TH350 1971 Cutlass

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#1
Make
Oldsmobile
Model
Cutlass
Year
1971
Miles
58,000
Engine
350 Rocket
i everyone,

I have the transmission from my 1971 Cutlass off and in my basement, taken all apart right down to the bare case. The "modules" still have to be broken down and rebuilt, but I am following the instructions in the TH350 rebuild guide by Cliff Ruggles and haven't gotten to that part yet. I am basically on the page where he is pressure washing the case off. I have labelled zip lock bags all over the place and all the pieces have been carefully placed on the table in the order they were removed. I also have a lot of pictures taken throughout the disassembly. So far so good I think.

The only thing that my inexperienced eyes have caught that was an obvious issue is that one of the 17 springs at the low/reverse area was broken. It came out in one large piece and two small pieces. What kind of issues could this cause in terms operation?
I found this: https://www.ebay.com/itm/GM-Turbo-TH...-/221720709529
It says it fits anything from 1969-1986, but it was noted in the guide that in later model with springs are attached where mine are not. Would there be any issues replacing mine with one that has them attached? The only visible difference I can see is that the face of mine was smooth where this one has holes where the springs attach on the other side.

I also noticed that the valve body gasket was basically like plastic where the new one looks to be paper like and flexible. I don't know if this is normal or maybe the old gasket just became brittle and was causing leaks.

Other than that nothing looked obviously broken or worn out so far, but maybe I will find more once I get those modules opened up. One thing that I saw and thought might have been an issue initially was on the valve body side of the case, there were what looked like two large broken holes right near where the shifter linkage connects. I thought they were not supposed to be there because the edges seemed fairly jagged, but after looking around it seems like they are all like that and it would be really strange for something to punch a hole of those shapes in those spots. There was also no debris or metal in the case.

Anyway, if someone knows what problems that broken spring would/could cause and if the newer style assembly is interchangeable I would really appreciate it. Thanks! 20190303_125251.jpg 20190303_125548.jpg 20190303_125605.jpg
 

billr

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#2
Left-hand picture (springs):
Nothing too exciting there. The broken spring would result in slightly poorer engagement of that clutch, but I doubt you could ever notice. The TH350 is pretty "robust", so slipping with a stock engine is unlikely; especially in a lower gear like 1st. And how often do you use WOT in R??? The bigger concern with the broken spring is that the little bits could migrate somewhere and damage gears. clutches, jam things, etc. You are past that now, and it doesn't look like those pieces wandered anyway. As to the replacement of a slightly different design, I think it will be OK.

Center picture: I'm not sure what I'm looking for there

Right-hand picture: That looks like a clutch "druml" to me, with a couple of holes broken into it. I'm not liking that, but would like to see more pictures.
 
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#3
Hi,

That is good to know and a bit of a letdown at the same time, lol. The issue that lead to the rebuild was not having third gear. We tried all the exterior issues like kick down cable calibration, vacuum pressure, the modulator that the vacuum connects to, the governor, shifter linkage calibration, nothing made a difference. I was kinda hoping that broken spring might have had something to do with it.

The picture from the valve body side is in looking at those holes just from the other side. That was what concerned me was that they look jagged and broken rather than designed to be there, but from the other side they seem to fit and it would be unlikely they could break that way. I am trying to find other pictures on line to see if they are there in others cases or not. There was no debris matching this in the pan, but that isn't to say someone changed the fluid before and discarded them...

Anyway, thank you for your help. Worst case if I had to find another TH350 case to put everything back into that should be too hard.
 

billr

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#4
Do I understand correctly now, the center and RH pictures are of the same part (case), from opposite sides?
 

billr

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#5
The case looks thin there, those could just be casting "flaws" where the metal didn't flow all the way.
 
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#6
That is correct same case and area, just from both sides. After looking through my guide I can see in a couple of pictures that one of those jagged looking holes looks to match the same, so I think you are right. That is good to know. I would rather not go hunting for a replacement case.

I will hope to find something wrong with the remaining bit of disassembly I have left that would explain the third gear issue. If not I have been told I may not find anything obviously wrong - could just be a small fluid leak internally that will be fixed in the rebuild that I may never know about. And that would be fine with me. As long as it works after it is re-installed I will be happy.
 

billr

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#8
It has been years since I worked on a TH350, but I think there is a planetary-gear unit (the planet carrier itself) that is tender and often goes bad.

Post a close-up photo of one of those holes in the case, we may be able to tell if they are cracks or casting flow. If they are casting flow, I still believe the case is OK
 

grcauto

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#10
This guy is a very good tranny man and his videos will explain the common problems and how to correct them.
He goes through the entire tear down and rebuild of this tranny.
 
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#11
Thanks, I will check them out.

Here are a few more pictures, I held a paper towel behind it to try and make the holes show up better. Looking at it closely there are not any hairline cracks or anything like that and from the outside they do look clean. A few people, similar to what has been said here have told me that it is just the way the casting worked out and it is nothing to worry about. It has also been suggested that I could gently take a dremel type tool and smooth them out if it is something I am concerned about, but as long as there are no loose pieces it will be fine. What do you guys think?

I also found a fairly cheap direct replacement plate and springs as pictured above. I only need the one but it can't hurt to have them all. I see there is a similar piece somewhere else in the transmission. Hopefully it uses the same springs to if any of them are damaged I will have spares.
 

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grcauto

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#12
I think the area I thought was bad was the other pictures and the angle. That looks OK. Was there any pieces, other than the broken springs, floating around inside? If not, I think the case is OK. Check out his video.
 
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#13
Thanks grcauto, that is good to hear. There was nothing in the pan and the fluid actually look fairly good so I suspect it was changed not to long ago so anything that was in there is gone. We just got it last year.
 

billr

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#14
Looking at the new pictures (2nd one, mainly), I still think the holes were there when cast.
 
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#15
I was leaning that way with my limited knowledge but am confident they were now with everyone elses opinions and some online pictures and videos I was able to find. Thanks for the help.

Any special steps to clean the case or just coat it with degreaser inside and out, scrub and pressure spray?