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I posted this in the engine forum, but I figured it couldn't hurt to post it here also just in case someone visits these threads instead of the engine threads and might be able to help me. If you want to mods, delete this if it rubbs you the wrong way. I'd just like to find out what the heck is going on with my car.



As many of you know, I have a 1969 SS 396 that's been bored out to a 402. Well after I had the transmission rebuilt I took it out for a spin. After a few minutes I decided to remotely get on it and give it a little more than 1/2 throttle. When I did it seemed like the tranny just sat there and free-rev'd. It continued to do so all the way home which thankfully wasn't very far.

So Dad and I thought it was the transmission and decided to take it back after calling our tranny guy. On the way out of my street it seemed to do the same thing, but this time in first gear...just reving, not going anywhere. It crept along, but it felt like the transmission just wasn't sending back any power. I slowed down to a complete stop and kept trying to go forward but had the same results - engaged until about 1500 RPMs where it felt it just let go. Well after I turned onto the main road, everything seemed to be fine except the fact that it was holding each gear for an extended period of time. I'm used to my old 250 L-6 that never got above 1800 RPM's when you were just baby'ing it...but this was holding it out to almost 3000 at times.

So anyway, on the way out I tried giving it gas again once it seemed like it was sort-of-OK. 'Same thing - just reving.

Our tranny guy takes me out (me driving) and asks me to get it up to 55 mph. I do and he pulls the shifter back to 2'nd, and sure enough the engine just spooled up and seemed to loose about 70% of power (with my foot in the exact same place).

He says it's the carb having vaccum problems. We took his word for it and ordered a Holley spread bore 650 from our local Advance Auto. Not only was it a B!TCH to install, it can't idle, it has a catch in the throttle, and the air filter assembly won't fit anymore.

SO...what seems to be the problem to you guys? When you're sitting a dead stop and you don't go anywhere, that sounds like the tranny to me. But while driving, pulling it down into 2'nd seemed to feel like what the car was doing earlier. It just seemed like I was getting about 50% of my power back to the rear.

Carb, or tranny? That is the question. Tranny has a fresh rebuild - like 10 miles on the tranny. Any help will be appreciated.
 

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Just guessing I'd say it sounds like a Torque Converter although, it could be the center seal in the transmission. I don't think it would be the Carb but that is just my opinion. I haven't drove the truck so it is sort of hard to diagnose not being there. But if I had to put money on it now... I'd go with the torque converter. Did you replace it when you had the transmission re-built?

Do you get vibrations that feel like they are coming from the back part of the engine when you give it a little gas or do you notice and strange noises?

BTW,

The 402 was a standard on many Chevells and Elkys. My 72 Elky came factory with a 402.
 

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Discussion Starter #3
There aren't any strange noises or vibrations at all. The engine runs silky smooth. My initial thought was the torque converter also.

My 402 is a bored out #'s matching 350 hp 396 that's been balanced, and the TH400 is #'s matching also. A friend of ours down the road does have an original non-SS 402 in his 72 as well. Pretty neat stuff.
 

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This is Electrodynamics Dad....just a note to the people who have contributed to this thread. We finally got a remanufactured Quadrajet carb and installed it today. We no longer have the transmission acting up which was especially bad once it got into 3rd gear. It then seemed to want to slip or free-wheel and not drop back down into 2nd. Apparantly our transmission guy was right....that the carb had vacuum problems and was not allowing the trans to shift right. The car finally cranks right up.....no more pumping of the gas pedal to get it going. Thanks for the input on this matter. Knowledge is a powerful thing.
 

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I had the exact same problem. Have a similar setup too. BB 402 w/ Turbo 400 trans.
My prob turned out to be mainly the torque converter and some the trany. the trans man found water in the trans. (it sat out for many years)

Did the problem happen sudenly or did it gradually get worse? If it was instant;I'd say it's just the torque converter, specially if you can still manually shift through the gear like you were talking about.

$650 bucks later it was fixed and I got a shift kit installed free!
 
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