4R75W\E transmission case bore issue (4R70W/E, AOD, AODE)

[PenguinPin]

I'm rebuilding my 4R75W transmission. I found a chip inside the rear bore. The damage is located at the top of the bore, so I didn't even notice it on the first inspection.
Now I've been trying to find a reasonable solution for a week. I would like to share the results of my little research and I hope more experienced mechanics will share their knowledge.

What's happened with the rear bore
Here's the evidence

You can see the three lanes where the output shaft metal rings rides. Most of the damage is between two and three lanes. However, my output shaft only had side-to-side play, but not longitudinal play. So I have no idea how these furrows happened here.
Is this related to the transmission failure
Doesn't seem like that. Panther platform, 140k miles, never been hardy pushed, but tranny oil never been changed. Seems like OD bore wear caused wrong pressure and burnt forward clutches. Has nothing to do with the rear bore.

How to fix it
I found two ways to get rid of this problem
#1. Get a "new" used case. Guess what's wrong with this? This is a very common problem, so It's very difficult to find a case in good condition these days. There aren't that many cases on sale. All of them have who-knows thousand miles. Although "new" cases do not have such large furrows, the overall condition looks worse than my case. I've even seen cases with little furrows on sale.
Some sellers like to sand down the bores to remove marks from the metal rings. I wondering how bad it was before sanding? This is a cosmetic renovation that is unlikely to make it better. On the contrary, I believe that uneven material removal may cause faster wear in this area. Here is an example of a sanded bore (you can see that even after sanding some deep damage remains):

It all looks to me like bargain one trouble for another.

#2. I found a solution that at first glance seems like a panacea - installing a repair sleeve. Part number is T-1695-SLE, sleeve is available on transend. It requires a special tool (T-1695, reaming tool casting number is TA-103). But this tool has long been discontinued, not many transmission shops have it. The only visual instructions I found were on this forum: How to: - 4R70W Transmission Rebuild Diary
Here's a photo of the tool and the installed bushing, taken from the instruction:

Guess what's wrong this time?
I wondered why the tool been discontinued and why it is so difficult to find a shop that can do this repair, until one mechanic told me he had used this repair in the past, but it created issues. He said that new bushing will spin in the case no matter how I secure it. If so, then this is very critical, because when rotating the bushing will block the oil supply channels.

So I'm confused

1. Does anyone know what could be causing the damage between the metal rings?
2. Has anyone had experience with these repair bushings? Are they really that bad?
3. As a last resort, I could gently sand the damage a little until it is smooth (especially in the metal ring lane) and keep my case. Is this a bad decision?

 

[JK080]

1. Does anyone know what could be causing the damage between the metal rings?
2. Has anyone had experience with these repair bushings? Are they really that bad?
3. As a last resort, I could gently sand the damage a little until it is smooth (especially in the metal ring lane) and keep my case. Is this a bad decision?

I wouldn't worry about the damage to the case that is between the ring contact area, nothing rides there anyways. I would be more concerned about the undercutting the last ring has done to the case.

I would find a shop that has that tool and have them sleeve the case and also install a new case bushing for you, they are tricky to get right.

Here is an example of a case sleeve that I did on one during a rebuild.

This wear in the case has nothing to do with the forward clutch failure you are describing, most of the time the forward clutch will fail due to low fluid or a cracked forward drum and even the clutch can disintegrate due to age like the ones in the picture.

 

[PenguinPin]

Thank you, K080!

I would find a shop that has that tool and have them sleeve the case

What do you think about spinning this sleeve? Loctite doesn't hold it very well. It may make sense to make notches on the case and then fold the sleeve into these notches, similar to how it looks on the pump bushing. Have you ever tried this?

between the ring contact area, nothing rides there anyways

This is the whole mystery. Any ideas what could have caused this damage? I can't shake the feeling that my transmission is under-repaired until I find out what caused it.
Stupidly, I threw out the old filter. However, no critical damage other than clutches was found.

undercutting the last ring has done to the case

This is some photo effect, in reality it is smooth, I can’t even catch it with a hook.

 

[JK080]

If someone had that sleeve to spin then their tool cut the bore too large. I have done at least a hundred of these sleeves and that sleeve fits every tight and with loctite that thing isn't going anywhere. I have even had to sleeve a sleeved case before and had to use the tool to cut the old sleeve out.

If there is no undercutting I would just hit the bore with some emory cloth and run it. That damage was most likely done during the assembly of the transmission at one time and it's in an area that won't cause you any issues.

Another area to be concerned with is the overdrive servo pin bore wear in the case, we sleeve that too with a brass bushing. Also, the Pressure Regulator valve and the AFL valve in the valve body cause lots of issues with this transmission. Look over and read some of the Tech Resources found in the 4R70W section on Sonnax's site, lots of good info here.

 

[PenguinPin]

had to use the tool to cut the old sleeve out

Cool. Does your tool have casting number TA-103?

That damage was most likely done during the assembly of the transmission

I thought about this too, but doubted that this could happen at the factory. But I completely agree that this will not create any issues.

the overdrive servo pin bore wear in the case, we sleeve that too with a brass bushing

I hope the sonnax overdrive servo pin will be enough in my case, my OD pin has only minimal side-to-side play. Especially considering that I have not encountered the symptoms described on the pin bore sleeve sonnax page.
I plan to use sonnax zip kit, and then use a vacuum test and find out if this is enough.