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The Myths of the TA

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John In Iowa

02-06-2001 22:58:46




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After seeing a lot of posts about what causes a TA to go bad, I thought I would take the time to set things straight as I sit here tonight with my 400 sitting in a neighbor’s garage split in half and the TA case sitting on the bench with parts covered with clean rags waiting for Uncle Sam to return some of the money that he has borrowed from me (tax return). I got this 400 Farmall back in 1991 with the engine stuck. After rebuilding the engine and hearing it run, I was filled with joy only to discover that the over running clutch in the TA was weak. I did find out that after letting it warm up good that the TA would work most of the time. That was until this winter. I pull up to shed and got off to open the door to put it up for the night when the engine backfired, shuttled and came to a stop. The last time I heard an engine do that was when our family’s M broke the cam gear on the cam shaft (that’s another story). I pop off the disturber cap and found that I could turn the rotor any which way very easy and that my worst fears was coming to past. I got the other tractor out and push in the shed for the night and looked at it in the mourning. What I found was that the coupler from the hydraulic pump had come loose and the half moon key fell out. After putting everything back in order, I fired the old girl up and thought I would take it around the yard just to make sure everything was in order. I couldn’t move!!!! What I had found was about half the clutch face from the TA clutch laying in the bottom of the case and yes I had the TA in the high side. After taking it apart, looking at the TA and talking with some old IH hands I now understand what happen. The way the TA works is like this. You have an input shaft coming in from the engine that goes in to the planetary gear set. On this same shaft you have the TA clutch on it. On the gear set you have the pressure plate on the front side and the overrunning clutch assembly on the backside with the output shaft running through the overrunning clutch but not connected to it going to the output of the gear set. The outside part of the overrunning clutch assembly is bolted on the back bearing cage of the TA case. In this assembly you have 8 rollers that run up a ramp that lock the outside of the planetary gear cage to the back of the case, thus letting the input shaft turn the reduction gears in the gear set. On the high side with the clutch engaged the planetary assembly is lock with the input shaft, thus the output shaft is lock with the input shaft and turns the same as the input shaft. In the low side the clutch is released allowing the planetary cage to turn the opposed way until the overrunning clutch locks it to the back of the TA case stopping it and letting the reduction gears go to work. You would think that this would send a lot of shock through the TA but with everything moving it doesn’t. Were the real damage comes in is when the engine kicks backwards when you shut it off in the high side. With the planetary set locked to the input shaft with the TA clutch engaged, not letting any energy to go through the gear set and out the output shaft, it turn the opposed direction which engages the overrunning clutch which in turns brings everything to a halt. This is when you get a terrible shock through the whole TA assembly. One of the things that suffers the most is the rollers and the ramps in the overrunning clutch causing flat spots on the rollers and the ramps. With flat spots in the rollers and ramp its hard for the rollers to run up the ramps to engaged the overrunning clutch. In this case with me the overrunning clutch did hold this time tearing out the clutch in the TA. Coasting with the TA in the low side only lets the overriding clutch work like is suppose to, the same as if its in the high side. Hope this clears up some of the Myths out there.

John In Iowa

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the neighbor

02-08-2001 20:48:00




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
Does my John Deere have a TA?



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artie

02-09-2001 18:09:15




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 Re: Re: The Myths of the TA in reply to the neighbor, 02-08-2001 20:48:00  
yes,yes,yes.



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Phil Auten (TX)

02-08-2001 06:20:46




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
John,
I'd always heard that the reason the TA shouldn't be used in freewheeling mode going downhill was that there would be no engine braking, thus allowing the tractor (and any load hitched to it) to accelerate to a possible dangerous speed. I have also heard that the TA would not function except in direct drive mode in 5th gear. What's the real scoop here?

Thanks for a great explanation,
Phil

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John In Iowa

02-08-2001 09:09:36




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 Re: Re: The Myths of the TA in reply to Phil Auten (TX), 02-08-2001 06:20:46  
Yes you can go to dangerous speed going down hill with it in the low side yes you don’t have any engine braking. One should be careful and not go to the high side trying to slow down and use the brakes instead. Going to the high side at high speed, (faster than the tractor would be going in the high side) would also sent a pretty hard shock through the TA Assemble.

John In Iowa



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artie

02-07-2001 15:14:28




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
Dear John in Iowa,

Are you an engineer? Thats the best explanation
I've ever seen.Very clear.Thank you.



