The Stovebolt Site Forums The Shop Area Engine Shop TH350 Question

When I shift the trans manually, there is an audible "screech" from the transmission when shifting from 1st to 2nd. It's not as loud from 2nd to 3rd. It makes no noise when it shifts in drive.All shifts are nice & "crisp" though. Fluid is not brown or burnt. What could be the cause?
Thanks,

Jim Sgrig

Piewagon,
You didn't say if you have a shift kit put in or if you are using a floor shifter. This is a wild guess, but I have seen some wierd things in mechanics. Using a shift kit, the noise could be the hydraulic fluid forcing its way through a passage way when using manual shifting. If you are using a floor shifter, check your linkage, a rod or brace may be scrubbing the drive shaft or universal when the lever is moving during hand shifting and isn't touching when in the drive position. I have rebuilt many th350 trannys and right off the top of my head, I can't think of any internal problem that would act like you describe. I find in mechanics that a good visual inspection uncovers many probable causes.

Truck Tinker

hey Tinker,

I've got a TH350 in a '67 LeMans street/strip car. What mods do you recommend to get a crisp shift and good lifespan behind a big pontiac engine?

When manual shifting my car (B&M quicksilver) at 5,000 RPM out of 1st, there is a delay before the tranny grabs 2nd. What gives?

thanks

chip

TT,
It's a stock th350 w/50k miles on it. I've just installed the floor shifter. There is no interference w/cable or other components. I'm not familiar with the internals on a th350. I thought maybe one of you guys could shed some light on this concern. Fluid rapidly passing through one of the circuits sounds legitimate.
When shifting manually, doesn't that engage the band for second gear? I appreciate the input.
Thanks,

Jim Sgrig

I doubt very much that the screeching you describe is from hydraulics. Automatic transmissions are not supposed to make any noise and if they do, it is usually associated with the various rotating elements. Please clarify something... is the noise only occurring when you manually shift from 1 to 2 and 2 to 3? In other words, when you put the transmission in "Drive" and the transmission upshifts on its' own, does it still make the noise? This is important because there is a difference between 1st gear while in "LOW" vs 1st gear while in "DRIVE". Different components are locked/unlocked and it may be the key to your noise. My first guess is that you might have a noisy/slipping low/reverse sprag.

Only when shifting manually.

JS

The difference between Drive and manual Low is the low-reverse clutch. It's applied in Low range for engine braking, and the low roller clutch is the only thing holding in 1st. gear drive. I'll second the suggestion that the screech is probably the roller clutch. It's a weak point on the 350. Every snowstorm around here, I could count on at least one trans failure from people "rocking" the car from reverse to drive to get unstuck. The car would come in with no movement in drive, but it would pull away from a stop in low range.

Shift kits are a big mistake. Just about every failed rear end I've encountered was in a car with a shift kit, usually with an elongated hole where the spider gear pivot shaft fits. For a better-performing TH 350, I usually machine the clutch pistons enough to add a fiber and steel plate to the assembly, and don't mess with the hydraulic circuits. Now, I'm sure it's time for all the experts out there to inform me I'm all wet!
Jerry

I feel the same as Hotrod on the shift kit. I had one in my son's camero a number of years back. Don't remember the brand, but it was rough on universals and the stallspeed arms twisted off at the flex plate behind a much too powerful engine for a teen to drive. The 700 in my 91 has a snap shift and I have wondered when it would go bang since I had the truck, but after 13 years it still works well. It must be designed to take the pressure. You might go to a TH400 and get a better shift without having to put the accessories on for the overdrive 700. Piewagn, you might pull the pan and strain the fluid to see if you can detect any metal shavings in the oil fluid or pan. If it is a sprag or some spacer, it wouldn't necessarly burn your fluid and it could tell you if there is an internal problem.

Truck Tinker

Well Guys. When I first heard the noise I had a sneaky suspicion that turned out to be right.
The friggin' fan belt!!! I tightened it up a little bit, and, the noise is gone. That just goes to show ya, don't over analyze everything.
Sometimes it's the silly little things!!
Thanks for all the input,

Jim Sgrig

Don't feel bad, Piewagon, years ago I diagnosed an engine with a rod knocking and it was the fan belt. If I hadn't decided to turn the car around after I had the radiator, fan, belts and pulleys off and the noise stopped, I would have pulled the engine for a rebuild. That's the way it goes in mechanics sometimes. When in doubt, ask someone.

Truck Tinker

I'm just glad you didn't pull and disassemble your trans based on what I thought was going on!

Well my second thought was the band slipping. I know when you shift manually, the band reinforces the shifts. And, since the band releases into third gear, I eliminated the band as the source, because, I still had the noise into 3rd gear. That's when I went to investigate my first suspision. Believe me SoTx, pulling the trans was last on the list. Thanks for your input. TT, There was a guy that worked in the bay next to me.
He had a K1500 towed in with the engine locked up.
He never pulled the serpentine belt off to try a breaker bar on the crank pulley. He just went & ordered a short block. Put it all back together, same thing!! I suggested he try turning the engine over without the belt, engine started. Turns out the alternator was siezed. Condemning a major component is usually the last thing on my list, unless circumstances dictate otherwise!!
Thanks again guys.

Late getting to this one but I was going to say "Tire Squeal"
Chiphead,If you want a firm 1-2 shift, remove the accumulator cover, remove the heavy spring and install a 2&5/8 inch piece of oak broomhandle. The accumulator absorbs the pressure and slowly applys the clutches for soft shifts.
I have ran my current TH350 tranny for 7 or 8 years and working it hard Biggest load I had pulled was 20,220lbs on a slow 100 mile trip up 5 fairly steep passes.(until I had an accident, but it will get back on the road some time soon I hope).
Remember, ANY slippage of the clutches in an automatic tranny (soft shifts) means that the clutches are wearing