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Alright so hear me out. My ring and pinion gears went out about a year ago and so I replaced them with 4.10's (mines an auto). But I had them installed by some shop that usually doesn't do anything other than oil changes and alignments and the dude ended up charging me $750 to do it after quoting me at $250!!!! In the end, the stupid things cost me over $1000, which is just outrageous.
I'm not sure if the gears were set incorrectly or whatever but now I'm hearing the same noise as I did prior to installing the 4.10's. Anyways... I'm thinking about buying the 8.8" rear end (entire assembly) from a salvaged 2001 GT that had under 100K miles on it. The only hangup is that it had a manual tranny. My question here is will the manual gears in that 8.8" work with my automatic? And if not, will simply changing gears allow it to work in conjunction with my transmission?
 

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Not sure what your mean by "work with". Auto or manual didn't make much of a difference at Ford - GT and 6ers got the same ratio except the GT's 8.8 was bigger obviously. (Side not '03/'04 Terminator Cobras got 3.55's that worked better with the M112, but still utilized an 8.8 center section). That GT 8.8 is probably packing the stock 3.27 ratio which is what your car came with from the factory. So just imagine what your car felt like speed and acceleration wise before the 4.10's. Then add in the fact that the 8.8's are heavier. Without opening the cover and counting the teeth there's no telling what's inside.

So yes it will bolt up and be fine - but you will be back to putzing around with the slower gearset. It's also good knowing that part of the drivetrain is more or less ready if you go FI. (You could go with a 31 spline build for even more strength). Those 7.5s don't last long at all.

Building an 8.8 now as we speak. Found this fun a few days ago:
http://www.moddedmustangs.com/forums/v6-mustangs/279405-what-tech-did-you-do-your-sixxer-today-101.html#post10292122



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Discussion Starter #3
That's exactly what I was needing to know so thanks! I was confused because I had read somewhere that the gearing in the GT's was different in the autos and manuals. I've never had one so I didn't know from personal experience. I was thinking about doing the 8.8" for that exact reason (going FI), plans for forged internals and the like are under way atm. Should happen sometime mid-summer. And yeah IK the pain you're feeling with those gears lol. I'm not bothering replacing the gears in that stupid 7.5" ever again.
 

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Sounds like someone didn't have much of an idea of what they were doing. I kinda laughed when you said they originally only quoted you for 250 dollars to change it. I swapped mine to 3.73s about a year ago and haven't had a problem but I am only pushing like 220HP at the crank so nothing spectacular there. Other than that I am running a bigger Diff cover w/ larger capacity and I have been on the track and doing auto-x a couple times.
 
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Yeah I thought the $250 sounded reasonable. So I'm sure you can imagine my surprise when he called me to tell me it was done and the total. I almost :shitbrick . I've done basically all of my own work since then, lesson learned.
 

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Without opening the cover and counting the teeth there's no telling what's inside.
There is another way, actually. Grab the jackstands and get the axle in the air. Block the front wheels. Mark the driveshaft with a marker or something. Put the transmission in neutral. Spin one of the wheels full circle while counting how many times the driveshaft rotates one full circle.

Two and 3/4 turns = 2.73
Three and 1/4 turns = 3.27
Three and 1/2 turns = 3.55
Three and 3/4 turns = 3.73
Four turns = 4.10
Four and 1/4 turns = 4.30

You could check the axle tag (if its there), but the gears may have been swapped at some point so comparing rotations is the easy way to do it without tearing it apart, which would mean new lube and friction modifier.
 

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$250 plus parts is actually average price to do a gear swap from most shops
Hmmm all the shops around where I am quoted me 350 to 400. Still not 800 dollars. I would have told that place to go pack sand.

I ended up doing my swap in a friends garage for the low price of 7 hours of labor.
 

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I could be wrong but I am pretty sure you just remove the old one and put the new one back on. Drive shaft, shock and control arm mounts should all line back up. Should be about a 3 hour swap, maybe 2 if you have more than one person helping you and none of the bolts give you any problems.
 
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