Accident - will this kill your gearbox?

[wynanddb]

I have a friend who was in an accident a couple of weeks ago.

The engine is a OM612 mated to a 722.6 gearbox, he had a heart attack and drove into a wall. The engine was running, vehicle in Drive, with him incapacitated behind the wheel. We can assume his foot might have been on the accelerator or not.

Well he was taken away in an ambulance, when his wife went to pick up the vehicle, it would not move. Subsequent investigation of the mechanics found the clutches in the gearbox to have been burnt out causing sever slipping, they feel it could not have been caused by the accident.

My point of contention is that, after hitting the wall, the vehicle came to a dead stop, unable to move forward because of the wall. It was still in drive with the engine running, unable to go forward. This means there was no air flow over the oil cooler below the radiater, which would have caused the g/box fluid to overheat, losing its viscosity, without which, the clutch plate would have been running without lubrication, thus burning out. It is not known for how long the vehicle was straining to move forwrd, or how fast the engine was revving, so my contention is this could have caused the failure of the clutch plates.

What do you think?

 

[television]

One can do a stall test on the convertor, you pop the car in gear and rev the car up and it should not go over 2k rpm, if you over do this then the clutches will burn out.

Now if the drivers foot was on the accelerator and the car in D and up against a wall, then this will burn out the clutches after a minute or two

 

[Xtractorfan]

The wheel/s would spin before the clutches would burn out.. even with the brakes applied the rear wheels on an automatic will spin.

 

[EmilysDad]

...
What do you think?

How's your friend?

The car can be mended ....... after a heart attack your friend might not have been so lucky.

 

[wynanddb]

Spoke to him this morning, he's out of hospital and feeling better thanks

As far as wheels spinning I don't agree, maybe if you give a lot of throttle, but think about standing on a incline with your vehicle in drive, the vehicle won't move forward and the wheels wont spin. Give more power, depress the brake, same result. If you continue giving more and more throttle you might get to a point where one of the wheels brake loose and start spinning.

 

[Xtractorfan]

Foot on brake and floor the throttle is how to get an auto to spin.. prolonged sitting in drive with engine ticking over will put strain on the drive train, and the clutches will invaribly wear, but even sitting for 20 mins or so ticking over and in drive little harm will come to the clutches, as the torque convertor isn't locked up.

 

[whitenemesis]

Another vote for spinning the rear wheels. As the car hits the wall weight would transfer to the front, unloading the rear wheels allowing them to spin. once traction was lost they would continue spinning even as the car settled back.

 

[EmilysDad]

Spoke to him this morning, he's out of hospital and feeling better thanks

.....

Good news.

 

[whitenemesis]

Another thought, the impact force must have been low enough not to cause the fuel shut off relay to activate?

I presume the vehicle was removed from the wall before the wife went to move it? Could the box have been in drive as the car was pulled free of the wall?

 

[television]

Another vote for spinning the rear wheels. As the car hits the wall weight would transfer to the front, unloading the rear wheels allowing them to spin. once traction was lost they would continue spinning even as the car settled back.

That is too hard to say, the rubber heats up on the tyres and the grip increases. We do not know how far the throttle was pushed but if it was being revved to 2k ish its doubtful that enough power there to spin the wheels.

If you drove up to a car in front and pushed the throttle, you would need to have a lot of throttle to get the rear wheels to spin

 

[Xtractorfan]

It is one that would need to go to Mythbusters to confirm or deny... it is standard practise to leave autos in D whilst sitting on hills and in traffic,whilst being held on the brake, and we are told this is fine to do this...
If the clutches were to slip first then all fast take offs would burn them out in a few thousand miles.

 

[television]

Another thought, the impact force must have been low enough not to cause the fuel shut off relay to activate?

I presume the vehicle was removed from the wall before the wife went to move it? Could the box have been in drive as the car was pulled free of the wall?

Is there a fuel cut off device

 

[television]

It is one that would need to go to Mythbusters to confirm or deny... it is standard practise to leave autos in D whilst sitting on hills and in traffic,whilst being held on the brake, and we are told this is fine to do this...
If the clutches were to slip first then all fast take offs would burn them out in a few thousand miles.

The car in D at lights etc does not come into it as the pressure in the box is too low to move the car much, there is a big difference in revving it and doing the same

 

[Xtractorfan]

But we don't know if the car was revving or not so all scenarios must be taken into account and we are just guessing..Rev the car and it cannot move, the wheels will spin, even more so if there is no hold on the rear wheels aka brake..
The other possibility is that the car has been used for heavy towing and the clutches are weakened

 

[television]

But we don't know if the car was revving or not so all scenarios must be taken into account and we are just guessing..Rev the car and it cannot move, the wheels will spin, even more so if there is no hold on the rear wheels aka brake..
The other possibility is that the car has been used for heavy towing and the clutches are weakened

You would still have to rev the car more than 2k to get the wheels to spin, and only one wheel spins, the other thing is that if the car hit the wall and a pipe burst on the cooler, the fluid would be pumped out in no time, then no drive

 

[Xtractorfan]

It is always nice to get to the bottom of these things

 

[television]

It is always nice to get to the bottom of these things

I agree, a half shaft could have broken, who knows

 

[wynanddb]

this is quite interesting. Can I give you more details about the vehicle to eliminate some of the gray areas:

It is a 2002 Jeep Grand Cherokee 2.7 CRD (merc om612 with 722.6 gearbox) with a NV247 transfercase and the Jeep Quadradrive system. In a nutshell, the quadradrive system will send power to the wheel with the most traction, Jeep used to sell it saying you only need on wheel on the ground. It accomplishes this with hydra-lok diffs, front and rear, as well as a viscous coupling in the transfer case. You have 2 driving modes, 4wd high range and 4wd low range. If a wheel starts spinning, a gyrotor build pressure inside the diff which pushes clutches togethor which loks the diff.

With the extra info what do you think now?

 

[whitenemesis]

Well we now know how the transfer difs work!

Grey areas are still

How hard did the car hit the wall what speed was it doing?
Was the engine still revving?
Did the car get dragged clear with the 'box still in D?
How many miles has the car done?

 

[Triv]

Could drive have failed first, causing the accident which lead to the heart attack?