Broke my doubler last weekend. Convince me why I need an extra t-case support. - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 10-28-2008, 11:41 AM   #1 (permalink)
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Broke my doubler last weekend. Convince me why I need an extra t-case support.

As the title says, I did this to my doubler box this weekend:









First, a brief history of this setup. It's the NP231 Box-4-Rox from D.D. Machine, going to a completely stock Dana 300. I've had this setup installed & wheeling since April of '07, and I have over 3,000 miles on it in a rig that gets street-driven maybe once every two months. The gear reduction here, coupled with a 5-speed manual, takes some getting used to. As a result I broke a lot of stuff in the first few months of wheeling this:

- Stock 35-spline Dana 60 inner
- Stock 30-spline Dana 60 outer
- 30-spline drive flange
- 4340 30-spline Dana 60 outer
- 4340 35-spline Dana 60 outer (x2)
- Dana 60 Detroit locker
- Spicer Life Series axleshaft u-joint
- Dana 60 pinion yoke (forged, broke tab off)

In September of '07, I noticed the front seal on the D300 was leaking, and the bearing was worn. I hadn't rebuilt it when I installed it, so I pulled the t-case setup apart and did all new bearings & seals all around. This was after having broken most of the stuff I listed, and all the bolts were tight, and everything looked great.

Since then, I haven't had to touch the trans or t-cases at all. What finally screwed it this time was coming off a really big ledge and landing HARD directly on the front driveshaft, which is made from 1.75 x 0.25" DOM. Obviously the driveshaft wasn't going to fail, so the weak link apparently migrated to the NP231 housing.

Here's where it lives.



And here's what it looks like overall, with the floor off:



Engine mounts are the Bombproof polyurethane ones from MORE; you can see the trans mount in the above pic (standard poly bushings from Advance Adapters). These are well inside the motor mounts, so they don't limit anything.

The two biggest reasons people give for additional supports are weight and excessive torque. Here are my thoughts on that:

- Weight. The Dana 300 weighs ~80 lbs, the doubler half weighs around 10. So the overall weight is less than 100 lbs in a package not much longer than a stock NP231. I removed it from the truck, out through the floor, by myself, and I'm not a big guy. When I was doing the inside cage work I frequently used the transfer case as a step/seat. As long as the bolts are tight I really don't see the weight being a problem. If the bolts are loose, and the thing is really knocking back and forth, then maybe...but mine weren't, and if the bolts are loose you've got other problems to address. I'm also skeptical that just shoving a bushing under the t-case without preloading it does anything about the weight issue anyway, but that's kind of its own discussion.

- Torque. In theory doubler boxes are capable of generating huge amounts of torque. I have 185:1 overall crawl ratio. In practice, you will only generate as much torque as you can effectively use. Something will limit that torque well before you get to that big number, be it spinning tires or a driveline component breaking. Look at the list of broken stuff above...I've pretty much shot the weak link theory to shit. That's with 4.56 gears in the axles so it's not even relieving the t-case of that much stress, yet my stock Dana 300 outputs and 1310 driveline joints all around haven't flinched. With that kind of history, I can only conclude that I'm not exceeding the design of the Dana 300, which in any stock installation didn't have any kind of extra support.

So that leaves direct physical impact as the source of failure, which in this case can be fixed one of two ways: make dentable driveshafts, or stop driving poorly and pay attention to what's in front of you. I'll work on that.

Would a torque mount near the front output have helped in this case? Yeah, probably. But I'm not convinced it wouldn't have hurt in other areas. A mount that was rigid enough and restricted travel enough to prevent this would almost certainly limit things more than the engine mounts, which is a situation I want to avoid. I've seen many stories of aux. mounts causing loose bolts and other issues (see the current ASR thread).

So - with all that in mind, is there any reason I should consider adding an extra mount for it? If so, what kind? And if not...when does it become appropriate?
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Old 10-28-2008, 01:45 PM   #2 (permalink)
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As long as you dont make it to rigid, it will be fine.

Do one like roarks support rings.

What 300's had stock is irrelevent to your application, considering the abuse your rig goes through.

That said, the 231 stock, was not designed to have a 85lb case hanging behind it either. 231's complete are only about 50lbs, most of which is in the planetary housing. I would say they are used to having about 20lbs hanging of them.

