[krmike]

What's your opinions?

Was it a good decision?

Do you have to stay out of over drive now to tow well? I would personally think that you would especially in the hills.

Towing a 7500# 5th wheel all over the west. I have read some posts but
find it hard to believe the 308 gears would work. I am pretty sure I would lug in OD.

What rpm are you turning out of OD let's say around 65-70 mph?

Any other thing I should know? Thanks /ubbthreads/images/graemlins/cool.gif

 

[Rickie]

Why wouldn't they work? Oh, you must have an automatic transmission.

RPM's at 70 mph on 3.73's is roughly 2200. RPM's at 70 on 3.08's would be 1817. Check out gear ratios for your tranny. The 17.5% gear ratio change is similar to adding an overdrive, like a gear vendor or US Gear unit without dual range selection.

 

[coldair]

ust add a gearvenders overdrive

 

[NCHornet]

I had 3:08"s on a F150 and towing was like starting off in second gear. I wouldn't do it!!!

 

[DART505]

I would not see the application for such a tall gear.If you are towing you are Killing everything.3.73 is going to be the best all around & if you want lower rpm crusing without towing a Gear Vendors or such would be the ticket! /ubbthreads/images/graemlins/biggrin.gif

 

[SmokeyWren]

[ QUOTE ]
RPM's at 70 mph on 3.73's is roughly 2200. RPM's at 70 on 3.08's would be 1817.

[/ QUOTE ]

Ummmmmmmmmmmmm. No. /ubbthreads/images/graemlins/frown.gif

RPM with 3.73 rear end, stock-size tires, and a calibrated speedo is roughly 2,000. RPM with 3.08 rear end, stock-size tires, and a calibrated speedo is roughly 1,650. You're right that it's roughly a 17.5 percent reduction.

Any rear end ratio is a compromise between unloaded cruising and heavy towing. 3.73 rear end and stock-size tires is a near-perfect rear end ratio for grossing 16,000 to 18,000 pounds. A 3.55 is okay for grossing less than about 14,000 pounds. A 3.08 would be good for nothing other than unloaded commuting and grocery getting. Or maybe towing a rowboat or one Ski-Doo or one quad. /ubbthreads/images/graemlins/cool.gif

 

[444turbodiesel]

Why would you want 3.08's after you've already swapped to 4.10's?
Why don't you just put the 3.73's back in?

 

[krmike]

I'll go with Smokey he's right most of the time. There's been some discussion with other guys that have ps diesels where I live. I personally thought that 308's are only good for unloaded/no tow situations. Let me clear it up, I love my 4.10's. They are giving me around 13 mpg towing my 7500# 5th wheel. Actually I stepped up my tire size to 285/75 R16s so I am somewhere around 3.96 effective rear end ratio. I could be off a little. I did find myself driving slower, like around 65 on the highway to get 18-19 mpg but when towing 4.10s are the bomb. I saw my engine temperature (preturbo)drop around 100 degrees at highway speed. That tells me there is a drop in stress/load on my engine, not to mention my tranny. My friends were interested in hearing what some of the guys on the dieselstop had to say about running the 308's in their rig. I don't think there are too many people doing the 308 swap and still doing regular towing. I had read on one post that a tranny expert might want to be consulted before doing it.Mention was made of tranny fluid not circulating as quickly with the 308's. This is not my idea, just something I read. Anyhow I am always open to learning and welcome being corrected.

Has anyone did any towing up in the mountains with their 308's and what are they pulling?

I'm going to pass the real world comments back to my friends. Thanks. /ubbthreads/images/graemlins/cool.gif

 

[RigginUp]

Hey,

I have a 99 F-350 single wheel, 4 door, 4x4, Powertroke with 35 inch wheels with a total 7 1/2 inch lift. I have 3.73 gears front and back. I lost a good bit of power putting the bigger tires on it. I got a superchip programmer and put it on the middle setting. I would like to change my gearing to put my truck back at stock performance with the 35 inch tires. Also, my tranny is not doing so good. Who is the person or shop that rebuilds trannies and has a lifetime warranty. It is the trannies that they use in the truck pulls. He rebuilds the one you send him from your truck. Thanks for the input, it would help a lot.

Mike

 

[SmokeyWren]

[ QUOTE ]
I would like to change my gearing to put my truck back at stock performance with the 35 inch tires.

[/ QUOTE ]

Stock tires are 655 revs/mile. 35s are 601. 8.24 percent difference. 3.73 plus 8.24 percent = 4.04. Your wider tires and lift cause a bit more drag than stock-size tires. So you need a 4.10 axle ratio to get back to the about same performance you had with stock tires.

[ QUOTE ]
Also, my tranny is not doing so good. Who is the person or shop that rebuilds trannies and has a lifetime warranty.

[/ QUOTE ]

Nobody.

[ QUOTE ]
It is the trannies that they use in the truck pulls. He rebuilds the one you send him from your truck.

[/ QUOTE ]

You're probably talking about Brian Thompson at BTS (Brian's Truck shop). He builds a bulletproof tranny and installs a bulletproof torque converter that will hold up to severe abuse, but his warranty is only two years. Of course, if you can't break it with two years of drag racing or mud bogging or sled pullin', then it will probably last a lifetime. I have one in mine, only for towing my 5er, and I expect it to outlast the engine. But Brian guarantees it only for two years.

www.brianstruckshop.com

 

[krmike]

Smokey, it doesn't look like many people use these gears, not much of a response,huh. I would assume they don't like there setup.

