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TH350 Rebuild Thread part i

Discussion in 'The Garage' started by fireplug, Mar 9, 2007.

  1. fireplug

    fireplug 1/2 ton status

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    Part i The Research

    I will be rebuilding my TH350 myself, as a first timer! I of course will document, and photograph the entire process and hopefully it will make for good informative reading in the end.

    With your help, let the 'build' begin;

    I am hoping to install a valve body with compression braking. However I need to clarify some of the terminology with you guys first.

    I am looking to be able to put the transmission into a low gear and have the tranny limit my speed on a downhill just like a manual tranny would.

    TCI uses the term "engine breaking" in relation to an available valve body for the 700r4, while I don't believe this is literally engine breaking, I believe it is the effect I want. Can anyone confirm this? The part number for the 700r4 is 376015 http://www.tciauto.com


    B&M has a "Transpak" kit, the description includes, "downshift at any speed and hold...for heavy loads downhill..." there is a stage 1 or 2 kit available. This is part number 30228. Is this going to give me the desired effect? http://www.bmracing.com/index.php?id=products&sid=2&cat=13

    Art Carr's full manual has compression braking in all gears http://artcarr.com/catalog.pdf sorry no direct link.

    While there has in the past been some doubt as to whether such a valve body exists, I know it does as I remember a member posting he had one Jequist? That said I don't recall what company it was so any leads would be appreciated.
     
    Last edited: Mar 10, 2007
  2. boz42

    boz42 1/2 ton status GMOTM Winner

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    engine braking & compression braking are the same thing. try art carr, i think they make a valve body like that.
     
  3. LVJimmy

    LVJimmy 1/2 ton status

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    IF you keep the band installed and leave a large dia. convertor you should retain engine braking. Is there some reason why you don't have engine braking now?
     
  4. fireplug

    fireplug 1/2 ton status

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    Well, I won't rule out that my tranny is not up to par, but as far as I know automatic transmissions don't hold a vehicles speed in control very effectively in stock form. Am I off base on this?

    In addition I'm interested in manual/auto or full manual operation. Likely I will go reverse pattern as well.

    Thanks Boz42 I'll check that out now.
     
  5. roadnotca

    roadnotca 3/4 ton status

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    A full manual valve body is not streetable. That doesn't mean you couldn't drive it on the street, its just you or parts won't last long. Full manual is drag strip material.
    With a reprogramming kit, you can "leave it in D" or select shift. What that does is when you select first, it will stay in first (not upshift). Same with second. If you leave it in second and come to a stop, it will downshift to first, shift 1-2 as normal auto shift as you accel, and not upshift to third.
    Say you're at a crest of a hill, looking down. Drop to first and it will hold first, exactly like stick shift. The variables in the kits is the default auto shift point, and shift firmness.
    It really is the trick set-up for on/off road vehicles.
    My .02, TCI TranScat.
    To rebuild the TH350, you need this book; TURBO HYDRA-MATIC 350 HANDBOOK by Ron Sessions. ISBN 0-89586-051-1.
    Read/scan the book before you buy parts.:D
     
  6. LVJimmy

    LVJimmy 1/2 ton status

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    Automatics don't engine brake as well as a stick due to the torque convertor. some of the automatics will force an upshift at a certain rpm which can be overridden with a shift kit. Just for fun put you truck in manual first bring it up 4000 rpm, or whatever you feel safe with, and let off the gas. The tranny will cause engine braking, your RPM will stay above idle speed.
    Just wondering if you could be thinking of something like the engine braking you see/hear on semi trucks, they use exahust braking.
     
  7. fireplug

    fireplug 1/2 ton status

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    Great info! Thanks. :bow:

    If you don't mind I'd like to pick your brain a bit more in regards to the "reprogramming" kit. I haven't seen that term used yet. You gave the TranScat (you called it TCI but I assume you meant B&M?) as an example, do you know of any others?

    I will have to do some more research to decide on the auto shift point.

    Thanks too for the suggestion to read before buying. I knew to get the book but wouldn't have waited to order the parts.
     
  8. fireplug

    fireplug 1/2 ton status

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    In my original post I started to get off topic debating the terminology of engine/compression braking and yes exhaust braking. I do have some working knowledge of the latter as I have my truck license.

