Things I learned from completing a differential swap myself

Discussion in 'V6 3.7L Engine / Mods: Bolt-ons, Exhaust, Tuning' started by Jared_J, Aug 16, 2018.

  1. Jared_J

    Jared_J Well-Known Member

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    #1 Jared_J, Aug 16, 2018
    Last edited: Aug 16, 2018
    After keep postponing the project for half a year, I finally did the 3.55 differential swap because I can't take it with me moving to San Diego a couple weeks later. Apparently deadline is the most effective motivation.

    I spent 17 hours working alone starting from raising the car on jacks, to completed the BCM flash the 1st time. 16 hours of mechanical work + 1 hour of digital work. I had to spend a lot more time on BCM flash later to fix some warning codes. Hope this post saves you time and money.

    The work is doable with simple tools and jack stands, as long as you can properly raise the differential. I couldn't find a place in Columbus OH to rent a transmission jack that can work with the narrow space lifted by jack stands. That was one major reason I had to postpone the project many times because that "pumpkin" is 85lbs. No way to lift it by your forearms only when you are lying underneath the car, or even trying to stabilize it on a floor jack.

    The eventual solution I had is to purchase a Motorcycle Scissor Lift Jack ($50), and a cheap creeper ($30). The two things work together fantastically because they allow you to move the "pumpkin" in ALL directions. I was able to align the "pumpkin" very easily! I'm also so grateful that I finally purchased a creeper. Saved a ton energy from crawling underneath the car. It's also cost effective since a transmission jack costs $150, and you can only use it for transmission. The price local transmission shops quoted me were all around $800 for the install!

    The first difficult step was to remove the cat-back exhaust, since there are rusts though I have mine from Borla. But take your time and try wiggling the pipes around, they will eventually come off.

    Afterwards not much rust issues. Just follows lots of the steps from the manual, be very patient, be easy with yourself and with your car. If two days can't complete the work then take three days. Curse as much as you need to but stay calm. I could only find Shelby's differential work manual, but they are about same. Search "FordInstShtM-4000-M8SGT350".

    I also find CJ porny parts' half shaft install video very useful, big thanks to them:


    I was too tired in the end when installing the caliper, and looked at the wrong bolt's torque value from the manual and slipped the bolt. I had to go to ford dealership to fix the bolt and they charged me $80. Don't be like me.

    Pry the half shafts out may also be a bit nerve breaking and frustrating, but just be patient. Buy a proper pry bar with length not too short for torque not too long to fit underneath the car. A screw driver won't work at all.

    Since you pretty much need to dissemble all the rear suspension, might as well do your suspension upgrade at the same time. This time I also installed the ford performance rear toe link, in complement with cradle bushing lock and vertical link I had installed before. A HUGH DIFFERENCE IN HANDLING! Maybe it's because the three upgrades work together and there is finally no weak link. The car is VERY planted and no longer wants to kill me with a surprise slip when accelerate out of a corner. Though a firmer ride, but the handling is exactly I look forward to.

    You can easily fill the differential fluid by buying differential oil with a plews pump. You need two quarts of them.
    https://www.amazon.com/gp/product/B079YVZJ5M/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

    If you have automatic transmission, you need forscan to correct the BCM. You need to buy the OBD tool, I bought this one, works great:
    https://www.amazon.com/gp/product/B01F0GVBWY/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

    Forscan is free, but it takes two days to request a license. Take that time into planning. Refer to this page for learning usage of forscan:
    https://www.mustang6g.com/forums/threads/modifying-as-built-data-guide.61773/

    Before changing the BCM, it's safer to flash your engine tune to stock. And you need to clear error codes later on with vehicle in stock tune anyway, if you are unlucky as me.

