rocktrac 241or the inside scoop. aka i believe toasty is right

['round n' back again]

tonite i split the case on the rock trac. toasty feels these are a modest servicable t case. i had an assumption they were much more stronger ; along the lines of the BW 4407.
alas , toasty u were closer to the truth than i.

here is what i found:

4 planets instead of 6. 4 huge, heavy planets easily 1.5 " across
4 planets served quite nicely until the mid nineties when diesels started spitting them out the sides of the case. the engineers went to 6 on the hd cases.
they also went to a 1.5" chain.
a mid shaft support bearing and webbing

what i found in the rock trac, i liked.
quality machining
1.25" chain (stretched),
us made bearings.
good seals
i think the case is too lightly constructed with not enough webbing.

the chain quality is pathetic. it needs and will get a morse chain.

i was hoping for 1.5 chain, a mid shaft support bearing and greater strength in the case. the outer ring of the planets, the ring gear, is held in place by the front input bearing plate i would like to see a snap ring like the other t cases have to hold this gear in

my guess is now inline with the comments toasty has made ; that this is a handy mid-level case that can take average use and abuse, but is not on par with the mitsu case or the boutique makers cases.
im trying to guess that with a 3.06 first gear a 4.01 low range, and 4.6 axle, how much stress is going through the system and where is the weak link.
im guessing the case. the unknown is how much torque can be applied b4 disintigration.
the outer joints are really a joke. like toasty said, they are grenades. drive flanges or yokes if your cheap are a necessary upgrade both front and rear; shafts are 32 spline.
now, interesting discovery. i was bellyaching that my case came from a 2012 automatic. this auto the 580 series uses a rare 26 spline male on the t case input. this fits no known trans other than the 580. i expected to buy a new inputshaft, possibly a bearing retainer face plate , bearing and seal. grumpy.

on very close inspection i noticed this male spline had the slightest play in it. hmmmm. taking two pry tools, i worked them behind the splines between the splines and the seal, pressed down, with some force and the little bugger jumps right up and onto the shop floor. turns out that beneath the weird spline is a normal 23 spline female shaft like all the other cases. this weirdo, had a stub shaft that fit into the 23 spline female.

so now my case should, theoreticaly fit the common 23 spline trans output shafts.

we will see . for my putt putt ways in the wilds (i hate walking out), it should get me an my little trailer whereever i want to go. for throttle stabs and jackrabitt starts in low range, well im unsure.
i can only reacll the mindless abuse the old 208, 1356, 1345 series got and they held together...kind of.

do yourself a favor if you buy one of these cases , at very least, inspect the interior case for stress cracking, and fer heavens sake put a morse chain in. its a 45 minute job.

thank u for listening..

 

[Toasty]

I think it will be great for your application, good find on the 26 spline removal. It kind of makes me realize i should have rolled the dice on a $400 Rocktrac i found a while back (i passed on it due to the spline count). Excellent info, thanks for sharing!

I'd like to add that the comparison between the NP and Mitsu T-cases isn't apples to apples, our low ranges are not planetary gears but spur gears so the case construction is very different.

 

['round n' back again]

a further note

the pickle we rocktrac fans have now found ourselves in is this:

most or many of the rocktracks will have stress fractures or outright cracks in the cases. the case i bought from a kid; he complained that "the case was leaking". i finally borught it out that he had shoved his front driveline into the case and cracked it.
"oh well i give you 150 for it and take my chances".


here is the pickle.

THERE ARE NO CASE HALVES ANYWHERE IN THE UNITED STATES.

so unless NV reissues the case halves, the roctrack that is cracked or suspected to be cracked-is junk.

At dodge , there is an active number, and a price, ($556.00) but no known cases in existance, and no word on reissue. Obviously this has been such a problem that the available supply has been bought up/out, and the funny numbers at the dealer may mean they are going to re-issue or they will not. could go either way. i'm betting on not. a new case is about 1900 dollars. to split a case and replace parts at the dealer is about....1500 dollars; just guessing. what would you do?

of course, me too. so there you have it.

there is no way to tell if there are stress fractures without splitting the case. unless the crack is obvious outside. which makes the case obviously worth little.

BUYER BEWARE!!

 

['round n' back again]

further note II,

i talked with my hillbilly welder evil companion /neighbor/ partner in looniness/ friend, tonite. on some cases we are going to try an aluminum epoxy , filling all stress fractures from inside the case to stiffen them, and to hold the crack from spreading (hopefullly).
his opinion was that to weld so closely to bearing housing could distort the case sufficiently that is will leak no matter how well we seal up the actual crack. so around the bearing seat, we will literally fill the cavities and depressions with this epoxy to create a stiffener.

.keep everyone posted on progress.
.

 

[coffeegoat]

It may also be worth investigating "aluminum brazing rods." I say "brazing" in quotes because it's kinda borderline of actually being a brazing in terms of temperature, but you can pick the rods up at farm supply stores, I actually fixed an aluminum head with it once. The only trick is you have to get it really really clean since during the heating process any residual organics (including gear oil) will vaporize and even if you get the aluminum filler metal to wet and flow into the crack the vaporizing organics will fill your joint with bubbles...

Actually welding would likely be a no go anyways, most casting aluminums (or forgings for that matter) are not weldable using standard fusion welding techniques, that's why a braze where the base metal doesn't actually melt can be really effective.

To reduce distortion you can heat the whole shebang up in an oven to as high as you can go (500 °F) and then the differential thermal expansion will be reduced so it won't distort as bad (it'll also be much quicker than trying to heat the whole thing up with a torch.)

 

['round n' back again]

excellent advice.

in this case we are going low tech. the principle crack in this case runs at the 6 o'clock position on the front output shaft opening.
im going to use some high tech epoxy Devcon HVAC or equivelent, and build a "cast around the output opening.

inside and outside to stiffen the works up. it will be a lot of epoxy, but the tiny fissures that might exist and can't be seen now may not be a problem down the line. what i fear is the case cracking like egg shell or like glass.

i hope it works. if it does im a hero, if not ....im walking out.

 

[coffeegoat]

If you're going to use epoxy, make absolutely sure it's is clean - use a hot bath in TSP or high concentration degreaser or something similar, and a hot water soak/rinse. Best yet, after all of that cleaning, look into using a vacuum to impregnate the cracks, it may not be feasible given the size of the part, but it will pull the epoxy deep into the crack. You're really interested in stopping the crack progressing so you need to fill it all the way to the end because the crack can still grow even you don't get it all the way to the tip. It's similar in many ways to how you can stop a crack growth by drilling a small hole at the tip - you've blunted the point so it won't grow - if you just putty the other end, it may not stop the crack.