Author Topic: MC 21 spline 4.7 input gear fail  (Read 925 times)

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cavey

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MC 21 spline 4.7 input gear fail
« on: Jan 26, 2020, 04:17:46 AM »
It is Australia Day long weekend  down under so myself and one son and his son decided  to do a trip to Tasmanias' wild west coast  , me alone in the hilux and them in a petrol 80 Series  .We left Hobart on Friday Afternoon  for the 300km drive to Queenstown ,  camped about 10kms past Derwent Bridge  at 8pm , on the road again at 8 am with 90kms to go, topped up fuel at Queenstown and headed south and did the Mt Huxley track  in typical west coast weather 100% rain, after several hours wew completed the track then headed south again to tackle Mt Darwin track, we did about 2kms of Mt Darwin track and gave up because of the slipperyness of the track  due to moss etc , it was dangerous to walk on  so we came down and did the Mt Jukes track instead , and on the way back down  with the son in front  had trouble getting up one severe steep section which took him 3 attempts  to get up , then I had a go and couldnt get up and on the last attempt  i tried grabbing 2nd gear and it went bang and then no drive  front case was in low and the back case in high, had to winch it out , got it home and on sunday  removed both T cases, as the pictures show the 21 spline 4.7 input gear failed  in the rear case . yes I know it should be 23 spline  but when i first installed duals the engine was a 2.8 diesel with 60KW  driving a G52 ,21 spline gearbox and T case , so with duals everything was 21 spline , then upgraded to a 1KZ-T  ( 93KW  285Nm )  with a R151F  gear box , so had to get a 23 spline 2.28 input gear 
own a 1989  LN106r diesel with a 1KZ-T 3 litre turbo diesel  bolted to a imported R151F gearbox with snorkel Rancho springs & shocks & Detroit lockers F & R & 11x 32  cooper sst ultimate dual transfer cases 130 litre fuel tank   full floating disc brake rear end

Cheesemaker

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Re: MC 21 spline 4.7 input gear fail
« Reply #1 on: Jan 26, 2020, 07:37:26 AM »
I have been told you don't run the front case and not the rear, I am told this will result in sheered input shafts.
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gnob

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Re: MC 21 spline 4.7 input gear fail
« Reply #2 on: Jan 26, 2020, 07:37:40 AM »
And then....
hold this. . .

gnob

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Re: MC 21 spline 4.7 input gear fail
« Reply #3 on: Jan 26, 2020, 07:40:00 AM »
I have been told you don't run the front case and not the rear, I am told this will result in sheered input shafts.
How are you supposed to accomplish stock low then?
This is not entirely true and if it is entirely true, whats the point in having dual cases at all?

I run front case only ALOT.
hold this. . .

toyodaaddict

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Re: MC 21 spline 4.7 input gear fail
« Reply #4 on: Jan 26, 2020, 05:08:40 PM »
I have been told you don't run the front case and not the rear, I am told this will result in sheered input shafts.

I have heard this as well. I have been thinking about getting a 4.7 gear set but not if I cant safely run 2.28 most of the time. Bigmike said its all good to run 2.28 front case all day. The confusion come into play when people put 4.7's in the front case.

"It is perfectly fine to run the front case in low and the rear case in high. You might be thinking of how it's advisable to use the reduction furthest down stream, but because you wouldn't need the 4.70:1 ratio save only for 20% of your driving, you'd move up to what's most practical for you which would be the front box in it's current 2.28:1 low range. In fact Marlin is similar to you in that he also prefers a 2.28:1 ratio when he is pressed for time and in the Crawler Truck this is in front of not one but two X 4.70:1 low range gear sets. He has been doing this since the late 1990s. It is perfectly normal. (If you've ever wheeled behind Marlin on our annual time-sensitive TLCA Rubithon Sweep Run then you'll know just how fast he is; It is rare to find full-bodied leaf sprung rigs driven as fast as Marlin on difficult trails such as the Rubicon.) At the end of this article I plan to showcase the difference between a 2.28:1 ratio and our 4.70:1 ratio :D"
80 shortbed-22re,w56,Marlin 23 spline dual cases,HighAngle drivelines,RUF/63"chevy's,35''mtr's,30 spline Longfields, Allpro highsteer.87 rear axle,5.29 gears,rear spool,BudBuilt cm, marlin HD clutch,ramsey 8000 winch. 
     https://board.marlincrawler.com/index.php?topic=101882.0

Willard

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Re: MC 21 spline 4.7 input gear fail
« Reply #5 on: Jan 27, 2020, 08:20:56 AM »
I use my 2.28 all the time. I am by no means easy on it either running 40's. Have yet to have a failure  :dunno:
90'4runner......lots of goodies.

T-Revv

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Re: MC 21 spline 4.7 input gear fail
« Reply #6 on: Jan 28, 2020, 08:29:46 AM »
I use my 2.28 all the time. I am by no means easy on it either running 40's. Have yet to have a failure  :dunno:

Yes running just the front case in low is fine.  That's the beauty of a dual case, having the options, you can run 1:1, 2.28:1, 4.7:1 or 10.7:1.  As toyodaaddict said, the problems occur more often when people put a 4.7 in the front case, because this is taking the amount of torque that that input normally sees and applying 4.7 times that much torque, much easier for something to go wrong there. This persons particular problem occurred (from reading his story)because  he was spinning the tires (enough to grab second gear) and I'm sure it hopped which caused a shock load.  When the load comes off the tires and they can free spin and then is very suddenly returned as the tires come back in contact with the ground that puts an extreme amount of pressure very suddenly on a part and something is bound to break.  You can see that input completely twisted before snapping off. 
"I dunno I just woke up from a lil nap, it's a lil dark but you guys silly? I'm still gonna send it."

Willard

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Re: MC 21 spline 4.7 input gear fail
« Reply #7 on: Jan 28, 2020, 09:18:53 AM »
Agreed T-Revv


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90'4runner......lots of goodies.

cavey [OP]

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Re: MC 21 spline 4.7 input gear fail
« Reply #8 on: Jan 29, 2020, 02:12:31 AM »
 i agree with the above  except that it didnt hop  one nats whisker  looking back I should have had the front case in high and the back case in  low  with 2nd or 3rd gear  , back on the road again with a std rear case  for the time being 
own a 1989  LN106r diesel with a 1KZ-T 3 litre turbo diesel  bolted to a imported R151F gearbox with snorkel Rancho springs & shocks & Detroit lockers F & R & 11x 32  cooper sst ultimate dual transfer cases 130 litre fuel tank   full floating disc brake rear end

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Re: MC 21 spline 4.7 input gear fail
« Reply #9 on: Feb 01, 2020, 07:23:05 AM »
Very impressive.
I sure enjoy looking at carnage parts when they aren't from My truck.
Thanks for sharing them.
I am 1/5th of Perfect Fit
SqWADoosh [04:19 PM]: *sigh* I guess Chris is right and I just need to wait until I'm in a place where I have a tow rig and trailer before I get this caliber of truck
Mudder [08:28 PM]:   not try to be a jerk, but are you serious bestgen?
Prismo [06:11 PM]:   Done, time to relax or as Bestgen says....FREEDOM!
HogCanyonHopper [06:54 PM]:   I like my little rod. it gets the job done
H8PVMNT [03:30 PM]: I can go both ways.

 
 
 
 
 

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