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Thread: 700R4 - essential to buy a newer case?

  1. #21
    Join Date
    Apr 2001
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    CA
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    13,573

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    You do not need a computer to control the 700. It wouldn't know what to do with it. On emission controlled vehicles, the vehicle's computer ONLY controlled TCC (torque converter control), which is only an on/off function. This can be easily configured for automatic or auto/manual function.

    You will not need the updated pump. The 1990 model should already have it. You will need the Diesel spec governor. You should use the low stall TC, but it is not absolutely necessary. I recommend it, but I know of a bunch of them that are using a gasser TC. With the higher stall converter, you will give up a lot of the low RPM torque, economy will suffer a little (all that fuel to wind it up is not needed to get going), your "effective operating range" will be reduced, as the redline on the Diesel comes in a lot quicker, and if towing, it will generate a lot more heat at lower speeds. If all you are using it for is a high-geared grocery-getter, the gasser TC may be fine.

    The Trans-Go shift kit is HIGHLY recommended, as a starting point. If you have the thing scattered on the bench, you might as well add in some other "near bullet proof" hard parts. Otherwise, drive it sanely and save up or collect the parts along the way. Don't be fooled by the "I'm only running it behind a 6.2L so I don't need much" idea. Many times more 700's have been killed behind a 6.2L Diesel than much higher production, high-performance SBC's.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  2. #22
    Join Date
    Aug 2006
    Location
    Edmonton Alberta, Canada
    Posts
    52

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    Quote Originally Posted by DmaxMaverick View Post
    You will not need the updated pump. The 1990 model should already have it.
    Hi thanks for the info, since my trans is 21+ years old and and unknown history and miles shouldn't I just replace the pump with the rebuild? Or can it be tested it to see if it's good as is?

  3. #23
    Join Date
    Apr 2001
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    CA
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    The pumps were never a "problem", and rarely fail on their own. The later pump inserts (the "vanes" part) are only higher volume. You cannot "test" the pump independently, as they are integrated. They work, or they don't, with not much of anything in between. The 1990 700R4 was as good as they got, from production. The only place to go is into aftermarket hard parts, and the Trans-Go shift kit. The shift kit can be installed easily (valve body removal), but the hard parts require disassembly. If the tranny is otherwise healthy, I'd suggest only the shift kit, for now. Once installed and properly adjusted, you'll know what more may be needed. Unfortunately, that's the only way to know, short of complete disassembly.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  4. #24
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

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    As maverick mentioned, the computer only controls the ON OFF function of the TCC

    Now, this said the fellow at the tranny shop is partially correct. The late 700's (after about 88) do not have hydraulic shift valves for the TCC in the Valve body and they do the entire operation of the TCC with a solenoid valve run by the computer.

    The earlier Valve bodies have actual valves in the VB that do the work and the solenoid was the final link to engage or disengage the TCC.

    The 1990 model should have the valve bores in the VB and if so will accept the valve assemblies. (The bores have aluminum plugs that can be replaced with the valves)

    If the VB does not have the bores, simply replace the VB with an 87 model that does have the bores

    Transgo makes a great kit (700LU) or something like that to run the TCC totally with hydraulics and it can be tailored to lock up at the desired speed. NO WIRES. Its a great KIT

    The governor must be used for the diesel (lower RPM shift speeds)

    The pump changes were to increase oil flow volume.

    The early pumps were also somewhat noisy.

    Oil flow was the big issue though.

    The other biggy is to get the Sun shell upgrade (Its called "The Beast")
    The 2-4 band is also a needed upgrade (HD or better) they make kevlar, which is really good.

    The 2-4 servo needs attention too. The 3-4 clutch pack must be upgraded with more clutches.

    Upgrade the front sprag and the rear roller lock. (They are small and can break)

    The little 6.2 will literally shake these things apart, so dont think, as Maverick mentioned that "its just a 6.2" The little 350 MOUSE motors are real easy on a tranny in comparison.

    Have fun and good luck.

    Missy
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  5. #25
    Join Date
    Sep 2006
    Posts
    363

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    If it has not already been mentioned, I would look into buying a torque converter than has been opened and had all of the veins welded. There are some other high failure items in the torque converter that can be strengthened as well. That said, my dad had 3 transmissions that were completely wiped out due to the torque converter coming apart and sending steel shavings through an otherwise good transmission.
    1990 ¾ ton 4x4 Chevy Suburban
    -Cummins Diesel - 12 valve - factory rebuilt
    -6 speed bullet proof manual transmission - NV5600
    -Gear Vendors Overdrive
    -Upgraded Holset HX-35 turbo
    -NP205 iron transfer case
    -3.73 gears

    1982 ½ ton Chevy Suburban
    -6.2L diesel - high nickle crack free 1982 block
    -Stans headers
    -Ported heads
    -Timing gear
    -4 speed automatic
    -3.08 gears
    -30 mpg on freeway

  6. #26
    Join Date
    Aug 2006
    Location
    Edmonton Alberta, Canada
    Posts
    52

    Default Thanks, great info

    Really good to be here and get such great direction from everyone. Thanks for the great details I will use it all for my 700 rebuild!!!!!

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