Need to change diff fluid

[legacy_etu]

I thought I read here that the diff cover bolts were a one time use bolt. Seems strange if so to replace them when changing the fluid.

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[ShadowsPapa]

I thought I read here that the diff cover bolts were a one time use bolt. Seems strange if so to replace them when changing the fluid.

There are two reasons for "one time use" bolts -
Those that stretch to yield for torque purposes (connecting rod bolts, among others, like certain suspension bolts)
or
those that are treated with a thread locking compound, such as the steering pitman shaft nut.

If it's the latter, and it certainly has to be since those aren't torqued enough for any type of stretch, then one could clean them and apply thread locker (and should - because it also helps seal them besides preventing them from backing out from low torque against a thin cover)

With the trouble Jeep is having on transmission pan leaks - thanks for the idea - I may look into trying to find the torque settings and if the Jeep specs say they are "one time use" bolts for the transmission pan -then try to find out if the Jeep techs at dealerships are using them over again.

 

[BearFootSam]

Fun fact: Old diff lube (at least the "special" GM stuff) was actually made with whale oil.

Now it's made with bering seal oil.

 

[Hootbro]

I thought I read here that the diff cover bolts were a one time use bolt. Seems strange if so to replace them when changing the fluid.

They are one time use bolts if you expect to torque to spec of 30 ft-lbs. Like @ShadowsPapa mentioned, they are torque to yield and stretch.

That being said, if you back the torque off to 25 ft-lbs, you can probably reuse them. Reusing them and going to 30 ft-lbs and you have about a 50/50 chance of snapping the head off.

 

[legacy_etu]

They are one time use bolts if you expect to torque to spec of 30 ft-lbs. Like @ShadowsPapa mentioned, they are torque to yield and stretch.

That being said, if you back the torque off to 25 ft-lbs, you can probably reuse them. Reusing them and going to 30 ft-lbs and you have about a 50/50 chance of snapping the head off.

Strange that they're TTY bolts. I wouldn't have expected that. I would have expected shadowspapa thoughts around the thread-locker being the reason.

 

[Hootbro]

Strange that they're TTY bolts. I wouldn't have expected that. I would have expected shadowspapa thoughts around the thread-locker being the reason.

It could be the thread locker and my TTY statement misplaced. I just have learned the hard way that reusing them and taking to max torque, they tend to snap off sometimes. I think the reusable gasket material does not give a good feedback to let you know when you are about to torque them to fail.

 

[ShadowsPapa]

I think the reusable gasket material does not give a good feedback to let you know when you are about to torque them to fail.

The fact that the cover is not very thick means there's little bolt shank to stretch and warn you by "feel".

Question -
I've not had my own differential covers off as of yet. That will be in the future. So I've not personally seen the cover seal these use. Are they at all like used in the AMC 20 (which Dana bought the rights to) where it's square cut o-ring in a channel in the housing?
Here's a 20 I worked on years ago, you can see where the square-cut o-ring fits just inside the bolts. It allowed you to torque the bolts down and not distort a paper/fiber/cork gasket at all. These almost never leaked.

 

[ShadowsPapa]

Now it's made with bering seal oil.

Are you being straight with us?
Never mind, some won't get it...........

 

[legacy_etu]

The fact that the cover is not very thick means there's little bolt shank to stretch and warn you by "feel".

Question -
I've not had my own differential covers off as of yet. That will be in the future. So I've not personally seen the cover seal these use. Are they at all like used in the AMC 20 (which Dana bought the rights to) where it's square cut o-ring in a channel in the housing?
Here's a 20 I worked on years ago, you can see where the square-cut o-ring fits just inside the bolts. It allowed you to torque the bolts down and not distort a paper/fiber/cork gasket at all. These almost never leaked.

Yeah, I love that design. No worries about crushing the seal with that.

 

[Minty JL]

Also loosen the fill plug before you drain.

You beat me to it ?

 

[ShadowsPapa]

My rule is always loosen the fill plug first (diff, tranny, xfer case, etc.). If for some reason it doesn't come loose or you strip the plug, it makes it difficult to refill later on.

This guy found a way to refill when the plug wouldn't come out..

 

[whysoserious]

This guy found a way to refill when the plug wouldn't come out..

Hah!

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