Hi all,
I thought I'd write up the path that I took to replace a cracked front differential in my 2007 G35 all-wheel-drive X model.
This is mostly for the benefit of those doing an internet search on what is needed to resolve this problem, when the front U-Joint fails on the front driveshaft and flails around and damages the front differential. I'm finding out that it is not a rare occurrence. The lack of a greasable u-joint will cause the part to overheat and fail. Road salt and time are the contributing factors.
I found that local shops were not interested in this repair due to the complexity, and risk of damaging other functioning parts. I totally get it. I only found one local tuning shop that was willing to tackle the job, and they were going to pull the engine to get access to the diff. They wouldn't give a firm quote (wisely) but suggested the repair was going to be north of $3,000 when all was said and done. But they wouldn't know how much until they saw the car up close first. I should note that my local Infiniti dealer flat-out said NO they were not interested. they simply said the car was too old. I get it.....my Infiniti is now 16+ years old.
So I tackled the job myself. Not going to sugar-coat this.....It really sucked and was the most complex repair I have ever done. I've been wrenching on my own used cars for 40 years and this one nearly broke my spirit. It cost wayyyy more than expected and took two weeks from beginning to end.
I should mention that I have a modern home garage with a 2-post lift and a decent number of tools. But I still had to borrow and buy more tools and the lift was essential to do this. I can't imagine how difficult it would be to do this with a car only jacked up off the ground. I needed all of the 5-foot clearance under the car to swing leverage bars to break loose rusted bolts and nuts. And to see what I was doing.

So here is the list of things I had to do to get the car back on the road: THESE STEPS ARE NOT IN ANY PARTICULAR ORDER.
1) Go online and find a good clean used front differential. Look carefully at the pictures to make it sure it matches your original one. Cost about $350 with shipping. check the condition of the seals carefully. Replace them now if needed.
2) Buy a new front driveshaft. New ones are about $130 shipped.
3) Remove the u-joint from the new shaft at the transfer case-end. They are epoxied on but you will need to remove them and practice installing them. I measured the joints, bought a spare online and bought a c-clamp sized to fit to press in the caps when the new shaft is placed back in. There will be near zero clearance to install the new shaft, that is why you need to separate the u-joint and re-install it afterward. There is a high possibility the caps will go on crooked and the needle bearings will fall out and get pinched - that is why a spare joint is needed. It is worth the cost to plan for this.
4) Buy a new alternator and serpentine if yours is original, you will never have better access to do it than now.
5) Check the condition of your transmission pan and oil pan. If they are rusted, buy new ones cause they will get shaken around during this job and begin to leak slightly afterward. Happened to me, I now have new pans and I was not planning to do that.
6) Check the condition of your brakes, tie-rod ends, ball joints, etc. If they are marginal now, better get news ones beforehand.
7) Remove the front tires and the front calipers. Suspend the calipers out of the way.
8) Remove the underbody skidguards, all of them.
9) Remove the exhaust brace. Cut it off if it is too rusted to remove the bolts.
10) Support the transmission and remove the trans crossmember. Remove the front driveshaft.
11) Remove the O2 sensor on the passenger side. I DID NOT HAVE TO REMOVE THE PASSENGER CAT CONVERTER. The bolts were too rusted to safely do that anyway....
12) Remove front hubs.
13) Remove front sway bar.
14) Remove that huge support V-brace wing.
15) Loosen and pull away the steering pinion rack. Support it with rubber straps. Disconnect the steering fluid lines. You do not need to unbolt the shaft clamps.
16) Disconnect tie rods
17) remove bolts from lower control arms, let them hang.
18) Remove passenger side engine mount
19) Remove passenger side axle.
20) Pull out driver's side axle in one piece, disconnect it from the engine (3 bolts) you don't have to fully remove the axle, just get it out of the way.
21) Get ready to remove the sub-frame. This is going to suck and the most difficult part of the job. Place an adjustable single-post jack under the engine - a sturdy piece of wood under the oil pan. Get four ropes and four wires to suspend/hold the subframe. The engine jack will be in the way - be ready for that. Let the subframe swing about 2.5 feet below the car.
22) Once the subframe is out of the way, drain the diff fluid. Clean up any areas you want while you have access. Fix and replace anything under the car.
23) Lower the engine about 2" to give access to the old differential. Now remove the diff. Watch out for the vent hose and bracket. It will be tough to reach some of the bolts.
24) Carefully install the replacement diff.
25) Bag and tag every part that you remove, take note of the length and position of the nuts and bolts. There will be some very similar sized bolts. Take pictures of course along the way.
26) You will need a second person to help align the subframe, control arms, steering rack and some other tasks.
27) I purchased a Venom Heat Inductor from Napa to help with loosening all the rusted nuts and bolts. It cost $500+ but was essential to get these 16-year-old fasteners loose. Many fasteners seem to have a type of Lok-Tite on them from the factory and were a total b*tch to get free. There is often no safe place to use a torch to heat things up so this electrical heat gun was the way to go. I used that inductor a LOT. A cheaper one would probably not have held up.

