Rear Diff. Do I Need to Worry

I got a IRS rear end with low miles from a salvage yard recently and just starting pulling it apart earlier today. I want the 3.73 Torsion rear so I had to find one used but I looked for a while to fine one with low miles and thought I got a good one. Anyways, after I started pulling it apart I found the below.

Attachment 104849
Attachment 104850

Yup, the donor mustang must have hit something on that side hard. I thought it was in excellent condition and the damage was not disclosed in listing but after over $350 shipping it may be a bit late to do much. The aluminum is completely broken and I am having a hard time getting one of the bolt holding in on off, probably going to need to cut it off as it is really bound up. I'm not thrilled but I guess as long as the differential is okay I will be fine. I can get another knuckle easier and cheaper then I can get a decent 3.73 torsion.

I am no expert on any of this and wanted to check with everyone on if the though the differential could have been damaged when the car hit and broke the piece shown above. What can I check for if I do need to be concerned? I guess I will see if the salvage yard will send me a new piece to replace what is broken as I think I need that piece right. Anyone have quick access to that part number if I need to order a new one? Thanks for the help everyone.

The control arm I see broken is not needed for a FFR. If you need one for a Mustang I have several.

There is really no way of knowing until you use it or open it up and look at it. Looking at the pics I suspect its just fine. Buy a new knuckle and move on.
mike

I would do a very careful inspection of the diff housing on that side.
The energy that snapped the knuckle was also transmitted through the axle shaft to the diff housing. Hopefully the CV joints took the hit, not the housing.

You're not going to use the Ford axle shafts, so cut the boots off that side and see what the CV's look like. I'd also get in contact with the seller and see what they'd do about providing a new knuckle... never hurts to ask.

I'd tell them to send you an entire new rear suspension. On their dime. If they want the first one back, that's on their dime also. Document your request and notify ebay or craigslist or whoever. The diff may be fine but do you want to find out when your FFR is on the road and any recourse you have is gone because you bought it so long ago? More than just getting good parts you need, this kind of crap needs to be stopped.

x2 of what CraigS just said, hopefully you used Ebay or Amazon, they have good customer support.

Thanks everyone, I will reach out through Ebay today I guess but there was a 30 day return period on it and I am about a week past that now for what that is worth. I am going to look over the diff housing as well as I can and send an email to the company I bought it from on Ebay, hopefully thing will work out okay. They did describe it in the listing as "damage free." I don't have the best eyes for spotting little details like small cracks but I will put on my reading glasses and do my best. Thanks again everyone.

Even though you are beyond the 30 day ebay period I'd get them involved anyway. A lot of these places do a good % of their business on ebay and can't afford to muck that up. Maybe officially ebay can't help but letting the salvage people know you contacted ebay has to add a bit of pressure.

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Originally Posted by Gordon Levy

The control arm I see broken is not needed for a FFR. If you need one for a Mustang I have several.

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Thanks Gordon, I have followed some of what you have built and I think I will be ordering a few parts from you fairly soon. Unfortunately, I think it is the knuckle that is broken and I will need a new one. I could certainly be wrong, however, isn't that the part that attaches to the hub which is needed for the IRS cars which you need to trim a piece of? Maybe I am lucky and that is the knub I was going to need to trim off, however, I with how it is fractured apart, I am not sure I trust it to be fully sound even if I got luck and don't need that bit of the knuckle.

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Originally Posted by CraigS

Even though you are beyond the 30 day ebay period I'd get them involved anyway. A lot of these places do a good % of their business on ebay and can't afford to muck that up. Maybe officially ebay can't help but letting the salvage people know you contacted ebay has to add a bit of pressure.

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Thanks Craig, I have reached out to the salvage yard through Ebay and listed that the item was not as described. Well see how the handle it I guess, hopefully they will take care of me. I looked at each of the pictures on the listing and you can't see the damage in any of the photos. Maybe they did not know it was damaged, or maybe they took the photos just so you don't see. The salvage yard seems to specialize in mustangs so hopefully they can just send me another knuckle and hub. Like you said, they do a lot of business on Ebay and they do have a very strong rating so I hope they just did not know, the differential is fine, and they will send me replacement parts for what is broken free of charge.

If they don't end up doing right by me, I will post up who the salvage yard is so others can avoid them. I know others have been looking for the 3.73 IRS rear end now that you can't buy it new and they are hard to find. If one of the options is looking to take advantage of people, we can at least avoid them as a community.

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Originally Posted by Fixit

I would do a very careful inspection of the diff housing on that side.
The energy that snapped the knuckle was also transmitted through the axle shaft to the diff housing. Hopefully the CV joints took the hit, not the housing.

You're not going to use the Ford axle shafts, so cut the boots off that side and see what the CV's look like. I'd also get in contact with the seller and see what they'd do about providing a new knuckle... never hurts to ask.

