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18 Auto transaxle reassembly

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I apologize for asking a question that has probably been asked a 1000 plus times, but I have been unable to locate a thread discussing how tight to torque the four bolts holding the differential cases to the bull gear.  My repair manual simply states "tighten all bolts securely in sequence".  Is that ft. lbs. securely, or newton meter securely?  Seriously though, I know that bolts torqued below their specified limits can shear off or fail from fatigue forces.   I have torn apart several damaged D transaxles to find that everyone of their demise was the result of one of these bolts failing.  I was wondering if one of the D experts could direct me to an existing discussion of this matter, or give me some guidance.  Thanks!!

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Factory Dog-

 

I have been through that rear end twice on mine due to that darn parking pawl and the unhardened bolts. I would HIGHLY suggest that you upgrade those 4 bolts if you have not done so. That was a weak point from the auto 18 through the 1976 models. At that point they upgraded to a grade 8 bolt. When those bolts shear the heads off you are looking at about a 100% chance of that bolt dropping to the bottom of the case and getting caught between the bull gear and breaking the case. I would suggest you upgrade to a grade 9 and also put a mechanical stop on that pawl lever so it does not engage. 

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Thanks, I will look into the specs on higher grade bolts.  I had to disassemble four old rear ends to find one good parking pawl, the other three had either missing teeth or were worn down from riding on the gear.  I like the idea of installing a stop.   The three transaxles with broken bolts destroyed the casing just like you pointed out.  It would probably be wise to install new bolts any time one has the backend apart. 

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The pawl will break the gears when engaged and you forget and drive forward. It is not enough to hold back that power. When I sold mine a few years back I told the new owner "do not use the parking break, do not use the parking brake, do not use the parking brake". I said it at least 3 times in a row to get my point across. 

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Ken, keep in mind the ring gear {part#101622} and the two end caps {part #101621} that were on the 18 Automatics which used the 5/16" bolts, probably should not be bored oversized to accommodate 3/8" bolts; but, rather replaced with part #'s 105060 and 105061 as these were a little beefier in these areas.  One other benefit to the 3/8" parts, is the larger openings in the end caps, perhaps for greater lubrication to the pinion gears.

P.S. I am not saying it could not be done, I personally would not do it,: but, as you know my set up is for duals.

 

IMG_20160718_230312105.jpg

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Stevebo,  I noticed that the steel plate in front of the seat which locks the parking break lever in place was broken and would not have been able to hold the lever in the unlock position.  I wonder if that was what destroyed the original rear end?  When I picked her up the owner had already thrown another used rear end under her.  This replacement had a sheared key on the gear the pawl engages, so it did not work either.  For now I will put a bolt through the plate so the brake can't engage.  Thanks!

 

23 Auto,  I am at a crossroad at this point and not sure what I am going to do.  Due to the life changing events of the recent years, coupled with all the demands presently on this aging dog,  I am not sure if I will be keeping the old girl (18 auto).  I still need to restore my wife's electro 12, my Grandpas F14, an Advance Rumley steam engine, along with everyday stuff on the farm.  The rear end is on the bench ready for reassembly, but I really think it would probably be best to upgrade to the heavier components even if I decide to sell her.  I am assuming these parts are no longer available and I will have to find another parts rear end.  I will do some searching around and her set another week.  Thanks!!!

Edited by Factory Dog
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Two new to me pieces of info this morning:

 

" weak point from the auto 18 through the 1976 models."

 

and 

 

"grade 9" bolts!

 

I manage a hardware store and I've never heard of "grade 9"!  I will have to keep an eye out!

 

So only the "Automatic18"s and Ds up to 76 have this issue and the parking brake should never be used?  Later models were improved?

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Grade 9 is what I put in my D200

gr9.JPG

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On 7/18/2016 at 11:15 PM, 23 Automatic LSE said:

Ken, keep in mind the ring gear {part#101622} and the two end caps {part #101621} that were on the 18 Automatics which used the 5/16" bolts, probably should not be bored oversized to accommodate 3/8" bolts; but, rather replaced with part #'s 105060 and 105061 as these were a little beefier in these areas.  One other benefit to the 3/8" parts, is the larger openings in the end caps, perhaps for greater lubrication to the pinion gears.

