Rear end gears needing rebuild at 50k?

Discussion in '2005+ Mustang GT 4.6L Tech' started by Geosh, Mar 24, 2020 at 10:34 PM.

  1. Geosh

    Geosh Junior Member

    Took my 06 GT to the shop last week to get some 4.10’s installed. After a couple days of issues (bad bearing, needing a new spring clip thing) they have said that my spider gears are worn and it is making some noise still. They want to either rebuild it, or swap it out with a new differential assembly. The Ford Performance one is only $260 so it isn’t crazy (they also recommended and Eaton for twice that) but I’m surprised to be having an issue with my diff as it only has 50k miles on it.

    I’ve owned it for the last 10k miles, so I can’t say what happened the first 40k, but the car is in overall great shape and the previous owner was an old guy who didn’t beat on it.

    Wondering if this seems reasonable or if they might be throwing parts at some other issue trying to fix it. Trying not to spend any more than I have to.

    The noise they were talking he said was due to a chattering in the spider gears that was causing “a whirring during decel, mostly over 45mph”. He said it either needs to be rebuilt or replaced.

    Thanks guys, let me know what you think. Also wondering if it is bad, should I stick with Ford or is it really worth it to spend more for an Eaton for a daily driver that sees little time racing.
  2. tjm73

    tjm73 of Omicron Persei 8 S197 Team Member

    50K mile and bad gears in the axle? I don't buy it. Noise on decel sounds like poor installation of the ring & pinion. I suppose it could have bad part in the axle, but I'd be a really rare issue.

    Aside from that, if the rear end is opened up for work you should just change out all the bearings. They are reasonably cheap, so just change them.
  3. Mach2burnout

    Mach2burnout 05 Redfire GT

    Not the norm for sure. 4.10s are easy to miss the set up! Likely they are just looking to gain back a little of the labor cost to redo it.
    Could it be bad, sure! But I’d want to see it when it and while it was being disassembled. But then again I don’t trust anybody else to build my stuff.

    Sent from my iPhone using Tapatalk
  4. Geosh

    Geosh Junior Member

    I replaced all the bearings just in case too. Brand new bearings and Ford Performance 4.10s
  5. bujeezus

    bujeezus forum member

    Sounds like they don't know how to install 4.10s.
    skwerl likes this.
  6. RED09GT

    RED09GT Senior Member S197 Team Member

    My 4.10's made noise on decel after my first time installing them.
    I re-installed them using the shim from my original pinion (it was slightly thinner) and they are now quiet.
    It is probably the install, it happens. I would ask to see the pattern of the install once they have it apart before agreeing to pay for changing any new parts. I'll bet the decel pattern will be right near the outside edge.
    MrBhp likes this.
  7. Rick Simons

    Rick Simons Member

    +1 RED09GT
    I also had noise on decel after my first go-round; turns out the pinion was too shallow, despite what the pattern showed. I used the original pinion shim the second time around and the pattern was heaps better, and no noise. I can't speak for others, but it took me several trial fittings/shim adjustments to get the right combination of preload/backlash/tooth contact pattern. Spiders shouldn't make any noise unless the car is turning and they're damaged.
    MrBhp likes this.
  8. BottleRocket

    BottleRocket Junior Member

    I bought my 1st 4.6 GT in 2012. It had 34K and had a bad howl from the diff. The dealer rebuilt it and I had him upgrade to 3.55s. All new bearings, including axles. 20K miles later it was howling again. The dealer rebuilt it under my extended service contract (I went to 3.73s). 30K miles later it went out again. I went back to the dealer and was told to go away (I bought it from the local GM dealer). I went to my Ford dealer where I have it serviced and the service manager made me an offer, I buy the parts, he would install them for free. I was totally happy - for 30K miles when it started howling AGAIN! I traded it for a Tundra. I just recently bought my 3rd '08 GT/CS last February 2019. Everything is fine so far, but it only has 40K. I'm holding my breath.
  9. Geosh

    Geosh Junior Member

    One of the guys at the shop had similar issues with his stock diff and switched to a Eaton TrueTrack and it fixed it. He said my clutches are worn and there is some wear on the spider gears, which if why he was recommending the rebuild/replacement.

    I’m gonna do it and hope all is good after. Will update.
    skwerl likes this.
  10. Lime1Gt

    Lime1Gt Junior Member

    Why would spider gears whir on deceleration? As far a I know spiders theoretically only turn when turning off line. Straight ahead they aren't turning. Sounds more like your pinion gear setup was done incorrectly. Were they FRPP gears? I had access to the proper Ford depth setting tool when I did my FRPP 4:10's with new bearings and had no issues.
  11. Geosh

    Geosh Junior Member

    Yes. FRPP parts. They said the clutches are shot and the spider gears have some wear that would need replacing. Possibly the previous owner drove on a spare in the back for a while? Tire diameter wasn’t stock when I bought it....

    I’m gonna try to get down to the shop when they get the differential in so I can take a look firsthand what is going on.
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