On a lark, we picked up a 77 Vette at auction. Have no idea how the drive train is built but the engine runs pretty strong with a lumpy idle and solid lifters for sure. The car has a deep limited slip rear end. The engine turns 3500 RPM at 60. The engine and TH tranny look like they have zero miles on them since they were built and coupled together.

Here's the odd part. The tranny shifts very positively and, when cold, snaps into reverse. It can chirp the tires. When hot, (after running on the freeway for a few miles), shifting into reverse at idle stalls the engine. It's as if the torque converter is locked. Shifting from neutral into drive at idle also can stall the engine when hot, but it isn't a sure thing.


Anyone have an idea what might be wrong? We've installed rebuilt TH tranny's with no required break-in and have never had a tranny stall the engine when shifted into reverse and/or drive. But we aren't auto trans guys by any means, considering them black boxes insofar as our skill set is concerned.

Are there drag racing setups that have really tight torque converters? Is there a fix for a torque converter that's too tight (if that even makes any sense)? Is it possible that there's a lock-up mechanism on the torque converter that isn't hooked up correctly? What else should we be thinking about? Thanks for any suggestions.

DylanT

 

Which TH trans- 350, 400, 200-4R, 700-R4? Maybe even a 350C? Idle RPM?

 

I crawled under the car but couldn't find the tranny serial number. Let me look harder. Can't assume it is original that's for sure. The car is idling about 1000 rpm. I've since learned that newer trannies had solenoid activated clutches. I'll see if this one has that type of wiring.

 

 

great. if these patterns are looking up, then it's the 350. also the rear end has a red tag that says limited slip. Was this an option in 77 or did someone retro fit it from an earlier model?

the side pipes are so low that I can't see the side of the tranny very well. I need to take the car back to my "shop" and run it up some ramps if we require more visual info. This I can do tomorrow.

Thanks,
Rex

 

This is interesting. Can you hold the car in gear at a stop?

So what happens if you drive the car and get it up to operating temp. and then set the idle speed and mixture with the car in gear? I would try to set the cars idle when warm while at a stop in reverse.

You might check your timing numbers too while making these adjustments. My thinking is if you can get it to idle at a stop in reverse it may be able to transition between park and reverse without dying.

If the car has a big cam that is pushing your idle speed up and the previous owner went back with a stock torque converter , you might look into another converter that will slip a little.

 

Is it wired? Maybe somehow it was converted to a lock-up system?

A lock-up converter will stall any SBC engine if it does not unlock at idle.

 

Let me report back on setting the idle in reverse with hot engine. I don't think I can do it below 15 or 1600 rpm. But let's see. I'll check the timing just so we know.

But I'll also get under there and see what sort of wiring is coming out of the trans. I've now seen on some other discussions that failure of a TCC to unlock is not ALL that uncommon.

More later after I have more symptoms/info.

Rex

 

Sounds like a good plan! Being a rookie, I want to learn what happened and what can be done.

 

We spent some time with the car today and can report the following. First, the carb was way too lean on one side. Fixing that improved the idle. Second, the tach seems to be reading twice the actual rpm. We put a second electric tach on and also checked with a laser (external tach). The idle rpm we thought was 1000, dropping to 800 in drive, was actually 500 dropping to 400.

SO - we upped the idle to an honest 800 at idle and 600 in drive. This and the carb mixture adjust helped a lot. The car still stalled a few times once it was fully hot.

We may have to up the idle speed one more notch but it looks like we might be able to get things under control. There is no electric clutch on the th350 in the car. We're guessing that a higher stall torque converter would also be a good idea. If we let the car roll in drive at idle it moves pretty good.

Thanks for the tuning suggestions. We now have to understand why the tach reads twice the true rpm. But that's another topic. It fooled us though. ha ha. The cam doesn't seem so lumpy anymore either, now that the rpm is up to normal. We kind of liked the lumpy sound at 500 rpm!

Rex

 

Thanks for the info....that's about the same thing that happened to me today! I used about 3/4 throttle to merge....the '34 truck SBC wanted to keep on "trucking" at 50 MPH with my foot off the accelerator. After I found a place to pull over I managed to move every piece of carb linkage and both sets of butterflys----still 2500 RPM!

For some reason the idle adjust screw was three turns "too tight"!?!?!?

 

Vacuum leak and/or timing can cause stalling when placed in gear. I would play around with that first. Just mark where you started with the timing because obviously it sounds like that's far from a stock engine.

 

Vacuum leak and/or timing timing advance can cause stalling when placed in gear. I would play around with that first. Just mark where you started with the timing because obviously it sounds like that's far from a stock engine.