Hello I recently bought a 87 f250 6.9 Idi and after spending some money to make it shift right(vrv was bad) I don't think this has anything to do with it but I run about 3,000 at 55,is it possible I have low gears or is this normal and if this is caused by low gearing what kinda mpg can I expect.or could it be from lack of power such as the pump turned down too far cause even at 3,000 there's no smoke what so ever.I don't tow a whole lot I haul more stuff in the bed and I figured a f250 would do just fine and I had heard the 6.9 gets around 20 mpg on highway

 

my 4 speed gets almost 20 mpg highway. 3,000 at 55 seems a little high for an auto

 

Could the high rpms be caused by low gears.or maybe its not going into third gear(havnt really paid alot of attention to what gears its going in) id assume its going through all the gears.running 55 about what rpms should i be running wether not i have 3.55s or 4.10s i dont know.any help would be appreciated

 

you have 4.10's

leveling kit on front if its 4x4, will fit 35's and that will lower RPM's real fast ..

I have 35's and 3.55's and im running 2400 @60 , 2600 @65, 3K @ 70 .. give or take 100 RPM's

 

I was just kinda wanting to keep it stock heighth.even if i put it on 35s i wouldnt imagine it would drop the rpms that much.how cost effective would it be if i swapt out the gears for 3.55s an im sure i would notice just a hint of loss of power but im use to driving a 4 banger s10 so im sure it wouldnt be that bad.how much work would it be to swap out the gears and what all will i need from a donor truck

 

If you have a C6 transmission and 4:10 gears, those rpms sound about right. Gear swapping isn't something to be taken lightly however. You need special tools to do it right, if the gears aren't properly meshed, they wont last long. If your truck is 2wd, it should cost about $500 to have a reputable shop do it. That should include new gears and a master rebuild kit along with the labor to install both. You may be able to save some money by getting your own parts and having the shop install them. A cheaper option may be to swap the entire axle for one that already has the gears you want. Rear axles can usually be had for $150 up to $1k depending on the seller. They seem to average about $300 out here.

 

500 buck will get you the gears for the sterling rear diff, another 500 for labor ...

I would check E-bay for a diff .. or CL, or local junk yards and such ..

 

Iv never changed gears but ive done the outer seals on the axle i dont know if its about the same or not.im not real familiar with tearing into axles.the truck is 4wd.my dad has changed gears and he said hed help an that its not hard just more time consuming.i know i have change bothe axles to 3.55 (thats what im hoping to go to)but could i do the rear axle just for the moment until i get more cash to do the front axle?

 

Holy crap, I had both axles done on my F-250 for only $1200 and that was without me supplying anything.

Yes, you can do one axle at a time but as a precaution I would pull the front driveshaft to prevent an accident in case you forget or loan the truck to a friend who forgets or doesn't know the gears are different. If you were out west, I saw a guy selling a sterling rear and a TTB D50 with 3:55 gears, asking $350 for the pair.

 

That was for my 14 bolt 10.5" .... and i did it my self ... the shops wanted 12-1800 otherwise ... so i saved the 800 and bought a new carb and intake, distributor, etc ..