big66440 Posted June 30, 2016 Share Posted June 30, 2016 Hey guys I have to get my Dana 35 rebuilt and was wondering if going to 3:73,s from 3:55's would make a huge difference in performance/mileage. My tire size is 235/75/15, according to the online calculators at 80MPH it would make a difference of less than 200RPM. This is for my daily driver which sees quite a bit of street and highway miles, thanks. Link to comment Share on other sites More sharing options...
Jeepman Posted June 30, 2016 Share Posted June 30, 2016 I try to keep my RPM's as close to stock number or lower whenever possible so its really about what are you after, more power or better mileage as you will rarely get both... Link to comment Share on other sites More sharing options...
88mjblue Posted June 30, 2016 Share Posted June 30, 2016 Are you sure you really need a new ring and pinion setup? Sometimes it's just the bearings that are shot and you can reuse your ring and pinion gears, but if those are truly in need of replacement, then I say why not, it will have a bit more "kick" driving around town... Link to comment Share on other sites More sharing options...
cruiser54 Posted June 30, 2016 Share Posted June 30, 2016 I'm going to 3.73s in my 87. Link to comment Share on other sites More sharing options...
johnj92131 Posted June 30, 2016 Share Posted June 30, 2016 If you have to get a new ring and pinion anyway, my suggestion would be 4.10 rather than 3.73 - Why? 3.55 to 3.73 is only a 4.2% change. Your change in tire size from 225/75 x 15 to 235/75 x 15 was a 2% change. The change from 3.55 to 4.10 is 15.4% And if I remember right, Don reported about 1 or 2 mpg improvement on his 91 when he changed from 3.55 to 4.10 rear end. I don't think you will feel any change in the real world with 3.73 gears. Link to comment Share on other sites More sharing options...
cruiser54 Posted June 30, 2016 Share Posted June 30, 2016 If you have to get a new ring and pinion anyway, my suggestion would be 4.10 rather than 3.73 - Why? 3.55 to 3.73 is only a 4.2% change. Your change in tire size from 225/75 x 15 to 235/75 x 15 was a 2% change. The change from 3.55 to 4.10 is 15.4% And if I remember right, Don reported about 1 or 2 mpg improvement on his 91 when he changed from 3.55 to 4.10 rear end. I don't think you will feel any change in the real world with 3.73 gears. Yeah..... Link to comment Share on other sites More sharing options...
gogmorgo Posted July 1, 2016 Share Posted July 1, 2016 Unless you're really 100% sold on keeping a 100% original truck (which I'm guessing you aren't if you're considering regearing), it's probably best to not throw money at the Turdy5 and upgrade the axle. Lots of people have swapped in Ford 8.8's because they're super common, I personally have a low-mile C8.25 out of an '03 Liberty 4-cyl waiting to go in, which I chose because of 4.10's, rear disc brakes, and a much closer width to the original than the 8.8's... every inch counts! Link to comment Share on other sites More sharing options...
big66440 Posted July 1, 2016 Author Share Posted July 1, 2016 Unless you're really 100% sold on keeping a 100% original truck (which I'm guessing you aren't if you're considering regearing), it's probably best to not throw money at the Turdy5 and upgrade the axle. Lots of people have swapped in Ford 8.8's because they're super common, I personally have a low-mile C8.25 out of an '03 Liberty 4-cyl waiting to go in, which I chose because of 4.10's, rear disc brakes, and a much closer width to the original than the 8.8's... every inch counts! I would love to upgrade to a a different rear end but I just dropped $350.00 to get a brand new drive shaft made besides my truck is 2WD and I really don't see the real NEED to go bigger and or stronger at the moment. Looking at the math with the 4:10 ratio it seems the engine will be revving 357 RPM higher at 80MPH, I'm assuming that would be a considerable difference on a long distance trip?. My truck sees stop and go street driving 95% of the time, sorry for the ignorance but wouldn't the 4:10's cause the AW4 to shift too quickly through the gears? Link to comment Share on other sites More sharing options...
cruiser54 Posted July 1, 2016 Share Posted July 1, 2016 Yes, it would shift more quickly as it would be appropriate for the lower gears. some serious overthinking going on here. Link to comment Share on other sites More sharing options...
