Rear end gears needing rebuild at 50k?

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.

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.

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.


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tjm73 said:

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.

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

Sounds like they don't know how to install 4.10s.

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.

RED09GT said:

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.

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+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.

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.

The

BottleRocket said:

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.

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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.

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.

Lime1Gt said:

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.

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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.

Rick Simons said:

+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.

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100% Agree Simmons and red09gt. Not to mention, only 50k miles. Cmon

Also, shops will lose their tailend if they truly worked with the install like they should. So they will bail out as soon as they can, and if there is a return visit due to issues, they will crab walk towards part failure to cover the labor. Then recommend a rebuild that will take them through the process they should have invested the time on the first time.

Anti said:

100% Agree Simmons and red09gt. Not to mention, only 50k miles. Cmon

Also, shops will lose their tailend if they truly worked with the install like they should. So they will bail out as soon as they can, and if there is a return visit due to issues, they will crab walk towards part failure to cover the labor. Then recommend a rebuild that will take them through the process they should have invested the time on the first time.

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Well stated, Anti!

Ok finally got the car back from the shop. Didn’t get a chance to see everything while it was apart because it’s hard to get around with only one car for the family.

Driving the car, it makes a little noise but nothing too terrible - except from 35-40 miles per hour. I drove home with the windows down and all seemed good, mostly doing 45-50. Cruising at that speed or faster, and the gears whine Just a little bit but I probably wouldn’t hear it over the radio. Crusing at 35-40 though, and I start to look for the spaceship that sounds like its flying by my car. Just a consistent whirring sound, which stranger seemed to get a little worse if I was on a curve (maybe I imagined it). But if I speed up a little past 40, it quiets back down.

I’m assuming something isn’t right with this setup, or do new gears take a little bit to settle in. I’m at a loss at the moment as I’m really tired of this shop and if they can’t get it right at this point I’m not sure they ever will.

To recap: all new bearings and seals, FRPP 4.10s, and a brand new Ford Traction-LOK differential.

looking for your thoughts. Maybe I’ll go record a video of it to show the noise.

Something still isn't right. Even with new gears there should be no noise. As far as break-in, I read that the gears are lapped in at the factory, then get a new coat of black oxide to prevent corrosion. My instructions say to take it easy for 30 miles before hammering it.
Increased noise in a corner would point to a carrier bearing since they deal with all of the lateral thrust.
What does the noise do under acceleration/deceleration?

Noise all the time. Gets louder when I’m BARELY giving it any gas and cruising.

Posted some videos:


It’s back at the shop for them to fix it. It got about 30 miles on it before bringing it back to them. I probably should have just turned right around and given it back.

I've been installing gears for four decades, and not all successfully. But I've never heard anything quite like that from a gear set or diff. Anxious to hear how this works out.

Ford has installed millions of 3.73 and 4.10 gears in Rangers for decades, plus F150's and other trucks and cars. They don't whine. Every time I see someone with noisy gears, I know it's the install 95-99% of the time.

The 8.8 seems to be sensitive to install tolerances.

MrBhp said:

I've been installing gears for four decades, and not all successfully. But I've never heard anything quite like that from a gear set or diff. Anxious to hear how this works out.

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The nightmare continues unfortunately. I’m keeping the shop name private for now, but if you are ever looking for a performance shop to work on your car in AZ, I’ve got a great place never to take it to!!

Went by there to check on it and found my car out back with the chin spoiler folded back on itself from parking way too close to a curb and hitting it.

What should have been a quick 1 day install for gears, and now I’ve also swapped out the pinion bearing again, a new differential which was “needed” as the “old one was too worn out” and needed rebuilding or replacing. Now I’ve surely got damage to my 5 week old chin spoiler and maybe my bumper too.

Geosh said:

The nightmare continues unfortunately. I’m keeping the shop name private for now, but if you are ever looking for a performance shop to work on your car in AZ, I’ve got a great place never to take it to!!

Went by there to check on it and found my car out back with the chin spoiler folded back on itself from parking way too close to a curb and hitting it.

What should have been a quick 1 day install for gears, and now I’ve also swapped out the pinion bearing again, a new differential which was “needed” as the “old one was too worn out” and needed rebuilding or replacing. Now I’ve surely got damage to my 5 week old chin spoiler and maybe my bumper too.

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That sucks.