2011 F150 FX4 4.88 Gear Install Completed
02-06-2014, 12:15 PM
#1
Senior Member
Thread Starter
2011 F150 FX4 4.88 Gear Install Completed
Other may have read about this already, but wanted to post a short how-to along with part numbers to help others who may be interested in upgrading from the stock 3.55/3.73s.
I have a 2011 F150 FX4 (Build Date Oct 4, 2011) 5.0L, 6" ProComp Stage II, and 35" Toyo M/Ts. I found that it was a bit sluggish down low, turning the big tires. I got the tranny pretty hot one time driving across a 3 km lake one time, in semi depp snow, so I figured it was time to look into lower rear end gears to help make the tranny's job a little bit easier. I searched and searched and called various places looking for something lower than 4.10s, as that was all I could find for 2011+ F150s. I could find whatever I want for 2010 and older, but 4.10 was the lowest I could find for 2011+. This didn't make sense to me. The actual diff is the same, the only thing that changed was the size of the pinion.
I called East Coast Gear Supply, in Raleigh, NC and asked them if there was anything available for 2011+, and the answer was no. When I asked if 2010 gears would work in the 2011 diff, they said it should work, but wouldn't confirm because they had never tried it. I decided to pull the trigger and see if I could make it work.
Here are the parts that I ordered:
F9.75-488-YG
*Note, I do not recommend this with a 4-speed transmission, the top end rpm would be too high at highway speed, but with the 6-speed it is great.
I have a 2011 F150 FX4 (Build Date Oct 4, 2011) 5.0L, 6" ProComp Stage II, and 35" Toyo M/Ts. I found that it was a bit sluggish down low, turning the big tires. I got the tranny pretty hot one time driving across a 3 km lake one time, in semi depp snow, so I figured it was time to look into lower rear end gears to help make the tranny's job a little bit easier. I searched and searched and called various places looking for something lower than 4.10s, as that was all I could find for 2011+ F150s. I could find whatever I want for 2010 and older, but 4.10 was the lowest I could find for 2011+. This didn't make sense to me. The actual diff is the same, the only thing that changed was the size of the pinion.
I called East Coast Gear Supply, in Raleigh, NC and asked them if there was anything available for 2011+, and the answer was no. When I asked if 2010 gears would work in the 2011 diff, they said it should work, but wouldn't confirm because they had never tried it. I decided to pull the trigger and see if I could make it work.
Here are the parts that I ordered:
F9.75-488-YG
F9.75-488-YG Yukon Ford 9.75 - 488 Ring and Pinion
F9.75-MIK-B MK F9.75-B: 00-07 Ford 9.75" Master Install Kit -
F8.8-488R-YG
YG F8.8R-488R YUKON FORD 8.8 REVERSE RING
AND PINION 4.88
F8.8-MINI
F8.8-MINI MINI INSTALL KIT FORD 8.8- *** Should Have Bought MASTER INSTALL KIT
ASI-F8.8IFS
F8.8 IFS Front Inner Axle Seal - Fits Left and Rigth side -
Ref 2L1Z-3C084-AA / YMSF1004
By the time I actually went to put the gears in, a few months had passed, so I phoned East Coast Gear Supply back to ask if there might be anythign else I need. Since then they had tried it and realized the following bearings and races were needed as well:
INNER AND OUTER PINION BEARINGS HM89443 & 4T-JHM807045
RACES HM89411 & HM807010
RACES HM89411 & HM807010
Once I had all of the correct parts, it was not a big deal to put in. I work at a Ford Dealerhsip and had one of our Tech's put them in for me, I don't recommend doing it if you do There is a small portion of one of the teeth on the ring gear that must be ground down in order for the pin to slide in (because the 4.88 crown is so much bigger), on both the front and the rear. You can buy a special pin that has this section already ground out of it for an extra $75 or you can just grind the tooth down for free.
As far as actually having 4.88s and driving the truck goes, before I put them in, I was second guessing it and maybe should have went with 4.56s but I already had the 4.88s on the shelf, so went ahead with it anyway. Now that it is done, I am glad I chose the 4.88s. The truck has way more useable power and there is almost no downside, as far as what I use the truck for anyway. I rarely see highway use and from what I could calculate, this effectively makes the truck have 4.20-4.30s with stock tires. Yes it is a bit lower than stock, but it only helps turn the big tires, and with the six speed the highway rpm is completely fine.
at 100 km/h or 60 mph, rpm is right around 1900
at 120 km/k or 75 mph, rpm is right around 2200
at 120 km/k or 75 mph, rpm is right around 2200
I find that the truck will be in 6th gear at 50 km/h just driving around town, but I can shift it down using the button on the shifter and have whatever RPM and gear I want. I am 100% happy that I went with the 4.88s and do not regret it or wish I had done something different at all.
*Note, I do not recommend this with a 4-speed transmission, the top end rpm would be too high at highway speed, but with the 6-speed it is great.
I hope his helps people who want gears lower than 4.10s but are unsure as to whether or not it is possible. 
Last edited by Arctic_Ragtop; 02-06-2014 at 12:19 PM.
02-09-2014, 11:57 PM
#2
Seriously?!?!?! Top gear in both trannies is basically the same (.70 vs .69)...Not to mention people have done it 4-speeds for how many decades?
02-20-2014, 05:08 PM
#5
Senior Member
Other may have read about this already, but wanted to post a short how-to along with part numbers to help others who may be interested in upgrading from the stock 3.55/3.73s.