    All you need to change is 4 gear ratio digits, and 2 "checksum" digits. In "BdyCM As Built" from "configuration and programming", go to line "726-12-01". My 2015 V6's stock BCM setting with 3.15 transmission has values at "013B-0832-550B ". First 4 digits refer to 3.15 gear ratio, middle 4 digits refer to tire size of the original crappy 17 inch hankook tires. For 9th and 10th digits (55 in this example), I don't know what they are for, but they screwed me when I set them wrong. The last two digits are the so called "check sum", which suppose to be the sum of the first 10 digits but in Hex form. Changing ANY of the first 10 digits, the last two digits needs to be recalculated. Forscan will shoot you a warning if you set them wrong, before confirming flashing them.

    In the beginning I only changed the first 4 digits of gear ratio, without changing the last two digits of check sum. Forscan warned me it's wrong. So I went online and found some other dude's 3.55 ratio mustang's code, which is "0163 0827 6538". "0163" refers to 3.55 ratio. Flash was successful, the car starts and drives fabulous. No power loss at any RPM region as some people had, and shifts MUCH faster than 3.15 ratio even with stock tune. But, there were lots of error warning codes and air bag light was on.

    Concerned that I may create a mess, I decided to visit dealer to let them flash it right. I explained the situation, told them I changed the gear ratio in BCM, but they still couldn't figure out anything. They propose further investigation by charging more, but not guarantee can fix it. So I declined. Nonetheless, they insisted charging me $110 for looking at it though they didn't provide me any useful information, and they said they could address it in the begining. They just read me the info that I had already read from forscan. I was very f**ked by dumping $110 to the dealer.

    After spending more time searching around and trying different settings, I figured out the 9th and 10th digit is specific to the vehicle's hardware. "XXX-XXX-65XX" wasn't right for a V6 as it indicates other hardwares that are not available in V6 model, and confused the PCM. We should stick to "XXX-XXX-55XX".

    Using the calculation tool from this page:
    https://www.mustang6g.com/forums/th...ometer-error-no-flash-or-tune-required.67564/
    I also changed the tire setting to reflect 235/50/R18 I currently running, and the eventual setting I flashed into the car is "0163-0837-5538" for 3.55 gear ratio. The air bag warning light was immediately OFF when flash is completed!
    Using the PCM relearn method from the same page just mentioned, and perform a DCT code reset, all codes are gone.

    I really like how peppy and proactive the vehicle is with 3.55 gear. The gearbox shifts really fast with a shorter gear ratio. However, I paid so many "tuition fees" in the process and learned the lessons in a nasty way. Hope my info can benefit you guys. Don't recklessly go to a dealer asking help for a tuned car! They may know nothing and they would be extra mean and they make sure to f**k you up!

    20180812_133219.jpg

    39087646_2164626196944294_4118259366346358784_n.jpg
     
    matteos, Atticaz, TX-Ripper and 10 others like this.
  2. Fuse

    Fuse Well-Known Member

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    Nice job figuring things out and taking the time to do a write up. Chalk one up for another terrible dealer experience.

    I wish i knew to look for 3.55 gears when I bought the car, that was the only option missing for mine.
     
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    Jared_J

    Jared_J Well-Known Member

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    When I was buying my car I know I want 3.55, but to specify the $400 3.55 option you have to purchase a bigger wheel + spoiler + electrical seat package, which I value none of them. Also because the dealer needs to order vehicle from Ford rather than selling an inventory, he would take off $400 shop incentive. In the end just to get a different ratio, I need to spend more than $2000.

    So it's much more cost effective to look for an used pumpkin and do gear swap yourself. If you end up selling your differential, all you need to pay is a shipping, a pumpkin price difference, some new bolts and oil, and some tools that you can use for many other things. That's just about $200 + tools you are looking at.

    Just don't dump money to the greedy dealers. They aren't so keen on your project but they are very keen on charging you money.
     
