pinion seal repair question (7 Viewers)

[Kernal]

There was a good discussion on this topic about eight years ago:

Don't think anyone uses FIPG on splines as mentioned above; about any grease (or Moly paste) would be more appropriate for splines IMHO.

Replaced front pinion seal today

The front pinion seal on my 96 FZJ-80 has been seeping for awhile so replaced it today. I marked the pinion nut, pinion shaft, flange, and 3rd member before starting the job, and I noted that there was barely one thread of the pinion shaft showing past the pinion nut. With the vehicle on it's...

forum.ih8mud.com

 

[TurboDennis]

Talked with Zuk (@gearinstalls.com ) about this recently, actually.

The crush sleeve doesn’t know the difference, so remove the nut, pull the flange, replace the seal and install the nut to stake in the same position as before. I trust his word on this.

And you would be wrong to do so. Zuk's site is a great resource, and he certainly helped a lot of people set up their diffs, but he is FAR from absolute authority on differentials. I don't want to knock him, but A LOT of his methods (especially in the earlier days of his website) would be frowned upon by real professionals.


I really dont want to get dragged into this never-ending argument. This topic comes up regularly and every time it does there is a large number of people who will claim that "they reused the crush sleeve successfully", and therefore its perfectly fine to do that. So i'll try to explain as briefly as i can in point form why it is NOT ok to reuse a crush sleeve.


1) First you have to understand what the purpose of the crush sleeve is. Many people mistakenly believe that it has something to do with the pinion bearing preload. This is not the case. You dont need the crush sleeve AT ALL to set the proper bearing preload. The sole purpose of a crush sleeve is to allow you torque the pinion nut to correct torque without overloading the pinion bearings.
2) Then you have to understand the significance of correct torque on the pinion nut. Anytime the differential is stressed, the pinion will naturally want to deflect away from the ring gear. The higher the stress, the more it will deflect. When it deflects, the teeth on the ring/pinion move apart, reducing the contact between them. The crown (top) of the tooth is much weaker than the root, obviously. This is how, and why the differentials "grenade".
3) Correct (very high) pinion nut torque is one of the main ways of reducing this deflection. The torque is typically north of 200ft/lb. This high torque is critical to making sure the pinion is tight, and can not "strech" and deflect much under stress.
4) With all of that out of the way, you now have to understand what happens when you reuse a crush sleeve. When you "return the nut to original position or slightly tighter", as most people recommend doing, the torque would be maybe 25-50% of what is required. I actually measured this once for the sake of curiosity, and it was about 60ft/lb. And you cant go tighter because doing so will overload the pinion bearings.
Many people mistakenly believe that the purpose of this high torque is to keep the nut from backing out. THIS IS NOT THE CASE. Many people make this incorrect assumption and think that they will be OK if they compensate by staking the nut or using locktite.

So.. this brings me to my final point. Can you reuse the crush sleeve and keep driving to work for many years? Absolutely, and most people do. This applies to 99.9% of cars on the road which never experience severe stresses on the differential. This is why it's such a common practice to reuse the crush sleeves by nearly all "regular" mechanics.
Can you reliably expect your differential with a reused crush sleeve to hold up when you take your 7000lbs truck with lockers and 37's off roading? Absolutely not.
For the extra hour or two that it takes to do the seal replacement job properly, it's just plain stupid in my opinion to take this shortcut.

 

[80JDM]

And you would be wrong to do so. Zuk's site is a great resource, and he certainly helped a lot of people set up their diffs, but he is FAR from absolute authority on differentials. I don't want to knock him, but A LOT of his methods (especially in the earlier days of his website) would be frowned upon by real professionals.


I really dont want to get dragged into this never-ending argument. This topic comes up regularly and every time it does there is a large number of people who will claim that "they reused the crush sleeve successfully", and therefore its perfectly fine to do that. So i'll try to explain as briefly as i can in point form why it is NOT ok to reuse a crush sleeve.


1) First you have to understand what the purpose of the crush sleeve is. Many people mistakenly believe that it has something to do with the pinion bearing preload. This is not the case. The sole purpose of a crush sleeve is to allow you torque the pinion nut to correct torque without overloading the pinion bearings.
2) Then you have to understand the significance of correct torque on the pinion nut. Anytime the differential is stressed, the pinion will naturally want to deflect away from the ring gear. The higher the stress, the more it will deflect. When it deflects, the teeth on the ring/pinion move apart, reducing the contact between them. The crown (top) of the tooth is much weaker than the root, obviously. This is how, and why the differentials "grenade".
3) Correct (very high) pinion nut torque is one of the main ways of reducing this deflection. The torque is typically north of 200ft/lb. This high torque is critical to making sure the pinion is tight, and can not "strech" and deflect much under stress.
Many people mistakenly believe that the purpose of this high torque is to keep the nut from backing out. THIS IS NOT THE CASE.
4) With all of that out of the way, you now have to understand what happens when you reuse a crush sleeve. When you "return the nut to original position or slightly tighter", as most people recommend doing, the torque would be maybe 25-50% of what is required. I actually measured this once for the sake of curiosity, and it was about 60ft/lb. And you cant go tighter because doing so will overload the pinion bearings.