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Thanks Fixit, at first look I am not seeing any damage to the housing but I can only see the top of it right now. I figure I will finish taking things apart, get it up on my bench where I can get a good look and see if it spins freely. I'll try to take a good look over the CVs like you said. Thanks for mentioning that. Hopefully it is okay. Not sure if it is even possible or not but it seems to me that maybe the axle got hammered into the side of the differential pretty hard. Hopefully the suspension arms took all the force. Anything else I should look over?

New spindles are not going to correct your issue. Fix the problem first before investing in new parts. Tons of FFRs running around with donor spindles and no centering problems.
mike

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Not sure if it is even possible or not but it seems to me that maybe the axle got hammered into the side of the differential pretty hard.

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That's what I was eluding to... my guess is the donor car got T-bone'd.
The impact force was on the rear wheel, which transferred to the hub/knuckle (cracking it), and whatever was left over got transferred to the CV/axle and the rest of the rear cradle/diff/etc.

I'd bet the brunt of the force was absorbed by the bodywork/tire/wheel/hub/knuckle, and because the diff is mounted in some pretty soft rubber bushings it probably survived... but check and make sure.

Does anyone else think maybe this happened in shipping? just a thought...

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Does anyone else think maybe this happened in shipping?

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If they dropped it off a 2-story loading dock...

My IRS was shipped in a similar manner, on an oversized pallet and band-strapped. No way (even if dropped on edge) the knuckle could get cracked. This was donor crash damage.

Cool. I only saw the one pic and havent played with IRS, so just jumped in the discussion long enough to say something stupid. ;)

Clearly the seller should be responsible if the part conditions were misrepresented. Although in their defense that cracked knuckle could get missed. I agree likely not shipping damage. Obviously no way to know for sure, but IMO if that's the only damage unlikely the diff is hurt. The inner CV joint slides in/out quite a bit, so there's a pretty good chance the force didn't make it to the diff. Even if it did some, those things are really rugged. I'd even guess the CV joints would be damaged before anything internal to the diff. If it looks OK from the outside, I'd bet it's OK. But again, only guesses FWIW.

As for the knuckle, Ford Performance sells both sides plus the bearing hubs as part number M-5970-M, street price in the $430 range for everything. The individual knuckles are available as service parts, FR3Z-5B759-B is the left, FR3Z-5B758-D is the right. Street price $200 - 300 for each, and that doesn't include the hubs. So the set from Ford Performance is the best value. But a good compromise IMO would be to ask the seller to pay for a replacement knuckle and you keep what you have. Assuming no further damage is detected.

Thanks for all the help everyone. This really is a fantastic community and it allows dreamers like me to take on these types of things for the first time with confidence that others can help fill in the blanks in our knowledge. Obviously this is something I have never dealt with before but all of you have helped me gain confidence and even allowed a little of my venting.

I did hear back from the vendor today. They immediately offered to send me a replacement part for what is broken and apologized. They did note that you can't see the damage in any of their pictures and I believe that they did not know of the problem. They did ponder how the missed it and I understand mistakes happen so as long as the replacement part shows up, they are okay in my book. I did not notice the broken piece myself until I got another part off.

I still plan to give the differential a good look over, but I think you are all right that it is probably fine. I am thinking that the side really did get hammered hard in a crash, maybe rolled but that the suspension arms took most of the force and the rubber bushings holding the differential would have absorbed some blow if the force did make it that far. I will update once the replacement part comes and I have fully inspected the differential.

p.s. Any of you all gong to be at the London Cobra Show? I am trying to get time off work to go and get a up close look at some of your cars and learn a few things. If any of you are going to be there, I'll buy you all a drink or two to helping me out so much, though I might bug you with a question or two while you drink it.

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Originally Posted by Clover

p.s. Any of you all gong to be at the London Cobra Show? I am trying to get time off work to go and get a up close look at some of your cars and learn a few things.

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I'll be there with #8674. You're welcome to check it out. Has this IRS installed.

I'll be at LCS, too, with my Challenge Car. Great show, great fun and all for a great cause, the Cystic Fibrosis Foundation.

Garry

Good to hear that the vendor is going to make it right!

It took a bit of back and forth before I got the replacement part I needed, however, it finally came this afternoon. I don't think they had the replacement part I needed at first, so they gave me the run around for a bit but at the end of the day they did the right thing and got me a replacement for what was broken. I already drilled out the hole to 5/8" and cut off the chunk that needed removing. Took me forever to cut those chunks off but I stuck with it and eventually my cheap tools and perseverance got the job done. Tomorrow I am going to clean then up and apply POR the knuckles and the iron part of the differential. Woo Hoo! Feels great to be back on track.