I have a 69 f250 4x4. It has a t18 (4 speed manuel) tranny. When I am on the highway going 65 my motor (360) runs at about 2400 rpms. Just from the feel and sound I know it tops out at 2800 rpms. I try and keep it at 2200 rpms for the best gas mileage. I am trying to find the best way to get more speed at lower rpms. I have looked into conversion kits (www.advanceadapters.com) and gear venders. From what I have learned I can get an adapter with a high and low range to fit on the back of my transmission that will give me a 22% increase in highway speed and keep the same rpms. So this would give me an extra gear between 1st and 2nd, another between 2nd and 3rd and another between 3rd and 4th and a 5th overdrive gear. this is new to me and I am hoping someone can give me some advice? Would it be better to get a five speed transmission? dose ford make a five speed trany for my truck? were would be the best place to buy a overdrive kit? Any help would be much apreciated.....rick

 

Rick, F250 4X4s & good gas milage do not fit on the same page. If you had a F150 you could change your rear end ratio. Sorry, but there isn't an inexpensive way to get it done.
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John

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In the cool still quiet of night, you can hear chevies rusting away.

 

I think 12 miles to the gallon is pretty good! I am not complaining. I am looking at this atlas 2 transfer case (512.00). It is suppose to be way better than the 4.11 ring and pinion gears. it has an out put ratio of 3.8 to 1 and a wheel to engine rpm final output ratio of 54.29 to 1. Could you explain what these ratio's mean? I don't get it. I am looking to spend around 2000 dollars. Don't you think that should get the job done? ....rick

 

Check my post in the 73-79 section under 'has anyone ever put in an overdrive?'. I installed a NV 4500 in a 72 F-250 4x4. It works good. I also bought an overdrive for my 87 F-350 4x2 460-C6. It was a Milemarker unit. It has been in that pickup for over 100,000 miles and works fine. It does have a whine in high range (and I can live with it) aand it has a harsh shift. Sure makes a 4.11 rear axle liveable for long highway trips.

 

Rick I'll try. All non over/under drive engine/trannys turn the same rpms at the drive shaft in hi gear 1 to 1. Getting to hi gear the engine to turns faster than the tranny output, That is the first ratio, next the speed of the engine/tranny vrs the axles is the next. A
4.11 means that the drive shaft turned 4.11 revs for the tires 1. 3.00 engine 3 to the tires 1. I know that is kinda lame but hope it helps some.
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In the cool still quiet of night, you can hear chevies rusting away.

 

So jowilker might you want to explain to me why you can change the gear ratio in a f-150 but not in a f-250????????????????????
The last time i looked in a parts book they listed gears for both the Dana 60 and the Dana 44. Am I missing something here???????????????
When I wanted to slow my engine rpm's down a little on my 250 I just put on taller tires. It helped my millage too. I'm now getting close to 15 mpg at 55

 

I have been collecting all the numbers from my truck. On the transfer case it says "ratio 196" C11313 U. Can anyone explain this to me? I found a rebuilt five speed tranny. It cost 1250 dollars with a 250 dollar core charge and does not include shipping. Is this a good deal? That would be a lot cheaper than getting a 2000 dollar overdrive. And if i am not happy with it I can always get an overdrive on it down the road. Would getting and overdrive on my four speed be the same as going to a five speed? Would it be worth exchanging my tranny for 250 dollars when there is nothing wrong with it? .........thanks rick

 

Too damn complicated Dave, you can just pop out a 9" center chunk, but changing the Dana's is a little too much for me. How about you, have you done it yourself?
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In the cool still quiet of night, you can hear chevies rusting away.

 

First off not all 5 speeds are overdrive. I think all the NV 5 speeds are overdrive. Before you buy it, make sure it's a true overdrive 5 speed made for a TRUCK.

1200 for a 5 speed overdrive truck tranny is a good deal, much cheaper than an add on overdrive. You'll probably have to buy an adapter for that tranny so call around before you buy it. Advance Adapter sells adapter for almost anything and I think the NV's are included in their list.

The Clark 5 speed might work with your stock bell housing as well as the NP 5 speed.

As for the ratios, these are sometimes called crawl ratios. The number is derived from adding up the the gears as follows:
transfer case: 2:1
rear 4.11:1
1st gear 6.85 (guess)
2x4.11x6.85 = 56

This is just a number used to compare gears, the higher the number, the slower the truck moves in it's lowest gears. But you have to consider the tire size as well.

The 4:1 transfer case is another option, but that only effects things when your in the lower gear, otherwise it's just a 1:1.

In other words, you have to consider how you use your truck. For most, going to a taller gear is not a real problem as the 1st gear allows for excellent pulling power anyway. If you overgear it, you can use 4 low in the transfer case to get a lower gearing for pulling up steep hills.

You might want to play with the math a bit before you decide what to do. http://www.prestage.com/carmath/default.asp has some neat calculators.
Hope this helps...

 

Rick, I like your thinking here. The gear vendor units are way coool, but they are exspensive. The Clark 5 spds are findable used or rebuilt, but you will neeed the FT bell housing and flywheel and clutch (no problem, bolts right on). Most of the Clarks are direct in 5th, there is supposed to be an overdrive model, but I have never found one. Have you considered a brownee ? It is a 3 spd box you can bolt in between your transmission and T-case. 2.35 low/1 to 1 /.75 ratios. CharlesF350 put one in his. Might be able to get this unit used for a whole lot less money than a GV. DF

 

>you considered a brownee ? It is a 3 spd box you can bolt in
>between your transmission and T-case. 2.35 low/1 to 1 /.75
>ratios. CharlesF350 put one in his. Might be able to get
>this unit used for a whole lot less money than a GV. DF

The Spicer 5831 (among others) was an option in the larger Ford trucks, according to my 1965 shop manual. There are a variety of ratios available depending on the letter suffix (-A through -F). The best one if you could find it would probably be the -A which has 1.54/1.00/0.73. This would go well with the wide 2:1 spacing in the NP435. The -E is 1.27/1.00/0.73 which might also be useful. There are also all-underdrive setups like 2.00/1.54/1.00 available too.

I found a 5831-B for $250 which has 2.35/1.00/0.85 so it's not quite as good an OD as I wanted but still drops my 4.88 gears (235-85R16 tires) from 3025 rpm at 60 down to 2570. The 2.35 UD is also great for backing into tight spots slowly (you can go less than 1 mph without slipping the clutch), or starting out a heavy load uphill.

It's not that cheap either by the time you get through fabricating driveshafts, shifter and linkage, and frame mounts, but a lot less than the $2500 you'll put into a GV setup!