Pete M Posted July 1, 2016 Share Posted July 1, 2016 I think you'll be happy with the 3.73 gears. :D they are pretty common in dana 35 or 8.25 flavors under ZJs and KJs with disk brakes. an 8.25 with disk would be swwwwweeeeet :banana: side note: in some years the 4banger-automatic came with the AW4 and 4.56 gears so 4.10s aren't harmful at all. the trans will shift at the appropriate time just fine. :thumbsup: also, I killed the dana 35 under my 2wd daily driver in spectacular form when ring gear teeth started parting ways. I just don't trust them and would never spend money on them beyond new gear oil. :fs1: Link to comment Share on other sites More sharing options...
gogmorgo Posted July 1, 2016 Share Posted July 1, 2016 You would probably be better off in stop and go traffic with the lower gears, at least in my mind. More torque to the wheels means the engine isn't working as hard and hopefully that leads to better mpg. But I won't profess to be an expert. Only the 4-banger KJ's came with 4.10's, the rest were 3.73's. I'd have to measure and haven't done that, but comparing the two my 8.25 looks like the pinion's maybe an inch longer than the d35's so that might cause a problem with the driveshaft length. All I'm suggesting with the replacement axle vs the rebuild is that rebuilding with a regear is going to cost you a significant amount more than a good used axle would. My guess is it would be much more than getting your driveshaft shortened. A small lift would also be a way to get around the need for a shorter driveshaft. While the D35 isn't necessarily a toothpick (I have no reason to suspect mine isn't original with 315,000 miles on it) it's still not really worth throwing money at it. Link to comment Share on other sites More sharing options...
Rockfrog Posted July 1, 2016 Share Posted July 1, 2016 235 75r15's and 4.10's will have you screaming down the highway. If you are mostly driving around town, it will definitely improve mileage. The trans will shift quickly through the gears and the whole drive train will work less. As soon as you hit the highway you'll also wind out quickly and be revving very high (for a 4.0) rpm's. The 4.0 seems happiest between 1800 and 2400 rpm. Over that and you are burning fuel for fun, and below that you are lugging and burning fuel to keep up. I'm swapping an 8.8 3.73 into my MJ, but I have a manual, 32's and aspirations to tow a load (with plans to drop to 31's). But, if you find you need to travel the highway more, toss a set of 32's on and the AW4 will roll in prime mileage territory for the highway. As an example my XJ rolls on 35's with 4.56 gears and an AW4 behind the 4.0 ... I limit myself to 2500rpm as I don't want to be screaming the motor down the highway, and that limits me to about 110kph (so what about 65mph) and the speed limit is 120kph. I can go faster, but the fuel tank empties faster. If I drive 90kph (about 60mph) it actually saves me a lot of fuel. Around town I get about equivalent to highway mileage (likely because of how I drive). But she's built for the trail, not the pavement, she just has to get there over it. It's all give and take, what works in stop and go, generally sucks on the highway, and what works on the highway generally sucks around town. If you mainly do stop and go driving, why calculate a gear need based on an 80mph speed? Try 55mph and go there. My MJ mainly sees highway time and until I was going to tow 3.55 was my desired ratio as 3.07 and 32's knocked me from 21mpg (w/ 235/75r15) down to 18mpg. Sent from my SGH-I337M using Tapatalk Link to comment Share on other sites More sharing options...
gogmorgo Posted July 1, 2016 Share Posted July 1, 2016 I should also have clarified that my plan for the 4.10's was to match them with 32 or 33" tires. But you'll know I have to try them out with the 235/75/15's when it eventually happens. :thumbsup: Link to comment Share on other sites More sharing options...