  4. DANA44

    DANA44 Well-Known Member

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    Nice write up, I swapped mine out also a while back. Huge difference proper gearing for the 3.7.
    For the 6M guys you lose a little with 0-60 because of the extra shift but the highway pulls from 60 + make up for it.
    This and a MPT tune is the best bang for a buck.
    At this point there should be plenty of carriers in salvage yards
     
  5. OP
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    Jared_J

    Jared_J Well-Known Member

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    Thanks guys!
    Shoot me messages or posts if you need more clarifications for the project.
     
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  6. OP
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    Jared_J

    Jared_J Well-Known Member

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    Another clarification, after talking to my colleague, he told me there should be an equation for "checksum" calculation, may not be simply summing up digits.
    "0163-0837-5538" works (our V6 with 235/50/R18 tires and 3.55 ratio) because the digit values compensate each and the sum is same as "0163-0827-6538" (some other mustang's calibration from Ford).
     
  7. Lbj

    Lbj Well-Known Member

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    Nice write up I am still going to put mine Differential in but my Lift is not hooked up yet . One thing you mention Is Forscan to change the Bcm . Win I bought my tune from MPT they told me I could change the gear on my tuner and it would work. So now I need to get Forscan right
     
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    Jared_J

    Jared_J Well-Known Member

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    That's not true at least for S550. The tuner affects ECM and the gear value is in BCM. I see people report that when not properly make change in BCM, gear shifts are wrong and high RPM region lacks torque.
    I think the gear value in the tuner only affects the shift map from MPT. If you also load shift map from MPT, then both places should be changed.
     
  9. Lbj

    Lbj Well-Known Member

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    Ok I just got off the phone with Mpt & they tell me after I change the differential and put the new one with 355 gears all I have to do is plug in my tuner and go to the gear setting and change it to 355 and It set .also I told them I have a automatic transmission So I hope they are right I was told that for the. 2015 / 17. V6
     
  10. OP
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    Jared_J

    Jared_J Well-Known Member

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    This has been discussed in other threads. I noted them down and got the conclusion from them:
    https://www.mustang6g.com/forums/threads/gear-change-no-whipple-flare-tool-required.78954/
    https://www.mustang6g.com/forums/threads/changing-gears-youre-gonna-need-one-of-these.36247/
    https://www.mustang6g.com/forums/threads/v6-gear-swap-from-3-15-to-3-73.69075/

    You are originally supposed to do it through whipple flare tool, which seem to be a company purchased license from Ford and thus charge you plenty for a flash. But forscan is just the free equivalent hacked version by Russian guys, if not even more powerful.

    You may always start things by using tuner only. If it doesn't work right, then use forscan to correct it. It's actually not a steep learning curve to use forscan.
     
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  11. Jay-rod427

    Jay-rod427 Well-Known Member

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    @Jared_J are you looking to sell your 3.15 pumpkin?
     
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    Jared_J

    Jared_J Well-Known Member

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    Yes I will create a ebay selling page tonight. Actually I need it to be gone quick since I will be moving.
    I see the 3.15 ones from the junk car yards are priced at $300, and a broken one is priced at $200. So I will mark mine at $250.
    It has 42,000 miles on it.
     
  13. Jay-rod427

    Jay-rod427 Well-Known Member

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    Iron housing right? I’ll save you the eBay listing and PayPal ya $250+ whatever shipping is. Pm me if you want it gone ASAP.

    Edit: nevermind I see above yours is auto which I believe should be the aluminum housing even on a v6 car. Let me know though.
     
  14. OP
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    Jared_J

    Jared_J Well-Known Member

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    Mine is V6 auto. It touches like iron, but I'm not sure. Maybe you could tell from the part numbers on the stickers? Below are the images I just took.
    I thought aluminum is the more premium constructing way? Like you can get more strength for less weight?

    20180818_110154.jpg 20180818_131426.jpg 20180818_131536.jpg 20180818_131553.jpg 20180818_131643.jpg
     
  15. Jay-rod427

    Jay-rod427 Well-Known Member

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    That’s for sure a;uminum. Yes it’s lighter, but at bigger power the ears are weak.
     
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