Re-Gearing 7.5 LSD from 3.73 to 3.08, manufacturer recommendations for Ring and Pinion Gear set.

[superj]

man, a company already makes a fast back camper for a truck. that is cool

Michigan Vehicle Solutions (mivehiclesolutions.com)

 

[bhgl]

i htink you should make one of those cool aero bed covers that slopes down from the top of the cab and sticks out the back a bit to come to a point. i saw on some fuel efficiency forums where people made their own aero camper shells and they looked super slick.

I'm definitely tempted, but I'll be honest I'm not super sold on the look.

When travelling I do a lot of stealth camping, and the otherwise understated farm truck look goes a long way to folks not bothering me haha.

 

[superj]

this guy has a 98 b2500 and his lifetime average is 29.9 without the cool mods

Details: B2500 - 1998 Mazda B2500 SX Fuel Economy - EcoModder.com

 

[bhgl]

this guy has a 98 b2500 and his lifetime average is 29.9 without the cool mods

Details: B2500 - 1998 Mazda B2500 SX Fuel Economy - EcoModder.com

He has done a few things notable, specifically a power steering and radiator fan delete. Plus I'm sure have 2.5 helps a lot.

I would love to get 30 MpG

 

[cbxer55]

2020, I went from 3.73 to 4.10 in my 98 3.0 Ranger. Don't regret it one minute. Had a friend with a shop a mile away. Dropped it off there, walked home. When he told me itwas done, walked back and got it.

Had him refresh everything while in there. Spider gears, bearings and seals. Now, when the rear tires are up on jack stands, I spin one, and both go round and round for two minutes. One spinning one way, the other opposite.

The difference between 3.73 and 4.10 is .37, so 10%. But what a difference. Now it no longer hunts between third and OD. Even going uphill. Oddly enough, I still prefer driving it OD off in city or town.

 

[Uncle Gump]

man, a company already makes a fast back camper for a truck. that is cool

Michigan Vehicle Solutions (mivehiclesolutions.com)

And... for the low low price of $7500.00

 

[bhgl]

2020, I went from 3.73 to 4.10 in my 98 3.0 Ranger. Don't regret it one minute. Had a friend with a shop a mile away. Dropped it off there, walked home. When he told me itwas done, walked back and got it.

Had him refresh everything while in there. Spider gears, bearings and seals. Now, when the rear tires are up on jack stands, I spin one, and both go round and round for two minutes. One spinning one way, the other opposite.

The difference between 3.73 and 4.10 is .37, so 10%. But what a difference. Now it no longer hunts between third and OD. Even going uphill. Oddly enough, I still prefer driving it OD off in city or town.

Now I wish I had a friend like that nearby, I spoke to a couple shops today about it and they quoted me 3-5 business days, and 2 weeks upon me delivering the axle respectively.

If I moved to 4.10 gears my RPMs would for sure be outside of the ideal powerband, and closer to 5K when at my cruise speed. Luckily I've got a 5 speed auto, (4 + OD). Sticking with a 3.73 would be the preferable option over 4.10s.

 

[cbxer55]

I don't know, don't have a tach. Rarely ever hit the highway, most of my driving is in town / city.

My truck has a bumpy hood, looking for one of those old school hood tachs. So far all I find is stuff

for V-8's. None calibrated for a six cylinder.

 

[sgtsandman]

What's interesting is that the air/fuel ratio really does lean out on the one test after 70 MpH, I've got no information as to what transmission is being used, but it ought to be running in it's final drive ratio for a dyno-test.

That could explain why I was able to achieve pretty good fuel economy despite the high RPM. I should definitely consider dropping down to a 3.45/3.55 instead after I do some more number crunching.

I agree with the idea of going to 3.55. Even 3.45 might be too much but the only frame I have for reference with that gear is in a 1998 Ranger with a 2.5 Lima engine. It couldn't get out of it's own way with that gear and fuel mileage was only about 21-22 in a truck that was supposed to be able to get 27 or so. It also struggled to maintain speed on the highway until it reached 70 mph. Even then, it wasn't great and a big enough head wind would drive it right back on the struggle bus. Moving to a 4.10 axle gave it much better performance and the fuel mileage didn't change.

Being you have a 3.0 with more horsepower and torque, it should handle a higher gear better but I still wouldn't go with a 3.45. 3.55 would probably get you closer to your goal.