P.S. I am not saying it could not be done, I personally would not do it,: but, as you know my set up is for duals.

 

IMG_20160718_230312105.jpg

Thought I would do a side by side of the end cap from an 18 Automatic (top) to an end cap from a D-180 (bottom) to illustrate the difference in the size of the openings for lubrication of the pinion/axle gears.

Please notice the "U" shaped cut-outs at 12:00, 3:00, 6:00 and 9:00 o-clock on the end cap in the lowest picture vs the little round holes in the top end cap at 3:00, 6:00 and 9:00 o-clock.

 

P.S. You may have to click on the image in order to enlarge.

 

IMG_20160731_105455.jpg

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Thanks for the pictures!  I have never seen the later assembly.  I found some information on the shear rating for grade 8 bolts.  It appears that the 5/16 has a shear rating of around 6,980 lbs. while the 3/8 is rated around 10,050 lbs., which is a very significant difference.  I am not sure what the grade 9s are rated at?  The bolts I removed from the ring gear assembly showed extensive wear.  The 3/8 bolts would provide a much greater wear surface along with the increased strength.  I am going to be very busy for the next couple of months, but I will try to make some calls and see what I can round up.  Thanks again for everyone's input!

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Thanks, that is an extremely important point that some folks may not be aware of.

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     It has been almost a year now since I started to reassemble the rear differential of my 18 Auto and it still sitting on my bench.  A fellow should never rush to quickly into anything!  During that time I did finally find a flush drain plug through McMaster-Carr.  As it turned out these were not standard 1/4" pipe plugs, but are what they call a flush fitting plug that has a 7/8" taper that differs from a standard plug.  They were only 60 cents a piece, but cost $3 for shipping.  I also ordered all new seals for the hydro manifold.  I also found that Motion Industries does carry a single lip rotary seal that is a replacement for the old parking pawl seal, it fit perfectly. 

     At this time I still am not sure if I will keep her, but it is time to get her back together and running.  There is a local gentleman who is interested in her, but I would only sell her to someone whom I know will taker care of her.  If I can find the parts I will upgrade the rear end differential, otherwise I will reassemble her using the older style having the 5/16" bolts.  The gears I have are actually in excellent condition. 

     I will probably have some questions when I start putting her back together, in fact there is one I already have.  Does anyone know where the relief valve kit goes, or if the 18 Auto even had one.  I have a couple extra valves, and am not sure if one of them had been pulled off of this tractor?  :unsure:

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There are two relief valves, a charge pump relief and an implement relief.  Both are in the pump housing.

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     Ooops! Sorry Pfrederi, I am referring to a remote set of relief valves that are contained in a box approximately 5" long, 3" tall, and 1-1/2" deep.  It is shown in my 1975 D manual as item number 4-110.  I don't have a clue what it is for.  If I get some time today I will try to take a photo, and see if my sweetie will help me get it on the computer.

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Posted (edited)

That was a dampener assembly they used on some years.  It was to relieve the strain of people jerking from forward to reverse.  Early and late models did not have it.  There is a manual or TSB showing how to retrofit it.  i bought one but have never gotten around to installing it.  Take your time going from forward to reverse and you will not need it.

 

 

Edit it is Service Assembly 101678

 

 

Edited by pfrederi
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Thanks Pfredre!  I will look the information over.  If I don't need it, I probably won't install it.  I am pretty easy on my equipment.

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           Finally made the decision just to reassemble the original rear end.  From what I have seen the problem with the bolts breaking off has had more to do with the nuts loosening than the actual shear strength of the bolt.  The 3/8" bolts may buy the tractor more time, but eventually they will fail also.  I am ordering some 5/16" - 24 grade 8 bolts to replace the 5/16" - 18 grade 8 bolts I was originally going to reassemble her with.  I learned that the fine threaded bolts have less tendency to loosen because of the lower pitch thread, along with a greater load capacity because the threads are not cut as deep.  I also read in the supplier descriptions that the distorted-thread locknuts have greater gripping strength than nylon-insert locking nuts of the same grade.  So I chose some center-lock distorted-thread nuts.  I wanted to upgrade to grade 9 bolts, but I could not find any with fine threads.  I want to thank everyone for their input.

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