88mjblue Posted July 1, 2016 Share Posted July 1, 2016 Or, if you do plan to re-gear to 4.10's, then just drive slower on the highway to keep the rpms down, and in turn you'll get good mileage around town driving normally. Link to comment Share on other sites More sharing options...
Pete M Posted July 1, 2016 Share Posted July 1, 2016 you shouldn't use the word "screaming" if the factory sold trucks with 4.56 gears and even smaller tires. Link to comment Share on other sites More sharing options...
Rockfrog Posted July 1, 2016 Share Posted July 1, 2016 With a 4cyl and an automatic, which would be about right for the 4cyl considering it was generally 4.10 with a manual. About the same jump as 3.07 to 3.55 with the 4.0L. What is good for the 4 is not so much for the 6. If I put stock tires on I'd hit redline quick fast and blow the low revving 6 to hell and back just as fast. Sent from my SGH-I337M using Tapatalk Link to comment Share on other sites More sharing options...
big66440 Posted July 1, 2016 Author Share Posted July 1, 2016 Yes, it would shift more quickly as it would be appropriate for the lower gears. some serious overthinking going on here. Sorry Cruiser didn't mean to upset you :D , I think I'll stick with the 3:73's it may not be much of a difference from the 3:55's but I'll be able to "scratch that itch" . I know some XJ's and MJ's were equipped with 4:10's and 4:56's but I'm guessing it's simply because the little 4 poppers they came with from the factory needed the gear reduction more than the 4.0. If I had my dream house far from the city I wouldn't hesitate to go with 4.56's but that's a story for another day. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 1, 2016 Share Posted July 1, 2016 Yes, it would shift more quickly as it would be appropriate for the lower gears. some serious overthinking going on here. Sorry Cruiser didn't mean to upset you :D , I think I'll stick with the 3:73's it may not be much of a difference from the 3:55's but I'll be able to "scratch that itch" . I know some XJ's and MJ's were equipped with 4:10's and 4:56's but I'm guessing it's simply because the little 4 poppers they came with from the factory needed the gear reduction more than the 4.0. If I had my dream house far from the city I wouldn't hesitate to go with 4.56's but that's a story for another day. I'm not upset... Link to comment Share on other sites More sharing options...
Pete M Posted July 1, 2016 Share Posted July 1, 2016 What is good for the 4 is not so much for the 6. If I put stock tires on I'd hit redline quick fast and blow the low revving 6 to hell and back just as fast. rpms are rpms. doesn't matter how many cylinders there are. heck, my dakota has a 5.9 v8 and 3.92 gears and tires that are just a tick over 27 inches in diameter. Link to comment Share on other sites More sharing options...
Rockfrog Posted July 1, 2016 Share Posted July 1, 2016 Yes, but rpm's and gears are matched to a particular motors power peaks. The 4cyl makes power in a different range than a 6 ... Wana try a 4cyl 5spd with 3.07 gears and stock tires? The inverse is the same with a 6cyl and 4.56 gears. Like I said, what makes a 4cyl happy doesn't work for the 6. I'm also pretty positive the 4cyl would barely move rolling 35's with an AW4 and 4.56 gears. It all comes down to where the motor likes to live within those rpm's. Sent from my SGH-I337M using Tapatalk Link to comment Share on other sites More sharing options...
Pete M Posted July 1, 2016 Share Posted July 1, 2016 yes, they all have happy torque ranges, but they aren't as narrow as you might think. I'm just saying that the 4.0 won't be screaming any more than my v8 and it does just fine. plenty capable of hitting that 112mph computer limited speed. not that I would know that. I've just heard. :D Link to comment Share on other sites More sharing options...
mikekaz1 Posted July 1, 2016 Share Posted July 1, 2016 I have 4.10s on my TJ with 32s with the 3 speed tranny. 70mph is 3k rpm. And will run that all day getting 15mpg. Link to comment Share on other sites More sharing options...
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