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#1
08-19-2011, 12:09 PM
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Which tranny for my 69FB?
hey guys.... I've got a 69 firebird ragtop, was originally an OHC6. Im gonna be fitting a 400ci real soon & ive got two trannies to choose from, a th350 & a th400. I'm aware of the differences, one is stronger and heavier, the other faster & lighter.
I'm worried about the crossmember, will i be able to modify it to accept the th400 or should i just use the th350 and call it a day. I wont be able to get the correct crossmember, parts & shipping are always a problem for me, but if i really have to get it, i probably will. I want the car to be rock solid and reliable, more than anything, im also hoping to get 400+ hp from the early 400 mill. Any suggestions? |
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#2
08-19-2011, 12:34 PM
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You definitely need the right crossmember for the TH400. Either a stock one or an aftermarket one. The 350 crossmember (which is the same as a 3 or 4 speed manual) is very different. Also, dont forget about your driveshaft, you need to have it shortened for the TH400.
If you want rock solid in factory form the TH400 is what you want. If you have really good builders and spend money on it the TH350 will work.
__________________
 68 Firebird, trying a q-jet now. 434/10.5:1/997's/240-242 HFT/4L80E/2800 Yank/3.42's/ Vintage Air/ 13.0 @105 mph 70 Lemans, 350/350, A/C, mostly stock 14 Ram CC, 5.7 Hemi, 8-speed, 3.92 lsd 97 Trans Am, HPP Aug 2012 http://www.highperformancepontiac.co...tiac_trans_am/ ***Sold*** |
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#3
08-19-2011, 12:56 PM
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The TH-350 will swap right in using the ST-300 2 speed auto trans as well.
I ran a TH-350 because it was so easy to not have to modify the driveshaft or get the TH-400 crossmember. Now I have a M-20 Muncie to row my own. No driveshaft or crossmember changes required. |
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#4
08-19-2011, 03:58 PM
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Thanks guys, some very interesting points.
I don't need to worry about the driveshaft, the one im gonna use is from a buick so ill need to alter it one way or another. I don't intend ever going manual. Where can I get a th400 crossmember? I was thinking maybe i could weld a plate to the th350 member & drill new holes or something, seems like thats a bad idea huh? Whichever box I don't use I will need to sell, and we don't come by them too easy around here.  Don't wanna sell the wrong one. 
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#5
08-19-2011, 04:03 PM
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okay, i see Ames has the th400 member for $135
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#6
08-19-2011, 05:09 PM
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The TH350. You have the right driveshaft and crossmember already and it will handle 400hp. No need to make it difficult for a gain you won't use.
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#7
08-19-2011, 05:35 PM
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I would go with an OD trans.
so much better with that extra gear(or 2)
__________________
Everything comes and goes Pleasure moves on too early And trouble leaves too slow |
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#8
08-19-2011, 06:45 PM
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Why is it that the th350 is usually found hooked up to a 350ci and the th400 to a 400ci?
I think ill just keep both transmissions. I'll use th350 & stash the th400 so if ever im having problems, ill just get a cross-member, resize the shaft & swap them out. Atleast ill get to enjoy the faster gears of the th350.  It's easier finding a th350 than a th400, so i dont think i should sell the th400, just might need it one day.  Overdrive is cool but then ive gotta hunt one down again
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#9
08-20-2011, 09:48 AM
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the numbers used to somewhat correlate to torque ratings in foot pounds.
that all went by the wayside when electronic controls came out.
__________________
Everything comes and goes Pleasure moves on too early And trouble leaves too slow |
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#10
08-20-2011, 10:24 AM
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Okay - Just a word of caution on the TH400 cross member.
The original TH400 cross member pad where the tranny mounts is centered. This is really important since, any of the after market members for Camaros were offset a 1/2 inch to the passenger side. This is because Chevy only offered the TH400 in the Camaro with a big block. I just ordered a TH400 member a month ago from Ames and, all they really have are Camaro members. However, I had the guy I was speaking with when I ordered it, measure it for me to see if the mounting pad was actually centered. It was not, but they had another cross member from another manufacturer in stock. That one measured only about an 1/8 inch off center. So, I purchased that one. Easy enough to alter to make up an 1/8 inch. This one fit great and is in the car and I'm racing. Hope that helps - joe |
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#11
08-20-2011, 04:10 PM
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Thanks for the heads-up Joe.
Now im convinced that the best thing to do is use the th350 & if I break it, ill swap it out for the th400.
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#12
08-28-2011, 08:12 AM
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The 350 be fine. I have run several, in different cars and never had a problems. I would consider a O D trans as well!!!.probably the single best thng I ever did !to my car!! I hae a 200-4R i n mine. Lower 1st gear
__________________
Chris Collier 1969 firebird, pro touring build. Full Global West suspension 474 Stroker with Molnar Crank and Rods, DCI Ram Air 5 Top end, Holley fuel injection, Vince Janis 200-4R trans "There is no such thing as too much horsepower" |
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#13
08-28-2011, 08:14 AM
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17 mpg!!
__________________
Chris Collier 1969 firebird, pro touring build. Full Global West suspension 474 Stroker with Molnar Crank and Rods, DCI Ram Air 5 Top end, Holley fuel injection, Vince Janis 200-4R trans "There is no such thing as too much horsepower" |
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#14
08-28-2011, 11:37 AM
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GM OD trannys are probably not easy to come by in South Africa. Just a guess.
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#15
08-28-2011, 12:21 PM
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What about on 68-72 A-bodies....are there different cross-members for th350 & th400 or can the cross member be moved on the frame?
Maybe I can use the th400 on my 70 Skylark?
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#16
08-28-2011, 04:39 PM
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Quote:
Yes, you can move the cross member on the A-body frame and use the TH400 there. good call. Keep in mind you can find the 200 4r OD trans in GM RWD cars from 1982-1990. But generally used behind BOP engines except in Chevy Monte Carlo and station wagons. (using it behind SBC engines) You might still have a good shot in SA? A monte Carlo SS version just sold on protouring.com for $150usd |
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