Again, these steps are not in any true order but instead listed to give someone an idea of the time and effort needed to do this job. I'm sure I left out some things and I did NOT do a video. I would have been cursing too much to make it through the censors anyway. Every day I got sand and dirt in my eyes from working under the car, even with safety glasses.

My car is now back on the road after about 25 hours of labor, parts buying & research, and thanking friends and mechanics for loaning tools and giving advice. I don't have a total cost because it would be too sad to gather all the receipts and face the fact that I spent more time and money than most people would on a 16-year-old 4-door sedan. Let's just say it was over $1,000. Wayyyyyy over $1,000. I have some new tools now though and an intimate knowledge of how this car is assembled.
I hope this thread is helpful as an archive and resource to people when they learn their u-Joint failed and cracked the differential. Oh, I should mention that there is no way to fix the original diff. It can't be 'JB-Welded' in place or on a workbench. Once cracked they are beyond salvage due to the type of weak casing material and the likelihood of the gear teeth being damaged inside.

If you can find a shop capable and willing to do the repair - let them do it. They will earn every penny you spend. It is a messy job to do this. As an alternative to how I did this job, you can choose to pull the engine instead. It is probably about the same amount of work but also opens up the risk of damaging wiring harnesses and all the hoses, A/C lines, computers, etc. My engine was running fine so I extracted the diff from underneath. Plus my cat converter was too rusted to remove without damaging it and new ones that will pass our annual emission inspection would cost 800 bucks apiece. I didn't want to mess with the cats since they were working fine.
I'd welcome any tips added to this thread of people who did the same job. If it helps keep our cars on the road instead of being junked because of a cracked diff, then it is all worth it.

Maine35X

 

My goodness!!! I have the same car, love the car! bought it new! but as each season comes and goes I worry about some of the things that could break, (particularly the electrics) that I would have zero idea on how to fix. I have around 95,000 miles on mine and it hasn't had to go out in ALL of the winters here just a few. It runs so damn good! but they are a fairly complex car that if something like this happened to mine... I just would not know what to do! Thank you for sharing this super big time repair!!! and WELL DONE SIR !!!!

 

*Thank you Triton3.5.*

I should also mention to everyone that since that front driveshaft does not have zerk fittings to load the joints with grease, the best we can do is slather some hot bearing grease all over those joints as often as possible. Especially for those who live in the north where road salt is used every winter.
Hopefully some of that grease will find it's way into the caps by centrifugal force when driving.

And at the first suspicious sound of the U-joints drying up, replace them before they fail and ruin the shaft & differential.
What I heard from the previous owner of this G35X is that there was a noise under the car and before she could find a good place to have it looked at, the damage was done. I bought the car after the diff was ruined.

Tom

 

Hey, sorry for going off topic, but im new to this website and dont know why its not letting me msg you privately, from your older posts i noticed you said you are on eibach springs? I recently (1 day ago) put my 08 G35xS on eibachs, but the front is looking a little high to me. Do you have a picture of yours? Wanna see how it would look fully settled. Thanks!!

 

Maxbalahura...who specifically are you trying to respond to? I have never put Eibach springs on my car.

 

nice write-up, OP! i just had an '06 M35x pop up on my local FB marketplace with a cracked diff and oil pan, so i was wondering what all is involved. granted, it's a DE and not HR (so going by prior experience might be a lot easier than this lol). i guess you could've strapped the engine/tranny from the top and then dropped the subframe w/o having to support it from the bottom. honestly, i'd have probably deleted the awd at this point if i were you lol