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GM Overdrive....700R4

Discussion in 'Off Topic Threads' started by over the hill, May 18, 2011.

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  1. over the hill

    over the hill Active Member

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    I'm playing around with a 700R4 GM overdrive for a friend that was to alleviate boredom this past winter.

    Anyone a Trans. Tech???

    In setting up the clutch packs in the input drum, I find a host of specs.

    A video says to give the 3-4 clutches about .010 per clutch or about .070 total.
    Gil Younger of Transgo says he likes .015-30 total
    An ATSG book I have says .049-.113.

    Since I have no past experiences with Overdrives, what do you like???


    Thanks....Regards....Gerald
     
  2. Quack Shot

    Quack Shot Active Member

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    It's been a long time, but I seem to remember about .050", or a bit less, as the total target with new plates.
     
  3. grntitan

    grntitan Well-Known Member

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    Put a B&M shift kit in while you have her apart. It will make it shift more agressively and will actually help it last longer. They aren't too bad to do when you have it out. I've installed several laying on a creeper on the older 350 turbo transmissions. Not fun to do while laying on your back. Its alot easier to keep the little metal balls in place when doing it on a work bench.

    The smooth shift that most auto transmissions have now are kind of a controlled slip and puts undo wear on the plates. Just say'n...............
     
  4. Straight99

    Straight99 Member

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    grntitan is right about the GM 700R4. You do not want this trany to slip. Shift kits are the way to go.
     
  5. CalvinMD

    CalvinMD Well-Known Member

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    Between .050 and .060...the 700r4 has a lot of good factory parts available by just specifying you want the late 80's Corvette componant....just switching to a lighter accumulater spring and Vette governor and mild rv style shift kit makes for a sweet street rod trans with crisp shifts just a bit over 5400rpm..perfect for a mildly hot smallblock
     
  6. K-GUNS

    K-GUNS Member

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    Early models of the 700 r4 had internal leaks,actually tried to apply the reverse unit when it was in drive-they drilled a small hole in the reverse to relieve pressure but when you did go into reverse it took several seconds before it would engage then. Otherwise you would hit reverse, hit the gas and the engine would rev until pressure would build then snap in and chirp the tires. There were several shop bulletins floating around but that was back in 88-89 I think. They were junk back then but have come a long way. Many people use them for racing now days.
     
  7. AveragEd

    AveragEd Well-Known Member

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    cl3, your memory is correct - the early THM700-R4s were problematic. In fact, the first few 1982 trucks we got in with that transmission were actually recalled before they arrived at the dealership and we had to replace the transmissions before we could sell the trucks. A few years later, GM got the problems sorted out and it became a decent unit.

    You don't mention what model year that transmission is but I would check with a dealership for TSBs on updated parts before you reuse any for which there are better replacements or buy new ones that are not updated. As I recall, there were improved versions of just about everything inside the early ones.

    Ed
     
  8. Shooting Jack

    Shooting Jack Active Member

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    Not to steal this thread, but my pickup has a chip in it and it has very firm shifts now. Is that bad or good for the transmission? I like to feel it shift and hear the tire chirp ever now and then. Jackie B.
     
  9. AveragEd

    AveragEd Well-Known Member

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    If it has an overdrive transmission, and most electronically-controlled transmissions are, I'm not so sure I'd want tire-chirping-firm shifting - that's pretty hard on carriers and the ones in those units aren't the strongest.

    Ed
     
  10. showdawg

    showdawg TS Member

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    The 700R4 shifts with decant cable & fluid pressure, the late trannys are electronically controlled, and fluid pressure can be increased through programing or chips, ect. ( Thats why u get firmer shift when u put a late model Chevy in "Tow Mode", the fluid pressure along with shift points are changed electronically) The shift kit simply diverts more volume of fluid to certain areas of the valve body which makes the shift very firm when the shifting governor does yield to fluid pressure. ALL & I mean ALL 700R4's need a tranny cooler. they tend to really heat up in OD, and any towing what so ever torches em.
     
  11. grntitan

    grntitan Well-Known Member

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    Great explanation showdawg.


    Eds right but usually a firm shift is better than a long winding shift. Alot of vehicles were made to shift very smoothly. This was achieved by lengthening the shift as if it were slipping. A firm shift is alot easier on your clutch plates as it doesn't allow the slippage. I think there is less parts wear with firm shifts than soft winding shifts. With most shift kits there are options to customize the firmness. Like anything though it can be abused and cause damage. I've always found the worst thing for a transmission is to add more HP/TQ without upgrading the driveline.

    Now with alot of the new Computer controlled transmissions, they/you can simply use a programmer and adjust. Personally i love when the tires chirp at every shift.
     
  12. Quack Shot

    Quack Shot Active Member

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    One of the newer strategies with the computer controlled units under load, is to back off engine timing just before the shift and then make the shift as fast and hard as possible. Once the engine timing is restored, the shift would have felt "soft". There is very litle slippage when they do this as a result. It all happens rather quickly, so you really don't feel much else, other than the impression of a "soft" shift.
     
  13. AveragEd

    AveragEd Well-Known Member

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    Quack's right - I forget the GM nomenclature for that feature but they introduced it for the 3800 V6/THM440-T4 combination first (in 1987?) and it reduced transaxle failures due to part breakage so much that they started including it in more powertrain packages.

    "Transmission Controlled Spark"? Or was that something from the carburetor emission control days?

    Ed
     
  14. justanother99

    justanother99 Member

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    When I built the 700R4 in my truck, I used the heavy duty 3/4 clutch pack that allows you to put in up to 9 frictions and 9 steels. It seems to me that the recommended clearance with that kit (for the life of me, I can not remember the manufacturer but it's listed in the TransStar catalog) was about .030 to .050 It includes the frictions, steels, pressure plate and a different snap ring. There are a couple of different options for setting up the pack depending on if its for heavyduty/RV or street/strip. I also like to replace the 2-4 band servo with the Corvette servo package. Those mods in addition to the TransGo shift kit make for a stout 700R4.
     
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