Hi, i am buying a used F150. I am deciding whether I should get a 3.55 or 3.73 limited slip axle. I know the 3.55 should get better highway gas mileage and the 3.73 should have more power. Does anyone else have some more insight into this decision. Also does anyone know of either ratio being more or less dependable or having issues than the other. Thanks. Also where can I look on a truck to see what axle ratio it has (is there a sticker or something in a specific spot). THanks for any help and insight - James

 

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Which engine and trans, and what do you expect from the truck? If you are going to be towing, get the 3.73's. I don't tow, and even with the V6 and a stick shift the 3.55's are fine - and actually I'd prefer 3.08's to get better highway gas mileage. I can second gear start without slipping the clutch.

 

I will be getting the 5.4. I am mainly wondering if one axle ratio has shown up having more problems than another.

 

3:55 and 3:73 have very little difference. Overall I'd go with the 3:73. On the highway your motor may be turning maybe 200 more rpm's than with the 3:55's so it wont affect your mileage as much as you think.

 

Go with the 3.73. Your already getting terrible mileage, what's a little worse really? 13.5 mpg vs. 13.2 mpg?

 

If you are buying a used truck, I wouldn't let the axle ratio influence your decision as much as I would the condition of the rest of the truck. Either ratio will be fine with a 5.4 unless you are trying to get every bit of acceleration and towing power you can get.

 

My old truck was a 99' F-150 5.4L 2wd SuperCab with 3.55 LS rear axle and it would average about 18-19mpg, my new truck is a 2007 F-150 5.4L 4x4 SuperCrew with 3.73 LS axles and it averages anou 12-14mpg. The 3.55's are a much better choice for hwy driving, but the 3.73's are better for towing/hauling.

 

Off hand, I would say if you drive around town more than the highway, get the 3:73's. I would get the LS in either situation. If you drive more on the highway, you might get a little bit better gas mileage with the 3:55's. As stated above, you really wont notice the difference enough to sacrifice the drivability around town. You will have more fun with the 3:73's. If you pull/haul anything, get the 3:73's.

 

In a truck a 3.73 LS is hard to beat, although I had my ring and pinion changed in warranty at 11k miles. Bad batch of gears supplied in 2004 model truck's mostly built at the KC plant. I've gotten a little over 18mpg hwy with my 3.73's.

 

x2
Very little difference...only 5% or so.

 

X2 Don't buy a POS just cuz you think it has everything you want, make sure your seller can tell you things about the truck, how often he had it serviced, etc. Even if you know nothing about trucks look under the hood crawl underneath it and make sure theres nothing obviously beat up. Take it out for a drive listen for pings, test the 4X4 if you go that route. I'm sure you knew all this. And finally, if possible go with the 3.73, cuz the 3.55 sucks for pulling. I'm personally movin up to 4.10 LS when I get some 305/65R17's later this spring. Hope you get a great new (to you) truck