Engine/Transmission (1994 - 1998) Thoughts on gear ratio..

[JeppinHackSaw]

So, currently I'm getting about 12-14 mpg no matter how I drive my 3500 98 12v 4x4 auto w/ 4. 10's



I don't pull that much, that often. . but, I when I do, I need the truck to do so. Also, I can't afford another vehicle or deem it needed to do so as I enjoy driving a diesel... so, that's not an option (I ride the harley most of the time to work in the spring/summer/fall. . )



Now... the question I am asking is...



Would I be further ahead to change my gearing to 3. 54 and boost my mileage to the high teens and low 20's?



I figured it, at diesel at 2. 70 a gallon (what I paid today)



I would save 814 dollars driving at 19 mpg vs 13 mpg @ 2. 70 a gallon over the course of a 12K year (hahahah, driving 12K a year... thats funny. . more like 30)



But, to be reasonable, I kept the calculations to a standard number. Anyways. 811 dollars would by far pay for a ring and pinion and set up kit for the f/r axles. That's paying for itself over the course of a year, and then some.



The real question is. . would I be happy with this combination? I am going to say that I will probably pull a jeep on a trailer a total of 2-3k miles this coming year going to diifferent off-roading places (as any MI'er knows, the wheeling here pretty much sucks). How do you think that 3. 54's would tow with a trailer w/ a 4k ish jeep on it...



Also, in the future, I am looking at a gooseneck to haul 2 jeep/whatevers to wheeling trips (34ft gooser) I am guessing gross trailer weight to be around 12K... with trans mods of course (in the next month or so, followed by injectors and what not coming soon, trying to get over the holiday slump before justifying the purchase of go-fast parts)



What are your thoughts?



Is the gear change going to be benneficial enough or am I going to jepordize towing to much to make it worth my trouble?

 

[MAshley]

Could you just drive a little slower ... hehe I think a tire swap would be a better option, you can experiment a little cheaper then with the gear changes, IE once you change the gears your stuck with them, and when you decide to tow you could down grade sizes and still have the power to tow well. I found a Excell spreadsheet here b4 that you can change your tires size amd or gearing and get RPM's and your millage could be computed to some degree.

 

[zstroken]

I think you will have over 500 in just labor on the r/p swap for the front and rear. Plus the d80 requires a new carrier to hit 3. 54.

 

[JeppinHackSaw]

Well... the gears would be set up for a lot less than 500 dollars in labor. I'm guessing around 600 in parts... and a night or 2 of actually working on it to set them up with a buddy of mine.

 

[bdcraig]

The 3:54"s will handle that light of a load easy. Your auto will need to be upgraded. Might think about a US-gear or a GV overdrive. That way if your worried about pulling you can down shift to the lower gears and go on with it. I know with my stick and the GV I run 5th with the GV locked in on the straight streches with any load under 25,000 GVW. I typically haul within the 28,000 to 36,000GVW range. Truck weighs 9500, trailer(flatbed) 6500, tractor(with cab)9700, and mower 3700.



brian

 

[CToney]

I don't no much about the auto's but my brother in law swapped 4. 10's for 3. 54's in his dually. But he had a 5sp. I think if you upgraded you auto as well you should be ok. Once you get guages keep the boost under 30-35psi. This will keep your headgasket happy. Keeping boost under 15psi and no black smoke helps keep mpg up.

 

[onestackdram]

I think you will shocked at the price of carrier's and ring and pinion price for the dana 80/60's. I have been working on doing this swap for a while now. I already own the gears, but need carrier's front and rear, and so far they've been expensive. I'm holding out until i find a deal somewhere.



As far as towing. Going to 3:54's won't be that big of an issue. You might be surprised at what the old 12v can do with a hair more tweeking, like timing. But no matter if you do gear swaps, or engine mods or both. If your going to start towing 2 jeeps, you need transmission UPGRADES FIRST. But I will not make a reccomendation on these boards as to who I would reccommend, as some of the older members know never to do that anymore... LOL

 

[JeppinHackSaw]

Transmission upgrades are coming in the next month at the least. It won't be any big-name build. It will be built by a very reputable guy around here that builds transmissions for drag cars... has built a few autos holding up to stacked 24V's too... the 12V isn't going to be anything super high power. . but, throw some timing and a little more fuel at it (plate grind), possibly injectors and thats most likely it.



I looked at a gear vendor... 3000 bucks. . no thanks. . if I wan't a 10 speed, I'll buy a KW.



I've already bought gears (and spool for Dana 60's and 70's) so, I'm sure the shock won't be that bad. . especially knowing a good vendor.

 

[CSchafer]

I think the biggest thing to research is the milage you might get with 3. 54's. My 96 won't get anywhere close to 20, 17-18 on highway and as low as 13 around town. Dad's 94 2500 4x4 3. 54's has the timing bumped for milage and everything else set for it as well. It got 20 once on a perfect 60-65 mph trip but most of the time it's the same as mine. I'm sure 3. 54's would help but I'm not sure they would help as much as you hope. I hear these claims of 20-22 all the time but I just can't see it, Not calling anybody a liar because I'm sure there is a few that can get it but I don't think it is in a 3500 4x4 auto.

GM2C

Cade

 

[zstroken]

Carrier in the front will work with a 4. 10 or a 3. 54. It is the Dana 80 that the carrier break is 3. 73. You can get a thin 3. 73 ring and it will work on the 4. 10 carrier. Then you could put 3. 73's in the front. The Dana 60's and 80's are a pain to set. They don't have crush sleeves like the fords. A good bearing puller is a must. The shims go in between the bearing and the housing, so make up a set of dummy bearings. I wouldn't be afraid of doing a carrier swap(open to arb), but a pinion set looks like it sucks. Everyone I talked to said you need the pinion block(or whatever it is) to set it up. If someone has set up a 60/70/80 without one let me know. I have 4 axles I need to change the raitios on.

