What rear end to run in the 5 speed?

[pschand]

Ok guys, here is my dilemma… I just swapped out my E4OD for the 5 speed manual and now my gear ratio is real low. I have the 4.10 rear end and now my truck can barely to freeway speeds without sounding like the motor is going to blow up! So, what should I do? Do I put the 3.55 or the 3.73 rear end in? I’m thinking the 3.55 would be good, but I don’t want to be so high geared that I can’t pull anything….

Did Ford only give two options from the factory for rear ends? Was it the 4.10 for the auto and the 3.55 for the manual? I know that they put the 3.73 in the 6 speeds, but was the 3.73 an option for our 5 speeds? Also, I have 315x75xR16 tires on my truck…

[bugman]

I have the 5 speed and a 4:10 from the factory and my truck is a towing machine. I have no problems running at 80 mph unloaded, or even loading a couple of 4 wheelers on the top of the bed and heading 800 miles. Unloaded I can get 18 mpg and as high as 22 if I really want to watch my speeds. Just guessing that with you larger tires your final gear ratio at the tires may be towards the 3:73's but I'm not sure.

[96strokerlb]

i also swapped out my e4 for 5sp. i beleive 65 is around 2-2.3k rpms about 2.5k at 75 and i beleive i have 3.55 gears....i also used an 86 F-450 5sp for the swap i do not know if they are geared down more then a F-250-350 trans

[DaveBey]

There were only two gear ratios available for the Sterling rear axle from '94 to '97: 3.55 and 4.10.

With the larger tires, you are effectively raising the ratio which would decrease your RPMs at highway speeds.

There were different S5-47 ZF transmissions available for either gasoline or diesel engines. Transmission, Manual, Model S5-47 ZF: Description

Cheers from Claremore, OK!
Dave

[96strokerlb]

my F-450 trans is a ZF S5 -42 not 47 i dont know what ratios the internals maybe have come in. and as i recall there is a post on here where a guys dad bought and OBS and had an optional positrac rear end or something like that put in and it has 3.73 ratio...there is a possibility then of a select few being out there

[RWF350]

I'm surprised it made that big of a difference. Final output on most trans w/overdrive is approx 20%.

[pschand]

Ok guys, I looked on the side of my transmission and it had the gear ratio stamped into it. It says it's the S5-42 with 4.14 - .77 So I'm assuming that I have the Close Ratio S5-42.

With my 4.10 rear end here is my approx freeway speeds and RPM comparisons.
75MPH = 2500 RPM
70MPH = 2250 RPM
65MPH = 2100 RPM
60MPH = 1950 RPM
55MPH = 1700 RPM

I don't know about you guys, but my RPM seems to be too high for the size of tires that I have on it and not to mention, I don't know how I would ever get good fuel mileage with this set up. Does this RPM seem high to you guys? Really don't know if I should go to the 3.55 or not?


Close Ratio S5-42
(Diesel)
4.14
2.37
1.42
1.0
0.77
3.79

Close Ratio S5-47
(Diesel)
5.08
2.60
1.53
1.0
0.77
4.66

[96strokerlb]

just went for a cruise after installing my water temp gauge which tells me i need a new thermostat sadly 170 degrees tops at highway speeds but

70mph - 2,000 RPM with 3.55 rear so i was off on my previous thoughts and i beleive 265 85 or 75 i know its a 31in tire. and a close ration s5 42 and a wide ratio wont has a different bell houseing anyways and wouldnt bolt up without adapters.

and have you had your speedo adapted to the tires? 75 might actualy be 80+ i know my cousin went from 31 to 33in tires on his 07 dodge and 65 was actualy something like 68 or somewhere in there

[powerstrokin1997]

sounds ok to me. i have a 5spd 315's and im at 2500 rpm at 75 mph with 4.10s and my speedo is adjusted properly. i also swapped in the S5-42 instead of the S5-47 i am much happier with it.

[sdan27]

If you go to this site, Randy's Ring & Pinion. The Differential Experts. Auto Parts & Services., it gives a calculator where you can put in your tire size, transmission, and gear ratio to find engine rpm vs. mph.

[Patrick Feeley]

Mine runs 2550 at 70 mph in 5th gear with 235/85-16's. Cheers!

[pschand]

So I did some checking and it looks like it would cost me approx $800 to replace my rear and fron diff to 3.55 ratio. That is alot of dough to change my rpm... Not sure it's worth it? Ive been thinking about getting new wheels and tires anyway, so should I just get a 35" tire and that would help me out a little right? I checked my current setup out with the gear ratio calculator and it says that i'm equivalent to a 3.73 ratio if I had stock tires. So I guess it's not that bad... I pull a 30' RV trailer and atvs so I pull alot of weight, would the 3.55 setup be bad for me in the mountains?

[travis23]

my truck has 3.55 if you are interested i am going to switch mine for 4.10 looking for a set email me at lmikeberry@yahoo.com

[sdan27]

Pschand, so from your signature you're running 315/75R16s? I got the 4.10 gears in my truck but would love to drop down to something like a 3.73. I don't tow or carry a lot of weight often but when I do I don't want it to be a problem so I think 3.55s would be a little too low. From all that you're towing, I think 3.55s might be a little low too. Maybe next time I get tires I'll do some 315s like you. A lot better price, plus new tires, than new gears. Are you able to run those without any kind of lift?

[pschand]

If you have the dana 60 front end then you most likely have the F350. If so, then you can run 285x75xR16 without lifting the front, but if you go any more, then you will need to install an add leaf or better yet like I did, install the reverse shackle kit... it adds 3" to the front, levels out your truck and makes it ride so much better... I measured my tires and they are approx a 33" tire. This is strange cause all the calculators say that a 315x75xR16 should measure 34.6" but mine measures 33.2". Anyhow, i'm thinking of getting a 35" tire with 18" wheels and that should make my gear ratio approx a 3.65 or so...... That would be perfect. So I think i'm gonna keep my 4.10s and just go a little bigger on the tires..