1981 Camaro Z 28 350, 399 horse W/ 350 turbo transmission three speed automatic
Hello. I’m working on my 6th transmission on a car I’ve had for ten years. This one was “built “ at a professional transmission shop. Transmission went out just months after warranty expired. Going up a hill and it’s like the car went into neutral. I was able to coast it home. I have park and 4 neutrals now. I put it in drive and I can see the tourqe converter is moving but it’s not translating to my transmission. What could be possible issues?

It is a gen 2

 

Have you put a new torque convertor in with each new trans?

 

Imsport’s question is vitally important, to that I’ll add were the transmission cooler lines and the internal to the radiator cooler throughly flushed or replaced?

Bogie

 

Yes, this last one was built and installed by transmission shop.

 

I can see that the torque converter is spinning when I put it into gear, the drive shaft does not spin. It doesn’t make any noise, it’s like neutral.

 

Have you checked the fluid level, engine running and trans in park, at operating temperature?

Torque converter is a fluid coupling, just because the external case is spinning doesn't mean the internal turbine is transferring power to the input shaft.

Low fluid level, clogged filter, broken stator in converter, broken front pump gears, burnt clutches are all possibilities when it won't function.

As a test, start the car and then crack a trans cooler line fitting loose to see if the front transmission pump is actually pumping fluid....if no pumping, you'll have no gear activation in the trans.

 

Have you checked the fluid level, engine running and trans in park, at operating temperature?

Torque converter is a fluid coupling, just because the external case is spinning doesn't mean the internal turbine is transferring power to the input shaft.
Low fluid level, clogged filter, broken stator in converter, broken front pump gears, burnt clutches are all possibilities when it won't function.

As a test, start the car and then crack a trans cooler line fitting loose to see if the front transmission pump is actually pumping fluid....if no pumping, you'll have no gear activation in the trans.

Thank you, I will try that first thing in the morning.
Fluid levels appear to be fine. I checked that first thing. I was driving uphill, had it screaming, halfway up the hill it was like it went into neutral. It didn’t make any pops or bangs.
I will drop the transmission tomorrow as well. I will pull a cooler line first, with the car running.

 

I cracked the upper line going into the radiator. As soon as I did, fluid started pushing out.

 

Sounds like pump is fine then, so you can eliminate broken pump gear from the list.

To check further you'll need a trans pressure gauge, to see what pressure is when in each gear position, this would be to diagnose if the manual valve came unhooked inside the pan without having to remove the pan first.

From this point it could be manual valve unlinked, or it broke or stripped splines off a shaft or sun shell or other geartrain failure. Maybe input shaft stripped out of the forward clutch drum. Could also be input shaft spline twisted out of torque converter turbine.

 

I was going with a pump issue until you mentioned checking the cooler line. Now I am leaning towards the rooster comb coming loose allowing the manual valve to slip out of place. Without a trans pressure gauge available, you would need to drop the fluid and pan to take a look.

And while I don't want to beat on a trans shop - that's never a guarantee that the trans is right. A lot of places pull a unit apart, slap a rebuild kit in it and out the door it goes. Unless broken parts fall out of it, the same hard parts goes right back in it.

 

Since this car is a 1981.... Does it still have the Thm-350C transmission? Or is there a THM-350 non lockup transmission installed? The lockup converter on the Thm-350C had internal durability problems. A turbine hub broke off would stop all power transfer as you describe. A Thm-350 non lockup converter can have the same turbine hub problem inside , but is far less common of a failure.

 

This...

 

I will drop the transmission and check the spline.

 

This is the 6th transmission in 10 years.

 

Brother if I were you and all the money you have spent I would just call up Summit or Jegs or even Jasper and get something that's going to stay together just saying

 

TH350 or TH350C?
This may be one of your problems.

 

TH350 or TH350C?
This may be one of your problems.

I don’t know, what is the difference? I may be able to tell you more.

 

If the “C” is for computer, it hasn’t one. It is a 3 spd auto

 

The “C” designation indicates a lockup converter.

