I have a 94 with an F350 cab on it (7.3 IDI and 5 speed stick). All parts I have purchased for the chassis need to be for a larger truck. Parts for a T57 fit the brakes and other chassis items. If I remember correctly, I also bought 550 parts that fit. It's had a cab and title change.

My problem is the old truck turns up too high on the highway. It's screaming at 60. I need at least 70 if I am going to keep it. I have 235 tires on the front and four 215's on the rear. I'd change the 215's to 235's on the rear but all my rubber is like new and my spare is a 215. Anyway I'm not sure just increasing the tire size would give me enough RPM change. I have 10 lug 16" wheels.

The chance that the axle tag is intact is small but if you tell me where it is
normally located I'll look for it. If possible, I'd like to find a rear end in a
junk yard that will fit to lower my RPM. I first need to know what I have now.

If the tag is no more, I will put a mark on the wheel and drive shaft and count the turns taking into account that the differential doubles the rotation if one wheel is on the ground. First though, where should I look for the tag?

 

so you have an f-super duty (pre-f450 name) which has either 4.88 or 5.13 gearing,that you put shorter tires on back making the gearing even lower and your looking at doing what with the truck? gearing up will hurt your big combined gross rating,so if you need that you'd want to install an aux od unit to your zf5 and leave the axle alone.if you don't need that,have you considered selling and buying the lighter 250/350 truck instead with 3.55s or 4.10's already? many try so hard when its just cheaper and easier to sell/buy in some cases.

the code is on the tag of the axle.look for it on one of the diff cover bolts.you'll see .88 for 4.88's or .13 for the 5.13 the bolts just covering up the first number.
no point in looking though.either one is too steep for 70 mph hwy lol especially with the shorter rubber.


tip;
the operating cost of the lighter framed f250/f350 and in srw form would be far less than the operating cost of the heavier duty f450 drw even w/ double over.
the larger the truck,the more money they can make potentially during the same time frame.if it's not going to do this for you,id strongly suggest selling and rebuying what fits your needs better.this economy we're in has no room for error anymore...........if only the government could be convinced lol.

 

the tag should be under one or two of the bolts that hold the cover onto the differential on the rear axle. its a little piece of sheet metal with the info stamped into it. clean it with a wire brush and your spray can of choice until you can read it.
if its not there, then counting rotations is your best option.

for a point of comparison, guys with 4.10 gears and no overdrive usually report it screaming around 60, but capable of reaching around 75. i've got 3.54s in mine and no overdrive, and have seen 85 without having the governor stop me.
since your 5 speed does have overdrive and you're screaming at 60, i would guess your gear ratio is probably 4.56 or so.

note that you'll probably have to look in a heavy truck junkyard, as your car junkyards don't see anything bigger than an f350 with its 8 lug wheels, and you obviously want your axles to fit the same wheels, and not lose capacity in the swap.

depending on what you use the vehicle for, another option you might have is to step up to bigger rims and tires on your current axle, probably 19.5s or something in that range.

 

Thanks for getting back to me so quickly. I'll look for the tag this afternoon. The truck came with the 215 tires. I don't need much weight carrying capability but if I'm going to use the truck on the Interstate, I've got to go more than 50 to 60. I've never been comfortable with any engine screaming. That may just be me.

 

you should be aware that these diesels are designed to last a long time running as hard as you can run them. the engine is happy if you run it all the way up to the governor and hold it there all day. not saying your wife will be happy with that, nor your wallet at the fuel station, but the engine is ok with it.

since you don't plan to be hauling much, selling it off for something lighter might be the best option for you. say you were to step down to an f250, it sounds like that would fit your needs and save you a good bit on fuel, especially if you find one with 3.54 gears and that 5 speed

 

You can buy a ring and pinion set new for maybe a couple hundered, you just have to know what rear-end is in the truck. From reading i dont even know what kind of truck you have so its hard to even guess at what rear is in it.

 

The tag says 513. The other numbers are VF2TA MA and it looks like a SN of V805461-2.

Now since we know I have a 513 rear gear, what do you think will be my best and cheapest way to drop my rev's? It will break my heart to junk my (5) 215's but that is an option. I wouldn't want to try that without being certain that new wheels would do the job.