 

[bhgl]

I agree with the idea of going to 3.55. Even 3.45 might be too much but the only frame I have for reference with that gear is in a 1998 Ranger with a 2.5 Lima engine. It couldn't get out of it's own way with that gear and fuel mileage was only about 21-22 in a truck that was supposed to be able to get 27 or so. It also struggled to maintain speed on the highway until it reached 70 mph. Even then, it wasn't great and a big enough head wind would drive it right back on the struggle bus. Moving to a 4.10 axle gave it much better performance and the fuel mileage didn't change.

Being you have a 3.0 with more horsepower and torque, it should handle a higher gear better but I still wouldn't go with a 3.45. 3.55 would probably get you closer to your goal.

I think you're right, ideally if my engine can keep up it would be preferable to have the lowest possible ratio within reason, but I need to make sure the truck can get to a reasonable cruising speed, and still make passes safely.

I'll do some more number crunching and testing to see what RPMs I would be looking at given different gear ratios. I'll also focus first on improving aero, reducing weight, and trying to free up power from the engine before going to a lower ratio.

I think I could get away tomorrow with 3.55s, but with a focus on long distance highway driving I do still think a lower overall ratio would benefit the truck overall, but it looks like the pinion ring and gear swap will need to be supported by things like aero, power, and weight reduction in order to actually see the benefits.

 

[19Walt93]

If the only reason for the change is to increase mpg, I'd do some more math first. Get an estimate for the gear swap and divide it by the price of a gallon of gas, then you can calculate how long it will take to pay for the change based on the miles you drive. If you're paying someone to install the gears, it will take years to break even.
We used to sell a pile of Super Duty trucks, mostly with 4.10 gears a few with 3.73's for customers who thought they'd save gas. In our hilly area, the 3.73 trucks didn't get better mileage because they shifted down so much and they experienced way more transmission problems.
If you're doing it because you want to, that's the best reason to do anything. If it's an attempt to save money I'll be startled if it works.

 

[bhgl]

If the only reason for the change is to increase mpg, I'd do some more math first. Get an estimate for the gear swap and divide it by the price of a gallon of gas, then you can calculate how long it will take to pay for the change based on the miles you drive. If you're paying someone to install the gears, it will take years to break even.
We used to sell a pile of Super Duty trucks, mostly with 4.10 gears a few with 3.73's for customers who thought they'd save gas. In our hilly area, the 3.73 trucks didn't get better mileage because they shifted down so much and they experienced way more transmission problems.
If you're doing it because you want to, that's the best reason to do anything. If it's an attempt to save money I'll be startled if it works.

Funnily enough, the goal isn't to save money really, it's more about trying to get to 30 MPG in a truck that everyone has told me will never do better than 23.

From all the math I've done prior to realizing the truck has more efficient fuel burns at specific, higher RPMs, I could expect a substantial (10-17%) benefit to fuel economy strictly at highway speeds with a 3.08. That does get more complex when I take into account the fuel economy I was able to achieve with the truck at a near constant 2500-3500 rpm for multiple hours.

Also for my use case, less time at the pumps and more time moving is incredibly important as it allows me maintain a higher average speed over a long distance.

 

[scotts90ranger]

I've had I think 4 different tire sizes on my '97 Ranger (2.3L, 4.10's, extended cab 5 speed) starting with some worn out out of round 27" all terrains, some 235 75 15 all season then the 225 75 (maybe 70, don't remember) 15 P rated. I used to get 21-22mpg until I switched to the car tires then get 23-25. Too much shifting with the 235's, I was going for mileage too but it didn't change anything and I was shooting for cruise speeds under 3000rpm which is at like 73mph which is perfect for my needs...

 

[superj]

I have 4.10 with my 5 speed and 3.0 and i dont even run at 5k rpms at above highway speeds.

 

[cbxer55]

I have 4.10 with my 5 speed and 3.0 and i dont even run at 5k rpms at above highway speeds.

I'd like to get a tach on mine and find out what it's running with 4.10s, automatic with low profile 14 inch tires. Had it on the highway a few weeks ago, and it was running 90 mph with ease. Speedo is off about 5% due to the low profile tires, and yes, I factored that in to get the 90 mph.