I have a 2011 F150 FX4 (Build Date Oct 4, 2011) 5.0L, 6" ProComp Stage II, and 35" Toyo M/Ts. I found that it was a bit sluggish down low, turning the big tires. I got the tranny pretty hot one time driving across a 3 km lake one time, in semi depp snow, so I figured it was time to look into lower rear end gears to help make the tranny's job a little bit easier. I searched and searched and called various places looking for something lower than 4.10s, as that was all I could find for 2011+ F150s. I could find whatever I want for 2010 and older, but 4.10 was the lowest I could find for 2011+. This didn't make sense to me. The actual diff is the same, the only thing that changed was the size of the pinion.
I called East Coast Gear Supply, in Raleigh, NC and asked them if there was anything available for 2011+, and the answer was no. When I asked if 2010 gears would work in the 2011 diff, they said it should work, but wouldn't confirm because they had never tried it. I decided to pull the trigger and see if I could make it work.
Here are the parts that I ordered:
F9.75-488-YG
*Note, I do not recommend this with a 4-speed transmission, the top end rpm would be too high at highway speed, but with the 6-speed it is great.
I have a 2011 F150 FX4 (Build Date Oct 4, 2011) 5.0L, 6" ProComp Stage II, and 35" Toyo M/Ts. I found that it was a bit sluggish down low, turning the big tires. I got the tranny pretty hot one time driving across a 3 km lake one time, in semi depp snow, so I figured it was time to look into lower rear end gears to help make the tranny's job a little bit easier. I searched and searched and called various places looking for something lower than 4.10s, as that was all I could find for 2011+ F150s. I could find whatever I want for 2010 and older, but 4.10 was the lowest I could find for 2011+. This didn't make sense to me. The actual diff is the same, the only thing that changed was the size of the pinion.
I called East Coast Gear Supply, in Raleigh, NC and asked them if there was anything available for 2011+, and the answer was no. When I asked if 2010 gears would work in the 2011 diff, they said it should work, but wouldn't confirm because they had never tried it. I decided to pull the trigger and see if I could make it work.
Here are the parts that I ordered:
F9.75-488-YG
F9.75-488-YG Yukon Ford 9.75 - 488 Ring and Pinion
F9.75-MIK-B MK F9.75-B: 00-07 Ford 9.75" Master Install Kit -
F8.8-488R-YG
YG F8.8R-488R YUKON FORD 8.8 REVERSE RING
AND PINION 4.88
F8.8-MINI
F8.8-MINI MINI INSTALL KIT FORD 8.8- *** Should Have Bought MASTER INSTALL KIT
ASI-F8.8IFS
F8.8 IFS Front Inner Axle Seal - Fits Left and Rigth side -
Ref 2L1Z-3C084-AA / YMSF1004
By the time I actually went to put the gears in, a few months had passed, so I phoned East Coast Gear Supply back to ask if there might be anythign else I need. Since then they had tried it and realized the following bearings and races were needed as well:
INNER AND OUTER PINION BEARINGS HM89443 & 4T-JHM807045
RACES HM89411 & HM807010
RACES HM89411 & HM807010
Once I had all of the correct parts, it was not a big deal to put in. I work at a Ford Dealerhsip and had one of our Tech's put them in for me, I don't recommend doing it if you do There is a small portion of one of the teeth on the ring gear that must be ground down in order for the pin to slide in (because the 4.88 crown is so much bigger), on both the front and the rear. You can buy a special pin that has this section already ground out of it for an extra $75 or you can just grind the tooth down for free.
As far as actually having 4.88s and driving the truck goes, before I put them in, I was second guessing it and maybe should have went with 4.56s but I already had the 4.88s on the shelf, so went ahead with it anyway. Now that it is done, I am glad I chose the 4.88s. The truck has way more useable power and there is almost no downside, as far as what I use the truck for anyway. I rarely see highway use and from what I could calculate, this effectively makes the truck have 4.20-4.30s with stock tires. Yes it is a bit lower than stock, but it only helps turn the big tires, and with the six speed the highway rpm is completely fine.
at 100 km/h or 60 mph, rpm is right around 1900
at 120 km/k or 75 mph, rpm is right around 2200
at 120 km/k or 75 mph, rpm is right around 2200
I find that the truck will be in 6th gear at 50 km/h just driving around town, but I can shift it down using the button on the shifter and have whatever RPM and gear I want. I am 100% happy that I went with the 4.88s and do not regret it or wish I had done something different at all.
*Note, I do not recommend this with a 4-speed transmission, the top end rpm would be too high at highway speed, but with the 6-speed it is great.
I hope his helps people who want gears lower than 4.10s but are unsure as to whether or not it is possible.
02-20-2014, 06:20 PM
#6
Senior Member
Thread Starter
I didn't realize the top gear was that close between the two. I was told that 4.88s wouldnt be good with the 4 speed so was just repeating that info. I didn't mean to mislead anyone.
Last edited by Arctic_Ragtop; 02-20-2014 at 06:50 PM.
02-20-2014, 07:08 PM
#7
Senior Member
Thread Starter
Yes I do, however an EcoBoost reaches 90% of peak torque at 1700 rpm, so would not be as necessary, but it definitely won't hurt. In comparison, a 5.0L hits peak torque at 4200 rpm. Of course there are going to be guys who disagree with me on this opinion, but the fact is that the Eco has way more low end power than the 5.0L, so yes I do recommend the gear swap, but may not make as much difference. By the way, I am a strong 5.0L supporter!
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08-02-2014, 11:00 AM
#8
2008 October TOTM
How are the gears holding up? I'm getting some soon going to 37s and want 4.56. It's my DD. Does the shop you got the gears from have the $75 pin that has to be ground down? Did your guy says there was any different process bc of the different pinion shaft? I have a 2011 also
11-23-2014, 09:27 PM
#10
Senior Member
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