I did add the additive to the stock rear diff. I just used regular oil on my stock diff. didnt want to find out if changing to synthetic made It unhappy. used synthetic in the 9 in. im using now.

 

Ok, will do. I know u said you're not a transmission guy but maybe the same advice for trans oil, stick to conventional to be safe?

Just curious, is it really a thing with old trans fluid's composition or properties kind of marrying itself to the old transmission internals, almost in a symbiotic way? Or, is that a fallacy? I've heard that "fear" for many years here and there that changing the fluid with fresh screwed up the tranny but I never really researched it for its validity.

 

really old trans fluid will get particles of clutches and other wearable parts in it and its said it helps the trans clutches to hold. if your changing the filter and oil in pan stick with regular trans fluid. a large part of the old oil is still in the trans and converter and oil cooler.

 

So, does a total flush (including converter) make it less risky to replace with synthetic since only a nominal amount of old fluid would homogenize with new? Or, am I still flirting with disaster. A flush seems more for owner satisfaction anyway. It doesn't "fix" anything except maybe lube the seals a bit better and keep some lines from getting cloggy. Unless it's slipping and whining of course, fresh blood can't hurt I guess but there's prolly other issues no fluids gonna help.

Ok, so I'll do diff fluid first as most damage should be obvious (hopefully). Then, the tranny next. I never knew that converter "shudder" was a thing and the 45mph symptom metric across the internet sounds way too coincidental.

Importante (maybe?): Since the pan is coming off should I torque the valve body bolts?
I guess, "Over time, the valve body gasket will shrink from heat and the bolts will start to loosen. The loose valve body can develop cross-leaks in passages. This will cause your transmission to fail. Tightening these bolts properly will prevent this problem". So, a few others I looked at said it may be a good idea also but no more than 8lbs per bolt.

 

every time I got a flush with old fluid they made me sign a release that if trans failed soon after they were not liable. I just change the filter every so often. stock trans is still around here somewhere. burnt up the built one once, trans and converter so sent in and had both built stronger about 40k ago, changed filter at 30k clean and looked good, very little clutch dust on the bottom of the pan

 

So, are loose valve body bolts a thing u think?

 

lol got no idea. can't be good but being I've never seen it on here dont think its common.

 

Yeah, I was kinda thinking the same thing. A microns-thick gasket making bolts loosen enough to actually need a readjustment seems rare-unless they weren't torqued enough initially. If anything, as with a million other car parts, I could possibly see constant vibration(s) loosening up the valve body bolts.

 

Since I do the labor myself on everything, I can get the highest quality materials available, usually. But, with a trans that has 127,000 miles, it might not matter, yes? Is there a longitudinally tested tried and true super fluid out there?

I have like almost 8 full quarts, prolly from 20 years ago, of Wally World Supertech Dex III, which Bob (oil guy) said several years ago was made by: Warren, Amalie, Citgo, ST, etc.. I guess it's regional, like a lot of wally world stuff. I've heard of Citgo but none of the others really. One of Warren's factories is 20 miles from me here in rural Southern Illinois and was, evidently, put here more than 20 years ago. Nothing on their site says Supertech is made by them so I still don't know.

Anyway, I guess the new Supertech stuff ain't perfect but it did pretty good in one review I looked at. Project Farm did a nice side by side with ACDelco, Mobil 1, Supertech, and Redline (winner). Overall, Supertech came in 2nd. However, in one of the most important variables, the wear test, it came in last. The Supertech fluid was the "newer" partially synthetic Dex VI though so no telling if it had a different viscous quality, as well as potentially other differences, to the old stuff I have.

Dex III isn't even made anymore and I guess and Dex VI is recommended now. I'm gonna guess that anything newish has at least a partially synthetic formula. So, even if I use the old Dex III now, it looks like, eventually, a blend or full synth is inevitable.

 

Ok, took tons more vids from several angles again underneath while axle floating. More strategic camera angles this time. The ones basically under trans had the clunky sound louder. And, when I trigger the clunk at 45 mph (still) u can see a VERY slight vibration in the back of the trans and the whole general area. Rear trans seal is leaking a tiny bit also now. So, changing the fluid and filter screen didn't help. It's gotta be the "45 mph torque conv shudder". I even took a vid of the engine and it's very steady.

I don't if it's normal but, while elevated, the tach and speedometer are not in sync during acceleration. They both stay synched initially to about 20 mph but then the tach drops off and seems to rise slower than I remember. I don't know where the tach should be at 30, 40, 50-55.