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  1. #1
    jim510
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    Default 4 + 3 transmission

    Hi all...I just bought my first Corvette....a 1987 coupe with a 4 + 3 trans....the car was stored for a few years and I guess the guy just wanted to get rid of it....anyhow, I seem to be having a few problems with od....sometimes the light would come on for a few minutes and then go off....now it seems it doesn`t go into od....I put fluid in the box and I also replaced the relay...no luck...other than that, the car runs pretty good....I didn`t find any loose wires, and I`m not sure where to go next....any help with this would be greatly appreciated....thanks in advance......Jim

  2. #2
    Member
    Join Date
    Aug 2002
    Location
    wilkes-barre,pa.usa
    Posts
    769
    Corvette(s)
    1988 white 4+3 coupe 99 Torch Red 6spd. coupe

    Default

    Service the O.D unit, filter and fuild, you hear horror stories about the 4+3, but mine has been no trouble, yet. When I bought the 88, I serviced the OD unit , the magnet was covered pretty good with particals, which indicated to me that it wasn't serviced much. I got the filter/gasket from Ecklers and had a problem leak from the pan, I dropped the pan the second time and used RTV silicone instead of the supplied gasket, which is what the repair manual recommends. Since then the OD unit is working flawlessly. We can only hope that my luck continues.....................I also put Redline trans. lube in the 4spd and shifting feels better..................

  3. #3
    jim510
    Guest

    Default

    Thanks....will order the filter and replace fluid...

  4. #4
    Member
    Join Date
    Aug 2002
    Location
    wilkes-barre,pa.usa
    Posts
    769
    Corvette(s)
    1988 white 4+3 coupe 99 Torch Red 6spd. coupe

    Default

    There's other outlets for those OD filters, search this site......................

  5. #5
    Moderator Toms007's Avatar
    Join Date
    Sep 2004
    Location
    Southwest Kansas
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    5,198
    Corvette(s)
    2007 Atomic Orange Coupe

    Default

    Welcome to CAC Jim. You'll find really nice people here more than willing to help with any thing they can.

    Mods....I think this particular thread would be better in C4 Tech.

  6. #6
    jim510
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    Default

    thank you all....nice to meet you all

  7. #7
    rrubel's Avatar
    Join Date
    Oct 2001
    Location
    Glen Burnie, MD, USA
    Posts
    2,423
    Corvette(s)
    1986 Bright Red Coupe

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    Welcome to the CAC... This site - http://www.corvetteobsession.com/ - has a ton of great info on the 4+3 (its originator was a fixture on CAC before his death). You may want to check the switches on the side of the transmission that tell it what gear it's in, and also have you tried manually switching in and out of OD?
    [RICHR]

  8. #8
    jim510
    Guest

    Default

    What I found is that I have a small leak around the gasket in the od pan....i topped it off again, and the light came on again....I tried to buy a filter in every auto parts store around here and nobody had it....I had to order it online and it will take a few days to get here...at least I know what I`m dealing with now...thank you all for your input...Jim

  9. #9
    rrubel's Avatar
    Join Date
    Oct 2001
    Location
    Glen Burnie, MD, USA
    Posts
    2,423
    Corvette(s)
    1986 Bright Red Coupe

    Default

    IIRC the filter is also the same as the auto transmission filter for the Ford Ranchero, which is carried more places (believe it or not).
    [RICHR]

  10. #10
    Member JimBobC4's Avatar
    Join Date
    Aug 2004
    Location
    Canton Ga
    Posts
    343
    Corvette(s)
    1995 Dark Red 6spd Convertible

    Default

    Quote Originally Posted by rrubel View Post
    IIRC the filter is also the same as the auto transmission filter for the Ford Ranchero, which is carried more places (believe it or not).
    [RICHR]
    The Ranchero came with 4 different auto transmissions.

