# Front diff 410 rear 373.....



## gotsnow? (Mar 28, 2007)

I'm looking at a 84 Chevy 2500, seller says the front differantial is 410 gearing and the rear is 373..... Is this gonna cause any problems when locked in 4x4??? I would think so, but what do I know... let me know guys!


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## Western1 (Dec 4, 2008)

*No Expert*

I am no expert but the front should match the rear. You could check it by jacking it up and spinning the wheels and counting the turns on the front and rear shafts. Sounds fishy!


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## NBI Lawn (Oct 15, 2007)

Is it a "mud truck"?


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## ABES (Jun 10, 2007)

Yes it will cause severe drivetrain problems if 4x4 is used.


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## JDiepstra (Sep 15, 2008)

ABES;771652 said:


> Yes it will cause severe drivetrain problems if 4x4 is used.


That's for sure. Imagine the fronts going 40 mph and the rears passing them at 45mph?????????


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## B&B (Nov 4, 2006)

gotsnow?;771643 said:


> I'm looking at a 84 Chevy 2500, seller says the front differantial is 410 gearing and the rear is 373..... Is this gonna cause any problems when locked in 4x4???


You better believe it. Don't pull the stick back until you have them matched or at least verify the sellers remarks.


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## JDiepstra (Sep 15, 2008)

I suppose you could throw some 315's on the front and some 265's on the rear and hope it fixes things?????????

Water would just run right out the back of your bed that way and you would look like you were accelerating real fast all the time! wesport


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## gotsnow? (Mar 28, 2007)

How much would it cost me to change the gearing in either one?? I don't really care if its 410 all the way around or 373. 
No, it's not a mud truck either.... It's an old farm truck that the owner was using for his "daily driver" and needed "better fuel economy" so he figured changing the rears to 373 and not using 4x4 was his best bet.  I'm thinking the asking price minus whatever it costs to change the gearing back to original would be wise, eh?


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## 2COR517 (Oct 23, 2008)

gotsnow?;771930 said:


> the owner was using for his "daily driver" and needed "better fuel economy" so he figured changing the rears to 373 and not using 4x4 was his best bet.


A had a suspicion it was something like that. Or he blew the rearend and put in whatever he could find. Did he change the whole rearend, or just the gears? Maybe he still has the old parts. Try a junkyard for pricing. Probably a whole rearend would be easier to change (at least for me).



gotsnow?;771930 said:


> I'm thinking the asking price minus whatever it costs to change the gearing back to original would be wise, eh?


What's he asking for the truck? Something in that price range your probably only going to be able to take a few hundred bucks off. If it's a real (factory) 3/4 ton, and in good shape, it's a great truck. Give the frame a good looking over. Check the body closely. Around here they get eaten up by the salt pretty badly. In particular check the rocker panel, cab corner, floor board and cab mount. Pull up the carpet/mat so you can see the steel. Drivers side is usually worst. If it's all good, buy it.

You could put one of these in, with the ARB, of course.

http://www.dynatrac.com/products_gm_7391hdsraa.html


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## wild bill (Feb 10, 2007)

*miss match*

yes you can have catastrophic failure ,if you engage it .a truck i bought had factory 4:56 gear's ,and they replaced the rear axle with a later model with 3:73 and they blew the front Axel apart .destroyed the ring gear carrier ,right Axel shaft and joint,the front Axel drive shaft .it got expensive quick when you don't watch what your doing .payup


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## Brookside (Nov 24, 2005)

JDiepstra;771688 said:


> I suppose you could throw some 315's on the front and some 265's on the rear and hope it fixes things?????????
> 
> Water would just run right out the back of your bed that way and you would look like you were accelerating real fast all the time! wesport


All kidding aside, I bet you could probably get in the ballpark by mixing tire sizes, front and rear, at least temporarily...


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## IMAGE (Oct 21, 2007)

You can get a rear axle that will bolt right in for less then $100. $75-100 for a 14 bolt semi floating, or for a 10 bolt also. Just depends on the mood the junk yard guy is in. If you deal with a junk yard that just crushing, all they want is the weight, so you might be able to trade the old one towards a new one, and just a little cash to boot.


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## IMAGE (Oct 21, 2007)

I've got a 14 bolt with 4:10's here in Fargo, it has a full detroit locker in it also... $500(just because it has a new detroit with less then 500 miles on it)


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## mkwl (Jan 21, 2005)

JDiepstra;771676 said:


> That's for sure. Imagine the fronts going 40 mph and the rears passing them at 45mph?????????


Yeah- it's not usually good to see your rear axle going by you as you drive down the freeway lol


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## gotsnow? (Mar 28, 2007)

Well, for anyone that's wondering I won't have to worry about changing out any differential... I ended finding a differant 84 Chevy K20 w/ a nice Meyer blade for $200 cheaper then the one with the messed up gearing! So I bought it. :bluebounc
Thanks for everybodys advise, I knew the 410 on 373 just didn't sound like a good idea...


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## saldana17 (Sep 22, 2009)

Different Ratios front to back on new 4x4 trucks is usually a very small difference.
like a 3:23 front and a 3:33 rear. 
The reason is that the front should travel slightly faster so as to pull the truck.
If they were the same the one would hold the other back in certain conditions.
I know this to be true as a mechanical engineer purchased a new Durango from me
and he told me they were different. I wanted to argue but held my mouth. When he left
I looked it uo and it was like a 49% / 51%. 
The front will always pull you forward. Never being passed by the rear.


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## Mark13 (Dec 3, 2006)

saldana17;855708 said:


> Different Ratios front to back on new 4x4 trucks is usually a very small difference.
> like a 3:23 front and a 3:33 rear.
> The reason is that the front should travel slightly faster so as to pull the truck.
> If they were the same the one would hold the other back in certain conditions.
> ...




