newbe with 9" differential
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From: Denver, CO
newbe with 9" differential
I am new at trying to do anything with a 9" differential and have some questions. Right now my diffy was taken out of a 76 3/4 ford truck and has a 3rd member with a 3.00 ratio. I would like to change the ratio to a 3.50 or 3.55 ratio 3rd member. The diffy has a 28 spline axle. It is behind a
429 with a C6. Can I purchase a 3rd member and just swap my 3.00 for a 3.5X without knowing that much? This is just something I have never attempted. I am mechanically able to do it but need guidance from the experts here. Thanks in advance. Dennis
429 with a C6. Can I purchase a 3rd member and just swap my 3.00 for a 3.5X without knowing that much? This is just something I have never attempted. I am mechanically able to do it but need guidance from the experts here. Thanks in advance. Dennis
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A '76 "3/4" would not have had a 9" axle.
Does your axle look like these?
http://broncograveyard.com/images/addon/9inblowup.jpg
Specifically, a drop out carrier.
Or like so:
http://assets.hemmings.com/story_ima...00-0.jpg?rev=1
with a cover in back????
If you do have a nine, you can buy the whole works and bolt it in. Expect about $1000, maybe a bit more. Shop here for anything you want:
http://www.currieenterprises.com/cestore/3rdmember.aspx
Does your axle look like these?
http://broncograveyard.com/images/addon/9inblowup.jpg
Specifically, a drop out carrier.
Or like so:
http://assets.hemmings.com/story_ima...00-0.jpg?rev=1
with a cover in back????
If you do have a nine, you can buy the whole works and bolt it in. Expect about $1000, maybe a bit more. Shop here for anything you want:
http://www.currieenterprises.com/cestore/3rdmember.aspx
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From: Denver, CO
It might not have been a 3/4 but a one ton. Here is what the diffy looks like
Yep it is a 9". Thanks for the link. Doesn't look that difficult to complete. So, if I change the diffy to 3.55 or one lower, would that drastically make the gas mileage go down?
Yep it is a 9". Thanks for the link. Doesn't look that difficult to complete. So, if I change the diffy to 3.55 or one lower, would that drastically make the gas mileage go down?
Last edited by retro48/52; Mar 27, 2014 at 08:41 AM. Reason: ADD PIC
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Only "1/2 tons" got a nine.
As for mpgs, it won't help. If you are worried about gas mileage with a 429, you are in for a lot of worry methinks.....
You can plug in your axle ratios and tire diameters to see the difference in cruise RPMS. Unless you are running some giant tire, a 3.0 would probably be a good cruise gear.
Novak Conversions - Gearing & Gearing Math for Jeeps
As for mpgs, it won't help. If you are worried about gas mileage with a 429, you are in for a lot of worry methinks.....
You can plug in your axle ratios and tire diameters to see the difference in cruise RPMS. Unless you are running some giant tire, a 3.0 would probably be a good cruise gear.
Novak Conversions - Gearing & Gearing Math for Jeeps
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LOL. ThanksNumbersDummy, Thanks. Got it. I have a 9". My buddy set me straight. It was 7 years ago we did the RE. The RE came out of a 1/2 ton 1972 F150. Bot when I am wrong I go all the way.
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Off the line, 3.89, 3.91, maybe a 4.10 depending on tire. You will need a lot of tire. What suspension do you have? If just leaf springs, you will need traction bars.
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Now I never thought of that. Traction bars, good idea. So I should look for 3.89s or so and a good set of bars. I can do that. Might as well go all the way. Anything else I should think about?
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Your engine, is it stock or a bit warmed up? What RPMs is it capable of? Your trans, is it stock with a stock stall speed? Are you going to really race this thing or is this for street use? How many miles will you be driving at a time--any long freeway runs?
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F150 introduced in 1975.
But when I am wrong I go all the way.
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My engine is not stock. It is a mild build. All new innerds. I have 1068 miles on it right now. It is suppose to be able to rev to 6000 rpm. The tranny was reworked with a 2000 rpm stall speed and a light shift kit. It will be used for the street only. I will put at least 5000 miles on it and the driving conditions will be 30% main street 70% freeway driving.
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