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Matching front & rear gear ratios?

 
  #16  
Old 08-07-2009, 08:31 PM
atomicjoe23
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I have access to a lathe, I have welder. . .and if push comes to shove one of my old weld instructors has a gas forge. . .

I didn't think that converting a 14-bolt to a front axle was cutting corners. . .I was under the impression that a 14-bolt was stronger than a D60???

It's a cost vs. benefit analysis. . .I'm looking for best bang for the buck for a '49 *****'s that wont' see hard off-road use. . .only mild trail use. . .just enough to get it dirty. . .it's a vintage vehicle and we have 2 4WD utility quads, a '79 F-150 4x4 and a YJ Wrangler for the hard offroad use. . .this is more of show it off type of project. . .but I don't want to break things just by running larger tires. . .so we are gonna upgrade the axles.
 
  #17  
Old 08-08-2009, 08:55 AM
mistakenID
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It's common at least in older 4x4's to have the front axle slightly faster than the rear like a 4:09 front, 4:10 rear. Idea was to have the front pull a bit while in 4x4 to aid in keeping the vehicle straight.
 
  #18  
Old 08-08-2009, 08:31 PM
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I've got a dumb question, and sorry to hijack...but I'm planning on putting a 3.70-geared 9" into my '89 half-ton, and I'm thinking that I'd be OK with 3.73s in the front (as that seems to be the only gear ratio around 3.70 for the Dana 44). I either read it on here or someone told me that ideally, it's good to keep the front and rear ratios within 1% of each other.

Does that sound like a plan?

Pat
 
  #19  
Old 08-09-2009, 03:41 AM
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come on dont discourage him, i like people that think outside the box.. lets hear more about this 14 bolt conversion! sounds interesting!


Ray
 
  #20  
Old 08-09-2009, 02:59 PM
atomicjoe23
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Let me do some more research on the 14-bolt conversion and then I'll post up. . .

. . .it's pretty straight forward. . .I just need to measure the axle tubes and cut one side down, then I just need to to know where they got the steering hardward for the axle at and you weld that on. . .you use an oil seal from SealsIt and you're good to go. . .that's the break down as simple as you can. . .I'll post up when I find out the specifics.
 
  #21  
Old 08-09-2009, 06:58 PM
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I thought you were going to cast and forge your own, along with a reverse rotation gear set??? BUYING all those parts--you going to buy them new, or buy a donor steering axle?

I know I'm going to win the Nobel Prize for being an A-hole on this one, but think about all the crap you have to BUY in addition to the basic axle.

Plus your time.
 
  #22  
Old 08-09-2009, 07:15 PM
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It's an option. . .it may be cheaper for me to convert a 14-bolt to a steering axle than to buy a D60

. . .it's something I'm going to look into. . .and I know it can be done since I've already seen it done once. . .
 
  #23  
Old 08-09-2009, 07:34 PM
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Originally Posted by mistakenID View Post
It's common at least in older 4x4's to have the front axle slightly faster than the rear like a 4:09 front, 4:10 rear. Idea was to have the front pull a bit while in 4x4 to aid in keeping the vehicle straight.

Thats not the reason why front gear sets and rear gear sets were a slightly different ratio. This ended up being this way because of the location of the pinion relative to the ring gear. Front sets that were either a low pinion of even a high pinion had a different bevel or cut and had to have a slightly different ratio because of the number of teeth they had. This "hypoid" design did not permit the identical number of teeth for the pinion and the ring gear so the ratio was slightly different.
We were discussing this exact thing over a few adult beverages the other night and we came up with some of the many myths that are similar to this.

From our discussion:
Have you ever heard that the gear ratio in the front of a four wheel drive has to be higher (lower numerically) so that the front wheels will pull more? Well this is simply not true. Over the years there have been many different ratio combinations used in four wheel drive vehicles but never so that the front will pull more. Gear manufactures use different ratios for many different reasons. Some of those reasons are; gears strength, gear life, gear noise (or lack of it), geometric constraints, or simply because of the tooling that they have available. I have seen Ford use a 3.50 ratio in the rear and a 3.54 ratio in the front, and I have also seen them use a 4.11 in the rear and a 4.09 in the front. I have found that as long as the front and rear ratios are within 1% that the vehicle works just fine on the road, and can even be as different as 2% and work just fine off-road with no side effects.

1 point difference in ratio is equal to 1%. To find the percentage difference in ratios it is necessary to divide, not subtract. In order to find the difference divide one ratio by the other and look at the numbers to the right of the decimal point and how far they make the answer different from 1.00. for example 3.54 3.50 = 1.01 or 1%, not 4% different. And likewise 4.11 4.09 = 1.005 or only a 1/2% difference. These differences are about the same as a 1/3" variation in front to rear tire height which probably happens more often than we realize. Just look at normal tire wear and consider how much the tire diameter changes when we "air down". Not too many of us run the exact tire pressure on all 4 corners, in fact the rear typically gets less air than fronts and this makes the tire smaller in the back.

The design of the gear and limitations in gear design diactate a particular number of teeth required to make the greatest gear contact and this has an affect on how the ratio turns out. This is why we see the slightly different ratios from front to rear. High pinion and low pinion axles will have a slightly different ratio than a rear and this is simply be the design of the hypoid cut gears.
 
  #24  
Old 10-09-2018, 08:21 AM
Wildcat13
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Originally Posted by 85e150six4mtod View Post
Hundreths don't matter much:

3.50/3.55
4.11/4.10
4.11/4.09 all ok.

Tenths, hhm, now you are in the worry zone:

3.25/3.50 is a no-go for example.
3.73/3.91 I don't think so.
What about 4.56 in the front and 4.62 in the rear?
 
  #25  
Old 10-09-2018, 10:44 AM
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Looks like a 1.3% difference. Probably ok off road in the slow and slippery.
 
  #26  
Old 01-26-2019, 01:47 AM
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on a 78 (or similar) Bronco is anybody running 3.54 front D44 and 3.55 9" rear??
my reasoning is the front is heavier so the tires squat more. wouldn't you want a lower gear ratio in the rear because of the "taller" tires?
would that help steering as the front is pulling instead of being pushed?
it has the NP203.
 
  #27  
Old 01-26-2019, 02:35 AM
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9 inch would be 3.50. Those ratios would work in slow slippery going.
 
  #28  
Old 01-26-2019, 01:17 PM
78Broncoinpieces
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Originally Posted by 85e150six4mtod View Post
9 inch would be 3.50. Those ratios would work in slow slippery going.
that's what it has. I'm wondering if the 3.55 would be better. looks like this one fits.

https://www.jegs.com/i/Richmond-Gear/836/F9355/10002/-1

as my user name suggests, this truck ain't going nowhere anytime soon. I dismantled it over 30 years ago to restore it. life, especially children, got in the way. now the grandsons are in the way. but that's a good excuse to teach them something that involves using tools.
 

Last edited by 78Broncoinpieces; 01-26-2019 at 01:27 PM. Reason: more info
  #29  
Old 01-26-2019, 02:31 PM
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Not worth changing.
 
 
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