Hello All,

I have been working on my first C3 for about a year now, progress is slow but it's coming along and fires up first on the try and drives around the block without falling apart. I have heard that the acceleration is nothing to write home about on the old C3s but I feel like mine is especially slow and was looking for some input as I dive into this. It's a 3 speed automatic and I am starting it in 1st gear (1 on the gear select panel, if I try 3 it wont even budge), sounds fine as it idles, both my vents open up on the carb after it warms up, but when I put it in gear I need to really rev it up to get it to start moving, and it feels like if I start it on a hill with even a 20 degree incline it might not be able to take off. Once it gets going it drives really nice and even has some punch to the acceleration, just not so much from a standstill. My plan is to flush the transmission and dive into the carb a little deeper to make sure it's getting enough fuel and replace the fuel pump if necessary. Am I on the right track or is there something else you guys would look at? Or is this kind of acceleration actually normal?

Also just to note the reverse gear has significantly more power in it than 1st gear, accelerating in reverse feels like how I would expect a car to normally accelerate.

Any advice is appreciated, Thank You.

 

Sounds like a transmission problem.
What does the fluid look like?
What is the fluid level?
Your trans should operate normally with the shifter in the "3" position.

After that, make sure your carb secondaries (Bottom plate) are opening fully at wide open throttle.

 

Certainly sounds like a transmission/torque converter issue.

Otherwise your stock engine is basically an old 350 cube 300 H P with lowered compression. The factory 74 distributor has very stiff centrafugal springs killing timing advance, minimal total timing probably until about 4,500 rpm.

Get an advance spring kit, lighter springs, and with a dialback timing light get around 36 mechanical advance in around 2,800 rpm.

That simple change, and if carb, etc. all in good working order it will run like a late 1960's SBC. That old 300 H P cam combined with a Qjet is instant throttle response, just runs out of breath around 4,500 rpm.

Doug

 

Secondaries are fully opening. Transmission fluid was low when I got it and I filled it with Valvoline ATF full synthetic and checked it with the car running, the level has been holding good ever since and still looks clean. I'm not too familiar with transmissions but I thought doing a full fluid flush and pulling the plate off to see if there was any gunk in there would be a good place to start.

 

Email @lars for his timing papers. Following his instructions (with a new distributor) made a huge difference in my 79 L48.

It's still a dog, though, thanks to that TH-350 auto and stock torque converter. Adding a third pedal is always the correct way to handle automatic transmission problems.

 

Sounds to me like the transmission is slipping.

I'd be looking for a new or different transmission. Fortunately the TH350 is among the cheap transmissions. Didn't say what year this corvette is, so it could be TH400. either is among the cheaper transmissions.
If you get a new one I would recommend one with a shift kit. Makes the shifts much more positive. With a new transmission you will have to get a new torque converter as well to make the warranty good.
Having it rebuilt by a reputable shop is also an option and may be cheaper since they may not require a new torque converter for warranty. Check around and see.

 

He actually states its a 74 in the title of thread, so Th400.

 

Lol, missed that somehow.

 

Thank you,

I'm gad to see that transmissions aren't over the top expensive. I'll probably still try to flush it out and clean it up while I save up for a new one. Worst that can happen is that it still doesn't work right and I learn a little about transmissions during the process.

 

if you need a transmission, you can't justify not going to 200 or 700r overdrive unit. drop pan. change the filter. check the kick down solenoid. check vacuum line. i think 1st in drive uses a sprag gear and 1st with the shifter holds it with a clutch. so it still may be driveable as a manual shifted automatic.

 

Definitely go with overdrive, they have been around for decades, I bet it will cost about the same.

 

P.S. It is still going to be slow, these things came with less than 200 H.P., even Toyotas today have more power.

 

True a 200-4r costs about the same. It will take a different torque converter and some additional set up to get the pressures right,so it will likely cost a bit more, but may be worth the effort and $$ in the long run.

https://www.monstertransmission.com/...E#.YmsOvn7MJBM

or this base model rated for up to 250 HP

https://www.monstertransmission.com/...E#.YmsOiH7MJBM

 

I'd make you a deal on the th400 in my 74 as im going to be swapping a 2004r into my car but the way things are going I dont know when ill ever actually get to it.