1986 cimarron transmission
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Cadillac Catera and Cimarron Forum Discussion, 1986 cimarron transmission in Past Cadillac Vehicle Discussion; Hello, I have a 1986 cimarron that runs great (v6 2.8L). The only issue with it is on the highway, ...
  1. #1
    tj86cimarron is offline Cadillac Owners Member
    Automobile(s): 1986 cimarron 1995 Eldorado ETC
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    1986 cimarron transmission

    Hello, I have a 1986 cimarron that runs great (v6 2.8L). The only issue with it is on the highway, going 70mph or so, it is always looking for another gear. The tranny is a 3 speed automatic (THM125). I was wondering if anyone knows of another tranny with a 4th gear (or overdrive) that will drop right in -OR- a way to solve the 3200rpm at 70 mph issue...

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    CDConcours's Avatar
    CDConcours is offline Cadillac Owners Member
    Automobile(s): 97 Cadillac Deville Concours
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    Re: 1986 cimarron transmission

    Hello I'm a Cimarron fan. I've been researching the cars and different upgrade ideas. The 2.8L is a 60 degree Chevrolet v6 same family as the 3900 VVT V6 239hp in current Impala LTZ. Chevrolet has been advancing this engine since 1980 introduction. Along the way there's been at least one 4 speed automatic. Currently all 3.5 and 3.9 have a 4 speed OD. The 440-T4 is a version of your Cimarron's THM125, introduced in 1985 renamed 4T60 1985-1993 A Body: Buick Century, Olds Ciera. 4T65-E is the newest version used in the current Impala. It's really just a question of how far your willing to go? I love how interchangeable GM's are. If I were doing it and I didn't have to think about money I'd go with the 3.9L and 4T65-E out of an Impala 06-current! If your real creative you possibly could run traction control! I always wanted to build the ultimate Cimarron! Another more Cadillac upgrade Idea is HT4900 and 4T60-E it should be doable, I read a story some kid put a Northstar in his Cavalier. If you have any questions feel free to ask.

  4. #3
    tj86cimarron is offline Cadillac Owners Member
    Automobile(s): 1986 cimarron 1995 Eldorado ETC
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    Re: 1986 cimarron transmission

    Hello CD, I have already made some performance upgrades to the heads..It is an 86, so it still has steel heads..I took them off, match ported the ports to the intake gaskets - and removed the air flow dam in the ports, which (for some dumb reason) is an intentional design of these heads -- approx 10 hours worth of grinding....It now has a considerable increase in torque and power...Which is the reason I want another gear. I don't want to build the ultimate Cimarron (or put a v8 in like that kid did LOL) Can you tell me if the 440-T4 or the 4t65-E bolts right in place of the THM125? And what type of upgrades are necessary for this Ex: computer - half shafts etc. etc. Any info sources??? Thanks BTW - the Cimarron is on the J-body GM platform...

  5. #4
    CDConcours's Avatar
    CDConcours is offline Cadillac Owners Member
    Automobile(s): 97 Cadillac Deville Concours
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    Re: 1986 cimarron transmission

    Hello, I wanted to explain the most extreme options to you. My best recommendation from what I've read is the 4T60 it's directly related to the THM125 uses the same bell housing, should bolt right up. Make sure you don't get the 4T60-E (electronic controlled) that's the only time you'll need wiring or ECM upgrades. The 4T60 is adjusted via a TV cable just like your THM125. Any # 1985-1993 A platform car with the 2.8 up to 1989 or the 3.1 after that should work. I would recommend re-manufactured do to the age of these cars. As I understand the original FWD HT4100 Deville (1985) used the exact same bell housing. Here's the Wiki link http://en.wikipedia.org/wiki/Turbo-Hydramatic_125 It's a pretty well written. Above all if you enjoy cruising above 70mph your going to love the overdrive. The THM125 gets bad millage above 65mph, neither my dads 1990 2.2 Cavalier or my 95 2.2 Cavalier or my first car my 1988 Celebrity Euro Sport (same drive train as your car) got good millage over 65.
    As far as mounts go I would find a auto parts store with your mount in stock and compare it to the mount of a possible donor car. Sounds tedious but it's the best way to make sure. Same with half shafts. Another source is a j body fan site: jbody.org or v6z24.com I've seen a few 3.1 swaps done maybe one used the Auto 4speed also. I'm trying to be as helpful as possible, I do not want to give the wrong advice.
    If you have any questions just ask and keep us posted on your progress.

  6. #5
    tj86cimarron is offline Cadillac Owners Member
    Automobile(s): 1986 cimarron 1995 Eldorado ETC
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    Re: 1986 cimarron transmission

    Awsome!! Thanks..I'll keep everybody posted..BTW - believe it or not - after modifying and rebuilding the heads - I get 24 mpg on the highway averaging 70 mph and 3300 rpms. I know it sounds impossible but I figured the milage using the same gas station - same gas pump - filling the same time of day. 197 miles drivin - 8.2 gallons of gas used..I did this 3 times so far..
    This car was givin to me for free with 45000 miles on it - the interior is in showroom condition - so maybe some day I will attempt to make it a Super Cimarron -- but for now I just want another gear..Thanks again!

  7. #6
    CDConcours's Avatar
    CDConcours is offline Cadillac Owners Member
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    Re: 1986 cimarron transmission

    Wow! Very impressive millage. I've gotten 23mpg or so out of the Deville as long as I did nothing but highway, probably 80mph or so. I had a K&N and Tornado in the Deville it made the millage worse. Because I live in Chicago I mostly get 15mpg, when I had a K&N and Tornado I only got 12.5mpg.
    What color is your Cimarron? You should post pictures, sounds like you got a hell of a good deal. Best of luck with the trans.

  8. #7
    tj86cimarron is offline Cadillac Owners Member
    Automobile(s): 1986 cimarron 1995 Eldorado ETC
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    Re: 1986 cimarron transmission

    Do you know if the 87 to 90 Allante f-7 transmission is the same as the 4t60?
    My Cimarron is dark grey metalic -- and I will post some pictures as soon as I can figure out how,,I'm not exactly computer literate -- but I'll figure it out...

  9. #8
    GoodImp is offline Cadillac Owners Member
    Automobile(s): '86 Cadillac Cimarron 2.8L 3sp
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    Re: 1986 cimarron transmission

    I've been interested in putting a 4sp in my Cimarron. I was told that it wouldn't be a good idea. Either way, I'm still interested in if this would work flawlessly. When I'm on the highway, I run my car at around 80 mph at 3800 rpm. With a red-line at 5000, I'm impressed. I would definately like to a "Super" Cimarron, myself.

  10. #9
    tj86cimarron is offline Cadillac Owners Member
    Automobile(s): 1986 cimarron 1995 Eldorado ETC
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    Re: 1986 cimarron transmission

    It is proving difficult to find a 4sp tranny (worth rebuilding)..but I'm in no hurry, so when I do I will post back to let you know how it goes...FYI - I don't know what size wheels are on your cimarron (mine had stock 13 inch), but I put 14 inch wheels on -which brought down the RPM issue by about 250 or so. Now at 70 mph I get up to 2950rpm = +or- a few....

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