Hey, ive got an 88 f350 4x4 IDI banks turbo non wastegated. C6 3 Speed auto. 33'' all terrains. I THINK 4.10 gears.?

I do about 68mph flat out hitting governor at 3300rpm.

Im trying to figure out what my options are as far as changing my gear ratio. I was told over the phone by a local rear end shop that the highest gear ratio i could go with the size of my front and rear end (which i am not sure either, or how to identify the difference between) is 3.55. he said i would be doing about 70mph at 2500 rpm. Does anyone have a truck with this gear ratio, or any information to point me in the right direction? I dont pull a heavy load very often, the main concern is going to be cruising at freeway speed.

 

Yes, if you are 4x4 a 3.55 front and 3.54 rear combo willdo you alot better, the front can be had from a salvage yard.

 

i have basically the same setup, but with 36 inch tires. top speed is 80 mph at redline.
has your speedometer been re calibrated for the 33 inch tires?

 

In reality, your probably doing something like 75 with your 33's.


My van has 4.11's with the C6 and I top out at 70 with stock 235/85 tires.

 

you guys are nuts! i don't drive that fast with my E40D and 3.84 effective gearing!
don't you guys like having some money for parts and mods? you need to join me @ 45 mph granny style.
shoot with a c6 and 4.10's id be 35-40 mph tops (im not kidding.)

 

well after i swapped in my c6 with 4.10s and 33inch tires at 3100 rpm i can only go about 55

 

holy crap 85! how do you hear yourself think? i see those rpms from time to time loaded up going uphill in 2nd.i couldn't imagine full time.
what kind of fuel economy can you get with the truck 50-55 mph? maybe im worrying way too much about trying to keep her primarily under 1500 rpms when possible.

 

well fordf250hdxlt Im still working on getting the interior and the paint job done! I love your paint job you did to your truck it looks amazing!!!! ! anyways its really not very load in the cab I put sound deadner and near carpet pad and carpet in so its really quiet! Anyway Im thinking on putting 3.73s in and a gear vender to get it where i want it! we have been driving it back and forth to work for about a month now! about 30 miles round trip on 3/4 of a tank on the back tank so dont seem like to bad of fuel milage! Im gonna have to check my mileage!I havent really drove it for awhile this is my busy season !!!

 

i get 10 mpg. my transmission is in high gear at 30 mph. yeah, im sure, ive checked by gps.

 

well,if you can find a friend to help,you could hit up a local salvage yard for a front and rear axle from a truck w/ 3.55's.grab some new hardware,and likely for $500 or less,have 3.55 front and rear axles swapped in a weekend.that would be a very good start.
the old C6 though.man.if you could find a whole donor truck with a t19 (of course a zf5 preferably,but just a manual direct drive trans would help) you could swap that out too.
a 4 speed manual/3.55 srw pickup should be able to hit 15 mpg all easy.that's quite a bump from your current 10.swapping axles is very easy and basic.you just follow your nose,and you can't go wrong.simple unbolt (preferably torch out u-bolts) unbolt shafts etc..........ah crap.i just noticed F350,and i was thinking f250.them front D60's don't come cheap like the $100-200 D50 TTB's.nuts.that changes things unless you can find someone willing to swap and help each other do the work.might be worth posting a Craigslist add.you never know.have to be careful there though,cus he could have worn out king pins/joints etc,where yours might be good.that's a tough one.paying someone to install a gear set up front isn't cheap either.....then again neither is fuel.
of course you've always got to consider when its more practical (if funds allow) to just throw in the towel and start considering buying a newer truck w/ correct gearing for your needs and OD trans already too.you've got some thinking to do.
all depends on how much you drive too of course.if your not driving much,then 10 mpg isn't that bad.

 

ok i dont want to step on toes, but it seems like every other thread i see you saying literally almost the same thing word for word. I realize fuel prices suck, and getting a little better mileage never hurts. buuut if its THAT big of a deal why not but a jetta tdi or something... sure my truck will probably jump to 20 from 17 if i drove 35-40... but seriously... who would do that?? I would buy a scooter if mpg was an issue, and i sure as hell would have my undies in a twist over 17.7 mpg compared to 18.2. Regearing costs money, not everyone has that money or wants to do it. In the end it takes ALOT of driving to actually make up the difference. For instance, 4.10 to 3.55 lets say that gets us from 15 to 16.5 thats 1.5mpg increase now how far do you have to drive to save the $400+ dollars a shop will charge you for parts and labor... its a long ways.

To the OP: Sounds about rightish to me, had 31's and 4.10s in my 77 she was done around 75 and that was a gasser. My dad has an 88 with 3.55s and 235/75s with a C6 and he cruises 75 at 3000, just told me he got 15.2 on his last trip.

 

because a jetta tdi or something couldn't carry much for wood or chips.
im sorry man.i don't mean to sound like a broken record.im just tossing some idea's out there to help him.the cheapest thing to do of course would be to slow down.i have no clue if he or anyone else reading can drive their trucks as slow as 35-40.around here for the most part you could.just not on the larger roads.might need to pull over once in a while to let some people bye,but shoot if it's ones only option to save on fuel cus they lack funds to swap axles/trans,then you betcha im gunna make sure to post all free and cheapest things i can think of to help first.these prices are hurting us all.

 

Something tells me I'm not gonna like my van on long trips

4.11's C6.


And 85% of the driving I do is highway, or rural roads. I also do alot of driving! I travel 16 miles to work each way, and on the weekens, I can do over 300 miles.

 

oh boy.85% hwy,screams huge benefits of a nice custom low front air dam.if you can live with the look of the things (?) you could see larger gains than i did cus i drive rural roads mostly and it was a nice jump just for that driving style.hwy speeds of 55 or more,you could really see some nice gains.im sure you could find something free on hand like i did.
if they're black (like what i should do to mine with a cover of some sort) they wont stick out so much.i know its goofy looking,but they work.

 

I actually wouldn't mind making one for the van. Just gives me more surface to add all kinds of things like light, and CHROME


My highway speed is 55, probably gonna be 50 in this damn beer can though. lol