So.. this brings me to my final point. Can you reuse the crush sleeve and keep driving to work for many years? Absolutely, and most people do. This applies to 99.9% of cars on the road which never experience severe stresses on the differential. This is why it's such a common practice to reuse the crush sleeves by nearly all "regular" mechanics.
Can you reliably expect your differential with a reused crush sleeve to hold up when you take your 7000lbs truck with lockers and 37's off roading? Absolutely not.
For the extra hour or two that it takes to do the seal replacement job properly, it's just plain stupid in my opinion to take this shortcut.

Yup! It's just like I remember from trade school. I shouldn't be surprised to know that this is still one of the most corner cut procedures at any shop and even some driveline shops too I would bet. I admit to doing exactly the same while cutting my teeth as a starving apprentice working flat rate at the dealerships where "Get it out the door man!" was all that really mattered. I will not argue with the adage that 'good enough is good enough' but while I'm not Rockefeller, I'd like to keep that kind thinking to a full tank of gas, wash fluid or touch up paint. Not my gears . BTW, I have asked the question directly to Mr. Zuk so that he can speak for himself. Thanks to all of you for your contributions. I am new to this forum and didn't think that I would open such a hornets nest so soon. But I'm very happy to start this important discussion. At least I think its important.

 

[-Spike-]

And you would be wrong to do so. Zuk's site is a great resource, and he certainly helped a lot of people set up their diffs, but he is FAR from absolute authority on differentials. I don't want to knock him, but A LOT of his methods (especially in the earlier days of his website) would be frowned upon by real professionals.


I really dont want to get dragged into this never-ending argument. This topic comes up regularly and every time it does there is a large number of people who will claim that "they reused the crush sleeve successfully", and therefore its perfectly fine to do that. So i'll try to explain as briefly as i can in point form why it is NOT ok to reuse a crush sleeve.


1) First you have to understand what the purpose of the crush sleeve is. Many people mistakenly believe that it has something to do with the pinion bearing preload. This is not the case. You dont need the crush sleeve AT ALL to set the proper bearing preload. The sole purpose of a crush sleeve is to allow you torque the pinion nut to correct torque without overloading the pinion bearings.
2) Then you have to understand the significance of correct torque on the pinion nut. Anytime the differential is stressed, the pinion will naturally want to deflect away from the ring gear. The higher the stress, the more it will deflect. When it deflects, the teeth on the ring/pinion move apart, reducing the contact between them. The crown (top) of the tooth is much weaker than the root, obviously. This is how, and why the differentials "grenade".
3) Correct (very high) pinion nut torque is one of the main ways of reducing this deflection. The torque is typically north of 200ft/lb. This high torque is critical to making sure the pinion is tight, and can not "strech" and deflect much under stress.
Many people mistakenly believe that the purpose of this high torque is to keep the nut from backing out. THIS IS NOT THE CASE.
4) With all of that out of the way, you now have to understand what happens when you reuse a crush sleeve. When you "return the nut to original position or slightly tighter", as most people recommend doing, the torque would be maybe 25-50% of what is required. I actually measured this once for the sake of curiosity, and it was about 60ft/lb. And you cant go tighter because doing so will overload the pinion bearings.

So.. this brings me to my final point. Can you reuse the crush sleeve and keep driving to work for many years? Absolutely, and most people do. This applies to 99.9% of cars on the road which never experience severe stresses on the differential. This is why it's such a common practice to reuse the crush sleeves by nearly all "regular" mechanics.
Can you reliably expect your differential with a reused crush sleeve to hold up when you take your 7000lbs truck with lockers and 37's off roading? Absolutely not.
For the extra hour or two that it takes to do the seal replacement job properly, it's just plain stupid in my opinion to take this shortcut.

