MR auto front diff query

MR auto front diff query

Postby mitzi1 on Wed Nov 11, 2020 5:25 pm

Was checking under truck yesterday and found something I have not struck before. Gearbox in neutral, transfer case in 2H, and engine off. Facing forward under the vehicle I held the front drive shaft and turned it to the left (towards the passenger side). There was a huge amount of rotational movement as I turned it. When it stopped I began to turn it back to the right. It only went a small amount and stopped with a very loud clack sound, and couldn't be turned any further. I tried turning it back and forward and it was locked up with a small amount of movement, pretty much like a normal amount of shaft play in any diff in good nick. Started car up backed it up and drove it forward again and repeated the sequence. Turn left, big
shaft play. Back a little bit, clack and apparent lockup. All play gone. Being thick did it two more times same result. Can someone please explain to me what this is all about. Thought it may be a faulty 4wd mechanism but the connect for that is in the transfer case and this appears to be in the front diff or axles. Doesn't come from behind where the transfer case is Any comments appreciated. I'm new to this brand of 4wd and it could be quite normal I guess but I've just never struck it before.
Thanks.
Last edited by mitzi1 on Thu Nov 12, 2020 7:17 pm, edited 1 time in total.
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Re: MR auto front diff query

Postby WUNSIE on Thu Nov 12, 2020 6:08 pm

Dibby, please explain :roll:
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Re: MR auto front diff query

Postby mitzi1 on Thu Nov 12, 2020 7:20 pm

Did have a front wheel off a while ago and there was a bit of rotational play in the axle, but nothing like the drive shaft.
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Re: MR auto front diff query

Postby srb on Fri Nov 13, 2020 5:22 am

This is normal, the click sound will be the 4wd actuator locking into 4wd position. It's a 'normaly closed' vacuume operated actuator, when your engine is running and you've selected 2wd, vacuume is pulling the actuator open, this disconnects the front drive shaft for 2wd operation.

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Re: MR auto front diff query

Postby mitzi1 on Fri Nov 13, 2020 9:42 am

Mate are you saying the lockup is in the diff?? I thought it was in the transfer case and the drive shaft was always being driven by the front diff. This is an MR series. For the vacuum actuator to be in the diff there would need to be a vacuum line to the diff. I can't find one. Not saying you're wrong, but I'm sure somewhere Dib said the lockup was in the transfer case and the front shaft was always drivien. Still trying to understand how this thing works. Could you explain the whole system to me so my slow brain can absorb it please.
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Re: MR auto front diff query

Postby mitzi1 on Fri Nov 13, 2020 9:44 am

Mate are you saying the lockup is in the diff?? I thought it was in the transfer case and the drive shaft was always being driven by the front diff. This is an MR series. For the vacuum actuator to be in the diff there would need to be a vacuum line to the diff. I can't find one. Not saying you're wrong, but I'm sure somewhere Dib said the lockup was in the transfer case and the front shaft was always drivien. Still trying to understand how this thing works. Could you explain the whole system to me so my slow brain can absorb it please.
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Re: MR auto front diff query

Postby mitzi1 on Fri Nov 13, 2020 11:34 am

Hi srb. Tried the thing with engine off this morning with same result. Switched engine on climbed under again. drive shaft turned freely in either direction. You're quite right. The connection is in the front diff. That means the front drive shaft is always driven I guess, wouldn't be disconnected in the transfer case as well. Thing that worried me was the amount play in the ffront shaft with engine off and shaft had locked in. I would have thought it would be tight like a normal diff. Every other 4wd I've owned has been. This morning shaft had about a quarter turn of slack before it locked up and about half that after it locked up. Is this excessive mate. It explains the play i found in the front wheel axle.
Cheers .
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Re: MR auto front diff query

Postby srb on Fri Nov 13, 2020 1:50 pm

The old saying goes... If it aint broke, don't fix it. Stop trying to find problems that don't exist and just enjoy your ride.

Your 4wd actuator is probably in the transfer case, because even the late MN's had this. Your front drive shaft will turn freely in 2wd mode as it should. The back and forth in the drive shaft is just the backlash, completley normal from what you're describing.


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Re: MR auto front diff query

Postby WUNSIE on Fri Nov 13, 2020 4:15 pm

I think you will find the front shaft is always rotating in relation to the front diff for Super Select to be employed, so you can shift from 2H to 4H on the move,
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