Rear diff input seal

[rabfan]

I installed a new differential Input seal. My question is while tightening the yoke nut it is possible to change the backlash through over tightening? I thought I was careful not to blam it on there......but
My rear driveshaft did have some rotational backlash before but now I'm wondering if I can feel it while starting off from a stop. it has the NV3550 manual.
thanks. RJ

 

[Big Al]

I'm doing mine soon and thinking you need a few special tools.

1/4" torque wrench to measure the pinion tapered bearing preload, it's like 10 inch pounds. You crank down on the pinion nut a little at a time and measure the rotational torque required to turn the pinion shaft as you go.

A chain wrench to hold the yoke from not turning while you torque up the pinion nut to around 250 ft lbs.
or make up a tool or buy the tool to hold the yoke stationary.

A magnetic base dial indicator to measure backlash. Off the top of my head, it should be around 0.006"

 

[tommudd]

I have done many with just counting the number of turns coming off
mark everything and count and then reattach and count same number back in plus a very little bit more, right past the line but not a smidgeon more, no issues, no leaks no problems

 

[Shankster]

I installed a new differential Input seal. My question is while tightening the yoke nut it is possible to change the backlash through over tightening? I thought I was careful not to blam it on there......but
My rear driveshaft did have some rotational backlash before but now I'm wondering if I can feel it while starting off from a stop. it has the NV3550 manual.
thanks. RJ

I'm about to dive into my rear diff (Chrysler 8.25) too. Based on my research (not hands on experience I might add) the answer is no, I don't think you change the backlash by overtightening the pinion nut but you can definitely overtighten and put too much preload on the bearing which presumably would generate excessive wear on the bearing (and possibly fool you into thinking you have no backlash if you're trying to rotate the driveshaft by hand). I believe the only thing that would affect backlash in the pinion set up is the thickness of the spacer between the bearing and the pinion gear and it doesn't sound like you touched that. Seems the spacer can affect the depth of engagement between the ring and pinion and hopefully the factory got that right in the beginning. Then you can adjust backlash with a tool you insert into the hubs on either side. If your engagement depth is out of spec (wrong spacer which seems unlikely) you can still get your backlash in spec but there may be some other repercussions in regard to wear on your ring/pinion. Without some fancy and expensive equipment I don't know how you measure engagement depth.

Did you install a new crush sleeve when you installed the seal? I don't believe they're reusable so could that be the issue?

Again, I'm a noob on diff work so don't take what I say as gospel but I do try to research stuff to death before I dive into new projects.

 

[tommudd]

Don't have to replace the crush sleeve when replacing a pinion seal

 

[Shankster]

Don't have to replace the crush sleeve when replacing a pinion seal

Yep, my bad. However the manual says:

CAUTION: Never loosen pinion nut to decrease pinion
rotating torque and never exceed specified preload
torque. If preload torque is exceeded a new
collapsible spacer must be installed.

So if the OP did overtighten, he shouldn't just back off on the pinion nut but should replace the crush sleeve. That's a LOT more work than I'm sure he bargained for.

I also don't know how he'd check pinion bearing preload without removing the carrier? I wonder if there is a rotational torque spec with the diff fully assembled and the axles in place? Might be something that should just "feel right"?

 

[Big Al]

If i was replacing just the seal, I'd mark the nut exactly where you found it. Say use a pin punch on the 2 surfaces. Then replace the seal and then tighten it up exactly where you found it. Then with a 1/4" torque wrench to measure the pinion tapered bearing preload. You crank down on the pinion nut a little at a time and measure. I've read that if your using existing (worn) bearings, use 5 in/lbs.
I'd even put a bit of removable loctite on the threads too.

 

[tommudd]

FOR FUTURE REFERENCE AND THOSE THAT DON'T KNOW
The pinion seal, also called a pinion shaft, is designed to keep oil in and any water, dirt or debris out. As long as the pinion seal is in place and performing well, the differential will stay in good shape and operate as it is supposed to. A failed pinion seal can result in a minor leak where fluid seeps out, or a major leak that can ruin the differential bearings and gears. As long as the seal is replaced in a timely manner, there will be little chance of any internal damage taking place.
⅜ Ratchet
⅜ Socket set - Metric and Standard
½ Ratchet - at least a 18 inches long for leverage
½ Breaker bar - 24 inch
½ Socket set - Metric and Standard
½ socket for pinion nut - this will need to be determined when disassembling
Ball peen hammer
Brake cleaner
Drain pan
Gear oil
Jack
Jack Stands
Mallet/plastic hammer
Metric wrench set
Paint marker
Pinion Seal
Puller set
Repair Manual - For torque specifications
RTV Silicone
Seal puller
Shop towels
Standard wrench set
Wheel Chocks

NO TORQUE WRENCH NEEDED
Remove the driveline mounting bolts. These are located where the driveline and axle meet.
Separate the driveline. Using a mallet or plastic hammer, strike the end of the driveline away from the flange.

Once the driveline is separated from the flange, you can either tie it up and out of the way or remove it completely from the transmission.
Make reference marks. Mark the position of the flange and pinion shaft with a paint pen. You will also want to count the exposed threads and write the number down.

This is done so the correct amount of torque is applied and it won't be overtightened.

Remove the flange/yoke nut. Remove the mounting nut on the flange/yoke.
Use the puller to remove the flange/yoke. Once the puller is in place and mounted, by slowly tightening the drive shaft it will begin pulling the flange/yoke off the pinion shaft.