 

[JeppinHackSaw]

Yea, you have to shim the pinion head. I'm not worried about the actual setup here folks. I'm weighing the pros and cons of doing it. . the cost or difficulty of the setup is not an issue. I've helped set up 60's before. . and have never heard of a pinion block



Measure the pinion depth, take the +/- number from the new gear, add or subtract the difference, add/remve shims to the pinion to get that number. Shim carrier bearings to get a good meshing pattern. Fine tune from for good patterns.



Now. . You won't need a good puller if you make a set-up set of bearings (although, if you arent going to do a bunch of axles, they aren't worth it. . as you need to take new bearings (D60 master kit runs about 80-100 dollars) and clearance the inside of them so they fall on the bearing surface so you don't have to press them on... it's way easier to fine-tune them this way as you dont have to pull/press the bearings every time. I have access to a bearing puller if need be...



I know what the options are as far as lockers, carriers and gears go. Like I said, I was more or less asking about the driveability/performance/mileage. . not the cost of labor. . thanks

 

[zstroken]

Sorry for the extra info, just don't know what people know. I have 3. 54's and I would say unless you tow 12K every day I would put the 3. 54. The only bad thing about the 3. 54 on the auto is the auto has a steep OD. On my six speed I tow about 12K and use 5th gear for anything below 55 or climbing. 6th gear is for the interstate.

 

[pwerwagn]

I have 3. 54's, with 33" tires and a 5-speed. The 5-speed has a lower OD than your auto, so this is not a direct comparison but close.

I have pulled a max of around 20,000lbs (not GCVWR, but trailer weight). I cant really use 5th with that much weight unless im going over 65mph.

But towing 14-15K, 5th is fine even down to 55-60mph. up hills, etc, no prob.

I usually average 13mpg towing, and the truck is also my daily driver. mixed town/hwy, I average 19 with the old non-ulsd fuel summer blend. Ive gotten a best of 22. 9, and that is correcting for the speedo error from the 33's.



My grandpa had a 02 3500 auto with 3. 55's, totally 100% stock except gauges. He towed around 12K usually, but in the hills/altitude of colorado. He thought the OD was to high for his uses. But he also refuses to run over 60mph with 12K as well.

hope that helps.

but need carrier's front and rear, and so far they've been expensive

Carrier for 3. 54 D60 is same as 4. 10.

If someone has set up a 60/70/80 without one let me know. I have 4 axles I need to change the raitios on.

Nope, no need for a pinion depth indicator tool. Set it up the same as everything else. Get backlash in the ball park, check pattern, and then add/remove shims to the pinion if necessary. It is really benificial to have a setup bearing for the pinion if nothing else. Its a pain to pull that bearing without ruining it.

Oh, and I dont know why you think crush sleeves are an advantage, I hate those things. The dana shim design of setting pinion bearing preload is superior, in my opinion. Way easier after you've done it a few times.

--Jeff

 

[JeppinHackSaw]

Nope, no need for a pinion depth indicator tool. Set it up the same as everything else. Get backlash in the ball park, check pattern, and then add/remove shims to the pinion if necessary. It is really benificial to have a setup bearing for the pinion if nothing else. Its a pain to pull that bearing without ruining it.

Oh, and I dont know why you think crush sleeves are an advantage, I hate those things. The dana shim design of setting pinion bearing preload is superior, in my opinion. Way easier after you've done it a few times.

--Jeff

I'm with this guy. . also, thanks for the real world answers! I'm heavily thinking of doing this. . I don't like the thought of the ol cummins screamin 2500 RPMs on the freeway (or the 12mpg doing it)

 

[pwerwagn]

With my 5-speed and 3. 55's, with 33's, I turn around 2300 on the freeway. not to bad. but mileage is still way better around 65 or so.



another thing about the 3. 55's and auto I now recall from my grandpa's 3500, he didnt like the fact that on steep slow mountains (like colo) how the trans would say in 2nd because of the 3. 55's. it would cause the trans temp to rise to 250-270* in a hurry with 10K plus behind it.

Just another thought. but if you are staying away from 25mph steep hills that are 3 or 4,000 foot changes in alt, your probably safe.



--Jeff

 

[JeppinHackSaw]

With my 5-speed and 3. 55's, with 33's, I turn around 2300 on the freeway. not to bad. but mileage is still way better around 65 or so.

Goin 85... ?

 

[zstroken]

So can I just turn my old bearings into the setup bearings??

 

[JeppinHackSaw]

So can I just turn my old bearings into the setup bearings??

In theory, yes... It depends on the shape of them though. . if they are starting to get worn out. . there will much more tolerence then a new set. . giving you a sloppy set up.

 

[jandtjil]

JHS

Keep tire size/lifts of the posts' in mind. Personally I think you are on the right track

for a veh that is mostly unloaded, and if you have less than 285 tire size it should still tame most any grade in 3rd (OD out) with the mods you have in mind. As mentioned earlier, if you are pulling around 10K and you do let your speed drop, you might get stuck pulling a hill in 2nd and actually enjoying the scenery. Good luck!



JJ

 

[JFaughn]

I've read a lot , that adding a little more fuel , increases the millage .
Dodge had Cummins detune [ below is max effency ] there eng. to work in the RAM , so once you get the trans. upgraded then add fuel not a lot just moderate .