Need Overdrive Trans - Any such Beast???

[broncnaz]

besides the fact I pull 16mpg in my 73. I dont see you pulling much better mileage than you get now with 400+ hp, bigger tires and a OD tranny as all the others have basically said its just not very easy to do in a bronco not to mention one with big tires and 400hp. the engine most likely needs to pull more RPM's to keep in its powerband so as was said lowering RPM's will probably cause a loss in mileage and you may find the OD almost unuseable.
If your going to 35in tires and a OD tranny than most likely you'll also need to swap axle gearing to at least 4.56 or 4.88's that will give you both low end and a better RPM range in OD.
As others have said your current mileage is about on par. While you might increase it a little your best bet is to just try the 35in tires first see if your mileage increases any. If not then OD is not going to help any without other mods.
basically broncos are not mileage masters if thats what your after remove the lift go with smaller tires and a OD tranny and you may pull more.

 

[Idaho Slim]

besides the fact I pull 16mpg in my 73. I dont see you pulling much better mileage than you get now with 400+ hp, bigger tires and a OD tranny as all the others have basically said its just not very easy to do in a bronco not to mention one with big tires and 400hp. the engine most likely needs to pull more RPM's to keep in its powerband so as was said lowering RPM's will probably cause a loss in mileage and you may find the OD almost unuseable.
QUOTE]

Well, I checked another tank last night, filled up neck to neck and calculates to 14.6 mpg, had to slow down as we all know, and never let it get above 2500 rpm (62-63 mph). At that rpm this motor has plenty of punch, I stabbed it a few times and with 4.11 gears know It will pull 35's quite easily.

I highly disagree with those that state never gonna get good mpg, this ain't my first rodeo with high powered, big tired trucks that act like a brick. This is my third EB and on a 73 w/302 & 33's I got EXCEPTIUONAL mileage. That being said those that just accept crappy mileage have not explored all our options. I have re-jetted to optimum, timed it as well as I think, and the only variable now is to match gearing with this H.P. and tires, it is obvious high RPM"s will kill good mpg............ and when I stab this motor it is such a joy that I know I need to temper the fun with ecomomics ;D;D

Getting back to the subject of the Overdrive tranny and speaking of economics, swapping to a ZF or the 4500 from WH's is spendy! $4000 - $5000 swap. With my latest tank showing improved mpg at a lower rpm, I am going to try the upgrade to 35's as I had planned then will know how the motor likes it and I will report back, gonna be awhile since new shoes ain't cheap neither Thanx for everyone's input.

 

[78Scronco]

Back to the original Question
well you can buy a reman ZF for $1000 or junkyard($150-600). new hydraulic clutch setup $200. build(Free) or buy($200) a zf crossmember. And you already have the np205,

not to bad for a good trans for $600-2000 ish.

 

[bmc69]

I highly disagree with those that state never gonna get good mpg, this ain't my first rodeo with high powered, big tired trucks that act like a brick. This is my third EB and on a 73 w/302 & 33's I got EXCEPTIUONAL mileage. That being said those that just accept crappy mileage have not explored all our options.

Pfft. In 35 years, 9 pickups, 3 full size Broncos and 11 EBs..professional engine builder of both stock and HP engines for a wide range of applications..offroad racer for 7 years (one of the 3 racers an EB) yadda yadda..;-)

but you go, boy...show us amateurs how to git r done.;D

Nobody said it was impossible to squeeze as much as 16 mpg out of an EB; I've hit 15 myself with 5.5" lifted truck on 35s. Just said its 'rare' and 12-13 is a good 'fleet average' fuel economy for EBs and always have been..since Ford first delivered 'em.

But here's a question: Calculate what the investment payback time will be if you spend $3000 and gain 2 mpg.;D If you put a lot of miles on the truck every year, it could be worth the investment risk. Me?..most I ever put one one was probably 5K in a year....

 

[Greg_B]

All these numbers seem crazy to me...

I just bought a new 2012 F150 with the new 5.0 and 6 speed transmission which is supposed to get great fuel mileage for a full size. I dont even get as good as some of these number being posted here. If I go look at my on board computer right now it is going to say something like 16.4 MPG.