By putting the 300 back there, you pretty much quadrouple the amount of weight that housing was originally designed to support.

I've seen your post before that claim a rear support shouldnt be used.

I think you have officially proved it to yourself, that maybe they arent such a bad idea

Last edited by bnine; 10-28-2008 at 01:45 PM.
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Old 10-28-2008, 02:00 PM   #3 (permalink)
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Quote:
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That said, the 231 stock, was not designed to have a 85lb case hanging behind it either. 231's complete are only about 50lbs, most of which is in the planetary housing. I would say they are used to having about 20lbs hanging of them.

By putting the 300 back there, you pretty much quadrouple the amount of weight that housing was originally designed to support.
however, his case didnt fail from the weight hanging off the back, but rather from essentially landing on a lever arm hanging off the side. so i don't see how adding the rear support would have helped. any support that he puts on the back of the 300 that can resist the driveline from moving to the point of failure in this instance, would probably also resist the tcase from moving the same amount as the other mounts in the driveline, thereby creating a scenario where his adapter would probably fail during normal use.
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Old 10-28-2008, 02:07 PM   #4 (permalink)
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In my rig, with a 4:1 231, and a 1.5x.188 front driveshaft...

I break the little bolts that hold the driveshaft in at the t-case end or the straps at the u-bolt end...

I've ripped the driveshaft off the pinion twice, and off the t-case once, and my Tera-low front half, and OEM rear half have been fine - and I'm still running the same shaft (new upper CV piece because the threads ripped out - but the same shaft)...

Maybe its a combonation of factors?

The cyclic twisting loading in excess of the 231's deign combined with what you know about the fatigue life of aluminum (and there is no fatigue limit) says that if you wheeled this thing for an infinite time, the t-case would break eventually

for the $75 to throw a rear output support on there, if might be worth doing?

maybe a solution is to use a 241 front half? I know my Dodge Ram 2500 with a CTD under the hood has a 241 in it, and none of the drag race guys have issues with the 241 cases (tranny input and output shafts go Ka-Boom! but the t-case seems to be fine [as long as you arent launching in 4wd])
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Old 10-28-2008, 02:36 PM   #5 (permalink)
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Why don't you just move the trany mount back under the adapter plate that the 300 bolts to.That way the weight and the twisting forces would be off of the alum doubler housing.


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Old 10-28-2008, 02:41 PM   #6 (permalink)
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however, his case didnt fail from the weight hanging off the back, but rather from essentially landing on a lever arm hanging off the side. so i don't see how adding the rear support would have helped. any support that he puts on the back of the 300 that can resist the driveline from moving to the point of failure in this instance, would probably also resist the tcase from moving the same amount as the other mounts in the driveline, thereby creating a scenario where his adapter would probably fail during normal use.
It would have helped by not allowing the 300 to pushed up and tear the planetary caes in half.

As long as bushings are used, and located properly, a rear suppost if not going to lead to adapter failure.

A roark support ring is just a press fit steel clamp. If you torque hard enough that you are twisting the drivetrain beyond the absorption of the bushings, the clamp would likely slip.

If he had a rear support, it would have moved the wek link to the driveshaft, or 300 front output.

Or, it might have just held with no failures. Cant say for sure. All you can say that the planetary case would probably have survived.
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Old 10-28-2008, 03:02 PM   #7 (permalink)
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X2 on that with a support it wouldn't have been able to transfer the torque to the doubler to break it! Bnine I think you got it right!
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Old 10-28-2008, 03:19 PM   #8 (permalink)
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I don't understand how you guys would think that having a support on the rear output would have stopped this breakage? A rear support would stop a break from happening from the 300 shaking up and down on the NP231,but would do nothing for the twisting of the 300.Sorry but don't see how clamping a support on the rear output would help.


Rue

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Old 10-28-2008, 03:22 PM   #9 (permalink)
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I say don't install one

Here's what happens to them when you do have a support


And here's what happens to stock D300 cases with a support on the output


note that in the background the np231 crawl box is fine. That's one trip before the carnage above.

In retrospect i don't think this setup will survive with or without the support but I think that A) an np231 crawl box weighs more like 20-30lbs not 10 and B) its not what the np231 weighs but what the D300 weighs behind it.

With a support in the back of the D300 I think you would have had much less chance of D300 rotational related damage.

ATM I can't find pics of my support but I think I had it in another thread on this subject over in Jeep-hardcore tech.

