Crawler Box Splines keep stripping.

Hey guys, I am in a pickle and was wondering if some of you guys that have dealt with the marlin's crawler tacobox have ran into this same issue and if there is a possible solution. Not trying to discredit Marlin Crawler, I do believe they build a solid product and they stand by it.

Started with a 2007 tacoma 2wd to 4x4 conversion and decided to install marlin's tacobox along a twin stick fj-transfer case. The conversion was installed by a reputable off road fabricator with plenty of experience in this area back in June 2015.

Ran into my first issue in Nov 2015, was driving to work and a block from my house I lost all power. All I could hear was grinding noises coming from my center console. Took the drivetrain apart and found out the female output coupler (Malin's Tacobox) and the male input shaft (FJ transfercase) had stripped all the splines (both sides). Discovered the input shaft had the splines slightly grounded down, when it was first installed ,to mate to the coupler. Figured we found the smoking gun and then replaced parts to get my truck back on the road.




July 2016, about an hour from my house, while on the highway, ran into the same issue lost all power. Took it apart and found out the coupler and input shaft had stripped splines. Threw new oem input shaft and marlin's coupler, my truck was back up and running.





Jan 2017, on my way back from a ski trip (about 500 miles from home) running 75 mph lost another input shaft/coupler. Thinking there might be something off with the crawler box or the way I was installing them. Sent both my transfer case and crawler box to Marlin for investigation. Due to the downtime and needing a vehicle, purchased a daily driver. Received both cases mated together and threw them on the truck.



Due to having the daily driver I don't put on as many miles on my truck as I used to, moved from texas to colorado. No more desert trails and time to do some real off-roading. Went on my first trip (Nov 2019) and while climbing a rock wall, my input shaft/coupler decided it was time to go. This time I did snap a driveshaft u-joint moments before.







And here I am trying to figure out what could be causing all this, has anybody ran into this before? Any input would be appreciated or anything I can look into.

P.s. I have been running 33's with stock gears and open differentials (mech lsd in the rear). Most of my issues have been driving in the highway except this last one. I do about 85% highway driving (80 mph speed limits, because texas) and did mostly light desert off-roading.

Sorry for the long post, was trying to keep it short.

 

whats going on with this?

 

Interesting. Following just to see the outcome. Good luck.

 

Damaged in transit, fixed it before installing it back on the truck.

 

Id be tempted to double check the part numbers and specs for both sides of the connection. Seems like something is out of spec.

 

@Littles Just built a similar set-up if I remember correctly. He may be able to offer some insight

I think he has a partial build log of it here:
https://www.tacomaworld.com/threads...-trans-to-4-0l-marlin-crawler-tacobox.622165/

 

My first thought was tolerances, but having 3 different set of parts give way seems strange and tends to point me in a different direction. I’m thinking the inner shafts are not collinear with each other and they may be stressing the couplers at an angle, unfortunately I dont know how to rule this out.

 

I wonder if you could strategically use some ring+pinion marking compound to see how they're mating up.

 

There’s a good amount of overlap between the shafts. I would think they are collinear just by nature of the slip fit. If there was binding, I would expect the bearings to wear out not the spline. But that’s just my guess.

 

I will refrain from going on a rant and just fuck Marlin.

I know they have issues with whatever adapter they were using in the manuals being too loose and causing fretting between the trans and crawl box but I have never heard or seen issues between the crawl box and tcase. Theres no adapter there.

Maybe it's just dark, dirty oil, but your shit looks rusted as hell man. If that's rust then you have a problem there. No reason you should have moisture between your cases. Maybe it's an older version, but that also looks more like a trail gear crawl box than a marlin, and trail gear doesnt make a crawl box for the 2nd gens.

Super stupid question...is it the same spline count on the tcase input and crawl box output? Should be 23.

Edit: just saw you said you sent it back to Marlin so it obviously their crawl box

 

Whats up with the weird wear patterns on the splines? Looks like some sort of ratchet mechanism rather than splines. I have zero experience with these things, but the same pattern is in all your pics, which seems like a red flag to me at least

 

This picture almost makes it look like the splines are only engaging less than half length - maybe the shaft is too short?

 

I'm throwing a link to this in the crawlbox thread. Lots of smart guys over there.

 

The input shaft of the transfer case is designed to be harder in comparison to the female sleeve it couples with ? because both components are aftermarket , it would be interesting to know if Marlin used two different metal compositions when producing these aftermarket parts . The female coupling should always fail before the transfer case splines . Judging by the wear on the splines , I would be double checking my differential ratios . if the parts are failing that quickly , I would be willing to bet your front and rear diff are out by 1 tooth . The transfer case spline is the weak link

 

That's not it. The tcase has a short input, the crawlbox has a deep output. Same thing with the transmission on the manuals which also has a female output. The depth of the output is greater than the length of the tcase input. He is getting full spline engagement.

 

Are botth the front and rear diffs the same gear ratio? Those being different is the only idea I can come up with as to what's causing that fretting.

 

don’t think that will work due to the full time contact of the splines.

The input shaft is toyota.

Wouldn’t having different differential ratios stress out the transfercase? The input shaft should see the same torque loading before the power is split front/rear.

TBH I’ve have never torn into my front diff, was planning on re-gearing in the future.

Most of my issues have been in 2wd driving on the hwy.

 

Had to go count, yes its a 23 spline. I don’t think its rust, more like the stripped metal that used to be splines. Once they go out, just start grinding like crazy. The first input shaft that stripped was grounded down, thats why it looks chewed on.

 

Do you have any growling vibrations at highway speeds? One or two piece driveshaft? Were your driveline angles measured and calculated?

 

I’m gonna guess no anti seize on the input and you got fretting. This is an issue that no one talks about on install. It needs to be done.

let me find the thread from ttora that has slot of crawl box issues discussed

this mostly talks about the dual row bearing but pretty sure it talks about other stuff