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Dan

02-07-2001 09:39:08




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
Think I started all this TA stuff a couple days ago. Thanks for your explanation. Will have to sit down with a service book on it and your explanation and figure it all out. I always thought everyone pushed the clutch in before stopping the engine, guess though if it was sitting, in high, main clutch engaged, transmission in neutral you would have a problem. Do you know of a source of the heavy duty rollers someone mentioned? Haven't taken mine apart and for the time am using it as a SM with live PTO and hydraulics. Eventually it will get the best of me and I'll just have to do it. With the heavy duty rollers to you still have to change the ramp? Thanks again for the great explaination

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dick

02-07-2001 08:30:38




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
The TA is one mystery I've been content to let remain mysterious up to this point, and would just as soon have it remain that way in the future. As long as it keeps working. About the only thing I know about it is how to adjust the clutch (following the directions in the user manual).

After reading these recent posts, I'm still left clueless as to what is being recommended to avoid unnecessary damage to the TA:

Are we recommending turning off the engine with the TA in the "low" side?

Is this potential damage from the engine kicking back when the TA is in the "high" side avoided if the transmission is in neutral when you turn the engine off? Or if the clutch pedal is depressed when turning off the engine? Or if you do both?

Are there other things to avoid, or have we decided they are "myths"?

Somehow, I'm missing the punch line(s) here - could someone who thinks they know how this thing works come up with a coherent, simple set of things to do, or avoid doing, without too much additional verbage? Surely would be useful, and appreciated by those of us who would like to use the TA properly, and hopefully avoid the more detailed knowledge to be gained by fixing it after having used it improperly. Thanks in advance to anyone willing to perform this service.

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John In Iowa

02-07-2001 08:52:11




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 Re: Re: The Myths of the TA in reply to dick, 02-07-2001 08:30:38  
The best way to avoid damage is to shut the engine down in the low side or the main clutch disengaged. Even with the transmission in neural , the TA will lock up when turned backwards in the high side. I agree that over time that you would develop flat spot from normal wear, but these ramps and rollers are very hard. I took the it to a machine shop to see if they could reface the ramps in it, but because of the heat treatment of the ramps they didn’t have anything to touch it. A new overrunning clutch assembly from IH is $427. I did find a remanufactured one for $117. Don’t take a genesis to figure this one out.

John In Iowa

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dick

02-07-2001 12:49:32




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 Re: Re: Re: The Myths of the TA in reply to John In Iowa, 02-07-2001 08:52:11  
OK, so I'll start stepping on the clutch pedal before turning the tractor off.

How about the other "rules" such as don't switch into low range when going downhill or in fifth gear? Are these "myths"?



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John In Iowa

02-07-2001 21:34:24




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 Re: Re: Re: Re: The Myths of the TA in reply to dick, 02-07-2001 12:49:32  

These are Myths. Like I said in the early post when you begin to coast, the planetary gear set starts to turn in the normal direction as if its in the high side. Would it doesn’t engage when the tractor slows down, this is the first symptoms that something it starting to be amiss.

Hope this clears things up.

John In Iowa



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Charlie

02-07-2001 07:31:10




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
How a TA operates has always baffled me and I guess until I see one torn apart it always will baffle me. I'm thankfull for the info on them as I have one on my 300 U that works fine and I'd hate to think I had to fix one because I did something stupid with it. I think a TA is a very handy accessory on a tractor.



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kev@IA

02-07-2001 03:43:21




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
Nice post there, I think from now on I will shut down the motor with the clutch pushed in. That said, a TA is like the clutch or tires it is gonna wear out, big deal, look at all the work it did for all those years.
kev



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Wardner

02-07-2001 01:18:17




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 Re: The Myths of the TA in reply to John In Iowa, 02-06-2001 22:58:46  
Nice job on your post John. I think that we can all agree that wear induced flat spots on either the ramp or rollers is what kills most TA's. I think that one re-manufacturer installs oversized rollers so that the old flat spots on the rotary ramp never come in contact with the new rollers. I like your explanation but don't you think that all TA's will eventually fail from prolonged and hard use. The repeated jamming of the rollers under high load and high rpm conditions has to take its toll.

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Dick Davis

02-07-2001 04:24:25




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 Re: Re: The Myths of the TA in reply to Wardner, 02-07-2001 01:18:17  
Thanks John nice explanation. I've read the book more than once and your version is clearer. If anybody wants to practice TA repair I have a SMTA that is available. It still functions but I am dreading the shutdown John experienced.



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George

02-08-2001 06:05:34




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 Re: Re: Re: The Myths of the TA in reply to Dick Davis, 02-07-2001 04:24:25  
John in Iowa:
Thanks for helping us all out! now that my 450 needs a clutch I will be fixing my ta, do you remember who has the re man roller clutch for $117
have heard good things about Hy Capacity but I don't think they sell retail, just dealers may be mistaken tho' Thanks again, George



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