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Old 04-19-2011, 05:18 PM
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Full Manual Turbo 400 Undo?

Hello Everyone,

I have a full manual Turbo 400 transmission that a local transmission shop modified for me. Is there any way for me to restore automatic shifting? I have two other 400s that can potentially be used for parts to accomplish this. I am in the early planning and research stages of weighing my options here.
I was thinking I could take the innards and swap them to another housing if necessary, but I just have no idea what was supposedly forever modified. I remember the guy telling me I could never go back to auto if he did the changeover.

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Old 04-20-2011, 02:21 AM
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well this is seriously not right, might be the clutchs, other words the pistons that squeeze your bands. Another thing it could be is your pump. Have you had this changed? Edit: also it could be your valve seals for drive, you might also have the wrong style convertor on it, not enough force to open the valves up at certain rpms. Could be wrong about the valve body, could just be the convertor or pump
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Old 04-20-2011, 03:07 AM
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Swap out the entire valve body, and consult the TECH ARTICLE WIKI/CRANKSHAFT COALITION under TH400 rebuild for guidance(see the header board). Not sure what 302builder18 is talking about; "might be the clutches, other words the pistons that squeeze your bands". Servos actuate/release bands (spring assisted release). Then, "force to open valves".??? Maybe he's referring to line pressure. Most "shift kits" will have 3 levels for trans performance, depending how it's to be used; street/towing, street/strip, full race(manual). Any idea what "shift kit" was used? It's got to be able to be taken back to stock, or some other level of performance.

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Old 04-20-2011, 03:39 AM
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well if you look closely at a transmission, apart the bands are the clutchs, and the servos are like pistons. The valve body lets in hydraulic fluid at a certain pressure and the servos push the clutch bands together, in first it would spin the planetary gears, even the sun gear and the spline, but with the bands tie some of the gears to the casing of the tranny. but then the which in this case make the plantarys stop turning, now thats second. therefore making a new higher gear ratio. And the same with the next set of gears, now am i correct? Thats how it is.
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Old 04-20-2011, 07:27 AM
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chevy302builder... I too have no idea what you are talking about. The original post is about a full manual shift t-400 that the person wants to convert back to automatic shifts.

leftyfork; This depends on what mods were made to the case and related parts for the full manual shift conversion.

Is this a forward shift pattern? Is it a reverse shift pattern? Different mods are made for different manuafacture valve body.

If the full manual shift was a TransGo kit , then changing back is easier
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Old 04-21-2011, 03:40 PM
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Thank you for responding. The transmission shop did the shift modifications on their own with no kit. It is standard PRND2L shifting, but full manual. It sounds like you guys are saying I can definitely undo the modifications. If I know that the clutch packs were setup with extra clutches and tighter tolerances, is my solution as simple as swapping the entire innards of the manual shifting transmission to another housing and valve body? I understand that I need to make some valve body modifications to get a nice street/strip feel while keeping it "automatic" Are all housings and valve bodies the same no matter the year?
The bottom line, is I want all the positive bullet proof feel of my manual shifting transmission, to convert over to automatic.
The manual shift transmission is a 78 OB, and the two transmissions I have to work with to hopefully make this happen are a 71 PD and a 73 P2T.

Kurt
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Old 04-22-2011, 01:57 PM
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o my bad... Conversion kits???? O wow i didnt know this intil now. Thought this was a transmission problem, consisted of the auto mechnism going out. Alot of times people have to manualy shift an automatic cause some of the stuff goes out.. column shift a car, i seriously thought there was a problem.. i feel stupid now sorry guys
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Old 04-22-2011, 05:25 PM
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It's all good, 302. When you get a chance, google manual valve bodies. They have reverse pattern manual valve bodies, regular pattern manual valve bodies, etc. It boggles the mind.
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Old 04-22-2011, 06:54 PM
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Some manual conversions remove a band, plug the accumulator feed, and disabled the servo for that band. There are also changes to the valve body.

What I would suggest is just getting one of the others rebuilt. The blue car in my avatar has a full manual Th400 in it with the mods I just mentioned, I wont be switching it back. I would just build another trans instead of trying to switch it back.
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