drive line slack

lilthom · May 16, 2018

Okay, I have NP435/Dana 20 to the 9 inch with Detroit locker. With it in gear I can lay under it and get about a full inch of rotation with the drive shaft. U-joints are all good. Is it the Dana 20 that is finally getting worn out? If I don't feather out the clutch I can feel the clunk from the slack.

langester · May 17, 2018

If it was me, I would pull the driveshaft and check the play on the rear axle pinion and check the output pinion on the t case and see where the most play is. That should give you a good idea where to start looking for the problem.

Good luck!

langester · May 17, 2018

You might want to inspect the splines on the drive shaft as well, I can't imagine them getting that loose but you never know. Also did you check the double cardan joint and the centering joint on the shaft on the t case side. Sometimes that ball or the post gets worn or broken and causes some slack as well.
Just another though on my end, Good luck!

DirtDonk · May 18, 2018

Detroit lockers are known for adding their own internal play to the rear end. So what you're feeling at the back is not necessarily wear and tear in the ring-n-pinion backlash department.
But that does sound like a bit for the D20. Don't remember how much is normal, but here again I don't believe that they're super tight like you might expect.

Someone that really knows what's up will fill in the blanks.

Paul

sprdv1 · May 18, 2018

langester said:
If it was me, I would pull the driveshaft and check the play on the rear axle pinion and check the output pinion on the t case and see where the most play is. That should give you a good idea where to start looking for the problem.

Good luck!

Yeah, prob best place to start

Good luck Thom

lilthom · May 18, 2018

Thanks for the input. Dropping the shaft and seeing which end is sloppy is a good start. I'm off for a 5th wheeling weekend this morning but will check this out on Sunday night and report.

bmc69 · May 18, 2018

DirtDonk said:
Detroit lockers are known for adding their own internal play to the rear end.

Yep. Every one I've run had quite a bit.

Broncobowsher · May 18, 2018

You must have been doing this on flat ground. Because if there were any grade there would be a load on the driveshaft and that would take up any slack.

Yes there is going to be backlash. Every set of gears, every splined shaft, they all add up. Any single one will be barely noticeable, but they will stack up into something noticeable.

And the Detroit locker has a lot of play in it. Between the teeth and the ramps it has to have play in it for the mechanism to work. That play is multiplied by the gear ratio. With a low set of gears, everything set up right, I've seen nearly a quarter turn of the driveshaft between reverse and drive (loaded each direction with an automatic).

Rustytruck · May 18, 2018

Yep my soft locker with 4.11 gears has close to a 1/4 turn with driveshaft removed. But the shaft with the tranny in park hooked up to the rear has very little movement.

Yeller · May 18, 2018

A 1/4-1/3 of a turn from the pinion is normal with a Detroit. An 1" of play in the trans/tcase wouldn't really concern me either if there are no bad noises and externally everything checks out

BUCKWILD · May 18, 2018

Sounds about normal to me ran Detroit's for years

lilthom · May 19, 2018

Maybe I will leave well enough alone. The Detroit doesn't have that many miles on it and I had the Dana apart to do the twin stick thing about the same time I added the Detroit. I will double check the joints once more for good measure.

Thanks,

sprdv1 · May 21, 2018

Good luck chief.. Hope the weekend trip went well

drive line slack

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