The crush sleeve requires a lot of force to compress to the correct dimension. It doesn't hold that force. That's why you're seeing a lower torque. It is still holding the dimension that it was crushed to. If you loosen and then return the nut to exactly where it started, it's holding the same force as it was before you loosened it. Yes, it's lower than it was the moment when it was installed at the factory, but it has been lower all along. Nothing else changed. If you didn't put in a new bearing or pinion or something else that might affect the sum of the length of the assembly, you don't need a new crush sleeve. Yes, a solid collar is preferable in high-load situations, but your logic on it being impossible to reuse a crush sleeve is faulty.

I would agree that it's preferable to set up the assembly fresh, but reusing the crush sleeve doesn't make it any worse than not having touched it to begin with. So, the lesson here is that everyone who stresses their driveline should replace the crush sleeve as PM, and use a solid collar.

Edit to add: sometimes the leaky seal is not just a leaky seal- it's leaking because the pinion is moving around too much. In this case, the preload needs to be fixed, and likely it's loose because either the bearings are worn or the crush sleeve got overcrushed (see @TurboDennis explanation of pinion deflection) or some other part is worn. Simply replacing the seal will only cover up the symptom, to fix the problem the diff should be set up again, likely with some new parts. Including the crush sleeve, or a solid collar.

 

[TurboDennis]

The crush sleeve requires a lot of force to compress to the correct dimension. It doesn't hold that force. That's why you're seeing a lower torque. It is still holding the dimension that it was crushed to. If you loosen and then return the nut to exactly where it started, it's holding the same force as it was before you loosened it. Yes, it's lower than it was the moment when it was installed at the factory, but it has been lower all along. Nothing else changed. If you didn't put in a new bearing or pinion or something else that might affect the sum of the length of the assembly, you don't need a new crush sleeve. Yes, a solid collar is preferable in high-load situations, but your logic on it being impossible to reuse a crush sleeve is faulty.

I would agree that it's preferable to set up the assembly fresh, but reusing the crush sleeve doesn't make it any worse than not having touched it to begin with. So, the lesson here is that everyone who stresses their driveline should replace the crush sleeve as PM, and use a solid collar.

Crush sleeve does "hold" quite a bit of that force. Especially if it's fresh.
If you put a new crush sleeve into a press and crush it to roughly the correct final length and then release, you will notice that it will spring back noticeably. If you take a used crush sleeve and compress it to the same length (which will probably only require a tiny amount of pressure, since it's already been crushed), it won't spring back nearly as much (if at all).

But i do agree that old crush sleeves will loose this tension over time, thus making the diff weaker. So yes, a solid spacer is superior for ultimate strength.

 

[TurboDennis]

Edit to add: sometimes the leaky seal is not just a leaky seal- it's leaking because the pinion is moving around too much. In this case, the preload needs to be fixed, and likely it's loose because either the bearings are worn or the crush sleeve got overcrushed (see @TurboDennis explanation of pinion deflection) or some other part is worn. Simply replacing the seal will only cover up the symptom, to fix the problem the diff should be set up again, likely with some new parts. Including the crush sleeve, or a solid collar.

I agree 100%. I have also noticed when rebuilding differentials that the outer pinion bearing is almost always the first one to go. It's way smaller than the inner and doesnt get nearly as much oil, so it makes sense. This is why i ALWAYS replace the outer pinion bearing with a new one when doing an on-vehicle seal replacement. It has to be removed anyway to replace the crush sleeve, so you might as well replace it with a new one.

Also on a lot of trucks in the rust belt (which im in) the seal will leak from a rust-clogged breather. Many times you can just replace the breather and the leak will go away.

 

[80JDM]

I agree 100%. I have also noticed when rebuilding differentials that the outer pinion bearing is almost always the first one to go. It's way smaller than the inner and doesnt get nearly as much oil, so it makes sense. This is why i ALWAYS replace the outer pinion bearing with a new one when doing an on-vehicle seal replacement. It has to be removed anyway to replace the crush sleeve, so you might as well replace it with a new one.

Also on a lot of trucks in the rust belt (which im in) the seal will leak from a rust-clogged breather. Many times you can just replace the breather and the leak will go away.

yup! I can confirm that the vent was seized and plugged. BTW, do you also pull the old race when you change the outer bearing?

 

[TurboDennis]

yup! I can confirm that the vent was seized and plugged. BTW, do you also pull the old race when you change the outer bearing?

You might have to. Depending on differential, sometimes the crushed sleeve is too fat to fit between the pinion and the outer race, so the race has to come out. Other times it might squeeze through. Removing the outer race also requires a puller, but can be done with a generic one (unlike removing the inner race) if you have a decent selection of pullers.

But again, i always remove the complete outer bearing and replace it with a new one regardless of whether or not it NEEDED to be removed.

 

[80JDM]

Gotcha!