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Discussion Starter #1
Well my 9.75 decided to self destruct.

I was exiting the interstate and turning on to a 2 lane highway. Rolled on some power maybe 1/4-3/8 throttle power,but boost was up, you could feel the torque pushing you in to the seat. You know what I'm talking about. All the sudden boom. Rear end grenades. I was able to drive it to a safe spot to park it and tow it home.

Looks like the ring gear side shim exploded. Part of it went into the pinion gear and wedged, pushing the ring gear back and breaking the head off of the carrier bearing cap. Most of the shim was in the axle tube.

Not sure what my plan is as of now. Its almost completely disassembled. Need to verify the carrier cap isn't bent/twisted, and i need to get the rest of the bolt out of the axle housing. If that all checks out, for about $450 i can have the parts i need to rebuild it completely.

I plan to replace:
Carrier/Pinion bearings
shims
pinion seals
axle seals
ring and pinion

I'm leaving the axle bearings because they look fine and I don't think anything made it that far.

If the cap is bent or I cant get the bolt out of the housing, I guess i found a complete axle with 15k miles for $1150, and the price just goes up from there. I havent been able to find a junk axle with bent tubes or something from a wreck.
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Ouch! Are you repairing this yourself? What kind of diff fluid was in there?
 

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Discussion Starter #3
Ya I will do it myself. its not that hard really. It was the stock fluid, 115k miles on it. And hard miles at that. I have towed a lot of miles with 7-10k trailers and done a couple truck pulls with it. The last one 6 months ago i broke a drive shaft/ujoint. I assume it may have had something to do with this.
 

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ujoint failure? interesting, I guess high miles and lots of towing, lot of work on the u joint. Surprised it blew up thoug, axles still good?

And wow, 1150 for used one? damn.

Have you checked your work/pinion angles being you're lifted and what not?
 

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2017 Ford F150 3.5 King Ranch
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Wow crazy very interesting to see the insides. Sounds like you were hard on the truck, but that's what they are built for right?
 

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I've been searching leisurely for a used 3.73 8.8 and can't find one of those much less either. Just searching online, I haven't seen anything locally but I also haven't looked.

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Discussion Starter #7
I snapped the u joint doing a truck pull. Axle hop is what actually broke the u joint, but that jolt probably broke something in the rear end.
 

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oooooo, the truth comes out!

Man def need those traction bars on truck pull
Hey at least we know that a stock truck can't handle truck pulls! Thanks for testing this!
 

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Hey, he clearly stated it has 115k miles, and "hard miles at that"

That's straight shooting from the start. Lol

I'm guessing that in spite of recent driveline breaks, it's been a good running truck for a long time.

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Discussion Starter #13
Ya thats not the one that i broke it.
 

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Hahahaha right on !
 

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IMO, it's just refreshing to see someone say "yeah, I worked it too hard and blew it up." Most people would jump on a forum and protest that they had driven their truck only a handful of easy miles when the rear end just self-destructed and Ford should buy it back or fix it for free.

Truck pulls do seem like a good way to convert expensive components into piles of debris...
 

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Discussion Starter #16
Ya I think the 9.75 is a great axle. The Elocker is a little wonky IMHO, but overall its a tuff axle.
 

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If you rebuild it yourself, the hard part is going to be getting the preload on the gears correct. That pretty much requires someone who knows how to do that. Otherwise your going to grenade the new rear end. This is really something you need to let an expert do. Either a really great dealer or a really great mechanic. I've been working on cars/trucks for 50 years and I wouldn't try to rebuild one of these new 10 speeds or the rear end. With all the options on these trucks like rear lockers, auto 4 wheel drive, hill descent, traction control, etc,etc,etc. I really dont think this is the kind of repair that you can do at home anymore.
Good luck if you try it. Be sure to get ForeScan and copy the existing software configuration before you start.
 

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Discussion Starter #18
Rebuilding the rear end was easy. Truck runs and drives great. But the elocker has an issue. When i engage it, it says check locking differential. I ohmd the connector and its 3.4-3.5 ohms. I had my dad check his 2015 rear end and it ohmd out at 3.1. I suppose im going to have to pull the cover and look for a wire issue.

Has anyone ever pulled the connector out of the housing? It has 1 bolt holding it in. Looks like it may be an oring fitting?
 

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Discussion Starter #19
If you rebuild it yourself, the hard part is going to be getting the preload on the gears correct. That pretty much requires someone who knows how to do that. Otherwise your going to grenade the new rear end. This is really something you need to let an expert do. Either a really great dealer or a really great mechanic. I've been working on cars/trucks for 50 years and I wouldn't try to rebuild one of these new 10 speeds or the rear end. With all the options on these trucks like rear lockers, auto 4 wheel drive, hill descent, traction control, etc,etc,etc. I really dont think this is the kind of repair that you can do at home anymore.
Good luck if you try it. Be sure to get ForeScan and copy the existing software configuration before you start.
I wonder what makes you think that I am not an experienced mechanic. No need for Forscan. I replaced the the pinion bearings/ carrier bearings, disassembled and cleaned the spider gears. Installed all said parts and set the pinion preload to about 25 in /lb, probably a little to tight, but it felt good. I had to do a lot of shimming from the OEM original shims to get the correct backlash of .008-.012". I ended up with .011". If i was going to be really picky i would have changed the shims on the pinion gear to get a little better contact on the pinion to the ring, but considering i would need a new crush sleeve to do that, i left it where it was. It wasn't horrible, just not perfect.

As far as the finished product, it drives great, no howling or noise. Its very smooth and sounds/drives like brand new. Except for the elocker not working. More on that.
 

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No worries here mate!

You got my vote as mechanic. In fact, just this thread alone is enough evidence that you know more than most of the local Ford dealership shop staff. (at least mine) And folks line up every morning to drop trucks off for those fellas to wrench on.

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