Diff or trans noise!?!

Gregomatic

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Hey guys, I'm in a bit of a quandary and I need to draw from your expertise.

History of diff:
Bought the car 3 years ago with rear differential problems (amongst many others) with full knowledge I'd be fixing it. It makes a low growl as you drive, up to a fairly loud resonating hum at high speeds.
Upon ownership, I opened the case to change the lube and inspect all the gears and concluded at some point the seal between the pinion and drive shaft had slowly leaked to the point it overheated.
I'll get some pics up tomorrow, but the spider gears are blued from being tempered and worn to the point they're getting rounded. Still flat at the top of the teeth, but very worn. The ring and pinion don't look near as worn, but if I pull the axles, I'm overhauling everything. (The pony is about to hit 200 thou and my baby needs back!)

Other things had to take priority to keep the car mobile, namely a clutch. (4 siblings learned to drive clutch in it as they got old enough)
I'm a big fan of 'if it works, don't fix it', so I decided to repair other things until the diff went South.
I've changed the lube twice and each time I inspected it, you'd think I was panning for gold.
I fill it back up with heavy weight Lucas oil with Lucas Oil Anti Shudder additive and it's kept motoring on.

Last week I went to pull out of my work parking lot and POP, sounded like I hit something metal. Got out and inspected, found nothing eventful.
Pulled out onto the road and CLANK CLANK, I pulled in the next parking lot to reinspect. At this point I thought, "Well, it lasted waaay longer than I expected!"
Suspecting a chipped tooth, I decided to hobble it home. By half a block it had clanked 4 or 5 more times, so I aborted and headed back to work, where she has resided since.

Every time I felt a clank (probably just over a dozen in all) I could feel for just a fraction of a second the entire drive train lock up. Absolutely the worse sound I've ever heard her make. Tonight I got a chance to take the back off and inspect again. Short of the usual galaxy of glitter in the lube, everything looked the same. No broken teeth on the spider gears as expected.

Here is the quandary.
A mechanic friend of mine said "Are you sure it's the differential?"
I thought Well of COURSE it is!, but then I remembered what my trusted mechanic Josh said when he put in my new clutch. He told me the transmission was low and that he replaced a bad seal that was causing it. MY biggest fear right now is What if it IS the trans?? What does a trans sound like when it's failing?

Due to a catastrophic and unexpected financial crisis over a year ago, I have not been able to do anything but what is necessary to this car to keep it going. If I'm looking at a failed transmission, she's looking at a looong sit. I need to put finances toward exactly what's broke. Is there any definitive way to tell if a transmission is bad? Just MAYBE it's a tooth in the gear trying to high center on the crown of another tooth, but if I fix the rear and it's the trans, it's gonna be game over for a while. The thought of not having my pony just rips me.

I'll have many more questions and other info updated tomorrow and even more Monday, but I sure could use some of your knowledge fellas.

Any initial thoughts are greatly appreciated.
Grego
 

badass98svt

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Dude, you grenades your rear end.
You'd know it if you were hearing the noise come from right below you in the trans/clutch.

I had a leaking pinion seal as well many moons ago and kaboom. It's only a matter of time. If you're lucky you just need new ring and pinion and a new differential/bearing kit.
On the bright side, now is the time to put some lower gears in there.
 
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Gregomatic

Gregomatic

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Dude, you grenades your rear end.
You'd know it if you were hearing the noise come from right below you in the trans/clutch.

When It popped (loud metallic clank like two hammers together) I could feel it in my seat and stick shift, so I wasn't sure. I figured it was the diff, but the gears didn't look much different than last time I had the case open. I'm getting ready to post some pics so you can actually set eyes on it.
With the sound it was making, I was sure I'd find a broken tooth, chips or a failing bearing. None of that. It did toast at one point, but the heavy duty lube has kept it going...until now...


I had a leaking pinion seal as well many moons ago and kaboom. It's only a matter of time. If you're lucky you just need new ring and pinion and a new differential/bearing kit.
On the bright side, now is the time to put some lower gears in there.
Kaboom? That sounds violent. I was intending to get on the highway so I guess I should be thankful it let me know in the parking lot! Do they breach the housing when they go South? I'm afraid it might snap a U joint or twist the drive shaft if the gears locked on the highway, so it's getting trailer'd to the garage.

I spent the majority of the day at Midway U Pull where they advertised a 2004 new edge with low miles 'recently arrived'. It was a skeleton. Out of a dozen sn95's only one was possibly a good donor but it had over 211,000 on the clock. Most with the diff cover off and stuff missing.

I thought switching out the rear would be easier, but I'm not so sure that's the way i want to go now.
I did find a good couple of rebuild kits at Jeg's that I'm considering.
I have beat myself up with the gear size decision!
On one hand I feel it would be wise to stay with the stock, especially with the rise in gas prices.
But when I put the large rims and tires on it, it made it feel sluggish, so I wondered if one size lower would compensate for it. (Maybe even make the spedo closer to accurate??)
The cost difference seems negligible.
What is the next lowest size?
Mine is a 7.5 3 - 27.