Good luck with it.
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Old 10-28-2008, 03:24 PM   #10 (permalink)
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I don't understand how you guys would think that having a support on the rear output would have stopped this breakage? A rear support would stop a break from happening from the 300 shaking up and down on the NP231,but would do nothing for the twisting of the 300.Sorry but don't see how clamping a support on the rear output would help.


Rue

Those adapters can take a shitload of twisting/rotational force and shockloads, but virtually nothing for any vertical up and down stuff.

The reason it let go is because upwards pressure was applied to the adapter.

Same thing happened to my 241 when a rear CV let go on me.

Rear support rings do add some rotational support as well.

All in all, theres a really good chance that failure would have been avoided with a support ring.
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Old 10-28-2008, 03:35 PM   #11 (permalink)
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Originally Posted by bnine View Post
Those adapters can take a shitload of twisting/rotational force and shockloads, but virtually nothing for any vertical up and down stuff.

The reason it let go is because upwards pressure was applied to the adapter.

Same thing happened to my 241 when a rear CV let go on me.

Rear support rings do add some rotational support as well.

All in all, theres a really good chance that failure would have been avoided with a support ring.
I can kinda see what your saying,but still think that a rear support would be just a bandage.To fix the problem the tran mount should be back as close to the 300 as possible.On the 231/300 doulbers that I have made,I made the trany mount part of the 300 adapter plate.that way the weight and other forces are taken off of the 231.


Rue

Last edited by ruefab; 10-28-2008 at 03:35 PM.
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Old 10-28-2008, 04:04 PM   #12 (permalink)
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From what I can see of the breakage it looks like the drive line pushed into the case and tension broke that side of the case and then the far side bent/cracked after. Soft driveline needed or a mount at the output flange, or two piece driveline with a carrier that can take the abuse.
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Old 10-28-2008, 04:20 PM   #13 (permalink)
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how about a mount on the right side of the case to the frame like a 205? looks like you dont have a mount for that and you might have to get creative. just a thought.
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Old 10-28-2008, 04:28 PM   #14 (permalink)
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I think you need to not land on your .25" wall driveshaft
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Old 10-28-2008, 04:41 PM   #15 (permalink)
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however, his case didnt fail from the weight hanging off the back, but rather from essentially landing on a lever arm hanging off the side. so i don't see how adding the rear support would have helped. any support that he puts on the back of the 300 that can resist the driveline from moving to the point of failure in this instance, would probably also resist the tcase from moving the same amount as the other mounts in the driveline, thereby creating a scenario where his adapter would probably fail during normal use.
But if he had a mount that connected to the front output the twisting force on his set-up would take up some the force on the np231 case.I had the tf727 to np203/205 doubler adapter break from the same kind of thing.I added the side mount to my 205 and havent had an issue since!!!!

And on my buggy that is just a single d300 case I made a plate that would mount up to three of the front output bolts.It cured my t-case to adapter bolts from loosening up and leaking.

edit:My adapter tf727 (stock cast iron mopar...)
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Old 10-28-2008, 06:07 PM   #16 (permalink)
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ive spent some time thinking about this, as my friend has broken 2 crawl boxes in almost 4 trips. They look almost exactly like yours, one big mess of shattered alum.. The only thing I can think of is similer to the last post (rock ape) said, some how tie the 2 boxes together so they aren't fighting each other nor adding any extra undesigned stress by hanging off the back. THEN with a common tied together mounting/brace use a single mouting, bushing setup to the frame.
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Old 10-28-2008, 06:42 PM   #17 (permalink)
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I also think that a rotational support could have helped save the case. Of course depending on how hard you hit. (probably too hard, I'm sure). Not sure if this idea might help, but I did it on mine anyway. I installed a rear support on the back of the 300, but put it out at the end directly behind the front output. I think, in my own little theory, that this setup would actually help fight any twist that might try to make it's way to the np231. A couple of us run this setup, and had good luck so far. We removed the bolts that hold the rear cover plate on the back of the 300 directly behind the front output. Install studs, ours came from extra intake bolts on a TBI 350 motor. You do not have to remove the cover from the 300 to do this. We drilled a plate to fit over the studs, attached a bushing with some gussets, and mounted it with tabs to the trans crossmember.

Here is a pic, since I know most of you like pics.