In most cases, continue driving the center shaft until the the flange comes loose and off the pinion shaft.

Removing the pinion seal
Set up a drain pan. Place a drain pan underneath the pinion seal area.
Remove the seal. Take a seal puller, hook the inside of the seal and pry to remove the seal. It may take a couple of different placements to get it removed.
Prep the area. After the pinion seal is removed, clean the inside surface of the pinion seal mounts.

Get any dirt and grime removed and the surface cleaned and prepared for the new seal.
Tighten the pinion nut. As you are tightening, inspect after every turn to watch the reference marks and to keep an eye on the number of threads exposed on the end of the shaft (where the red arrow points in the image above).
Line up the reference marks. When you reach the number of threads needed, check the paint marks to see if they are lined up as you marked.

If they are not lined up, you may have to tighten it up slightly to match.
Apply RTV silicone. Apply a small bead of RTV silicone to the inside of the flange/yoke on the splines.

Apply lubrication where needed. Apply a thin layer of grease to the smooth surface that is going into the pinion seal.
Install the new pinion seal. Position the seal according to how it needs to be installed against the axle housing.

With the seal in position, begin tapping on a seal edge to begin seating it. When tapping, tap in a cross pattern so you are installing the seal as evenly as possible. Doing this will prevent any damage to the new pinion seal.

Once the seal begins to seat, tap the seal until it is flush with the axle housing. After it is installed, inspect the seal to be sure it is flush with the axle housing.
Install the flange/yoke. Make sure to match the reference marks that you made.

Seat the flange/yoke. Once the flange is in place, you may need to use a mallet to get the flange/yoke to seat enough to get the washer and nut started.
Apply silicone to the pinion washer and install. Before tightening the nut, put a small bead of RTV silicone on the inside of the flat washer.

Install the washer and nut onto the pinion.
Reinsert the driveline. If you removed the driveline earlier, start by inserting the driveline carefully into the transmission extension housing.

If you just secured the driveling without removing it, just release the drive line from where it was tied up.
Mount the driveline. Lift, line up, and mount the driveline to the flange/yoke.
The driveline slides in and out of the transmission; this will give you the travel needed to adjust and mount the driveline.

Mount and tighten the bolts. Once you have the flange/yoke in place, start the mounting bolts. Tighten the mounting bolts to specifications.
Remove the axle fill plug. You will use your finger to check the axle fluid level. The fluid level should be just below the fill hole. If it is low, add what is needed.

Raise the vehicle. Raise the vehicle off the jack stands.

Remove the stands. Remove the jack stands and lower the vehicle by releasing the jack.

Release the brake. Release the parking brake now that your vehicle is safely on the ground.

Replacing a leaking pinion is very important in preventing any major repairs. The pinion seal leaking is a good indicator that something needs attention.

 

[tommudd]

The above is how I have done about 50 of them, PLUS the Lead tech at the local Jeep Dealership was at one , well quite a few really, of my Liberty M&Gs that we did monthly at my place
Was getting ready to do one and he asked how I did the ones I had done.
So told him and he laughed saying that is exactly how they did it at the shop. ( Chrysler/Jeep/ Dodge )
Now he had over 24 years experience and never touched a torque wrench either when doing them
So now let the games begin

 

[Shankster]

The above is how I have done about 50 of them, PLUS the Lead tech at the local Jeep Dealership was at one , well quite a few really, of my Liberty M&Gs that we did monthly at my place
Was getting ready to do one and he asked how I did the ones I had done.
So told him and he laughed saying that is exactly how they did it at the shop. ( Chrysler/Jeep/ Dodge )
Now he had over 24 years experience and never touched a torque wrench either when doing them
So now let the games begin

Seems like you're looking for an argument Tommudd? You won't get one from me - that's an excellent post and one I will come back to when needed. It doesn't contradict anything I said however which is I think what you're implying by the "let the games begin"

 

[tommudd]

It doesn't contradict anything I said however which is I think what you're implying by the "let the games begin"

Sadly you do not know me or you would see the humor in that statement
Oldtimers will, but oh well

 

[Shankster]

Sadly you do not know me or you would see the humor in that statement
Oldtimers will, but oh well

So do us new oldtimers a favor and explain

 

[tommudd]

So do us new oldtimers a favor and explain

Well first thing the comment was NOT directed at you or anyone really
I was just taking the time to put it all down in print for future references as many things are on here
Next its a simple statement
You read through, you get your tools out and lined up and " let the games begin "
For several years I held a Liberty ( mostly but other Jeeps showed up) M&G at my place once a month
At times there would be people from 7 states there to wrench, cook out, sit around the fire and BS etc
Some weekends it was all working on, lifting whatever, some weekends 4 wheeling one day or so
As most people showed up later on Friday evening, sitting up tents , big old bonfire and if not me someone else would yell out " let the games begin"
So you see it has nothing at all to do with you , get over yourself and have fun on here
We do know what we are doing


Oh and the Oldtimers are all pretty much gone, they were the old ( 60-67, now it's me that age ) motorheads that I hung with when I was in my 20s, taught me a lot about cars, building something out of nothing, but would be very out of place in this world where everyone gets butthurt about everything . Man I miss them. They always told me the way to pay them back was to help and teach the younger crowd coming up, hard to do now ,they think they know it all at 19 LOL