3.70:1 gears questionssssssssss

[convincor]

you'll need to watch wether it be 28 or 31 spline.
For you Ryan, I do have a 28 spline 2 pinion traction lock here.
You'd have to get the gear set and assemble in your case.
Do a ebay search for 28 spline 9". a lot of time guy's are selling them rebuilt. And for what it cost to buy a locker, the gears, bearings and assemble it and set-up you may as well buy one done for $400-500.

[1971ford]

wow, i should of gave more info

heres some info:
-im talking about my 69 f100 LWB 2wd.
-it has a 360(4 barrel), and a c6 auto.
-i want to run ~30 in. tires.
-this wont be my daily driver (im going to buy a ricer once i get driving for a DD). the 69 will be driven on just weekends mostly.
-im debating if i should make this truck for having fun on the beach/dunes or for just cruizing (but quick), so im not sure on that. either way it will be a truck that sure gets up and goes.
-driving conditions here are... it hardly ever rains here. its summer allready. temp is low 30's to 115.
-im not looking for 100% fuel efficiency, since it will be a weekend truck. but i dont want it to get tooooooo low of gas milage.
-i want a ricer to be like "never though 5000 pounds could move so fast!" or something like that

hope i covered it all there.

so if i run 30" + or - 1" tires, what would you want for the info i listed, maybe 3.50??

then we can talk about lockers etc. unless we need to know that before we talk about gear ration being 3.50...


and THANKS for the help guys, especially you who took all the time to right that very helpfull huge post!

[71PA_Highboy]

I guess the onus is now upon me to answer

First, the 360 is a grunt and longetivity engine, not a power engine, so for quick you are gonna want a bit more engine... or at least something that spins better... a car 390 is the easiest suggestion... but that adds money, so lets put that on the back burner.

You state 30" tires... and then you say you will want to run it on the dunes 'quick'ly...
In sand, RPMs are your friend, so I would suggest 4.11s... even those can bog you if you upshift too soon, so get used to manually shifting your trans in the sand... and prepare for the motor to scream. When I am at SOB (a bronco event in Oregon), it is unheard of for guys to ever get INTO top gear unless they are running a sand suspension (or are in 4lo)... and guys are whizzing by at 50-60 MPH in 2nd.... the real crazy ones are doing 90 in second....

The 4.11's will really help with the ricers too.

Since you are updating a 9", I would suggest locating the local 4wd club, especially the Bronco types... 4.11's are common, and if you are 28 spline, even better as they are too. Then you are looking at a 30 minute swap... and if you keep your old gears, you can have the 4.11's for play, and 3.25 for work/cruising/a bit better MPG. (If you need to sell the 3.25's, look to the classic Mustang guys... 3.25 is great in a Mustang for cruising.)

As for lockers, I am sold on the selectable type... BIG FAN of ARB, but they are $$$. I personally have a Trac-Lock, and it is brand new, and I HATE the way it unloads going around corners downhill.... and I can't turn it off... with an ARB there is never that problem, and you only turn it on when you need it.

Remember though, you ALWAYS want you brakes better than your engine.... A truck with no engine is a trophy, but a truck with no brakes is a coffin. How are your brakes?

If I missed anything, or was unclear, let me know.

Last but not least, never feel embarassed about asking...

Regards,

Eric

[F100builder]

Then you are looking at a 30 minute swap... and if you keep your old gears, you can have the 4.11's for play, and 3.25 for work/cruising/a bit better MPG.

Good idea here. Did you say for sure that you were running a 9"? If so, it IS easy. If the truck is for fun weekend cruising and not a DD, then I would recommend locating a 3rd member in a wrecking yard, classifieds, etc. that was geared between 3.70 and 4.11 (learn to count gear teeth). It needs to be a 28 spline differential and a locker if that's what you want. If you find a 3.50 or 3.55 geared locker at a good price, I'd say go for it as you can change the ring and pinion at a later time and for less money than upgrading to a locker. A locker would be of more value to you now than a specific exact ratio.
If you decide to take on any of the gear changing or differential rebuilding yourself, I STRONGLY recommend this DVD how-to on rebuilding the Ford 9" rear end!!! I have not seen his transmission videos but I'm sure that they're great too. I bought the 9" rebuild DVD and it's awesome! The creator is, I believe, a retired Master Ford Technician and really knows his stuff. The video is easy to follow and helped me rebuild my 3rd member. Here's the link: http://www.badshoeproductions.com/products.html

Good luck dude and keep up the good work as well as the updates!