This F150 get better hwy MPGs than my 2008 Tacoma did and a lot better than my wifes 2008 FJ Crusier. So I find it hard to believe a 70s Bronco is going to get anywhere close to the same. Maybe I am wrong... In my Tacoma if I run 75+ it would only get like 14MPG... if I ran 65 to 70 it would get over 17. Slowing down makes a huge difference.

My EB with a 5.0 EFI, 35s and 4:56 gears probably gets around 9 or 10 at best.

Greg

 

[bmc69]

All these numbers seem crazy to me...

I just bought a new 2012 F150 with the new 5.0 and 6 speed transmission which is supposed to get great fuel mileage for a full size. I dont even get as good as some of these number being posted here. If I go look at my on board computer right now it is going to say something like 16.4 MPG.

This F150 get better hwy MPGs than my 2008 Tacoma did and a lot better than my wifes 2008 FJ Crusier. So I find it hard to believe a 70s Bronco is going to get anywhere close to the same. Maybe I am wrong... In my Tacoma if I run 75+ it would only get like 14MPG... if I ran 65 to 70 it would get over 17. Slowing down makes a huge difference.

My EB with a 5.0 EFI, 35s and 4:56 gears probably gets around 9 or 10 at best.

Greg

My ex-wife's Expedition with 4.6L maxed out at 18 mpg ..the Nissan Murano daily-driver Filly and I have now gets about 22mpg. Her '79 Bronc gets about 9 mpg and my '78 Bronc about 9 mpg on average although I once saw about 12 on a long trip lightly loaded... etc.

Back in the 80s, we had a guy that was absolutely obsessed with his car's mileage. Some old POS sedan..I've forgotten what now. Checked the mileage religously and reported it regularly over lunch break along with ad nauseum discussions of various 'tips and tricks' he was always trying to improve it. We got sick of hearing about it and decided something had to be done. For over a month, one of us would regularly sneak a quart or so to his tank, slightly but ever increasing how much went in as the days and weeks rolled by.

Of course, we heard even more about the fantastical ramping up in his mileage..but we could smile at each other and giggle about it.

One day we simply stopped adding gas. Thought the poor fella was gonna commit suicide the next time he checked his mileage.

 

[Broncobowsher]

I think the poor fella wanted advise on a transmission, now it has been hijcaked into a new car fuel economy thread. To the OP, I tried to answer the question. A few others did a little constructive advise as well. There are a few tidbits of info if you read around all the hijacking.

 

[bmc69]

I think the poor fella wanted advise on a transmission, now it has been hijcaked into a new car fuel economy thread. To the OP, I tried to answer the question. A few others did a little constructive advise as well. There are a few tidbits of info if you read around all the hijacking.

The 'poor fella' seemed quite eager to discuss fuel economy and stated that was the entire purpose of the contemplated tranny swap.

 

[blazinchuck]

i just took a 6 hr trip, wheeled the weekend,and drove back 6hrs...i got 13.7(which might be closer to 14mpg...speedo offf a lil bit) i run 33's,nv3550,with 3.50 gears and 3.5" lift


i couldnt use 5th gear tho...65 was round 2k rpm, 5th dropped it to 1400rpm.

 

[bmc69]

i just took a 6 hr trip, wheeled the weekend,and drove back 6hrs...i got 13.7(which might be closer to 14mpg...speedo offf a lil bit) i run 33's,nv3550,with 3.50 gears and 3.5" lift


i couldnt use 5th gear tho...65 was round 2k rpm, 5th dropped it to 1400rpm.

I can see yr problem..OD with bigger tires and only 3.50 gears. You need to let that bad boy air out on the plains...see what mileage ya get on..say..the Bonneville Salt flats....at 100 mph. ;D

 

[MarsChariot]

Well, I use to get 18.....at 55mph (stock tires). Man, 55 was nice. You could look at the scenery, things were not howling, and the mileage was good. There was a reason for that national 55 mph limit. I was the only person, apparently, that liked it. Now at 70 and 75, 14 mpg is very good. I hate driving 75 mph. But if you don't, you get run over.