What's your take? You agree? /ubbthreads/images/graemlins/phoney.gif

 

[SmokeyWren]

[ QUOTE ]
I would assume they don't like there setup.

[/ QUOTE ]

I've never heard of anyone running 3.08 final drive gears in a '99-up PSD. There may be a few rare birds that want a bling bling street cruiser for unloaded "look at me" cruising, but most folks want a pickup with some capability to haul or tow stuff, or a trafficlight drag racer with tire smokin' capability. 3.55 is about as high a rear end ratio that's common in a PSD, and you're sure not going to win any trafficlight grand prix with a 3.55 rear end. /ubbthreads/images/graemlins/cool.gif

 

[Dave Whitmer]

I’ve had 3.08s for about three years now and I am delighted with them. Few people can approach the MPG I get, and the 3.08s are a large part of that performance.

Contrary to popular belief, I tow quite nicely. If it lugs, I down shift to the most efficient gear – fifth. I have pulled heavy loads over the short steep hills of eastern KY and western WV and had no trouble at all. With 10,000 lb of building materials in the bed and trailer I got 15.5 MPG. I have no fear of Sandstone Mountain in WV.

I normal driving I get over 26 MPG on a regular basis in mixed urban/suburban/country road/Interstate driving.

Smokey is dead on about the RPM. With 3.73s and factory rubber 2000 RPM is 69 MPH. With 3.08s and OEM-sized rubber 1650 gives you the same 69 MPH. I run 1700 RPM which is 71 MPH on the slab. 1450 RPM gives me 60 MPH.

Slowing down the engine at a given road speed reduces the engine frictional HP and that is where the MPG gain comes from.

I have a manual transmission and I do fear that the slow-revving setup will destroy an automatic. Maybe Brian or Suncoast or some other respected transmission guru would care to weigh in on the subject. I am not objective about automatics after seventeen years of torment with my old 6.2 Brand G.

I have found the 7.3 to be a real torque monster at low RPM. It accelerates nicely at 800 RPM. I rarely rev over 2000. I’m still on the OEM clutch.

Any regrets? Yeah. I wish I could have found 2.73s for the Sterling 10.25” axle. The ring gear may be of too small an inside diameter to accommodate the differential, but the lack of 2.73 availability may just be a commercial thing. The engine could handle it, I’m sure. I’ve experimented with starting off in 3rd and it seems to do fine. 2.73 gears would push my 71 MPH down to 1500 RPM.

With diesel going for over $3/gallon, I estimate the payback on the mod at about 50,000 miles. A GV overdrive (had one on another truck – the automatic-eating K2500) would cost twice as much (installed) and I don’t care to push more than one overdrive mesh.

I have walked the walk on this setup. I have over 100,000 miles on it with no gearing, clutch, or transmission related trouble.

 

[krmike]

Thanks for the reply Dave.

Very interesting, your manual tranny makes all the difference. However with the auto the gear choices are a lot narrower. Like you said there is a danger of killing the tranny with the low rpm. OD could be locked out on the tranny and that might help, I believe that puts it in a 1:1 drive as opposed to the .073 final drive (OD). It just goes to show the strength of the 7.3 psd it truly is a torque monster. I wish sometimes that there was a 2 speed rear end for these trucks. What a setup that could be. What you think about that, Dave...Smokey?

 

[SmokeyWren]

[ QUOTE ]
I wish sometimes that there was a 2 speed rear end for these trucks. What a setup that could be. What you think about that, Dave...Smokey?

[/ QUOTE ]

Normal 2-speed rear ends are too big and bulky to fit under a pickup. Ford offers that option in the F-650, but not in anything smaller.

The closest you can get to a 2-speed rear end in your pickup is to add a Gear Vendors or U.S.Gear overdrive to your pickup. With a GV with a 0.78 overdrive, you would have about the same ratios available as a two-speed rear end with 3.73 and 2.90 gears.

In 2002 I was part of a Ford SuperDuty focus group. We discussed Ford making available an optional smaller, light-duty 2-speed rear end for our pickups. The Ford guy asked how many would be willing to pay $1,000 for the option of a 2-speed rear end for our pickups. Enough folks raised their hand, a few enthusiastically, that he put it down as something for Ford to consider. But we haven't heard any more about it, so I guess it couldn't be done for only $1,000 per unit.

 

[Dave Whitmer]

To tell you the truth I don't know anybody else who has tried 3.08s. There is a Cummins jockey on another site that is looking for gears, so he tells me.

Fuel economy freaks are a lonely breed.

 

[clydesdale]

Dave, have you thought about the regulated return or a dp tuner econo chip?

 

[Dave Whitmer]

I have a custom-burned economy chip. How it compares to the DP, I don't know. I tried the Edge Evolution, and while it was a lot of fun to drive, it hurt my MPG.

My truck has never been a cackler,and I am not of a mind to mess with the fuel system further. My in-tank and pre-filter mods did make the engine seem to run smoother, but I noticed no improvement in MPG.

 

[JamesVre]

What re the stock gears that come with the truck?

 

[Dave Whitmer]

It came with 3.73s.