You can sort of see the plate and the studs sticking out the back of the case. This was taken in the middle of building the brace. I can get more pics if some one might need them.
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Old 10-28-2008, 07:13 PM   #18 (permalink)
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I think the rear support should not allow any kind of significant movement in the rear drive line. Do like the yota guys and make a plate for the back and brace that to each side of the frame!
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Old 10-29-2008, 06:34 AM   #19 (permalink)
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Quote:
Originally Posted by toobad4u View Post
I installed a rear support on the back of the 300, but put it out at the end directly behind the front output. I think, in my own little theory, that this setup would actually help fight any twist that might try to make it's way to the np231. A couple of us run this setup, and had good luck so far. We removed the bolts that hold the rear cover plate on the back of the 300 directly behind the front output. Install studs, ours came from extra intake bolts on a TBI 350 motor. You do not have to remove the cover from the 300 to do this. We drilled a plate to fit over the studs, attached a bushing with some gussets, and mounted it with tabs to the trans crossmember.
How much natural driveline movement does this allow?

I'd estimate I get about a half inch either way of vertical movement at the front output, maybe a little more. The poly motor mounts are stiff but not solid.

Any option that reduces this movement at some point beyond the motor mounts is a step in the wrong direction IMO. That's when you have the different boxes start to fight each other, potentially leading to loose bolts and broken adapters. Keep in mind this needs to work in both forward and reverse - CW and CCW rotation - so the design of the bushing has to accommodate that as well.

I dunno...I'm still pretty convinced that if I hadn't played pogo stick with the driveshaft, everything would still be OK. My options are to replace everything as-is and keep an arrangement that has proven to be reliable for almost two years of hard wheeling, or introduce more bushings and supports into it and risk creating more problems.

Guess I'll think about it some more.
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Old 10-29-2008, 07:05 AM   #20 (permalink)
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I can kinda see what your saying,but still think that a rear support would be just a bandage.To fix the problem the tran mount should be back as close to the 300 as possible.On the 231/300 doulbers that I have made,I made the trany mount part of the 300 adapter plate.that way the weight and other forces are taken off of the 231.


Rue
I agree with this. At a minimum the main mount should be between the case and doubler.

I run mine like that, as well as a rear support ring. Everything is poly bushings, and the set up works well.
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Old 10-29-2008, 12:04 PM   #21 (permalink)
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I could be wrong, but it seems a support under the front output would end up being a pivot point. As the drivetrain twists, said support would not allow the trany to twist, but rather either lift or push the trany down, creating vertical and horizontal stresses that normally wouldn't be there.

I've thought about this alot because I will be running the same 231/300 setup on my next build. Flame on as I am new here, but to me this makes sense.
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Old 10-29-2008, 03:59 PM   #22 (permalink)
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Having not read theis entire thread I agree with some type of extra mount on the t-case. I have a 241/d300 doubler and I managed to make a mount that attaches to the front output aluminum housing and has a poly spring bushing in it. I also have 2 poly spring bushings under the tranny and one for each motor mount.

1 year of hard use, including 1 broken rear output shaft, broken front 4340 35 spline stub and inner shaft. I am now running a 32 spline output on the dana 300 and have found the new weak point to be the gears, but not the 241 housing.



You can see where the mount goes, but it is not shown in the picture

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Old 10-29-2008, 04:30 PM   #23 (permalink)
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You could swap the 231 box out for a 203 range box doubler. But then you'll just be breaking the tranny case. The way I see it a 231 box is a pretty damned good (and somewhat cheap!) fuse if you can't solve the source of the breakage.

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Old 10-29-2008, 04:40 PM   #24 (permalink)
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I have 545185:1 overall crawl ratio.
who needs to go that slow anyway. ditch the crawl box and you'll instantly become a better driver.
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Old 10-30-2008, 03:28 AM   #25 (permalink)
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I have broken the tail of a TH350 from too much weight on the front drive shaft with a D300. I also ripped a rubber motor mount at the same time, all due to the weight ont he front shaft... I now have poly motor mounts and poly tranny mount at the th350 and rubber tranny mount at the back of the 300 just for weight.

My solution is to do a 3 link front and keep the driveshaft higher than the lower right link in order to keep the weight off the drive shaft when playing ont he rocks. Its the only way to keep from breaking shit with a tortional load on the doubler or tranny housing.
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