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Unread 12-01-2013, 02:10 PM   #1
jeepn4life92
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d300 output strength questions

I understand the d300 has a reputation for poor strength output shafts, my only question is, it would cost approximately $500-$600 to upgrade both outputs with jb conversions kit and I just don't know if it'll be worth it. The cases are readily available and cheap and I'm not going to be running a high hp application. Just the stock 4.0 mated to an sm465 with a np231/d300 and some 41" tires. Just looking for some first hand accounts of what those of you were running when you broke them or if there are folks out there running bone stock d300's without any issues.

Thanks in advance

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Unread 12-01-2013, 03:21 PM   #2
gmakra
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I think the stock are plenty strong, having said that the output shafts were designed as a fusible link so they break first.
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Unread 12-01-2013, 03:39 PM   #3
jeepwhore
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I don't think it has a "reputation" for weak outputs. I'd say it's more like people that run doublers and 40+ tires expected too much out of something that was never designed for those extremes.......like trying to run 40's on a D30 or an SR-4 behind a 360.

The majority of failures I have read about are from setups like you are talking about......huge gear reduction and massive tires used in high traction environments, which isn't the most common direction for a build so I'd say there are alot less failures out there than success's. I'd say HP and torque aren't part of the equation unless you're shock loading the drivetrain. I've read of guys with the same set up you mention breaking more than one output and I've read of guys running 300+HP V8's break absolutely none.

If you ask around in the hardcore crawler circles I'm sure they'd recommend you either upgrade it or drop a little extra and get a stak or atlas case. I suppose you could just run what you brung, but after the first failure I'd be prepared to drop some $$$.

If you think about it is it really better to keep replacing stock D300's at 2-300 a pop? After the first failure that is half of the cost of the upgraded outputs and you'd be right back to having a stock case.
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Unread 12-01-2013, 03:57 PM   #4
LumpyGrits
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OP, where did you get this info?
I have run a D/300 for almost 29 yrs, haven't broke it yet.
Like it a heck of a lot more than those chain drive t'cases.
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Unread 12-01-2013, 04:05 PM   #5
foggybottombob
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Just as a data point,
The Dana 300 has a 26 spline output shaft. A Dana 44 pinon also has a 26 spline shaft. Dana 44's are not recommended for tires bigger than 37". So I think that 41" tires with a 26 spline D300 output shaft would be pushing it if you do any rock crawling.
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Unread 12-01-2013, 04:17 PM   #6
jeepn4life92
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Quote:
Originally Posted by jeepwhore View Post
I don't think it has a "reputation" for weak outputs. I'd say it's more like people that run doublers and 40+ tires expected too much out of something that was never designed for those extremes.......like trying to run 40's on a D30 or an SR-4 behind a 360.

The majority of failures I have read about are from setups like you are talking about......huge gear reduction and massive tires used in high traction environments, which isn't the most common direction for a build so I'd say there are alot less failures out there than success's. I'd say HP and torque aren't part of the equation unless you're shock loading the drivetrain. I've read of guys with the same set up you mention breaking more than one output and I've read of guys running 300+HP V8's break absolutely none.

If you ask around in the hardcore crawler circles I'm sure they'd recommend you either upgrade it or drop a little extra and get a stak or atlas case. I suppose you could just run what you brung, but after the first failure I'd be prepared to drop some $$$.

If you think about it is it really better to keep replacing stock D300's at 2-300 a pop? After the first failure that is half of the cost of the upgraded outputs and you'd be right back to having a stock case.

This is what I figured, the case would be plenty strong with no doubler or a trans that didn't have a granny low first. But I've essentially put together a perfect storm of all those things (granny low first, doubler, and big tires) and have just surpassed its original expectations for strength.
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Unread 12-02-2013, 08:33 AM   #7
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With the granny gear and 231/D300, you've got quite a bit of torque multiplication going on. Combine that with the 40"+ rubber and you're at a pretty good risk of snapping a stock 26 spline output.. especially the rear one.

Had a buddy who ran a 4.0, T18, D300 (with 4:1) and 38" rubber. He snapped a stock rear output on a seemingly easy climb.

If it were mine, I'd just pony up the $$ and do the front/rear 32 spline outputs. I ran those on my old buggy and they were pretty much bulletproof. V8 Power, auto, 4:1 and 42" rubber.. lots of throttle and no regard for the drivetrain, and they held up fine.
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Unread 12-02-2013, 09:28 AM   #8
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Quote:
Originally Posted by foggybottombob View Post
Just as a data point,
The Dana 300 has a 26 spline output shaft. A Dana 44 pinon also has a 26 spline shaft. Dana 44's are not recommended for tires bigger than 37". So I think that 41" tires with a 26 spline D300 output shaft would be pushing it if you do any rock crawling.
Not that I disagree with what you said, but the OD is just as important as the spline count, if not more. That said, the D44 pinion and the D300 output shaft are very similar in size as well as spline count.
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Unread 12-02-2013, 03:38 PM   #9
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Something to consider,

Ring and pinion gears factor into the stress sent up the drivetrain.

For example:
There is typically more driveline/drivetrain breakage with 4.10's and big tires than with 5.38's and big tires.

For this reason I've been running 5.38's and 40's reliably for years and haven't had any trouble with my dana 300.
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Unread 12-03-2013, 07:44 AM   #10
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Quote:
Originally Posted by JRPettet View Post
Something to consider,

Ring and pinion gears factor into the stress sent up the drivetrain.

For example:
There is typically more driveline/drivetrain breakage with 4.10's and big tires than with 5.38's and big tires.

For this reason I've been running 5.38's and 40's reliably for years and haven't had any trouble with my dana 300.
Interesting point. The steeper axle gears increase torque at the tires.. either causing them to break traction, or move the Jeep. However, depending on the axle, the pinion gear on a 5.38 gearset can be pretty tiny... minimizing gear contact. Also, if traction is good and the rig is bound up, the D300 output shaft is still in danger.

Incidently.. I know most know this, but a 26 spline D300 yoke can be swapped with a D44 yoke.

For a serious trail rig, I still think front/rear 32 spline outputs are relatively cheap insurance against a catastrophic trail fail.

I guess in the end, it boils down to looking at the whole package.. drivetrain strength, tires, gearing, and driving style.
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Unread 12-03-2013, 08:42 PM   #11
jeepn4life92
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Quote:
Originally Posted by BESRK View Post
Interesting point. The steeper axle gears increase torque at the tires.. either causing them to break traction, or move the Jeep. However, depending on the axle, the pinion gear on a 5.38 gearset can be pretty tiny... minimizing gear contact. Also, if traction is good and the rig is bound up, the D300 output shaft is still in danger.

Incidently.. I know most know this, but a 26 spline D300 yoke can be swapped with a D44 yoke.

For a serious trail rig, I still think front/rear 32 spline outputs are relatively cheap insurance against a catastrophic trail fail.

I guess in the end, it boils down to looking at the whole package.. drivetrain strength, tires, gearing, and driving style.
I consider myself to have more aggressive driving habits and enjoy trails that require a little less finnes and a bit more throttle and wheel speed. I think I'm going to go with Novak's new ultra short heavy duty d300 rear output kit and probably go with jb conversions front upgrade...ill definitely post up comments and review of this new Novak kit once its in and running to get the market a good idea of how it all went....
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Unread 12-03-2013, 09:42 PM   #12
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Quote:
Originally Posted by BESRK View Post
Incidently.. I know most know this, but a 26 spline D300 yoke can be swapped with a D44 yoke.
Also fits a D30... FWIW
Nice to be able to carry one spare yoke that fits everything.
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