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Old 10-18-2008, 02:20 PM
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Rearend Gear Swap

i have found a set of 4.11 gears real cheap in a junkyard they are out of the front axle of an 88 silverado 20 suburban the cover on this axle also has 10 bolts on it and i was wondering if they would fit in a 10 bolt bia housing with little or no modifications any help would be greatly appreiceated thank you, Eric

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Old 10-18-2008, 06:43 PM
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I don't know if it will physically fit.

But you do realize that front diff gears cannot be used in a rear diff, even if they fit.

The gears turn the opposite way, and the teeth are specially shaped in a way that means they are only supposed to work in one direction. I will work, but the diff gears will crap out very quickly if you do it.
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Old 10-18-2008, 11:06 PM
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Quote:
Originally Posted by AR_Racing_627
i have found a set of 4.11 gears real cheap in a junkyard they are out of the front axle of an 88 silverado 20 suburban the cover on this axle also has 10 bolts on it and i was wondering if they would fit in a 10 bolt bia housing with little or no modifications any help would be greatly appreiceated thank you, Eric
If the front gear set is from a 8.5 front diff,it will fit just fine in the rear 8.5,Its the same ring and pinion.
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Old 10-18-2008, 11:33 PM
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No it is NOT the same ring and pinion.

It may be the same size, and have the same number of teeth, and it will probably fit into the same housing, but it is different.

Just look at the ring gear.

LOOK AT THE TEETH on the ring gear.

They are not symmetrical. One face is vertical, and the other face slopes away at a very acute angle. That should tell you it is only made to run properly in one direction.
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Old 10-18-2008, 11:43 PM
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SilverShadow... he's right. Front and rear gears are the same. The teeth will point clockwise on both ring gears. The ring gear is installed on the opposite side of the housing (the differential is flipped) so that the torque is in the opposite direction but the thrust and coast sides of the teeth remain the same. I'm currently running 4.10s from the front axle of an 84 chevy pickup in the rear axle of my 96 Impala SS.

If the 88 has a solid front axle (not the independent suspension) then it should be an 8.5"
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Old 10-18-2008, 11:43 PM
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Quote:
Originally Posted by Silver Shadow
No it is NOT the same ring and pinion.

It may be the same size, and have the same number of teeth, and it will probably fit into the same housing, but it is different.

Just look at the ring gear.

LOOK AT THE TEETH on the ring gear.

They are not symmetrical. One face is vertical, and the other face slopes away at a very acute angle. That should tell you it is only made to run properly in one direction.
Chevys 8.5 straight axle front diff's are not a reverse rotation,They are the same part number as the rear.
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Old 10-18-2008, 11:47 PM
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Quote:
Originally Posted by curtis73
SilverShadow... he's right. Front and rear gears are the
The problem is that the 88 had an independent front axle which (IIRC) has an 8.2" ring gear. Its not the same as the 8.5" rear.
X2, The front cover statement throws me,He should not have a cover in that year.
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Old 10-18-2008, 11:48 PM
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Quote:
Originally Posted by prostreet6t9
X2, The front cover statement throws me,He should not have a cover in that year.
Actually I edited my post because I realized... he said it was a Suburban which didn't change in 88 like the rest of the trucks. It might be a solid axle.
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Old 10-18-2008, 11:55 PM
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Quote:
Originally Posted by curtis73
Actually I edited my post because I realized... he said it was a Suburban which didn't change in 88 like the rest of the trucks. It might be a solid axle.
I'm glad you caught the "suburban " I missed it
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Old 10-19-2008, 12:13 AM
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Are you guys absolutely certain about this ?
Think it through very carefully.

Sure you flip the diff upside down and that places the crown wheel on the opposite side and reverses the axle rotation. No argument there.

But the actual gears then turn the other way. Think about it.

Both front and rear tail shafts usually always rotate the same direction, because that is how the transfer case is most often built.

Stand in front of the vehicle and the engine turns clockwise, and so does each tailshaft. You are looking straight at the rear diff pinion, and the crown wheel will be on the right hand side (from that view).

Now stand behind the vehicle. the engine and all driveshafts turn anticlockwise from that view position. You are looking straight at the front pinion, and again the crown wheel will be on the right hand side (from that view).

The pinion in the rear dif rotates clockwise looking at the drive flange.
The pinion in the front diff rotates anti clockwise looking at the drive flange.

The teeth are cut for reverse rotation.

That is why the diff gear manufacturers cut forward and reverse gear sets of equal ratio.
They are definitely not interchangeable.

Last edited by Silver Shadow; 10-19-2008 at 12:25 AM.
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Old 10-19-2008, 12:29 AM
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Quote:
Originally Posted by Silver Shadow
Are you guys absolutely certain about this ?
Think it through very carefully.

Sure you flip the diff upside down and that places the crown wheel on the opposite side and reverses the axle rotation. No argument there.

But the actual gears then turn the other way. Think about it.

Both front and rear tail shafts usually always rotate the same direction, because that is how the transfer case is most often built.

Stand in front of the vehicle and the engine turns clockwise, and so does each tailshaft. You are looking straight at the rear diff pinion.

Now stand behind the vehicle. the engine and all driveshafts turn anticlockwise from that view position. You are looking straight at the front pinion.

The pinion in the rear dif rotates clockwise looking at the drive flange.
The pinion in the front diff rotates anti clockwise looking at the drive flange.

The teeth are cut for reverse rotation.

That is why the diff gear manufacturers cut forward and reverse gear sets.
They are definitely not interchangeable.
You're way overthinking that bud, The chevy straight axle is not a reverse rotation gear .
http://www.precisiongear.com/gm812.htm
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Old 10-19-2008, 01:04 AM
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I will leave this last point for each of you guys to ponder.

http://www.ringpinion.com/PartsList....b-Differential

Scroll down to where the red pictures are. These are all reverse rotation gear sets.

Why would an American diff gear company like Dana make both forward and reverse rotation gear sets when all American engines turn clockwise ?

Maybe you should tell Dana that all diffs are the same.

Or maybe Dana know something you do not............
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Old 10-19-2008, 01:09 AM
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Quote:
Originally Posted by Silver Shadow
I will leave this last point for each of you guys to ponder.

http://www.ringpinion.com/PartsList....b-Differential

Why would an American diff gear company like Dana make both forward and reverse rotation gear sets when all American engines turn clockwise ?

Maybe you should tell Dana that all diffs are the same.

Or maybe Dana know something you do not............
Thats a dana 30 for the front of a jeep,Not quite the same thing,We where talking about chevy straight axle. But I can tell dana for ya if you want,I talk to them a couple times a week.
P.S Dana gear set's are not made in the USA
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Old 10-19-2008, 01:20 AM
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Here is a photo. Nothing is flipped, really.

The red is the transfer case (yeah, don't laugh, I did it really fast), the purple is driveshafts, and the brown and green are pinion and ring.

The driveshafts turn the same way, and the ring gear is still getting thrust on the same side of the teeth, but the fact that its driving off the other side of the pinion makes the axle drive in a forward motion.
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Old 10-19-2008, 01:24 AM
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Quote:
Originally Posted by curtis73
Here is a photo. Nothing is flipped, really.

The red is the transfer case (yeah, don't laugh, I did it really fast), the purple is driveshafts, and the brown and green are pinion and ring.

The driveshafts turn the same way, and the ring gear is still getting thrust on the same side of the teeth, but the fact that its driving off the other side of the pinion makes the axle drive in a forward motion.
Aren't you the creative one!
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