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.

I'm so confused...when you say your tranny guy, what exactly does that mean? Did this guy rebuild your trans or did he just throw a different trans in your car? Was he a professional tranny guy? This sounds more like a slipping trans or a bad torque converter. Is the trans fluid level Ok?There's not a whole lot of vaccuum lines on your car, it shouldn't be too hard to find a vaccuum leak if you have one. Does the engine run OK when the car is in not in gear, does it bog and loose power? Tramp on it, what kind of throttle response do you get, instant or sluggish?

Sorry for the rather vauge post. I've just had a thousand things running through my head recently.

When I said "tranny guy" I mean he rebuilds transmissions for a living. He rebuilds and works on all the transmissions for Randy Marion Chevrolet (big dealer down here in NC). The transmission fluid level is fine and he supposedly put a new torque converter.

My initial thought was a slipping/bad torque converter. The throttle response is OK...except for the fact that it did backfire on us once. It has hesitation right off the line even when you take it extremely easy on the throttle. But after it starts going it seems to be fine.

Timing set OK? Vaccuum hose on distributor replaced? Gasket between carb and intake OK? You should be able to hear a vaccuum leak in the engine compartment if you have one. The vaccuum hose that goes to the trans, did you replace it?

It sounds like you have two different problems going on, transmission and carb and I hate to say this but I think your previous carburetor was innocent.
Your transmission seems to be the guilty party here. I assume you have a TH400 behind your 402 and those transmissions have a vacuum modulator that controls line pressure in the tranny according to load. In other words, the vacuum modulator gets a vacuum signal from the engine and adjusts the pressure accordingly. These modulators can go bad and when they do, your transmission acts like it's not engaging or slipping in all gears, Low, Drive and Reverse. The other possibility is that a so called low roller or sprag one-way clutch is malfunctioning, they are a notorious weak link in the TH400 and you've guessed it, the tranny feels like it's slipping in all gears (because it is!). My bet is on the modulator, get back with your tranny guy and ask him about this.

What kind of tranny are we talking about here?

You're correct, I do have a TH400 backing it up. The gasket between the carb and intake manifold is brand new, timing seems to be fine (nothing out of the ordinary going on there...although we will check it now), and the vaccum hose from the distributor was replaced after we put the Holley on...not when the quadrajet was on there. The vaccum hose that goes to the transmission seems to be in great shape, but I doubt it was replaced.

I'm currently about 3 hours away from the Elkie, but I'll have my dad browse these replies and take a look at it tonight. Thanks for all the replies!

Well my dad took the car back to the guy who cleaned up and replaced some parts on our Quadrajet. Apparently the main-guru was there and the first thing he noticed was that the primaries weren't working properly. So the carb is getting taken back off the car and fully rebuilt now.

I'll keep the board updated. Thanks for all your help guys!

This is Electrodynamics Dad After the carb guy looked at the car again this week, it really ran no better than before, so we went and got a remanufactured Quadrajet and put it on. Our transmission shifting problems are gone, so apparantly our trans guy was right in saying that it was all in the carb/vacuum system. The car does not still have the correct power, but......we know that after sitting for 6 years that we are going to have to drop the gas tank and do a visual inspection of the tank and sending unit(the gas gauge doesn't work as well). The main fuel line from the tank to the fuel pump is most likely a problem as the return line was rusted and leaking when we first got the engine running. We replaced the return line with 1/4" I.D. rubber hose for now until we can get a new stainless steel fuel line set. The car just doesn't have the power it used to have( I did take a ride in it right after the rebuild 6 years ago and it was a screamer). So it most likely is not getting the fuel it needs. All we need now is more money, as the first 3,000 went quickly for only having the car for 3 weeks. It is really frustrating at times, but we have to keep reminding ourselves what the final outcome will be. Thanks for all your input.

To add to what my dad put, I called a fellow muscle-car enthusiast who has an incredible knowledge about pretty much anything involving a car and talked to him about our lack of power. The first thing he mentioned was to check the timing again, and also check the dwell. If it's still not running the way it should after we replace the tank and fuel lines then we're going to look deep into the timing issue. Who knows...we might even do that while we're working on the tank. :)