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700R4 slips for a second, why?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigBurban350, Aug 12, 2002.

  1. BigBurban350

    BigBurban350 1/2 ton status

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    I rebuilt my 700-R4 tranny in my truck because it lost 3rd gear, it lasted for about 142,000 miles. I replaced the clutches and steels, and put new seals in where easyly accessable(I had to do it in about 5 hrs of time). I also installed a B&M shift kit utilizing the RV/Off-road option. The 1st to 2nd shift at low/half throttle shifts nicely. Then the 2nd to 3rd shift at medium/full throttle will slip up about 200 RPM for a split second and then shifts firmly. Its like how a school bus shifts, you hear the RPMs raise at the shift then drop as the clutches engage. Does anybody know if the shifting is normal? Is it the RV/Off-road option of the shift kit doing that? I'm afraid its wearing my 3rd gear clutches. Thanks for any help /forums/images/icons/wink.gif
     
  2. Blue85

    Blue85 Troll Premium Member

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    Maybe you could list out for us the changes that you made for the shift kit. You are experiencing "flare up" in the 2-3 shift. I used to get this and I actually solved it by converting my servo to a Corvette servo (my kit was a B&M SuperTrans Kit). The 2-3 shift is the most difficult one to get right in a 700, since it is the only shift with overlap. The 2-4 band releases and the 3-4 clutch applies. Time it too tight and you get binding (bad). Time it too loose and you get flare up (also bad). The 3-4 clutch is usually the 1st one to fail anyway, and this slipping will accelerate it's wear. The reason the 'vette servo helped me is that it has greater surface area, so more oil flows to engage and disengage it. This makes it slower, so the 2-4 band takes longer to pull off and it matched up better with the application of the 3-4 clutch. It also engages slower, but this doesn't matter since the 1-2 shift involves application of the band only. I couldn't get anyone at B&M to confirm this directly, but I suspect that they tune their shift kits for the 'vette servo, since they put it in all of their rebuilds. The 3-4 and 4-3 shifts truly are unaffected. The band is applied and released just like in the 1-2 and 2-1 shifts, but it is done with a seperate portion of the servo, which is unchanged.

    If you want to change the servo, you only need 2 parts. It is like $35 from GM for both of them. I can get you part #'s if you want. You might also get a whole servo assembly from local tranny shop.

    You have two other options, though.
    First, you can reverse the whole shift kit or the portion that is causing the flare.

    Second, you can work on the 2-3 sequence valve, which is what times and controls this shift. I have not tried this, but it may be as easy as trying some different springs in that valve. If you are intersted, we can look at this in more detail.
     
  3. Monster

    Monster Registered Member

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    I dont know much about Trannys but I just had my 700R4
    rebuilt and had a Trans go shift kit put in. I asked my tranny guy about the B&M shift kits and told me your out of your F#*king mind to use one of those. What ever the B&M kits do for the 700R4 is not good.

    Maybe he is wrong I Have NO IDEA.
     
  4. tipoil

    tipoil 1/2 ton status

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    just put the "street and strip"kit in .
    if it still slip then ur trany is bad .
    the b&m kit for the 700 is good ,u just have to put the stage 2 (street and strip) and this thing should kick butt!!!
     
  5. ftn96

    ftn96 1/2 ton status

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    Well, I dont have any experience with B&M. However, I can tell you that the kit TCI puts in their Street fighter will turn your balls inside out while breaking your neck--(if you hold it to the floor).
    Right now with a stock 350, minus headers, K&N, 36" TSL'R's, 4.56 gears and the TCI deal, I can make my rears bark pretty hard going from first to second. While BLue and I have experimented with the shift kit setups, I think Blue is dead on the money with the Corvette servo and using it with just a touch more firmness, I believe you would have the kick a$$ setup.
    Another thought on your flare up.....What torque convertor are you running? If you have a bit too high a stall and too high gear ratio you can get this too. The 700 shifts a little firmer than most trannys right from the factory, mostly due to the extra low first gear, which causes your pump pressure to increase considerably. Then when it does let go, you get Shaaa, bang..../forums/images/icons/laugh.gif
    Follow Blue on the tranny stuff. He wont send you down a dead end street. /forums/images/icons/grin.gif
     
  6. BigBurban350

    BigBurban350 1/2 ton status

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    I guess I will find a corvette servo and hopefully it will solve the problem. Other wise I could just buy another B&M shift kit and install the street/strip stage, which is easy to do anyway. Thanks for the help /forums/images/icons/laugh.gif
     

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