IRS Differential Issue - CV axles/Half shafts

Hello everyone,

I tried installing the CV axles and I'm unable to properly seat the passenger side axle. I looked at every thread that describes the same situation, and every video I could find of replacing half shafts for 2015+ Mustangs. I'm worried that I'm gonna get the same answer as every person who asks this question, but I've run out of options.

How does it look now?
This is the driver side axle. This one is the longer one and it seems to sit properly. I can't pull it out.
Attachment 163476

This is the passenger side axle. This is the shorter one and doesn't look like it's properly seated. I can pull from the inner CV joint and get the axle out.
Attachment 163477

Are you sure you don't have the axles mixed up?
Here is the measurement of the axle I can't properly fit on the passenger side.
Attachment 163478

Also, here's a closeup of the spline and ring.
Attachment 163479

I've used a dead-blow hammer and as much "elbow grease" as I feel comfortable using. Does anyone have any suggestions? What am I missing? Could my differential be defective or the axle be the wrong one? Perhaps the snap ring needs to be replaced?

Both the center section and the axles were sent to me by FF.

Thank you in advance.

Everything mechanical being right, I had to dip the splines and snap ring into a bottle of gear lube. I used the dead blow hammer on one axle also.

I would try removing he snap ring and see if it goes all the way in. If it doesn't then somethings wrong. Doubet it though. Probably just need a bigger hammer
Mike

You’ve got it right, longer shaft is driver side. As the instructions say, push in on the axle to compress the cv joint then give it several hard blows with a dead blow or rubber mallet. Will end up with the same gap as drovers side.

My experience is they bump in pretty easily once lined up and the inner CV joint collapsed. Assuming on the correct sides as yours appear to be. Couple taps with a dead blow hammer and they drop right in. The thing that gives me pause here is how skinned up that snap ring is. I wouldn't get too heavy handed beating on it.

Quote:

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Originally Posted by edwardb

My experience is they bump in pretty easily once lined up and the inner CV joint collapsed. Assuming on the correct sides as yours appear to be. Couple taps with a dead blow hammer and they drop right in. The thing that gives me pause here is how skinned up that snap ring is. I wouldn't get too heavy handed beating on it.

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Yeah, that snap ring is what is giving me hesitation to hit it harder. Since the driver side went in, I had a good comparison on the effort needed; with the passenger side I went a bit over that and still nothing. The weird thing is how it completely stops at the distance shown in that picture, about 1/4 inch away from where it should sit. I was pretty generous with the gear oil on the snap ring and still nothing. I went through a bunch of build threads and videos of installing half shafts on Mustang rear ends, and can't find anyone else being this stuck (aside from having the axles mixed).

I've emailed FF to see if they have experience with customers having a defective differential or axle.

Not sure what else to do at this point.

Where did you get the pumpkin? I've seen this with the old style IRS when it was assembled with the incorrect center section, also the shafts could be just a little too long. Pop the driver side back out, then see if the passenger side will go inIf it does, then the shafts are too long

Quote:

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Originally Posted by michael everson

I would try removing he snap ring and see if it goes all the way in. If it doesn't then somethings wrong. Doubet it though. Probably just need a bigger hammer
Mike

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Have you tried removing the snap ring like Mike suggests? This test should tell you a lot.

Quote:

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Originally Posted by rich grsc

Where did you get the pumpkin? I've seen this with the old style IRS when it was assembled with the incorrect center section, also the shafts could be just a little too long. Pop the driver side back out, then see if the passenger side will go inIf it does, then the shafts are too long

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I got both the center section and axles from FF. I tried removing the driver side axle but outside of getting a crowbar, I don't see how else to pop it out. Here is a picture measuring the travel distance inside the shaft tunnel:

Attachment 163569

Quote:

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Originally Posted by JohnK

Have you tried removing the snap ring like Mike suggests? This test should tell you a lot.

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Quote:

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Originally Posted by michael everson

I would try removing he snap ring and see if it goes all the way in. If it doesn't then somethings wrong. Doubet it though. Probably just need a bigger hammer
Mike

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Here is the snap ring out:
Attachment 163568

It's getting stuck at the exact same place, in the same way. No change in feel or travel distance with or without the snap ring.

Here are a few pictures of the inside of the center section:

Attachment 163570Attachment 163571Attachment 163572Attachment 163573

Lastly, a short clip showing my attempt without the snap ring:

https://imgur.com/1kVqekk

What is that, I circled in redAttachment 163578

looks like a piece of the c-clip??

looks like the spring on the inside of the diff

https://www.google.com/search?q=supe..._u1eE4Zz7PrLdM

Quote:

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Originally Posted by chmhasy

What is that, I circled in redAttachment 163578

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Looks like a clutch plate or a friction plate?? https://i.pinimg.com/originals/e6/ba...814c96e5f7.gif

I took better pictures without the flash. This one is completely straight, and you can see that plate would be blocking the full travel of the spline:

Attachment 163593

And here it is from a slight angle so you can get a better view of it:

Attachment 163592

Great eye, chmhasy!! Now does anyone know what I need to do to shift that just 1/8 inch out of the way?

i pm you

the friction spring shouldn't be offset the pin in the carrier should have held it in place

here is a video of a regular solid axel 8.8 teardown
https://www.youtube.com/watch?app=desktop&v=vUJ9h_-t_e0

Looking at the video, that is most likely the s-spring that isn't in the correct place. Try a long screwdriver or a prybar to see if you can move it. You may have to remove the rear cover to tap it with a hammer.:(

FF came back and said it looked like a slipped clutch or shim and that they are sending me a replacement center section.

I'm deflated to say the least. Not looking forward to removing the entire rear suspension, dismounting the pumpkin, and doing it all over again.

You can align it with a pry bar. The clutch pack is not compressed to a degree it will not move, while not in motion.
Protect you seal. It happens, locking rears, auto trans clutches, etc.
If you have a helping hand, rotating the axle while pushing sometimes helps.

Thats not a clutch pack.

I think you can leave all the rear suspension in
Place.
Mike