1991 super duty rear ratio

[Drollins]

Hi all!
I am brand new here and to a recently purchased 1991 F350 7.3 super duty DRW 5 spd with a utility body. The current rear ratio is 5:13. I will do mostly highway miles. I tow occasionally and never anything over 7k lbs. I will not have a lot of weight in the utility body about 1k lbs. The current RPM in 5th gear is about 2500rpm @ 58mph. I really want to get the best fuel economy possible. I am planning on changing the rear ratio. It is a Dana 80. I am thinking 4.10 or possibly 3.73. I don't want to go to far. The price for aftermarket ring and pinion is very reasonable but I don't want to do it twice. Any reason not to use aftermarket gears? Any thoughts are appreciated. Doug

 

[franklin2]

You will be doing 1998rpm at 58mph with 4.10's, 1817rpm with 3.73's.

 

[Shadetreemechanic]

In my searching I did not find 4.10's or 3.73's available for the Dana 80.
Best I could find was a 4.70? or something close to that. For that reason my superduty is a parts truck and I bought a 350 cab and chassis with a Dana 70. You have alot more axle choices with that one.

 

[towcat]

Our Dana 80 rears can go as low as 4.63:1. unlike the later model Dana 80's, there is no lower option without going through an expensive housing changeout and third member changeout. your money is better focused on a second overdrive unit.

 

[Drollins]

Thanks for the quick replies. That is bad news for me. I was hoping a gear change would be the solution. It sounds like I am going to have to live with the high revs for now. I don't think an overdrive unit is going to fit my budget. Does anyone know what is different about the older Dana 80's? There are a few aftermarket gear suppliers that list replacement R&P sets. Has anyone tried to install these? What about them makes them not work? Thanks

 

[GOOSE]

If you dig, you can source and install a brownie for less than a gear swap. With what you plan to tow and haul, you may consider selling what you have and finding an F350.

 

[Drollins]

I guess I need to do more research because I have no idea what a brownie is. Or what it would cost to purchase and install. Maybe I should start looking for a junkyard rear??? And keep my options open instead of just living with the high revs. Thanks for the additional info!

 

[franklin2]

Thanks for the quick replies. That is bad news for me. I was hoping a gear change would be the solution. It sounds like I am going to have to live with the high revs for now. I don't think an overdrive unit is going to fit my budget. Does anyone know what is different about the older Dana 80's? There are a few aftermarket gear suppliers that list replacement R&P sets. Has anyone tried to install these? What about them makes them not work? Thanks

I don't know much about the Dana 80, but with most rearends you can only change the small pinion gear by a few teeth before it becomes too large or too small to mesh correctly with the ring gear. So they have "ranges" of ratios you can have until you have to do a major move inside the rearend, usually they move the ring gear back and forth to accomodate a larger or smaller pinion gear. In your case you are wanting a larger pinion to get more teeth on it compared to the ring gear so the ratio is lower. So I am guessing they need to move the ring gear over to give it room, and that would be done with a different carrier that the ring gear bolts too, or someone may have mentioned they do not make such a thing for that rearend. I do know some of the rearend people make spacers for the ring gear to move it in when going to a smaller pinion gear, but that's only for certain rearend types.

 

[GOOSE]

A Brownie is an auxillary transmission that gives you an over drive and an underdrive. they came in many variations. You put them where your carrier bearing sits and get your drive shafts re done to accept this new piece. The 5000 series is about the size of an SM465 GM 4 speed truck transmission. Once its installed in your rear driveline, you run linkage or cables to a second shifter in your cab. They are quite stout and can be found for about $500 if you look hard enough.

4:63 gears and an auxillary overdrive would rock the house as far as making a sweet tow vehicle.

 

[Shadetreemechanic]

If you dig, you can source and install a brownie for less than a gear swap. With what you plan to tow and haul, you may consider selling what you have and finding an F350.

X2 that is what I did. the Dana 70 and Sterling axles both have lots of gear options.

 

[Drollins]

Ok now I am totally confused. I have contacted two different gear sellers. I gave them the info on the data tag from the rear. They say I can use aftermarket R&P down to 4.10 or 3.73 with a "thin" ring gear. They say they would except a return if it didn't fit but that is a big headache if it didn't work. Has anyone ever taken apart their Dana 80 only to find the supplied gears did not fit for some reason? Is there something "special" Ford did or used to make this rear an oddball? I tend to trust you guys because you have lots of boots in the ground knowledge. I don't think that an overdrive addition is a reality for this vehicle. Thanks again for everyone's input!

 

[FORDF250HDXLT]

Hi all!
recently purchased 1991 7.3 super duty DRW 5 spd with a utility body. The current rear ratio is 5:13. I will do mostly highway miles. I tow occasionally and never anything over 7k lbs. I will not have a lot of weight in the utility body about 1k lbs.

you may consider selling what you have and finding an F350.

agreed.a mistake was made in the purchase of the vehicle.no need to continue on,when it's likely it could be sold and the correct truck (f150-f350 pickup) bought for about the same money or less than trying to make an f-super more pickup truck type hwy friendly since it's gross weights are just not required.sometimes is cheaper to admit our mistakes and simply move ahead rather than live with them.

 

[mjs2011]

Why not go to a wrecking yard and find an all new rear end? I ended up putting a 3.55 in mine and still have the 4.10 laying around as a matter of fact.

 

[FORDF250HDXLT]

Why not go to a wrecking yard and find an all new rear end? I ended up putting a 3.55 in mine and still have the 4.10 laying around as a matter of fact.

because he doesn't have a pickup.he mistakenly called it an f350 super duty in his first post,but it's not.it's an f-450.
he could spend $ to downgrade the truck and hurt it's capabilities in the quest to drop some rpm's but it will always be over kill and extra heavy,therefore a much more waste of fuel to drive such an extra heavy framed beast around for no real reason.not to mention all the weight is robbing power constantly too.a much firmer ride and a much more expensive/cost of ownership by a great amount over a srw pickup.

Our Dana 80 rears can go as low as 4.63:1.

 

[Drollins]

Just to clarify it is a 1991 F-super duty DRW chassis cab. It now has a 10.5' utility body with a 4k lbs. capacity crane. For my purpose I like the larger storage of the DRW utility body and the crane. As I said I am not interested in towing heavy equipment etc. The truck is in great condition with 106k miles. It will last me many years. As it is with a regular (for me) working load first gear is useless. So it is like having a 4 speed trans. In the next month I am going to order 4.10 gears and give it a try. Unless someone who has done it can tell me that they tried and it just won't work for whatever reason. Two manufactures of aftermarket gears have reviewed the build number of my rear and say their gears will work. I won't trash the 5.13 gears and can always put them back if I hate it for some reason. Thanks for everyone's input and I will report back when the swap is complete or found to not work. Doug