 

[Idaho Slim]

The 'poor fella' seemed quite eager to discuss fuel economy and stated that was the entire purpose of the contemplated tranny swap.

And this poor fella came here for honest discussion about possibilities, and you decided that you are the kingshitdaddyknowitall of eb's, lifted trucks, horsepower and fuel mileage. Since you need to spout off yer credentials & demean rather than have a helpfull dicussion, put this in yer pipe and smoke it;
I am 53, make a decent living and can generally doo most modifications I want, I have had in my automotive life 11 lifted trucks all with over 6 inch lifts 3 mod motors w/ 2 built by me, 4 Corvettes all with modified motors, and 3 EB's all with modified motors, 2 built by me and all lifted, the 302 EB got an honest 17 - 19 hwy. good enuf credentials for you?? I frequent 6-8 forums all automotivie oriented, and you are what is called a troll. Butt out of my thread thankyou very much. Oh, and I have been a member of this forum since Oct 2003, kinda been around ya know ;D

Thank you all who have offered advice and Bronco tidbits to share, I am interested in getting the most from my Pony as I am sure you all are, in this day and age it doesnt seem to hurt striving for the best optimum power to mpg, sure we spend money outrageously on the EB's, never going to make it pay imho, but it is what drives us to our passion.

 

[73azbronco]

Idahoslim I reread the posts and really don't thin anyone is slamming the guy for asking, just offering their perspective.

You mention you get pretty good mileage, how? What engine mods, intake, carb? If you hold a secret to the mighty holly grail of mileage, help us out.

 

[Idaho Slim]

You mention you get pretty good mileage, how? What engine mods, intake, carb? If you hold a secret to the mighty holly grail of mileage, help us out.

Nothing secret, common good tuning combined with good parts. I have a holley Truck Avenger 670 carb which I re-jetted the primary down about 4 sizes, adjusted the floats. I run a mallory distributor/wires/coil with 34 degrees timing (18 initial here @ 5200 ft.), edelbrock intake, K&N intake, WH headers, The motor has 10:5-1 pistons, been bored .060 and balanced, competition cams w/ magnum roller rocker arms & aluminum heads.

I am fairly confident the motor is tuned to its optimum, the issue I think/know, is too high of rpm operating range, ( hence why I am considering an Overdrive trans.)
Only 3 ways to alter our operating rpm's that I can think of; Tires, Axle Gearing or transmission gear ratios ............. all spendy, for some reason I went to 33's awhile back, and even tho they say 33's, I think we all know once on a vehicle and used, that diameter goes smaller and smaller with each mile ;D I agree, the fuel mileage issue is moot when it comes to the enjoyment we get from our EB's (at least it does me), and that the point of diminishing returns versus cost needs to be considered, but I think the 5 spd overdrive route would be really trick! The few that have answered that have an OD seem to report decent fuel mileage and can still operate in their motors efficiency range.

For those that have a OD, when you are out wheeling, does the granny low gear have enuf low range control ?? I see where an OD would drop the first gear ratio to 5.0 something rather than 5.72 (?) on the NP435.

 

[Dave]

I have some opinions but decided not to participate because these threads all go down the same road. Here's another thread on the topic.

http://classicbroncos.com/forums/showthread.php?p=1694534#post1694534

 

[bmc69]

And this poor fella came here for honest discussion about possibilities, and you decided that you are the kingshitdaddyknowitall of eb's, lifted trucks, horsepower and fuel mileage. Since you need to spout off yer credentials & demean rather than have a helpfull dicussion, put this in yer pipe and smoke it;
I am 53, make a decent living and can generally doo most modifications I want, I have had in my automotive life 11 lifted trucks all with over 6 inch lifts 3 mod motors w/ 2 built by me, 4 Corvettes all with modified motors, and 3 EB's all with modified motors, 2 built by me and all lifted, the 302 EB got an honest 17 - 19 hwy. good enuf credentials for you?? I frequent 6-8 forums all automotivie oriented, and you are what is called a troll. Butt out of my thread thankyou very much. Oh, and I have been a member of this forum since Oct 2003, kinda been around ya know ;D

Thank you all who have offered advice and Bronco tidbits to share, I am interested in getting the most from my Pony as I am sure you all are, in this day and age it doesnt seem to hurt striving for the best optimum power to mpg, sure we spend money outrageously on the EB's, never going to make it pay imho, but it is what drives us to our passion.

