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Trail-Gear trans to t-case coupler failure

Rockbaron1

Rockbaron1

Member
Joined
Oct 8, 2020
Member Number
2921
Messages
7
My Trail-Gear trans to t-case coupler failed on the highway in Colorado and left us stranded 1700 miles from home. It also destroyed the output shaft on the transmission. I noticed the day I put it on, the fitment was much looser then the Marlin Crawler coupler on my 4runner that lasted 10+ years and still looked perfect when I sold the trans. The Trail-Gear coupler was about 6 years old. Trail-Gear declined to warranty or offer a discount on a new coupler. My truck has never had bigger then 35” tires and the stock engine. This failure was due to wear not brute force.

Kyle at Marlin Crawler was able to sell me just a new coupler from one of their kits and take some measurements to confirm it would fit with my trail-gear adapter plate.


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Well that makes me kinda happy I was able to get my Marlin stuff before he left us.
Looks like a pain man, hopefully the marlin parts will be better for you.
 
I've heard this is related to the looser tolerances, the frequency of the vibration just eats the splines over time until it's wore down enough to let go. Bummer, I have the same adapter on my tacoma but I don't recall if the fit was decent or not.
 
I believe this was the main issue. My new Marlin coupler was nearly a press fit on the new output. The Marlin coupler on my old truck could not be pulled off the trans output by hand even after 10 years of street and trail use. The Trail-Gear coupler was never a tight fit,
 
Marlin Crawler was having stock issues when I was building the tacoma which lead me to order the TG stuff in the first place. When I saw how bad the fitment was I wanted to reuse my old marlin coupler, unfortunately it had already been sold. I did a bit of searching on the issue at the time and couldn't find much talk about it. I figured they had been making the parts long enough, if there were serious issues they would have shown up by then. I guess I wrong or not looking in the right places? I think I do put more road miles on my truck then most people running these parts, maybe that contributed to the premature failure, maybe not?
 
Law of averages...
How many wil come back on us? VS we sold him ANOTHER
 
Yes, Marlin 23 spline 2.28 input, that actually survived though. Only the transmission side stripped out.
 
I had this happen in 2009 with a 23spline marlin crawl box to chain drive case coupler. It stripped out on the street almost one year after I installed it right before a trip (for really lucky there). I learned all about metal fretting, after that, which looks like what happened. Basically parts rub against each other and wear them rub more, wear more then they fail. Thats what the dual row marlin bearing and total spline input helps prevent on the crawl boxes. Interesting this happened on the trans side, trying to decide if that's better or worse LOL!!

Is your trans oil red colored by chance? I try to change my trans and tacse/crawl box fluid once a year to look for red in there, I used to do it every 6months when the truck was a DD, that's the coupler material rusting in the fluid and it means it's time to start dropping the driveline and tearing shit down.
 
Ive been aware of the t-case coupler fretting issue since I got dual cases. I actually rebuilt the entire dual case set up with a new input and coupler before I left for the trip. I failed to check the condition of the trans coupler, I guess it was a combination of it being hard to see behind that extended seal housing and the old one being perfect after years of use that made me just assume it was ok. And yes lots of that thick red clay-like shit in the failed coupler, I never actually noticed the oil change color though.
 
Rockbaron1 said:
Ive been aware of the t-case coupler fretting issue since I got dual cases. I actually rebuilt the entire dual case set up with a new input and coupler before I left for the trip. I failed to check the condition of the trans coupler, I guess it was a combination of it being hard to see behind that extended seal housing and the old one being perfect after years of use that made me just assume it was ok. And yes lots of that thick red clay-like shit in the failed coupler, I never actually noticed the oil change color though.
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That sucks!
 
I bought a brand new r150 from Toyota. If anyone else was thinking about one there’s only 5 left in the country now.


Im also rebuilding the old trans with an output from another blown up trans I have and a higher 5th gear from either a ax15 or r452. I already ordered the ax15 gears but the cluster gear has a smaller I’d so I need figure that out.
 
That sounds expensive buying a new transmission directly from Toyota. I did a r150/ax15 hybrid but I only changed the front input, bearing retainer, and bell to keep the round 6 bolt tcase pattern.
 
We gotta know :laughing: How much ish??

Wish rcv would get into more of the yota game...
 
It was expensive but I’ve owned this truck for 20 years and plan on another 20, so after considering all the options I decided to go for it. It was just under $2400 after tax, picked up at my usual Toyota parts department.
 
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Way more realistic than I thought.
Thanx:beer:
More than I piad 4 my 83:lmao:
Frickin rebuild kits are around what $500...
 
Rockbaron1 said:
It was expensive but I’ve owned this truck for 20 years and plan on another 20, so after considering all the options I decided to go for it. It was just under $2400 after tax, picked up at my usual Toyota parts department.
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That's not too bad! I had the output seal fail on mine and it leaked all it's fluid into the crawl box and vented over time and it blew up one day. I bought a rebuild from marlin for $1400 which was cheaper than what junk yards were asking at the time.
 
I have a trailgear 4.7 box for my 3rd gen Tacoma. I didn’t like the play in the trailgear coupler and refused to Install it based on a few issues I’ve seen like the above taking out the trans output. My options were get one made, or buy the Marlin 23 spline coupler and test it. I got it yesterday and right away the fitment was a little too tight but the spline interference was not much. I spun the trailgear box and cleaned the OD of splines with a scotchbrite pad. Took the slightest bit of material off, roughy a thou and now the coupler fits perfectly. Absolutely zero play in the coupler, fits like it was made for it. The length is slightly longer than the trailgear 3.72”vs Marlin 3.78”. But the coupler fits properly with all of Trailgear’s stuff, I’ve test fit the crawlbox and it doesn’t bottom out or interfere in anyway. Coupler is a press fit on the trans and very tight slip fit on the t case now.
 

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Anderson2162 said:
I have a trailgear 4.7 box for my 3rd gen Tacoma. I didn’t like the play in the trailgear coupler and refused to Install it based on a few issues I’ve seen like the above taking out the trans output. My options were get one made, or buy the Marlin 23 spline coupler and test it. I got it yesterday and right away the fitment was a little too tight but the spline interference was not much. I spun the trailgear box and cleaned the OD of splines with a scotchbrite pad. Took the slightest bit of material off, roughy a thou and now the coupler fits perfectly. Absolutely zero play in the coupler, fits like it was made for it. The length is slightly longer than the trailgear 3.72”vs Marlin 3.78”. But the coupler fits properly with all of Trailgear’s stuff, I’ve test fit the crawlbox and it doesn’t bottom out or interfere in anyway. Coupler is a press fit on the trans and very tight slip fit on the t case now.
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Were you able to order the coupler directly from Marlin's website, or did you contact them? When I have looked on their site in the past, I wasn't able to find the coupler as a stand-alone purchase option.

What was the price for it btw?

I have a 3rd Gen 4Runner that has a lot of play between the transmission and the 4.7 case as well. I'd like to remedy this before it become a failure.
 
Had to call them directly. They won’t tell you it fits. part number is MCTC-421 $180 shipped.
 
I was very careful when taking off material very evenly and slowly snuck up on it till it fit. Idk why that so hard for trailgear to do.
 
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