Motive Gear Performance 3.90 gear set

[rayjay]

Found these in the Summit catalog. 30 spline pinion and 1.626" diameter. Will these fit our rear ends? 3.90 ratio looks to be a good compromise between the 3.55 and 4.10. With oil prices rising again and $2.71 a gallon for 93 octane here, looks like the way I want to go.

[SergntMac]

Found these in the Summit catalog. 30 spline pinion and 1.626" diameter. Will these fit our rear ends? 3.90 ratio looks to be a good compromise between the 3.55 and 4.10. With oil prices rising again and $2.71 a gallon for 93 octane here, looks like the way I want to go.Yep, Motive part number F888390 will fit our 8.8 housing and diff. But, that set of gears is 229.95 vs. 179.95 for the 4:10s.

You're logic isn't adding up for me, buy the cheaper gear, put the savings back into the fuel tank. Performance wise, the 4:10s will treat you better than the 3:90s, and if fuel costs are really a serious concern for you, making any swap at all contradicts with that concern. Stick with the 3:55s and save 5-600 bucks towards 2006 fuel costs.

[Joe Walsh]

I was also considering the 3.90s instead of the 4.10 gears, but I've heard from some reliable sources that the Motive 3.90 gears are NOISY.

[rayjay]

Yep, Motive part number F888390 will fit our 8.8 housing and diff. But, that set of gears is 229.95 vs. 179.95 for the 4:10s.

You're logic isn't adding up for me, buy the cheaper gear, put the savings back into the fuel tank. Performance wise, the 4:10s will treat you better than the 3:90s, and if fuel costs are really a serious concern for you, making any swap at all contradicts with that concern. Stick with the 3:55s and save 5-600 bucks towards 2006 fuel costs.

Mac, thanks for your much valued opinion. My thinking was to add street performance (no racing, play factor) without taking the total hit on fuel economy. I'll watch where fuel prices go in the next few months. I may well leave it stock. The DR Cobra Exhaust and now the GMS coil connectors have up'd my fun factor and fuel economy. If I "pull the plug" next fall, things change also :coolman: decisions, decisions ....

[rayjay]

I was also concidering the 3.90s instead of the 4.10 gears, but I've heard from some reliable sources that the Motive 3.90 gears are NOISY.

FWIW, catalog says "quiet" and fits factory housing.

[GreekGod]

Noise from new gearsets can always be a problem. I talked to a Ford mechanic that had a bad (noisey) brand new gearset and he ended up having to send it back and install a replacement. Since he did the labor, it was all done on his own time with no reimbursement. A very good reason to have the whole job done by one of the vendors that support this website.

[RoyLPita]

There is a member here who has installed the 3.90 gears. Look around the site for the thread and PM him for info.

['03BlkMM]

I have the 3.90's and for me they were a good alternative to the 4.10's. I plan on eventually going with a lower profile tire. The difference in tire diameter will put me close to or beyond the 4.10 gear/stock tire RPM level depending on what tire I decide to go with. They are quieter than the stock 3.55's in my car, of course my factory 3.55's were installed wrong(too much backlash). You can get more info about them from any of the Mustang forums, they are used over there more often than around here. I bought mine at a much better price than Summit, check here www.mustangtuning.com (http://www.mustangtuning.com). They had the gears out to me in like 3 days. I also recently made a road trip to Arkansas. On my way back to Dallas I hit 24.1 mpg running 70+ mph with the AC cranking the whole way. Not too shabby for a car with a 10% increase in RPM's and a DR performance chip.

[rayjay]

I have the 3.90's and for me they were a good alternative to the 4.10's. I plan on eventually going with a lower profile tire. The difference in tire diameter will put me close to or beyond the 4.10 gear/stock tire RPM level depending on what tire I decide to go with. They are quieter than the stock 3.55's in my car, of course my factory 3.55's were installed wrong(too much backlash). You can get more info about them from any of the Mustang forums, they are used over there more often than around here. I bought mine at a much better price than Summit, check here www.mustangtuning.com (http://www.mustangtuning.com). They had the gears out to me in like 3 days. I also recently made a road trip to Arkansas. On my way back to Dallas I hit 24.1 mpg running 70+ mph with the AC cranking the whole way. Not too shabby for a car with a 10% increase in RPM's and a DR performance chip.

Thanks for the info 03BlkMM !