800 t-case question

[bigford]

I bought another t-case (13 and was going through it to make sure all was well; checking the sprags, replacing the seals and gaskets etc. I started to remove the large cover (the front drive was already off) according to the TM and could not get the input shaft to slide out of the bearing. I ended up removing the keeper and pushing the bearing out the back side of the cover. This was not easy. There was no way this could be reassembled with the bearing on the shaft. Using some brass wedges, a BFH and a gear puller it finally came off (undamaged I think). My plan is to reinstall the internals and put the cover on, then press the bearing back in. All of the references I found in several TMs did not mention the input shaft bearing as far as taking the unit apart and putting it back together. They did have checking procedures.
It is possible that I did not find the correct TM BTW.
Does anyone have any comments on the correct way to remove and reinstall the bearing? The one thing I did find after I got it off the shaft was there was some type of locking material on the shaft, almost like JB weld but I don't think it was.
Thanks in advance...
Jim

 

[Tornadogt]

Not sure if this helps any but, Loc-tite makes what they call "Retaining Compound" it is used for Slip fit bearing to "Lock" them to smooth shafts and lock races in place. I am not sure if it should or should not be on that bearing but maybe what was on it when you disassembled it.

 

[MatthewH]

Loc-tite calls it "609". Its a bearing retainer, designed to "take up" up to .005" tolerance between the bearing and the surface it rides against. It has similar characteristics to blue loc-tite, in the working times and temp range.
I used some when I reassembled my NP205 for my M37, required a puller to remove the bearings when I tore it down later

 

[tobyS]

I had mine apart but there seemed to be no interest here for me to document it, so I didn't. My pleas for help were unanswered.

Since I had the main gearbox apart about 3 times and and the sprag portion off about 10 times, I can probably help you. I dropped one of the sprag retaining rings under my pallet and it gave me fits until I found it.

I had a hard time with finding anything useful in the TM but eventually found a parts breakdown (that helped me identify the missing retaining ring).

Mine was a new unit that was not set up right and all three shafts had serious play. But I had not driven it much, given all the noise it made. After getting it out and split apart, not a single part had any signs of wear, bearings had no signs of use and the sprag...brand new. All of it was virgin. Output seal was not even damaged yet...amazing.

I scraped for quite a while on the gasket and made a strategic decision to use aircraft form-a-gasket, which I'm glad I did for two reasons...it facilitated taking it apart and putting back together (stays pliable and can be jacked back apart if necessary) and second, it is thinner than the gasket and brings both housings together a slight bit more than having a gasket. It doesn't leak. Taking it apart on the sprag section was particularly important.

When I put it together, I removed all of the shims that tighten the bearing preload, so the case would seat tight. When it's all together, then set the pre-loads on the bearings. I stared with the input shaft first, then the intermediate and then the output. I pushed them all snug and got the feel of the rotation by hand turning it. Then I tighten the outer race by tapping it more snug and then rotating it. I felt the point that it would start to bind a little (very little). To be sure, I went a bit tighter and felt a binding. That was the difference in a light preload to a heavy preload, from what I can tell. I had no guidance, so had to devise my own strategy.

I set all with a light pre-load, doing them individually, so I could feel the changes in the rotation resistance. I reasoned that as it heated up with use, they would then be a little tighter. It should rotate very smoothly when finished. You should have a selection of bearing shims if you use the form-a-gasket and thus don't need as much thickness of shims.

Cleanliness is everything. I de-burred everything as I cleaned it. For reassembly, I used lubri-plate in every sliding surface which makes it smooth until gear oil is in it (remembering you may have it apart a couple of times).

If you get pictures to jog my memory, I can probably guide you through about any part of it. It sure would have helped to have found guidance here when I did mine. I thing the parts breakdown is in the TM and you should copy it for reference.

Toby

 

[bigford]

Thanks for your input Toby. I did find the breakdown in the TM, but the bearing seems to disappear from one frame to another. No worries though. Reassembly set for tomorrow provided the rain holds off. I'm going to put the big cover on and then press the bearing back in. The bore taper is on the outside of the top case so somewhere along the way my guess is someone decided it should happen like this.

Also thanks for the Loc-tite info. Most likely this is what was there. A little diesel and a scrubber removed it.

 

[tobyS]

Sorry, I don't remember a bearing pressing on from the outside. Only the flanges seemed to be a tight fit...and they did not require a press, just tap into place. Pictures would jog the memory. I especially struggled with the spragg shifter fork rod. The air shift is confusing until you realize the piston is working in both directions (and in my case I had missed a retaining ring at one end of the spragg).

I don't know about Loc-tight but Permatex aircraft form-a-gasket is resistant to most fuels and oils. Lacquer thinner or acetone would cut it, but if it cuts with diesel it may also not hold the oil entirely.

The outer race of the bearings should move relatively freely and when you assemble the main case, the covers can be left off (but the outer race still in place). I found that laying it down was easiest and after the case was put together, then put the outer races in from the outside.
You should have no resistance in turning all three shafts when it's assembled. The covers and shims are what set the preload on the three main shafts...and you must have them right before the spragg is put on...in my opinion.