 

Changing tire size won't help enough to make it worth your while. Auxiliary over-drive or ring & pinion gear swap are really the only solutions if you want to keep that truck. R&P gear sets don't cost that much, but installing them and getting the gear lash correct is very involved, and pricey if you have the work done. Overdrive units are nice, but expensive. I hate giving this advice to anyone, but if you really don't need the weight capacity that truck was designed for you actually would be better off trading down to an F250 or F350 with taller gears.

 

the best and cheapest don't often go hand in hand lol.
but,if sticking with this truck is the only financial option for you at this time,and you don't need to carry heavy loads,then i personally in this case (i might not hear the end of this lol) would to be bolt in a sterling 10.25 from exactly:
an f350 cab and chassis with 3.55 gearing from '93-97
OR
you could also just buy a '93-97 srw pickup axle w/ 3.55's and have the spring mounts re-welded where you need them too.same results in the end.the duals would go right back on.
(you can use an older sterling.the first gen but you personally have no reason not to use the 2ng gen.stick with it.your donor axle is common/cheap.it is not the much larger/wider pickup dually axle.)

3.55's with 215 tires is like dropping in fords 3.73's (a tad lower) when keeping 235's tires on.this is my setup.

either way will set you up for 8 lug out back.personally id run srw.better fuel economy again compared to drw and either way,you'd need 8 lug rims.might as well go all the way and hit two birds with one stone via srw convert and higher gearing.bring them rpms way down compared and economy way up for 70 mph driving.

the best way however would be to bolt in another axle with 4.88's and add an gear vendors of course.........but cheap has no place here.

 

FORDF250.. you kind of blew me away with all that info. I gathered that you think I should get a 4.88 from a junk yard if I can find one? Are you suggesting I buy the whole axle assembly or just the gears? To keep my 10 bolts and tires I need the same size axle.

I can't change trucks, I have too much in this one. I put in a new injector pump, new glow plug relay, new master cylinder, rebuilt the oil cooler, rewired the miss wired fuel gauge, and the wiper motor wiring. Much more. I've got a lot of me in this truck.

 

I think a big question no one has asked, but everyone is assuming...

What do you use the truck for?? That will help us help you better. If you need the dual wheels and the weight capacity, you don't want to do too much to the gearing, or it will take you forever to get up to speed when loaded. However, if its mostly light duty use, then go for the best economy.

FORDF250 has the right idea, he's been tweaking his setup for a while and has some good wisdom. But please tell us how you use the truck and we can narrow it down some more for you.

 

This truck now has a 12' stake body on it. I use it around my farm and for hauling items too large to put in my car. If I can get the revs down, I plan to put a box body on in it's place. Since the chassis and engine are from a much larger truck than the F350 cab, it has way more power and weight carrying capacity than I need for any purpose.

 

lol sorry.
to cheaply make your f450 a "pickup convert" (something no longer able to carry or tow what it was made for,but still f350 pickup standards) head to your local salvage yard and a grab a common sterling 10.25 srw axle along with the two rims and all the lug nuts.you will see the spring hangers will have to be set inward.pay a welder to move 'em for you and the axle will bolt right in and you'll have a srw f350ish type truck ok?
if you see an f350 dually with a narrow frame like your f-super (the cab n chassis) that axle will bolt right in without the need to move the spring mounts cus they're already set to match your f450 spacing ok? however,all those were drw too.so you'll still need (i really do suggest it based on your comments) some srw rims from another donor still ok?

get one with 3:55 gearing because you have no use for even 4.10's let alone lower with shorter tires.

now with 3.55 (3.84 actual via shorter tires) gearing,srw,and zf5 trans,not only will revs be way down at 70 mph hwy speeds but economy way way up for ya too.she'll still sport 10 lug budd style up front and look a lil different,but it's your only economical way to make her a pickup.for just a couple hundred and an afternoon,you'll be done.


the 4.88 and GV swap info (not anything you'll be doing.just educational info.)
if you had a use for an f-super (f450) then you could find an axle with 4.88's and bolt it in but even still,depending on how you use the f-super,you might want to keep the 5.13's.
thing is for modern day use,with either gear set anyway you would need an aux od unit to set behind your transmission giving you double overdrive.BUT that piece alone would cost more than you payed for the truck.so forget this idea since you asked for cheap,and have no need for low grunt gearing at all ok?

 

OK guys. Thanks for all the info.