I was thinking, I have a granny 4spd and a low geered rearend. I take off in second gear right now like it's first, don't really ever use first gear. And it doesn't go as fast as I would like. So....I was thinking that if I raised the rearend ratio, considering the trans first gear is so low now, would that just be like eliminating the granny gear and still leave me with good take off in first gear and then be able to reach a higher top speed? I'm still learning as some of you may have noticed, but from what I understand this is correct. Am i right?
*jdbanks*

 

JD, There are a couple of things I'm thinking you may not understand. All trannys, not under/over drive have an out put of 1 to 1. So 3, 4, 5 speed trannys all are the same in high gear.

If you want to go faster, you will need to lower your rear ratio, like from a 3.75 to a 3.50 or 3.25, or 3.00. You will compromise power by doing so.

John

jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quiet of night you can hear chevies rusting away.

 

I do understand that. That's what I was stating in my post. I know if i get higher gears I'll get more speed, and that's what I want. What I'm talking about is right now I don't even take off in first gear, have to change to second at 5mph even if I do. So I basically take off in second gear all the time and never use first.

My thinking is since the tranny is geared so low in first gear, that if i change the rear gear to say a 3:1 or 2.75 to 1, then with first gear being such a low ratio I would then be able to take off in first gear the way I take off in second now and would have good take off and power doing that. Basically eliminating the granny gear in the transmission and giving me more top end speed. From what I've read I don't see why that wouldn't be the case, just making sure.
*jdbanks*

 

Your thinking is correct. Although I wouldn't go for a drastic change, like 4:10 to 2:79. I would probably keep the rear gear in the 3:00-3:50 range.





68 F-100 Short bed 2wd
302 C4 9" w/3.50 gears
Soon to be sportin' power discs and steering

 

Thanks, i just wanted the reassurance. I'm not all together positive what my rear gear is now, just learned where to look for the Dana tag. So we'll see how things go, but thanks for the wisdom again.
*jdbanks*

 

Don't just look at the tags, the gears might have been changed. Rotate the drive line or wheel and count the revs it makes. I found mine to be 4.10.

Your thinking is correct, but you need to know that 1st is not just lower but MUCH lower. I'd make a chart using percentages and see just how fast you can go in 1st, then multiply that by the percent increase from the gears.

In other words, if you can go 5mph now and get 10% faster gears... then match that to what you would want from 1st gear. The NP435 has about 6.8 1st and that's really low so you'd have to make a pretty big change to make 1st usable or just use 1st as a short gear and understand that you'll have to shift out of it real quick.

I really like your idea and I'm considering it too because of the extra cost of a 5speed or an overdrive. Another option is taller tires.

 

Thanks for the info. I've been meaning to do that trick to figure out the rear gears but I don't have a suitable place to do it at my place and never get around to going somewhere to do it. Need to get off my ##### I suppose.

I'm afraid I don't quite follow your math on figuring out what gear change to make. I believe it probably is the trans you mentioned, but I'm not positive. I had thought of trying to find a 5spd with overdrive to match up or something, but the word I got was that would be near impossible. So i thought If i could just basically bump all the gears up then I'd get the better top end I want and hopefully still have a solid take off. I'll let you know when I find out.
*jdbanks*

 

JD, Let's try this, It's not a good idea.

John

jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quiet of night you can hear chevies rusting away.

 

Well I realize you're entitled to your opinion, but might you actually support it with some reasoning?
*jdbanks*

 

Let me see if I can help a little. The biggest problem with the NP435 is that it has such wide gear ratios. As best I recall, 1st is 6.68, 2nd is 3.36, 3rd is 1.68, 4th is 1:1. Almost exactly a 2:1 spread between each of the first three gears.

So if you want the same rpm using first as you now have in second, a 4.10:1 rear with a 3.36 2nd gear would need 2.05:1 rear gearing in 6.68 1st gear. Then this would be too high in 1:1 4th for the engine to pull it on the highway, barely off-idle at 60 mph. And you can't get rear gears that tall anyway. You could consider something like a 2.76 or 2.94 but do the math and figure rpm and speed in each gear.

The five-speed option would still need a rear gear change, or you can do what I did and put an overdrive unit behind (or in front of) your existing transmission. I used an old 5831 3-speed "Brownie" truck auxiliary trans and it has underdrive also (great for backing up real slow). Hope this helps.

 

Thanks for the info, I can see how that could be problematic. Could you tell me more about the overdrive unit you mentioned? I don't have any experience with that. How much would it be and how hard are they to install? What exactly do they do?


And I've discovered a new mystery. My truck tops out at about 60-65, going downhill. So I was guessing it would have a pretty low gear rearend since my 360 is pretty strong and seems to run pretty well, except for a lifter knocking. Well I checked the VIN and it said it was a 3.5 ratio, I figured it had been changed out and I jacked up the rear today and had my dad turn it while i counted the driveline turns, and it came out to a 3.5 that way too. So I'm kinda lost at what is keeping this truck from hauling booty like I think it should. It's a 68 F100, 360 4spd with Dana 3.5 rear gears. Anybody have any ideas?

 

That doesn't sound right. I don't have a chart to look that up, but just off the top of my head, it doesn't sound right.

First off, the NP435 has an alum cover on the top (that doesn't really matter, just a side note) and the T18/19 has cast iron on the top cover.

350 is not a low gear, that's more of a freeway gear. 410 is a low gear and I'd consider anything 350 to 275 to be a freeway type gear. I'd double check the gearing one more time. The proper way to do it depends on the type of rear end.

If you jack up the back end and turn one tire and the other tire moves in the same direction, then just turn the tire one time and cound the drive line turns. If you have an open diff, I'd turn the drive line with one tire up and one tire on the ground and count the number of turn required to turn the wheel once.

Another issue here is how do you know your speed? I'd have a friend drive at 55MPH steady and run side by side and confirm your speedo setting. Any change in gears or tires requires a speedo change.

With a 360, you should be able to hit 5500~6000 rpm and with 350 gears that should put you into the 75+ range (just a guess)

On another note, I've checked the overdrives from Ranger, GearVendors, and US Gear and they all want a lot more than I care to spend (about 2500+) After you figure out exactly what speed your going and what the rpm is, I'd call some of the local 4x4 shops and ask them what gears would give you what rpm because the have a lookup chart that can tell them quickly.

 

Had both tires off the ground and they both spin in the same direction. So that would make my count correct I believe. And the fact that it looks orginal and the VIN says it should be a 3.5 to 1. And I'm pretty sure on the speed, ran along side some people and checked it. And i think the truck is all orginial so that would lead me to believe the speedometer is right too.

I'm really lost on why it doesn't have more speed than it does. It does have a lifter knocking but I didn't think that would cost it as much power as it seems to be missing. Another thought I had was that maybe the emergency brake was stuck on or something but after all the driving I did on it, it seems like it would have burnt it up and not been a problem. Are there any transmissions that might not have a 1:1 ratio in fourth gear? Maybe that came in a bigger truck, could have possibly gotten put into this truck?
*jdbanks*

 

are you sure it's a lifter nocking? you might have a flat cam lobe or a broken piston...

 

To be honest I'm going on what my Dad told me, he knows alot more than I do. But everyone makes mistakes and no-one knows it all. So maybe it is something worse, but the motor seems to run fine just a little tick, then when you have it up to speed and let off the gas you notice it alot more as it winds down. Give me any advice on figure out if it is a lifter for sure or something more serious?
*jdbanks*