    However the effect I'm looking for, as mentioned, cresting a hill, dropping the tranny into 1st and having the truck maintain its speed and thus control.

    So it is your opinion then that with an appropriately chosen and operating torque convertor that I will get the effect I'm looking for?

    Thanks for the input!
     
  9. LVJimmy

    LVJimmy 1/2 ton status

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    You will get engine braking but it will not work as well as a stick, due to convertor slipage. The only way that I am aware of to get the same engine braking with an autmoatic as a stick it to remove the convertor like some circle track cars or to use a transmission with a lockup convertor that has had the wiring modified to stay locked-up unless you flip a switch to unlock it.
     
  10. roadnotca

    roadnotca 3/4 ton status

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    Auto slippage maybe 10% at the worst??? Fireplug isn't deciding between auto or stick, in this thread.
     
  11. roadnotca

    roadnotca 3/4 ton status

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    I have an '85 Burb. I built the TH350 with that book (all heavy duty). I have an external trans cooler, tranny temp guage, TCI TransScat kit programmed for RV/Tow, TCI torque convertor for 4X4, and HURST Promatic2 floor shifter. It holds lower gears for descent. Whats also cool is holding gear for level or climb, like keeping the trans from up-shifting so as to keep the wheels spinning through mud or sand.
    Its Heaven.:D
    Edit; whats cool with auto for off road is you don't need three feet.:haha:
     
  12. LVJimmy

    LVJimmy 1/2 ton status

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    He is looking for engine braking similar to a manual. 10% slippage at worst only works when your are at a constant speed. Otherwise a 10" convertor wouldn't be any different than a 12" convertor. Upon acceleration and deceleration slippage increases.
     
  13. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    With my 700/241 in low box, going down trail so steep you'd have trouble walking them, my engine breaking keeps the truck to a very slow walking pace. That's with a TCI Transcat kit and RV/HD converter. You don't need much more than that!
    Don't forget that your R&P ratio will have an effect on this too.
     
  14. fireplug

    fireplug 1/2 ton status

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    Good stuff guys, the discussion is very useful!

    I realize I was confusing the TCI Trans-Scat with the B&M Transpak. I missed that on the TCI site.

    EDIT - ok, thanks again guys! So far TCI's Pro Super Kit which includes the Trans-Scat valve body is the way to go. My guess is that I'll go for the 'Ultimate' kit which is described here,

    Many of our popular overhaul kits are available in 'Ultimate' format as well. What's Ultimate? Quite simply, it's the best friction elements you can purchase. Best suited for applications exceeding 450 horsepower, TCI® Ultimate kits include Alto Red Eagle® clutches, Kolene® treated steels and extra-wide Red Eagle® Powerbands™ bands where applicable.

    I haven't confirmed that this is in fact available for the TH350 but I assume it would be. I find the TCI website is difficult to navigate.
     
    Last edited: Mar 10, 2007
  15. fireplug

    fireplug 1/2 ton status

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    For the benefit of others in the future I'll make sure to answer any questions, or uncertainties as I solve them.

    As such; the kit is available for my application:

    GM TH350, 1968 and later, non lock-up.

    It is NOT available for 1980 on according to the TCI site.




     
  16. roadnotca

    roadnotca 3/4 ton status

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    328800 and you're on your way:D
     
  17. fireplug

    fireplug 1/2 ton status

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    :D So far so good! Thanks again for the help. Stay tuned.
     
  18. fireplug

    fireplug 1/2 ton status

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    Lock Up?

    Ok, I'm just about to order my parts so I guess I better make sure I've properly ID'd my tranny.

    How can I determine for certain whether my tranny is Lock Up or Non Lock UP?

    TIA, Jason.
     
  19. roadnotca

    roadnotca 3/4 ton status

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    Ron Sessions' book covers that.
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd suspect like all other lockup GM trannies, there will be a little port/nub at the tip of the output shaft.

    Unless someone knows the EXACT location and design of all TH350 TCC plugs, I would not assume anything.

    There were plenty of TH350's made that had electrical connectors on them, but that was for timing/emissions scheme, not TCC.
     

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