Question for those with modified rear DIFF locks

[UrS4boy]

If you remove or cut the road speed signal wire to the rear diff controller, the rear diff will stay locked above 15 mph (25 kph). This is mostly a drag race modification because if you are NOT going in a straight line, the two rear axels should NOT be locked together. The question is, for those who have cut that wire (white with a blue stripe on a C4 UrS4 and 95 UrS6), at what speed is it safe to disengage the rear diff lock? (Normally this occurs automatically at 15 mph (25 kph) but with the wire cut, disengagement comes only via releasing the DIFF button).

[JP]

Ask will20v he uses it on the dragstrip.

[driftin jo]

As far as I can remember it doesn't matter as it doesn't disengage until you lift off and there is no power going through it, if you try putting the diff lock on and having the car in second gear at 10 mph then put your foot down and then while still accelerating switch the diff lock off, you will see that it won't disengage at 15 mph but at whatever speed you lift of the gas, well mine does anyway.

[Zoig]

I unlocked it when I was slowing down after dragrace, I was doing around 100km/h and worked without a problem.

UrS4boy, if you are doing a article for the UrS4 chassis and system map, then i can create a schematic how to connect the extra warning light for the cluster. As alternative to cutting the speed wire, few Estonian members have replaced the cut with a relay and connected later "ASR" button to enable or disable the speed signal.

Edit: one guy replaced the solenoid block with direct connection to intake, diff was allways locked on WOT, open in vac

[UrS4boy]

I unlocked it when I was slowing down after dragrace, I was doing around 100km/h and worked without a problem. UrS4boy, if you are doing a article for the UrS4 chassis and system map, then i can create a schematic how to connect the extra warning light for the cluster. As alternative to cutting the speed wire, few Estonian members have replaced the cut with a relay and connected later "ASR" button to enable or disable the speed signal. Edit: one guy replaced the solenoid block with direct connection to intake, diff was allways locked on WOT, open in vac

I am confused you agree that you need to slow down to disengage but you say you had it disengage at 100 kph. Or is it just off throttle that is the key? (I really don't know).

And good guess about the "article" for the UrS System and Chassis Map (did this one yesterday):

http://forums.quattroworld.com/s4s6/msgs/170940.phtml

[driftin jo]

You don't need to slow down as such just back off, I'm almost certain it will only disengage when you are off the gas.
Try it, you should find it only actually disengages when you back off if you hit the switch to turn it off while still accelerating.

[Zoig]

I didn't find this article when i searched for it before posting, probably didn't look hard enough.

When I disengaged it i was slowing down, off the throttle and on the brakes a bit.

[andy10v]

It will not engage or disengage under load easily, hence why it engages/disengages when you lift off. The lock is a collar that slides over splines, and the actuator does not have enough force to slide the collar when its loaded.

What do you mean a safe speed? You can engage and disengage it at any speed, I have only tried switching it on and off up to 70mph, the handling characteristics just markedly change, and it eats tyres/bushes and I don't imagine it does the drive line much good.

[UrS4boy]

Thanks Zoig, driftin jo and Andy10V for your answers. Confirms what I thought (you *can* disengage manually above 15 mph (25 kph)) but adds the fact that you need to be off the power to decrease the friction between the mechanical lock teeth of the shift coupling and the hub flange shaft so the vacuum actuator can pull the shift coupling off the hub flange.