Crawler Box Splines keep stripping.

As far as different ratios , thats the first thing I mentioned back on the first page because I was thinking factory OEM parts . In this application , the OP is running aftermarket equiptment . When you run 2 different ratios in the front and rear diff , the weakest link will always break . its not uncommon for guys to run higher ratios in the front diff . I would like to see the lube schematic for the aftermarket case in this situation. In my opinion , I think there is room for improvement . I am not a Toyota pro or a jeep pro for the matter , but I am a transmission technician . I see lubrication issues that can be fixed fairly easy . It wouldnt be difficult to change the lubrication from static ( one time supply) to a constant lube system . With this being said , lets see if we can get the OP to drill a couple holes . Drilling a couple holes will keep those splines lubricated on a constant basis rather than a 1 time application of lube . Its the first thing I would try if I was in the Op,s shoes

 

Interesting, I did not know that.

I am with you on that, but at this point I do want the differential ratios to be different so i can find a smoking gun and have peace of mind. Will check them this weekend if work allows.

I see your point and in my mind a u-joint or cv axle will go first, since the crawlerbox is designed to multiply torque should be able to handle this torque transfer through the drivetrain. Looking at Big Mike's (with marlin) triple reduction box he has installed in his 3rd gen I would think the splines would be strong to handle that much torque.

The crawler box wasn't designed with any lubrication ports to this connection. The transfer-case's input shaft is sealed from the rest of the tcase assembly. Although when the transfer-case is mated to the auto transmission (no tacobox) you do get transmission fluid contact at the splines. Could be poor design on this tacobox? if that would be the case wouldn't more similar issues be popping up around the country?

The crawler box doesn't feature a fluid pump like the transfer-case, it relies on its gears to move gear oil around for lubrication.

 

I completely agree with your reasoning. In my mind the fretting is being caused by "loose" tolerances and the constant shock of switching between acceleration and coasting while driving. But again I would expect these issues to be more common to just one isolated tacobox.

 

Do you know in which direction the fretting is occurring? To put that another way, the worn down splines look like a ratchet mechanism. Do you know if the 'worn' side is the acceleration or coasting side of the splines?

 

I think they only look like a ratchet now because they slipped under load and the splines got bent.

 

Is it possible your tacobox is missing some lubrication ports like a factory flaw ? Any chance you have pictures of another unit the same as yours . If they lube with the automatic , it wouldnt be very difficult to constant lube with yours . Add a gasket at the mating surface between the transfer case and the Tacobox , then two lube ports just below the center line of the Taco box . I would even drill the input and output shaft to accomodate that fresh constant lube

 

Just for the record all second gen v6 4x4 wether auto or manual have 3.73. All second gen 4cly 4x4 have 4.10

 

The plot thickens? Front ratio needs to be verified.

 

Yeah you never ever see +40s with duals on the con all summer long. I have only ever had to do a trailside input shaft repairs back in the old days when marlin first started getting big and I have been wheeling since 98. Shit the pinion is a much weaker link than any of marlins products. Running an atlas with toy 8” diffs is bassakwards.

 

Did the spin test, 3.73 gears in the front differential. Rear is stock as well so 3.73 both diffs.

Back to square one.

 

There has to be a failed bearing or something. When you install the crawl box, are the splines lining up nice before you start threading bolts? Can you get the crawl box all the way seated before you start bolting it in or are you sucking it closed with the bolts?

 

When I mate the crawlbox to the transmission, it bottoms up all the way smooth. Hang tight bolts to let the gasket maker dry then torque. Same deal when I mate to the transfercase, I may have to do some wiggling to get it flush. But never had a gap thats sucked by torquing the bolts. I’ve been installing them one by one vs together. Both sides have dowel pins that help w/ alignment.

 

I did rebuild the crawler box yesterday, bearings and needle bearings looked fine oil was a bit dirty, magnet had a little metal shavings from what used to be splines I presume. Only thing I did find was a “spacer ring” slightly burnt on one side which was a bitch to get off. Goes between the rear bearing and the large gear, over the rear coupler. Its locked to the coupler from spinning by a small ball. Could this be the culprit?

 

Those spines look kinda shitty? how much oil do you put in the crawl box?

 

Which Spines? The coupler’s?

I use half a bottle of Lucas Oil Stabilizer (recommended by RST), then fill it up with mobil 1 gear oil

$29 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 till the fill hole starts overflowing.

 

yeah the female coupler in the pic i quoted.

you might need some more oil. any time i filled up to fill line and went and drove it was low on oil. the oil moves into the cavity of the adapters between the crawl box and tcase.

think i put around 1.5 qts if not almost 2 when i fill mine

 

Thats a good point, when I was looking at the crawler box the fill plug sits level with the bottom hole that communicates with that cavity you mentioned, maybe im not letting enough oil through that hole before I stop filling up.

Bad side is I need 6 months to verify that theory lol.

 

So much for this being easy. If your rebuilding the crawlbox do you already have the new coupler?

 

This definitely doesnt look right to me.... Is there a replacement for that part in the rebuild kit? If not I would forward that picture to Marlin and see if that is what its supposed to look like. To me it looks like that was grinded away when in use.

 

yes I have the coupler, bought an extra last time in case this happened. But being that ring I found burnt I might wait for a replacement.

Already did, well the 2nd time this happened. Marlin is aware they just said to replace it. But didn’t say what caused the wear, could this be the reason I keep thrashing out couplers.