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

[lowspeedpursuit]

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.

Am I missing something? With 205/70R16 on 4.10 at 140kph (87mph), you'd only be turning ~4400rpm even in 4th. Cruising in OD, you'd be at 3300.

 

[superj]

Yeah, mine will do 90 all day long. Stupid top speed limiter almost get me killed on texas 80 snd 85mph roads though since everyone is doing 10+mph over the posted speed limit.

 

[bhgl]

Am I missing something? With 205/70R16 on 4.10 at 140kph (87mph), you'd only be turning ~4400rpm even in 4th. Cruising in OD, you'd be at 3300.

3300-3500 is my RPM at my current ratio of 3.73 at that speed... Strange, are you using the ratios for the 5r44e?

 

[bhgl]

Am I missing something? With 205/70R16 on 4.10 at 140kph (87mph), you'd only be turning ~4400rpm even in 4th. Cruising in OD, you'd be at 3300.

I just did the math and you're right, I for sure have an F6 axle, which is the 3.73 with an LSD. BUT now I'm wondering if a 4.10 gear found its way in there at some point before I owned it.

 

[lowspeedpursuit]

I'm using grimjeeper and autopopulating values for the 5r55e. Since we're talking about cruise, we're only really concerned with 1:1 and OD anyway.

I'd count driveshaft vs. tire revolutions to confirm real quick.

4.10 might be overgeared for a highway-focused, non-towing 3.0 with small tires, but I'd still be more wary of undergearing. My 2.3 basically couldn't use OD with 3.73s and 29"s, which give the same RPMs as 3.55s and your 27.3"s.

Even if the more powerful 3.0 can make that work, I wouldn't go any taller than that, or maybe 3.45 at absolute most, which other posters have also already suggested.

 

[bhgl]

I'm using grimjeeper and autopopulating values for the 5r55e. Since we're talking about cruise, we're only really concerned with 1:1 and OD anyway.

I'd count driveshaft vs. tire revolutions to confirm real quick.

4.10 might be overgeared for a highway-focused, non-towing 3.0 with small tires, but I'd still be more wary of undergearing. My 2.3 basically couldn't use OD with 3.73s and 29"s, which give the same RPMs as 3.55s and your 27.3"s.

Even if the more powerful 3.0 can make that work, I wouldn't go any taller than that, or maybe 3.45 at absolute most, which other posters have also already suggested.

Most definitely, right now I'm just absolutely befuddled about what ring and pinion is actually inside my differential. The door sticker says it's an F6 Axle, the RPMs at high speed are telling me it's a 4.10.

 

[sgtsandman]

Most definitely, right now I'm just absolutely befuddled about what ring and pinion is actually inside my differential. The door sticker says it's an F6 Axle, the RPMs at high speed are telling me it's a 4.10.

Do like lowspeedpursuit suggested to confirm what you have. Put the rear axle up on jack stands, mark the drive shaft with a line, mark the tire with a line, and see how many times the driveshaft spins with one tire rotation. A little under 4, you have 3.73. About or a little over 4, you have a 4.10. Of course put the transmission in neutral but you probably already know that.

The other, more messy way to check is to pull the differential cover and look at the side of the ring gear and/or the end of the pinion. The ratio is usually cast into them.

The latter is how I found out the junk yard I bought an axle for the '98 from tried to pull a fast one. I asked for a 4.10. They gave me a 3 73. Then proceeded to get angry and pontificate to me about how they knew better what I wanted when I called them out on it.

 

[scotts90ranger]

If someone did an axle swap right they would have kept the tag on one of the diff cover bolts, second row of digits is what's important, should be like 3L73 7 5 if it's a 7.5 with 3.73's, if the tag is missing all bets are off...

 

[bhgl]

If someone did an axle swap right they would have kept the tag on one of the diff cover bolts, second row of digits is what's important, should be like 3L73 7 5 if it's a 7.5 with 3.73's, if the tag is missing all bets are off...

Tag is unfortunately gone, or never existed in the first place. The truck is a bit of a frankenstein as it is, so who knows.

 

[scotts90ranger]

Oh it existed from the factory, but unfortunately someone actually did maintenance or did an axle swap and chucked the tag

I have an excel file with gear and tire calculators with trans ratios (I don't have the Ranger autos, just what I have being the M5OD, ZF5 and 4R70W but easy enough to change), I can't attach it but if you PM me with an email I'll send it to you if you'd like...

 

[bhgl]

Well folks,

It's for sure a 4.10 axle, I jacked up the rear, marked the tire and gave the driveshaft a couple of spins. Sure enough a little over 4 complete turns to spin the wheel.

What's most interesting to me is the fact that the door sticker lists it as being an F6 Axle, which according to the tech library at least, that's a 3.73 limited slip. It also says that the standard tire size is 225/70r15s.

Just about every VIN lookup I used however marked the vehicle down as having 4.10 Gears , and 235 tires.

I've actually called Mazda Canada to see if they could find any original documentation on the vehicle, specifically a build sheet or window sticker. The person on the phone was super helpful and genuinely sounded curious about the whole thing.

I even found a Mazda B-Series Brochure from 2003! (from the USA) To try and make sense of the what the hell this truck ACTUALLY is. From what I think the brochure is saying, the limited slip wasn't available on the B3000 dual sport models, only the B4000.

https://autocatalogarchive.com/wp-content/uploads/2019/01/Mazda-B-Series-2003-USA.pdf

My whole world is twist-turned upside down.

I wasn't planning on cracking the axle open anytime soon, but now I'm doubting my entire existence.

 

[Uncle Gump]

Consult a boomer... they'll talk you off the ledge.

The PO thought it was under powered and wanted a trak lock diff and a better gear. So they swapped a rear end into it.

 

[pjtoledo]

it's time to post a picture of the diff cover to compare 7.5 & 8.8 bolt patterns.
F.Y.I. both 9" and 10" drums fit either axle because the axle tubes & shafts are identical.

 

[scotts90ranger]

Plugging things into my spreadsheet with a 27" tire and 3.08 gears and a .75 overdrive you're at 69.5mph at 2000rpm and 104 and change at 3000rpm, to me that sounds like overdrive would be useless unless you section the roof down to reduce the cross section... drop the tire size to 25" and you get down to 64 and change at 2000 and 96.6 at 3000 which would be slightly better but still probably a bit much. Going to 3.45 gears and 27" tires puts it at 62mph at 2000rpm and 93 at 3000rpm

 

[Bgunner]

My Ranger albeit a '94, 3.0L with 3.45:1 gear ratio with the standard M5OD-R1 trans gets 24 MPG on the highways around here. I have mountainous terrain at times where I live so keep that in mind. At the time of this MPG calculation I was running 215/75/R14 tires. 26.7" tire

I wouldn't go below 3.45 ratio for highway driving as passing is slow with this ratio. I personally want to go to the 4.10 ratio because most of my driving is done around town and over mountains where My old 3.0's power range is in the higher RPM range than what yours is. 3.08 is silly in my opinion unless you live and drive mostly on flat land as the hills really kill the fuel economy gained from the tall gear.

Judging from my experience with my trucks set up I see just about what scotts90ranger just posted for the 3.45 ratio. There may be a slight ratio difference between our transmissions though. @ 50 MPH/80.4 KPH I see 2000 RPM's in overdrive/5th gear.

The 3.45 ratio seems to be a nice sweet spot for highway driving for me but lacks in power climbing mountainous areas with a 45 MPH / 72.4 KPH speed limit. I am constantly between 3rd and 4th gear due to how windy the roads are with grade changes coming out of the corners.

I hope my experiences and given info helps you narrow down the option that is best for you.