[1971ford]

well lets cancell the sand thing out, i think ive decided i wont be playing in the sand with this truck. so it will be drive on streets, it will get up and go, and mostly just weekends. still think 4.11's will be best?

so i should find out what spline my truck has? is the only way to tell to take the rear end apart?

and for lockers, think i could find a locker at a junkyard for whatever gear ratio/spline i choose?
how good does welding do in place of a locker

i am COMPLETELY redoing everything to do with brakes on my truck. rebuilding the rear drums completely, new lines, everything. upgrading the front to disc brakes. also the truck has power brakes.


F100builder,
thanks for the info and link, i saved the link

[F100builder]

Pretty sure all 9" rears in bumps have 28 spline axles. It's probably easier to find a locker in a truck vs. a car but they're out there. Most cars were 28 spline while most trucks after '72 (I think '72?) went to 31 spline. I don't recommend welding! If you're unsure about the spline or if the rear end is not the original, then you can pull just one of the axles out and count the splines on the end. I think it's somewhere on this site but I seem to remember that they went to a 31 spline with the dentsides which also have longer axles so you can't simply swap over to 31 unless you get the right length axles to go with it.

[1971ford]

im going to a 4x4 swap meet tomorrow......

so if i find 3.70:1's or 4.11:1's for a 9 in.(with or without locker) i should buy them right???

what can i expect to pay?

[1971ford]

cool

thanks!

[SteveC]

dont mean tp hijack the thread but the question is relevent and i didnt see a answer here.

What rear ened gears are the best for just plain 0-60 kinda get up and go..with a 352 a 3 speed auto cm and these tires... http://i169.photobucket.com/albums/u223 ... 0002-1.jpg
not sure on size but they are 16inch split rims and are larger than the stock tires that were on it...but they arnt much wider if at all wider.

i also have the d60 with 4.10 gears i think or is it 4.11 cant remember
just kinda curious what would give the best get up and go thanks

[F100builder]

dont mean tp hijack the thread but the question is relevent and i didnt see a answer here.

What rear ened gears are the best for just plain 0-60 kinda get up and go..with a 352 a 3 speed auto cm and these tires... http://i169.photobucket.com/albums/u223 ... 0002-1.jpg
not sure on size but they are 16inch split rims and are larger than the stock tires that were on it...but they arnt much wider if at all wider.

i also have the d60 with 4.10 gears i think or is it 4.11 cant remember
just kinda curious what would give the best get up and go thanks

I'd say you got 'em. It looks like a 29-31 inch tire you have there and with a 3 speed auto, a 4.10 set should be good to get you to 60mph in a hurry. Even better if that 352 gets warmed up a little with a cam. I couldn't pull the front end off the ground but it sure felt like it in my '56 once upon a time. It had 3.73's with a slightly warmed up 302/C4 combo and somewhere in the 27-29 inch tire diameter. The motor SCREAMED at 65mph though and sounded like it wanted to come out from under the hood......in pieces! I'm sure that more HP's would have pushed those gears a little better.

[SteveC]

thanks that is what i thought... just need to find out why the truck acts like it doesnt wanna get up and go... i probally have a few vacuum leaks to trace out...probally check the gasket below the carb spacer and the rubber hose going to the tranny still need checked...there could even be a pin hole in a line some were.

if that truck has more get up and go than my ltd with stock 351w and 2.75:1 9 inch rear end then that might be scary.... the car goes 0-60 pretty quickly and at 90 mph im only at 3000 rpm. i didnt want to try any faster

[1971ford]

well there were trailers full of rear ends, but they were mostly toyota. nothing i wanted. did snag a nice edelbrock carb and riser for $50 (see the GD thread i started).

ill keep checking out swap meets and im going to look for bronco forums

[1971ford]

allright so ive had a change of plans. the 69 isn't going to race, its going to be a daily driver and will need to be able to tow a car trailer with race truck for about 9 hours each way.

so what gears do you think would be the best choice for fuel milage, but still being able to tow a car trailer?

sorry to change it all up. decided to cut up a allready battered truck.

[SteveC]

from what i understand 3.50:1 or 3.73:1 or something close to those

[71PA_Highboy]

Ryan,

Again, gear ratio is going to be determined by the RPM range of the engine (mainly camshaft spec), and the size of the tires.

Try here:
http://www.westerndiff.com/rpm.html

That will get you in the right area...

If you were running a 4BT, ZF5 and 33" tires you would need 3.55 gears

If you were running a 4BT, NP435 and 30" tires you would need 2.45 gears.

If you were running a 360, NP435 and 30" tires you would need 3.25 gears

If you were running a 460, ZF5 and 33" tires you would need 5.13 gears.

Run the calcs yourself, play with the variables, and then decide what YOU want to live with.

Good Luck!

Eric