Wouldn't it just be easier to have both at 3.33 and spinning at the same speed to elimiate a difference in speed between the two axles that the tcase has to absorb? Seems to me that if the front wheels were going 30mph and the rears were going 29mph there still would be enough of a differerence to mess things up, especially over time.


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## basher (Nov 13, 2004)

saldana17;855708 said:


> Different Ratios front to back on new 4x4 trucks is usually a very small difference.
> like a 3:23 front and a 3:33 rear.
> The reason is that the front should travel slightly faster so as to pull the truck.
> If they were the same the one would hold the other back in certain conditions.
> ...


So to fix my Dodge which has the same rears front and back should I go with smaller tires or larger tires? Every time it rains and i turn the front wheels and stomp on the gas the rear tries to swap ends with the front. From reading this I think larger front tires will solve this by effectively raising my front axle ratio in relation to the rear but I wanted to ask an expert.


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## saldana17 (Sep 22, 2009)

Yes the front are faster but are not measurable because of the close ratio. 
You are talking extreme ratio differences.
http://forums.dieselpowermag.com/70/7080007/transmission-driveline/different-front-and-back-axle-ratios/index.html
Example: Typical 1/2 ton GM, 10 bolt, 8.5" rear axle and Dana 44 front axle. The 8.5" 10 bolt (used in cars and trucks from since 1970 or so) has a 41 tooth ring gear and a 10 tooth pinion to make a 4.10 ratio (41/10). The Dana 44 front axle could have had a 45 tooth ring and an 11 tooth pinion, giving a 4.090909 ratio (4.09).
The Ford trucks with the 9" rear and Dana 44 front would have 37 tooth ring and 9 tooth pinion in the 9" rear, giving a 4.1111 (4.11) ratio, while having the same 4.09 Dana 44 in the front. 
They need to be the same. Usually, the front is slightly shorter, so that it pulls away a slight bit from the rear, so they don't bind........like 4.10 front and 4.11 rear.


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## saldana17 (Sep 22, 2009)

Here is another link.
http://groups.google.com/group/rec.outdoors.rv-travel/browse_thread/thread/d587210cede14d4d


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## mcfly89 (Nov 2, 2005)

saldana17;855708 said:


> Different Ratios front to back on new 4x4 trucks is usually a very small difference.
> like a 3:23 front and a 3:33 rear.
> The reason is that the front should travel slightly faster so as to pull the truck.
> If they were the same the one would hold the other back in certain conditions.
> ...


the difference you are referring to is more commonly 4.11 to 4.10 or 4.09....and it has nothing to do with the front pulling the rear. that is a nonsense wives tale that has been circulating since the beginning of time, but its inaccurate. the actual reason for the difference is far simpler.its nothing more than geometry differences in the size of the ring gear. a dana 44 doesnt come in 4.10 or 4.11 ratio...its 4.09. count the teeth and do the math and it comes to 4.09 everytime, a dana 30 is 4.10 etc etc. the ratio is determined by the amount of teeth and their pitch as it relates to the diameter of the ring gear. no magic front tires pulling the rig thru the snow.

takes jeeps and scouts for instance. a 76 or newer international scout will have dana 44s in front and rear. the ratio is not different...it has 4.09s front and rear. one of the most capable 4x4s on and off the road in the world and it doesnt have the magic front tires pulling the rear...hmmm...odd indeed. lol.


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## saldana17 (Sep 22, 2009)

Did you read in my reply post # 19? I said the same thing.
Did you look at the link?
If not here it is again. http://forums.dieselpowermag.com/70/7080007/transmission-driveline/different-front-and-back-axle-ratios/index.html It is the post by MaddMexhanic.
Example: Typical 1/2 ton GM, 10 bolt, 8.5" rear axle and Dana 44 front axle. The 8.5" 10 bolt (used in cars and trucks from since 1970 or so) has a 41 tooth ring gear and a 10 tooth pinion to make a 4.10 ratio (41/10). The Dana 44 front axle could have had a 45 tooth ring and an 11 tooth pinion, giving a 4.090909 ratio (4.09).
The Ford trucks with the 9" rear and Dana 44 front would have 37 tooth ring and 9 tooth pinion in the 9" rear, giving a 4.1111 (4.11) ratio, while having the same 4.09 Dana 44 in the front. 
They need to be the same. Usually, the front is slightly shorter, so that it pulls away a slight bit from the rear, so they don't bind........like 4.10 front and 4.11 rear.


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## mcfly89 (Nov 2, 2005)

saldana17;856148 said:


> Did you read in my reply post # 19? I said the same thing.
> Did you look at the link?
> If not here it is again. http://forums.dieselpowermag.com/70/7080007/transmission-driveline/different-front-and-back-axle-ratios/index.html It is the post by MaddMexhanic.
> Example: Typical 1/2 ton GM, 10 bolt, 8.5" rear axle and Dana 44 front axle. The 8.5" 10 bolt (used in cars and trucks from since 1970 or so) has a 41 tooth ring gear and a 10 tooth pinion to make a 4.10 ratio (41/10). The Dana 44 front axle could have had a 45 tooth ring and an 11 tooth pinion, giving a 4.090909 ratio (4.09).
> ...


i apologize, i was so frustrated with the continuance of nonsense in post #16 i never made it to #19. Your engineer friend should really be ashamed of himself on this one.


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## 2COR517 (Oct 23, 2008)

So what happens if I have a 10 bolt front AND rear. Both with 3.73s. Is my truck going to break in half some day when I'm in 4wd driving down the road.

What if I have a lockout hubs. Does that help?


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## saldana17 (Sep 22, 2009)

1 He bought the Durango
2 I felt like a fool after I found that out.
3 Engineers are engineers. Some without common sense and always right.


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