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Mechanical Diode TA Question


Rick G.
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I was reading the other recent thread here titled “Looking at a 1086”. 

I didn’t want to hijack that thread so created my own thread here for my question. 

Will the experts here please edumacate  me about these so called “Mechanical Diode TA’s?

Say you are shopping for a tractor- How do you tell if the tractor has been retrofitted with one of these Diode TA’s? (Let’s say the seller has no clue one way or the other if you ask them)?

Is there any obvious external tell-tale signs of the modification? (I would suspect that there would not be any obvious visible external way of knowing)?

Will the tractor’s TA shift or act any differently than the standard TA to let you know that it had the Mechanical Diode TA installed?  

Bottom line- Short of asking the seller (if they even know and are being  honest with you), and / or seeing paperwork stating that the tractor does or does not have a Mechanical Diode TA, how does one protect themselves against buying said tractor if they do not want one with this style of TA? Or is it just a crapshoot?

Also, is this -Diode TA applicable to even older series tractors such as the ‘06, ‘56, and ‘66 series tractors, or is it exclusively an item for ‘86 series tractors? 

 

 

 

 

 

 

 

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The Mechanical Diode TA was an aftermarket (approved by CIH, still remember the CIH dealer days where they were extolling the virtues) replacement.   It was an attempt to replace the sprag clutch with a more positive acting system.   Instead of the sprag, it used a small welded assembly that had flat notched plates and hardened dogs springloaded to notch into them in one direction.  I remember the rep saying it was the same design as 1000HP dragsters used to shift gears fast. (no idea if thats true) 

You won't see any difference from the outside, it was a direct replacement for ALL the hydraulic TA's.  No external changes.  Since both designs do the same thing, you won't notice any difference in performance. (Well except the MDTA won't slip if the sprag is bad!)  Literally the sticker is the only indicator.  I assume the fact that these show up in 86 series is just the timing...released when 86 series were often the primary tractor.

I actually think these got a bad name due to some early mfg flaws....let me use my experience as an example.

1) We got a MD-TA and installed in our 1486.  One year later, it failed - tractor stopped in H or L...one ot the 2.  We tore it down, the weld holding the MD clutch pack together had broken, and allowed the assembly to chew itself to bits, filling the entire tranny with hardened steel chips.   

2) We drained, cleaned and replaced all the bearings, etc as well as possible...but we forgot to remove and clean out the differential!  Big mistake.

3) Installed a new MD TA under warranty.   Lasted less than 25 hours and locked up.  Tore down the tractor - realized that there were still chips all over the tranny.   Chips had gotten into the new MD assembly and locked it up.   Tore the whole rear end down completely and steam cleaned everything, all new bearings.

4) Installed a new MD TA under warranty.   Which is still in the tractor running just fine.

So, basically, because they did not have the original MD-TA welded properly,  it failed quickly and trashed the tranny.   Then because we were too "in a hurry" to properly clean out the transmission, it ruined another one.  The third unit is just fine.

Even though we went thru the above experience, I would not be scared of a tractor with the MD torque.  If its working now, its a good one, and will probably continue to work just fine.  

Others may be able to shed more light on these.

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You can install the Mechanical Diode T/A in any 06 thru 86 series tractor.  They used to come with a decal that you could apply to the tractor to indicate that one was installed.  Otherwise, you'd never know the difference.

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We used to own a 1066.  For a better part of the time that we owned it the TA was weak.  When the TA did get replaced, it was with a Mechanical Diode.  This would have been in the early 2000’s I believe.  Never had trouble with it, but we never used the TA hard either.

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Interesting info so far guys. Thanks for the knowledge. Keep it coming from anyone else who cares to chime in.

I must say that I’ve never ever seen any tractors displaying this sticker or decal that has been mentioned. Was there a specified location on the tractor where the decal  was supposed to be installed, or was it just random with no instructions on placement and anyone would just slap it on where ever they dang well pleased, or more likely not even put the decal on at all? And then on top of that there would be tractors that would get repainted and then the decal would then be gone, or it could just wear away or peel off or fall off I suppose. 

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6 minutes ago, Rick G. said:

Interesting info so far guys. Thanks for the knowledge. Keep it coming from anyone else who cares to chime in.

I must say that I’ve never ever seen any tractors displaying this sticker or decal that has been mentioned. Was there a specified location on the tractor where the decal  was supposed to be installed, or was it just random with no instructions on placement and anyone would just slap it on where ever they dang well pleased, or more likely not even put the decal on at all? And then on top of that there would be tractors that would get repainted and then the decal would then be gone, or it could just wear away or peel off or fall off I suppose. 

I put mine on the front of the battery box lol

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I worked at a case ih dealership when the mechanical diode TA's were the latest and greatest.   The decals tended to be placed anywhere.   Most were left in the box the TA came in. Many farmers were finicky about their tractor, so they were left off.  Several ended up on mechanics toolboxes and cabinets!  During that period,  my 856 needed a  TA.  I installed a Hy Capacity. 

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On 8/6/2020 at 11:21 AM, nepoweshiekfarmalls said:

I worked at a case ih dealership when the mechanical diode TA's were the latest and greatest.   The decals tended to be placed anywhere.   Most were left in the box the TA came in. Many farmers were finicky about their tractor, so they were left off.  Several ended up on mechanics toolboxes and cabinets!  During that period,  my 856 needed a  TA.  I installed a Hy Capacity. 

I have some extras still in my tool box.These were leftover when the tractor already had a sticker from the first MD TA.
 

We had mixed results with them. Later ones were better, especially after we started shimming the endplay in the TA.

 

EBAD9558-D870-4C87-8763-44B014AE29A6.jpeg

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When Allied was still in business I asked Jeff to show me the difference, and why or why not I would want one. After shown what they were, I was unimpressed and never installed one. The weld would break under any extreme load on that style sprag. Jeff-C-IL did a fine job of explaining how they were different and as others stated no difference in performance. If they got a good one, and didn't over stress it it would last a long time. I wish I would have taken a picture of it back then. Needless to say in my opinion they really were not worth a s..., well you get the idea. And I am as die hard IH as they come. The stickers are the most valuable part today.

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I installed a mechanical diode ta in a 3788 years back. That tractor was used to pull a 700 cu ft tmr mixer every day to feed cows. I also installed an extra hour meter at the same time to count running hours because the tach quit working. When the tractor left the farm my hour meter read over 4200 hours. This was daily use mixing feed and some occasional tillage. The ta still worked strong on both the high and low side.

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Had one put in our 1086.  The mdta went out in 25 hours.  Put another in and never had another problem in 4000 hrs before it went down the road.  Dealer said it was a manufacturing flaw.

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