 sec and then a big kick announces that rear wheels has engaged. Is it normal? To avoid this, I have to initiate the move slowly when I see green.

Re: kicks when rear wheels engages
 

This is not really normal, but it happens. It is the result of a delay in the line pressure engaging the Transfer clutch. A number of reasons, wear on the lathe cut oil rings that carry the pressure to the clutch leak, and the oil passages from the C solenoid to the transfer valve have small restricting holes, to have the clutch come on slowly to prevent harsh engagement.

Any dirt build-up will slow it even more. If it continues it will either break the transfer clutch drum off the Transfer gear, or the front diff.
This is the way the drum breaks.

http://www.ecutune.com/posts/run1/DSC_3381.jpg

To help to prevent this, use the Manual button to have the "snow" map do the 2nd gear start, it also uses more transfer clutch pressure to get the rear driving earlier.

Harvey.

Re: kicks when rear wheels engages
 

thanks Harvey.
When I adjust the TPS the delay changes: advancing TPS, delay shortens but engine power seems to go down.
Do you think TPS is my problem?
I'm planning to install LANs TCU chip this summer, do you think this would solve the problem?

Re: kicks when rear wheels engages
 

thanks Harvey.
When I adjust the TPS the delay changes: advancing TPS, delay shortens but engine power seems to go down. Some times, when TPS is so much advanced, the car brakes in close curves at very low speed. Seems like the rear axle is engaged from stop.
Do you think TPS is my problem?
I'm planning to install LANs TCU chip this summer, do you think this would solve the problem?

Re: kicks when rear wheels engages
 

The way the rear drive is engaged depends on basically 3 inputs.
Throttle position, gear selected, and the road speed.
1st gear, uses a higher pressure than 4th.
Low speed, uses a higher pressure than high speed.
The higher the throttle position, the higher the pressure.

As you are changing the throttle position to a higher setting than 0.5V, you are increasing the line pressure, that the C solenoid uses. This will bring the pressure on earlier, but it will also cause the pressure to be too high, at low speed, to cause the Transfer clutch to bind, and can also prevent 3rd gear engine braking. So you are upsetting the balance of the three inputs.

This is a hardware problem not a software problem, so TCU changes won't help. it is the delay in the pressure build-up in the clutch piston, due to wear, and "goo" that causes the problem.
As I say for the snow, use the Manual button. If you are doing a hard take off in the dry, hold the brake on and raise the revs to about 1500 to have the clutch take up before you launch.

Harvey.