rear end???
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Junior User
Joined: Jul 2004
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rear end???
ok guys im wanting to get better gas mileage out of my 81 f-150 it has a 9in with 373 gears and i found a rear end with 283 gears or close to that but the problem is its a 8.8 rearend out of a 1987 f-150 is the bolt pattern the same as my 81... and the salvage yard said they would trade for my mine with a little cash im just affraid that 8.8 will not hold up i have a 351 with a pretty big cam and ported heads with a built c6 tranny do you guys think this will hold up over time compared to my 9in thanks for the help trevor
Fleet Mechanic
Joined: Sep 2003
Posts: 1,279
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From: savannah,ga
the 8.8 is a good rear but nowhere near as strong as the 9 inch
I vote no change of rear
dont know if its a bolt in or not
no way to know the condition of that junk yard piece
getting better mileage probably wont happen
when you go to take off you will MISS that 3.73 WOOHOO
then the pedal will go to the floor, and the gauge will go to the E
only way you will reap better mileage is if you do 95% hiway driving
I vote no change of rear
dont know if its a bolt in or not
no way to know the condition of that junk yard piece
getting better mileage probably wont happen
when you go to take off you will MISS that 3.73 WOOHOO
then the pedal will go to the floor, and the gauge will go to the E
only way you will reap better mileage is if you do 95% hiway driving
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Junior User
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oh one more question is the bolt pattern the same as my 9in??? and i figured the 8,8 was not near as strong but im hopin it will hold up and he threw in a lil warrenty with the rear end i plan on changin the fluid and hope for the best and i do alot of hiway driven i get about 10 miles per gallon now but im also turnin 4000rpm at 70 so hopin these gears will help out thanks for the help guys
Postmaster
Joined: Dec 2006
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From: Rockford, Il
man i bet the salvage yard owner would like to trade you plus your cash. the nine inch is desired by lots of different auto and truck buffs, an 8.8 is a dime a dozen. keep your 9inch, buy the 8.8 and then go ahead and sell your nine inch. you should have money left over and then some after you repay yourself for the 8.8. there is no way you should be giving money plus your 9, hell he should be forkin the cash to you, by rights. he will make a couple of calls and unload that 9inch in no time and profit nicely. just my .02. Dan
Moderator
Joined: Jan 2001
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From: Virginia
The wheel pattern is the same. It should fit right in. If the u-joint is a little different, they make u-joints that will adapt one to another. Go to www.partsamerica.com and punch in both trucks and see if the u-joint is the same.
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1 other question: whats the best way to find out what gears you have in the diff without taking it apart? I read on here somewhere ( just can't seem to find it with the search) about marking and turning your rear tires and counting how many revs as to revs at the driveshaft. Once I find that out, how do I calculate it?
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Posting Guru
Joined: Jun 2002
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From: Suffolk, VA USA
I agree. Stay with the 9 inch rear end. I found a 2.49 9 inch chuck that I put in a little 82 F100 Stepside with a 300 and 4 speed...wouldn't pull worth a darn but was a great highway truck. And it took all of 45 minutes to make the change.
Bill
86 F150 4x4 5.0
Bill
86 F150 4x4 5.0
Last edited by ri_truck_guy; May 7, 2007 at 08:09 AM.
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Postmaster
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From: Rockford, Il
Texcan, just compare the number of revolutions. the tire makes 1 full rev to the 3. something or 4. something the pinion makes, will get you close. otherwise i think you would have to count revolutions until both pinion and tire get back to there starting point and dividing by the other to come up w/something more accurate. I dont remember which you divide into the other, just try both options. One will be a decimal and the other will be a whole number plus a decimal. whole number plus is your gear. the technique is a little foggy but that should be it. Dan
Moderator
Joined: Jan 2001
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From: Virginia
If you turn BOTH rear tires one revolution, and the rear gear you had was 3.50, the the driveshaft will turn 3 1/2 times for one revolution of BOTH rear tires. If one one rear tire turns, the spider gears mess up the calculation.
Posting Guru
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From: Florida
To find your rear...assuming it's the original 9......type your VIN into the Decoder under ARTICLES AND SPECS.......I bet he would love your money....he's taking you for a joker....there are mustang guys around here willing to pay as much as 500 for even a bad 9 inch...they're just gonna change the gears.....I hate the 8.8, even though I have one.....I'd rather not have the C-clip rear.and those what 2.39's?You probly won't be happy with....way to low a gearing won't even get out it's own way......pull the chunk in the 9 and swap it out for some lower 3's........no way would I trade that boneyard...if anything...do like someone already said and buy the rear seperate and keep the 9...just in case you decide you don't like it...andif you do...sell it....you gotta think too, just because you have lower gears doesn't mean yourmileagewill shoot up sky high....the lower the gears the harder your engine has to work to get it moving.....thus your mileage.I changed my 3.35's for a 3.55 8.8with a posi...my gas milage actuallystayed pretty much the same.....
Moderator
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From: Virginia
The only thing bad I have heard about 8.8's is the wheel bearings actually run on the axle. So if something happens to the bearing, or you have a very high mileage unit, the axles may be shot and you have to get new ones. I have heard they got rid of the 9 inch because it was so heavy and not very fuel efficient.
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Originally Posted by flareside_thunder
To find your rear...assuming it's the original 9......type your VIN into the Decoder under ARTICLES AND SPECS.......I bet he would love your money....he's taking you for a joker....there are mustang guys around here willing to pay as much as 500 for even a bad 9 inch...they're just gonna change the gears.....I hate the 8.8, even though I have one.....I'd rather not have the C-clip rear.and those what 2.39's?You probly won't be happy with....way to low a gearing won't even get out it's own way......pull the chunk in the 9 and swap it out for some lower 3's........no way would I trade that boneyard...if anything...do like someone already said and buy the rear seperate and keep the 9...just in case you decide you don't like it...andif you do...sell it....you gotta think too, just because you have lower gears doesn't mean yourmileagewill shoot up sky high....the lower the gears the harder your engine has to work to get it moving.....thus your mileage.I changed my 3.35's for a 3.55 8.8with a posi...my gas milage actuallystayed pretty much the same.....