 

Also, this isn’t factory engine. This was built by a guy almost ten year’s ago that doesn’t flinch at 7500 RPM. when this transmission went dead on me, engine spiked to near maximum before I lifted and it never sweated it.

 

Sounds like the motor needs a matching transmission.
TH400.

 

The ‘C’ stands for lockup convertor.
if there’s a switch above the pan rail on the shift arm side that would indicate a 350c.

 

Sounds like with the engine you have it needs to be backed up with a built TH400. If you’re eating a built TH350 every couple years it sounds like they aren’t strong enough for the torque going through them.

Do you have reverse but no forward gears or absolutely nothing?

Bogie

 

1981 Camaro Z 28 350, 399 horse W/ 350 turbo transmission three speed automatic
Hello. I’m working on my 6th transmission on a car I’ve had for ten years. This one was “built “ at a professional transmission shop. Transmission went out just months after warranty expired. Going up a hill and it’s like the car went into neutral. I was able to coast it home. I have park and 4 neutrals now. I put it in drive and I can see the tourqe converter is moving but it’s not translating to my transmission. What could be possible issues?

What kind of torque you got? Is the same 350 core being rebuilt over and over? Are you sure that the dipstick and tube match? If they don't you could be running a few quarts low of fluid. Also, the cooler could be restricted although not stopped completely.

 

I’m not sure of the torque, no different cores. The transmission before this one was a B&M. It lasted 2 years as well. Went this one failed, it never stuttered or coughed or a hiccup or nothing. It was as if it went into neutral. Now I have park and four neutrals.

 

1981 Camaro Z 28 350, 399 horse W/ 350 turbo transmission three speed automatic
Hello. I’m working on my 6th transmission on a car I’ve had for ten years. This one was “built “ at a professional transmission shop. Transmission went out just months after warranty expired. Going up a hill and it’s like the car went into neutral. I was able to coast it home. I have park and 4 neutrals now. I put it in drive and I can see the tourqe converter is moving but it’s not translating to my transmission. What could be possible issues?

Sounds like you blew the forward clutch pack Or stripped the spline off the input shaft. With close to 400 HP I would dump the 350 and go find yourself a turbo 400 to bolt in there. Used to rebuild these things back in the late 70s and found many broken 350s. Never saw a broken 400. Burned up clutches and bad seals but never a broken gear set os twisted off shaft.

 

Stock TH400 is going to take everything your 400hpSB is going to bring. Stop with the TH350 silliness unless you want to drop big $ into it.

 

Ok, advice taken. I will look into 400.

 

So the 400 should just drop in? Is any specific build I should look for? This is for a 3 speed automatic.

 

Might want to check out 350 and 400 length differences below. Not shown is output shaft spline count which is 32 compared to 27 on the TH350.

Also, the TH400 has electric kickdown. Instead of a cable the TH400 uses an electrical switch that is usually mounted on the carburetor linkage.

Finally, I'd talk to Phoenix Transmissions about your problems before giving up on a TH350. Sounds like your engine's torque (around 400 lb/ft?) can be easily handled by a properly built TH350.

 

Thank you !! I feel the same way. There’s no reason why a 350 can’t handle this motor. I am going to talk to Phoenix transmission before I moved to a 400, thank you for this information.

 

When the other trans have failed, were they taken apart to find the reason they are failing and have they all failed the same way?
Sounds like you need to determine the reason it failed, then you can figure out the cause, and then you can address how to fix it and what trans car needs.

Also is this a simple street cruiser or do you drive this like you stole it, which means your 2 years of fun could be equal to a 100k of easy street driving.

 

I drive it like I was 16. In town, I drive easy but seldom do I drive under 100 on the interstate. I don’t lite the tires often but I get to the speed limit ASAP. When I drive through Chicago, I race every BMW, Merc, Audi, Mustang etc that pulls next to me. It’s not uncommon to drive 125+ on the 55 or 94.