Is the next size a 38 tooth ring and 11 pinion 3.45 ratio, or is there one closer?
I've been fine with the stock, as I'm not racing, but it sure would be nice to get that little pep back.
I've fixed my own cars for years, never touched a rear diff, so I'm finding this quite the adventure.
If it were your 2000 V6, what might you put in it?
 
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Adfalenski

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The reason you feel it through the trans is that every time the broken tooth in the diff gets pulled through the ring gear, it sends a shock through the driveline all the way to the engine. If you don’t already have one, now would be a good time to upgrade to a limited-slip 8.8 junkyard rear end.
 

badass98svt

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Yeah, I was thinking you had a GT with an 8.8
If you plan on heavily modding the car down the road, I'd go ahead and upgrade to a used 8.8. Honestly, it's probably cheaper than rebuilding the little 7.5 anyway.


And yes, it can definitely blow a hole in the stock diff cover and leave you stranded. Ask me how I know. :rolleyes:
 
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Gregomatic

Gregomatic

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At this point, I don't see any heavy modification in the future for this car.
I've pretty much got it looking presentable again after hitting a huge deer, and I want it to be mechanically sound so I don't have to be concerned if it needs to take a road trip, but honestly I'm not looking to do any racing.
With that said, I would like enough pep to be able to to accelerate quickly out of a bad situation with defensive driving, and the big rims made it sluggish.

Would an 8.8 bolt right up?
 
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Gregomatic

Gregomatic

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V8 would have 8.8
V6 would have 7.5
But they are swappable
Thanks for weighing in buddy.
Your latest avatar pic just kicks a hole in it bro!
Looks fantastic!

Just last night I ran across this. It may not be ideal, but has my attention.
ModelDescriptionMilesPart
Grade
Stock#US
Price
Dealer Info
2003
Rear Axle Assembly
Ford Mustang
FD3D5C38835049F4973251A477005464001_thumb.jpgBase, (7.5' ring gear), (3.27 ratio), ABS,HAS ABS,RWD-176K
176,000​
A​
e1756 41178
$350.52​
Late Model Auto Parts USA-MO(Kansas-City) Request_Quote 1-800-800-8502 Request_Insurance_Quote

Question,
I don't think my car has ABS, but this axle does.
I can see how a car with ABS would need and ABS axle,
but would an axle with ABS be fine on a non-ABS car?
 
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Gregomatic

Gregomatic

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badass98svt

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It's called the differential. You may have a better time searching using that instead of "spider gears".
 
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Gregomatic

Gregomatic

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So the ring and pinion are the only gears that change size, the spider gears always stay the same size, correct?




USA STANDARD GEAR ZIKF75S28

qty_down_white.pngqty_up_white.png
$96.79
Price


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These are made by USA standard, they seem decently priced.
 
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95opal

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A kit similar to this is what I'd really like. But it has no spider gears!
Do the not make kits with ring, pinion and spider gears?
View attachment 15879
JEGS 60007K
Part Number: 555-60007K

GM 10-Bolt Ring & Pinion with Install Kit 7.5" & 7.625" Diameter Ring Gear


GM 10-Bolt Ring & Pinion with Install Kit
  • 7.5" & 7.625" Diameter Ring Gear
  • 3.42 Ratio
  • 41-12 Teeth
  • 27 Spline Pinion
  • For 3.23 Ratio and Numerically-Higher Carriers
View Details
$296.75

Yes they make they sell the center section separate. Just make sure your looking at the ford 7.5 not the GM.
 
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swapping in a newer diff is pretty fucking simple. and taking the car to a specialty shop that can do rear end work shouldnt cost that much. depending on deals you can probably get a diff, the rear end set and install for about $1000

 

RAU03MACH

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Thanks for weighing in buddy.
Your latest avatar pic just kicks a hole in it bro!
Looks fantastic!

Just last night I ran across this. It may not be ideal, but has my attention.
ModelDescriptionMilesPart
Grade
Stock#US
Price
Dealer Info
2003
Rear Axle Assembly
Ford Mustang
View attachment 15878Base, (7.5' ring gear), (3.27 ratio), ABS,HAS ABS,RWD-176K
176,000​
A​
e1756 41178
$350.52​
Late Model Auto Parts USA-MO(Kansas-City) Request_Quote 1-800-800-8502 Request_Insurance_Quote

Question,
I don't think my car has ABS, but this axle does.
I can see how a car with ABS would need and ABS axle,
but would an axle with ABS be fine on a non-ABS car?
I think your talking about the exciter ring that is internal in the diff

There is 2 type
 

Makoto

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normally i wouldn't recommend this but since 7.5 diffs have dried up y our best option would probably be to actually swap in a GT axle.
i only suggest this because it seems to be about the same effort as throwing another old 7.5" back there with the added benefit of actually being able to find parts for it.

 
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Gregomatic

Gregomatic

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Yes they make they sell the center section separate. Just make sure your looking at the ford 7.5 not the GM.

That was a good catch. This is what I need.​

Ford 7.5" Ring & Pinion with Install Kit 3.45 Ratio​

Part Number: 555-60021K​


View attachment 15928
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$350.55

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Lowest Price Guarantee

Ford 7.5" Ring & Pinion with Install Kit
  • 3.45 Ratio
  • 38-11 Teeth
  • 28 Spline Pinion
 

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