*UPDATE*
Solution - post #13







Hi guys,

Need your help again. I have a 1999 F-550 dually RWD, right know I have no idea what gearing it has, but at 65-70mph I'm nearing 3300rpm in top gear and my consumption is way off (7-9mpg)

I wanted to see if someone can tell me what gearing I need to put in (off of what truck - maybe f-350?) to get my rpms lower. I have no idea what I'm looking for, don't know any shops around that could help, but I wonder if it's a diff I need to swap out

 

you have a dana 110 rear axle i believe, so you need gears for that axle only. you can check the axle for the tag it should show you on it if not call a dea;ership and give them your vin and they can tell you. 450 and 550 i think come with either 4.10 or 4.88 some onw else will write in if im wrong but even with 4.88 that is crazy rpm are you sure something else isnt wrong?

 

You can determine what gear you have by going to Post #9 in the link below...

https://www.ford-trucks.com/forums/4...lder_____.html

 

Thanks for replys. I might exhadurated a bit about the rpms, but they are still very hight - no less than 2700rpms at 60-65mph. I checked my tires, I have dully 225/70/19.5 on that truck. I couldn't find the axle code and vin tag on the door is pretty washed off so I couldn't read axle code.

Where can I get some gearing for my rear end?

 

Those 225/70R19.5 tires have a diameter of 32.00". You should have a Dana S135 rear axle per the link below (Page # 53). Depending on which transmission you have in your truck, the link below (Pages #59-60) states that the final drive ratio is as follows:

5 Speed Manual - .76
6 Speed Manual - .72
Automatic - .71

https://www.fleet.ford.com/truckbbas...0/BBFSD00A.PDF

The reason that I am providing this information is so that you can use the "RPM Calculator" to determine which gear you currently have and which gear you need for the desired RPM's. To use the RPM Calculator, you will need the following:

Miles Per Hour - You stated you are driving at 60-65 MPH... you can only enter one value.

Tire Diameter in Inches - 32.00"

Axle Ratio - This is unknown... however, you can back into this value by monitoring the calculated value that displays in the "RPM" field. Standard options here include 4.10, 4.30, 4.56, 4.88, 5.19, or 5.38.

Transmission High Gear Ratio - Depending on your transmission, enter the appropriate value listed above (.76, .72, or .71).

RPM Calculator

Below is a link that states that there are 17 gear options for the Dana S135 axle. However, the site is down for maintenance so check back at a later time. Here is the link:

<CITE>www.thedieselstop.com/.../showflat.php-Cat=&Number=2242398&page=5&<WBR>view=collapsed&sb= 5&o=&fpart=1.htm</CITE>
<CITE></CITE>

 

Alright, I called the dealer just now and he told me I have 4.88 gears, and that the rear end is Dana (he couldn't give me more info on it).
Now, how do I figure out if my truck is 5 speed or 6? I mean the shift **** says 5 on it, but there is a lower (kind 6th gear) that goes to the left of 1st gear, so I assume it's 6 spd.

According to RPM calcualtor with my 4.88 gears it says I should be around 2400 rpm, which I might be (but I still think I need to go lower). Where do I get the rear end for my truck with lower gears?

 

99 F550's came with the Dana 135. 4.88 is the most common, and a manual with 5 speeds plus low is a 6 speed. I hope this helps.

 

So, at 65 MPH your truck "should be" turning 2,400 RPM's with the 6-speed transmission and 4.88 gears. You need to confirm this by actually driving the truck at 65 MPH. If you are at higher RPM's, then it is logical to assume that the previous owner installed a higher gear. If you want to lower the RPM's, then you can install a lower gear. The RPM Calculator will tell you the expected RPM's based on the gear that you enter... see examples below.

4.56 Gear - 2,242 RPM's
4.30 Gear - 2,114 RPM's
4.10 Gear - 2,016 RPM's

 

Thanks for your help Lschicago.

Furian, it seems to me that going with 4.10 gears would be the best, where can I buy those gears for Dana 135? I found a shop that works with Semi trucks, maybe they can install them for me. They were suggesting a complete rear end, but that cost upwards of $2K

 

Check out the link below. There are Part #'s for the 4.10 gear and the required internal components for this size gear, which were posted by "Robyn."

4.10 Gear - 360KG106-X
Internals - 360KQ102-X

TheDieselStop.Com Forums: Ford F550 Dana 135 Rear NEED 4.10 or 3.91 ratio

You can confirm these part #'s in this link.

http://www2.dana.com/pdf/AXIP-8941.pdf

I can't find a website that sells these parts so you may have to contact Dana/Spicer to find a retailer.

Contact Dana for information on automotive, commercial, and off-highway vehicle products and systems.

 

Great, thanks for all the help. I see their headquarters are in Toldedo, which is 90 miles away from me. I will call them tomorrow and find a distributor.

Now I have to find someone who can do the swap properly.
So you think I will only need gears and diff. case?

 

Ask Dana/Spicer when you call them. They should have a technical team who can answer that question for you. With parts and labor, it's still going to be expensive... maybe in the $1,200 to $1,600 range.

 

Alright, found Dana 135 rear end with 3.73 gears in it.
Paid $1200 for everything (including labor)... Truck has lost some power, but I am running 1600 rpms at 65mph now

 

wow thats a big jump...4:88 to 3:73.

 

yea, I just wanted something similar to F-350