LMAO. So you throw out a "I highly disagree with y'all and I know more about it" and ya get a reply in kind. Awww. And from another 53-yo, no less.;D

Carry on.

 

[bmc69]

I see where an OD would drop the first gear ratio to 5.0 something rather than 5.72 (?) on the NP435.

6.69 on the 435 granny low. As far as I know, no OD trans comes close to that..its an unusually low granny gear ratio, with only the T-18 approaching it.

This article has a pretty good tabular summary of the ratios of all commonly used trannys..

http://classicbroncos.com/tranny-np435.shtml

 

[DirtDonk]

I think you touched on it a bit ago Slim. Before you swap gearing/transmissions, put the 35's on and see what the rpm drop and weight/rolling resistance increase do for you first.
If your mileage goes up, you're on the right track and hopefully the change to OD doesn't go beyond and start negatively effecting mileage.

Just out of curiosity though, are you sure you're putting out 400hp or is that just an estimate based on the parts you're using? Just thinking that 400, even out of a 351, is a bit high for one that runs so nicely at lower rpms like yours does. Not impossible I guess, just unusual. Did you advance the cam a bit too?
Maybe not so hard to achieve for a modern engine family, but for an old Windsor with bolt-on upgrades, it seems like that'd be from a higher rpm cam setup to me.
Just commenting though, as your description of how it runs makes it sound like a nice setup.
I guess what I'm wondering is, just how low do you think you can go (rpm-wise) and still push the Bronco/Brick through the air efficiently at the speed (was that 70 or so?) you want to go?

And to add my numbers to the mix, my '71 DD got a consistent 9-10 around town and a VERY consistent 15.5 on the highway (55-60 mph max) with the stock 2bbl, 600 Holley, and 500 Carter carbs. Went down slightly for the Carter 625 (but ran real good).
Best I ever got was a consistent 17.5 on the highway with a Holley "Economaster" 450cfm 4bbl carb. Loved the mileage, hated the power.
Thing was wicked off the line with a beautiful idle and throttle response. Just didn't have any poop to speak of, so I finally got rid of it.
So mileage is there. It's just the combination of parts and circumstances that can make a difference. As you're hoping for.

Good luck. Let us know what, if any, additional mileage you find. At both higher and lower highway speeds if you don't mind.

Thanks

Paul

 

[Apogee]

6.69 on the 435 granny low. As far as I know, no OD trans comes close to that..its an unusually low granny gear ratio, with only the T-18 approaching it.

This article has a pretty good tabular summary of the ratios of all commonly used trannys..

http://classicbroncos.com/tranny-np435.shtml

FWIW, the only other trans I can think of that comes close tp the NP435 gearing but also with an OD is the 1993-1994 GM NV4500 with a 6.34:1 first gear. The only reason I know that is because I have a Dodge unit that was rebuilt with the HD GM mainshaft and lower GM first gear.

 

[Idaho Slim]

"I highly disagree with y'all and I know more about it" QUOTE]

I will just say this and then lets move on. I went back and looked at my posts & your posts & see where we went sideways was, you took my words which could have been better, as "I know more about it", (which I never meant, nor said), and you popped off and I took offence at. I have been around too many forums and gotten into too many cluster arguments for no reason and wont put up with BS when I am just looking for good sharing of info. I appreciate your follow-up post on tranny ratios, thanx.

DD, I am working on that now, gotta juggle some items and hope to get the new shoes within the month - always nice to get new shoes for the pony!;D
I will check back on the mileage, I see about the same as U that there is a sweet spot on mph, it's just a shame that our EB's it is about 62/63????? And the speed limits are 65-75 here. I will check at diff speeds, its easy for me since I drive my pony to work 52 miles round trip (WHEN its not too cold!! - Soft top);D