    1. the C-4 for Small block 289 302
    2. The C-6 for Big Block and some 351 C applications and 351 w ( I think )
    3. The FMX tranny in some early 1970's appications with a 351 M
    4. The Cruise O matic out of early Fairlanes and Mustangs ( Early C4 )

    What year of Ranchero is interchangeable ?

    It sound reasonable as I have read that the overdrive unit was
    designed by Doug Nash for Ford based RV chassis in the mid to late 1970's. I would be curious, if it was the C-6 version as that is what was in the Rv's at the time.

  11. #11
    Member
    Join Date
    Jun 2002
    Location
    Springfield, TN.
    Posts
    88
    Corvette(s)
    1982 Silver-Blue Coupe, 1986 4+3 Coupe

    Default

    Quote Originally Posted by JimBobC4 View Post
    The Ranchero came with 4 different auto transmissions.

    1. the C-4 for Small block 289 302
    2. The C-6 for Big Block and some 351 C applications and 351 w ( I think )
    3. The FMX tranny in some early 1970's appications with a 351 M
    4. The Cruise O matic out of early Fairlanes and Mustangs ( Early C4 )

    What year of Ranchero is interchangeable ?

    It sound reasonable as I have read that the overdrive unit was
    designed by Doug Nash for Ford based RV chassis in the mid to late 1970's. I would be curious, if it was the C-6 version as that is what was in the Rv's at the time.

    #3 The FMX transmission - Auto Zone has the filter for less than 10 dollars and is part # TF-124

  12. #12
    Member John '85's Avatar
    Join Date
    Mar 2006
    Location
    Fremont CA
    Posts
    57
    Corvette(s)
    1985 Red Coupe TKO500 Z51

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    Quote Originally Posted by muddywaters View Post
    Service the O.D unit, filter and fuild, you hear horror stories about the 4+3, but mine has been no trouble, yet. When I bought the 88, I serviced the OD unit , the magnet was covered pretty good with particals, which indicated to me that it wasn't serviced much. I got the filter/gasket from Ecklers and had a problem leak from the pan, I dropped the pan the second time and used RTV silicone instead of the supplied gasket, which is what the repair manual recommends. Since then the OD unit is working flawlessly. We can only hope that my luck continues.....................I also put Redline trans. lube in the 4spd and shifting feels better..................

    Hey Muddywaters, what grade of Redline did you use? MTL or MT90?

    John

  13. #13
    johnny80
    Guest

    Default

    Welcome to the CAC! This site has been a godsend for me since I bought my vette in 02. My 88 has the 4+3. I have gotten alot of great guidance from the folks here. I have probably saved myself thousands of dollars in repair expenses just by asking questions. I was never much of a wrench turner but over the years, my confidence has grown and I have been able to replace many parts such as alternator, battery, exhaust, cooling fans, TPS and much more by maximizing the expertise of the individuals on this site. Make sure you get your hands on a GM repair manual, it's worth the investment. Congratulations again on your vette.

  14. #14
    Member
    Join Date
    Aug 2002
    Location
    wilkes-barre,pa.usa
    Posts
    769
    Corvette(s)
    1988 white 4+3 coupe 99 Torch Red 6spd. coupe

    Default

    John85, I used MT90, the tranny (Not the OD unit, it uses ATF) shifts much smoother................

  15. #15
    New Member
    Join Date
    Jul 2008
    Location
    vermont
    Posts
    2
    Corvette(s)
    1985 Med. Bronze Coupe

    Default 4+3 O/D service

    Hi. I just joined this forum to see if I could get some info on my car. I have a 1985 with t he splendid 4+3 transmission. I was reading that these need to be serviced. I have recently started to get a symptom where the O/D cuts out at temps over 192 degrees. Even though this car has only 35.8k miles, I'm sure it has never had the tranny serviced. I did change the tranny fluid last summer. Does anyone have pix or other info on how to service this thing? There aren't many dealers in my area that I trust working on this car, so I would probably be doing it. I look forward to learning more. Thanks.

    Mike

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