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Author Topic: Changing trans to automatic, 85 TA  (Read 2359 times)

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  • Message Board Member not current NFTAC Club Member
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Changing trans to automatic, 85 TA
« on: May 17, 2007, 09:02:04 PM »
I am original owner of 85 TA with a 5 speed manual trans. But now my left knee says no more. So either I put an auto in or sell it, unless there are other options to bypass the clutch pedal. There is a shop near me that will put a 4 sp auto in. But I wonder if it will work with the current 3.27 axle ratio. I also wonder about how it will do with the engine power characteristics and computer controls. I haven't driven other TAs to know how they are, but mine has very little useable torque below 1500 rpm, at least not useable with the tall top gear ratio. I truly can't drive it below 1500 in 5th without a lot of bucking, knocking, etc. That corresponds to 55 mph. (I did drive a friend's Mustang GT with 5 liter engine, manual trans and same gearing - 55 mph at 1500 rpm - but it would drive nicely down to 35 mph in 5th gear) So if I put an auto in, and it wants to shift to it's overdrive top gear at about 45 mph, will my engine buck and knock? I have the LG4 engine, all still stock with 4 barrel, etc. According to the manuals, my father's 86 Bonneville also has the LG4 engine, but has the automatic 4 sp trans that shifts nicely into top ratio at about 45 mph, and runs smoothly there. So is his LG4 different from my LG4? The shop says my car will do fine, but they are of course a bit biased. And I don't feel like paying the $3000 gamble without sufficient knowledge of what to expect. Any ideas, suggestions much appreciated.


  • Firebird & Trans Am Club Tech Staff
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Re: Changing trans to automatic, 85 TA
« Reply #1 on: May 17, 2007, 11:35:06 PM »

And Hello Fellow Club Member, an nice to meet you!

I’m a-original owner of 85 TA also and in my option, a 700-R4 /4L60 is a good choice of A/T; alternative// I had a 3.08 Standard Rear End, and I converted it to a Posi / Limited – Slip Rear-End for a cosmetic look,
{ Posi,with Disk Brakes you know “The Look” but because I bought it from a local Auto-bone Yard at that time (and beg-ers can’t be choosers) It had a 3.23 gear in it / The only drawback is; it didn’t have quite the zippity do-da the 3.08 had; but still not to bad // so I converted the gear ratio to a 2.73 and it was like a new car// a re-birth of a muscle car { performed better then it did when it was new with the original 3.08 } In my option of course, with a manual 5 or 6 speed you just shift to some extra gears with not to much gain [Gear Raito’s that is] however a 6 speed has a slit advantage with its final gear ratio of .49 as apposed  to a  Automatic four speed Transmission with its .70 final gear ratio.

And as far as a $3,000 dollar gamble is concerned; the only gamble that you are really making is “will he do a good job?” an of course “The Money” ie. (The Moo-La) and as far as a LG-4 Engine is concerned an LG-4 Engine is an LG-4 Engine [305 carb.-ed] 

      Hear again nice to meet you!  ;D    &
      Hope This Helps
                                                   Justin K.
« Last Edit: May 20, 2007, 08:00:46 AM by T/A JLK »
I am a NFTAC, Member and I was at one time an auto mechanic working for a local GM dealer here in my home town back in the mid-to late '80's now  I currently enjoy working on my own Pontiac's especially on my '85 T/A // making maintenance repairs, repairs, modifications and performance modifications I also enjoy meeting and /or talking to other Firebird & T/A owners an get into technical debates;hopefully just as long as the debate's doesn't go into a to heated argument.

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Re: Changing trans to automatic, 85 TA
« Reply #1 on: May 17, 2007, 11:35:06 PM »


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