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Discussion Starter #1
I've been reading conflicting information on this topic. Some state that the 1970 Nova, if equipped with a Big Block 396 (402), a Turbo Hydro 350 Trans wouldn't have been available, only the TH 400 would have been. Is this true? My 396 appears to be original and does have the TH 350 with a floor shift but some have stated, this wouldn't have been a viable combination. ?
 

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:confused:I, like you am guessing, but I think it would have come with the 400. I think you could have special ordered a 400 with a smallblock, but I don't think you could order the 350 with a bigblock. I'm sure that somebody here will have the correct answer.
 

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TH 400 Tranny...

The TH400 transmission was available in the Nova for only 3 years [1968-70]
There were a limited number [48] of L-34 TH400 cars built in 1968 as a regular production option...additionally there were 50 L78 TH400 equipped COPO Novas built for Fred Gibb Chevrolet. These COPO versions were the first time Chevy put an automatic behind a solid lifter BB engine.

1969 and 1970 saw a larger number of BB Novas built with the TH400 in both the L-34 and L-78 platforms. There were a limited number of special COPO Yenko Deuce TH400 cars built in 1970...in this case the tranny was installed behind the solid lifter LT1 small block motor.

As to the TH350 behind your big block...are you sure it is a factory BB car?? and are you sure the tranny is a TH350??

Post a few photos of the car when you can...

wilma
 

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Discussion Starter #5
Well, I'm fairly certain it was originally a BB, has the larger core support, correct fan blade but I had some doubts on the originality of the TH350. Sounds like I will be switching it out to a TH400
 

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Well, I'm fairly certain it was originally a BB, has the larger core support, correct fan blade but I had some doubts on the originality of the TH350. Sounds like I will be switching it out to a TH400

Do you have any other info on the BB parts? ei, engine frame stands, heater box and core assembly, trans crossmember etc.
 

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Discussion Starter #7
The more I think about it, the less certain I am of anything on this Nova. I don't have much other info but the cross member doesn't look to me as what should be there if it was an original BB with a 400. But since I've invested so much into this, I have no choice but to at least make it correct by switching out the 350 to the 400. Is this doable with out too much modification?
 

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The more I think about it, the less certain I am of anything on this Nova. I don't have much other info but the cross member doesn't look to me as what should be there if it was an original BB with a 400. But since I've invested so much into this, I have no choice but to at least make it correct by switching out the 350 to the 400. Is this doable with out too much modification?
My 70 had the 400 behind the 396.
 

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Chevrolet never mated a TH350 to a big block of any size, in any body style. I am guessing they though there would be far too many warranty claims.
 

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The more I think about it, the less certain I am of anything on this Nova. I don't have much other info but the cross member doesn't look to me as what should be there if it was an original BB with a 400. But since I've invested so much into this, I have no choice but to at least make it correct by switching out the 350 to the 400. Is this doable with out too much modification?
The rear cross member is different(rear mount is further back)& would need to be changed, Also the slip yolk is bigger on the 400 trans & would need changed. If you want the down shift to work(passing gear), you would need the down shift switch that mounts on the carb & wiring harness.
 

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Discussion Starter #11
The cross memember is a pretty simple fix and I imagine the slip joint won't be a big challenge I think. My new wire harness has the lead for the kickdown switch... is the mechanical kickdown not used with the 400?
 

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The cross memember is a pretty simple fix and I imagine the slip joint won't be a big challenge I think. My new wire harness has the lead for the kickdown switch... is the mechanical kickdown not used with the 400?
No mechanical kickdown on the 400 transmission. They all have a electric kickdown solenoid.
 

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Discussion Starter #13
So, how is it actuated? If I have an edelbrock carburetor, do I need to find an applicable solenoid for the carb?
 

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It's actuated electrically, through a switch mounted on the left rear carb. So,yes you would need this switch. You can find them on eBay & aftermarket ones
 

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Chevrolet never mated a TH350 to a big block of any size, in any body style. I am guessing they though there would be far too many warranty claims.
No, but you could have had a powerglide behind a 409 in the early sixties:eek:
 

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Discussion Starter #16
It's actuated electrically, through a switch mounted on the left rear carb. So,yes you would need this switch. You can find them on eBay & aftermarket ones
Thank you, I appreciate that. My only other concern before doing this is, the linkage to the floor shifter. Do you see any issues connecting the linkage to the shifter?
 

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The shifter lever & linkage off the 350 trans will work on the 400 transmission.
 

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Interesting story I heard years ago. In 1968 when GM started putting the T400 in big block cars, the GM racers competing in NHRA were using neutral starts to launch their cars, the Chrysler guys, in order to compete were attempting them and grenading their Torqueflites, soon after, and to this day, neutral starts were forbidden by NHRA. A testament to the toughness of the T400 tranny.
 

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TH 400 Tranny...

The kickdown switch was mounted under the gas pedal on most of the 70 model year BB Novas...some early cars had the carb mounted switch. They all work the same way though...as mentioned the carb mounted unit is a simple item to locate online. A well built TH350 will survive behind a BB...but, if a TH400 is available, that would be the way to go.

**some early BB Chevys actually had the Powerglide tranny...go figure:rolleyes:
 
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