Hi All, 72 Cutlass 455 w TH350 both rebuilt in 2009 for mild street now with 15k miles. Moved to the mountains and going up one the other day trans hesitated multiple times (at 25 mph and warmed up). Fluid level and color is good. Has a reman. torque convertor with slightly higher stall & shift kit. Any thoughts? A tad nervous to run down the mtn and not be able to get back up. Tnx!

 

There are a couple possibilities. Beginning w/ the easiest check the automatic transmission modulator valve - is it leaking at the point it attaches to the transmission, not engaging, disconnected at the transmission, disconnected at the point where the vacuum hose connects to the metal vacuum tube (passenger side), vacuum hose came off the manifold port (it needs full manifold vacuum) or the carburetor full vacuum port.

 

Tnx for the response, will check the AT-MV, fingers crossed!

 

I reviewed several of your threads/posts to include incorrect routing of fuel/vent hoses e.g. canister/puking fuel. Hopefully that's been resolved. Hopefully you have an original OEM 1972 Oldsmobile Chassis Service Manual (CSM), if not buy a used paperback edition. Literally it's the bible for your car, tune-up, brakes, engine, cooling, fuel system, ignition, electrical (color wiring diagram) - just a plethora of info. Also, the 1972 Product Information Manual (PIM), sometimes referred to as the FAS (Factory Assembly Manual) illustrates exactly how your car was assembled as it rolled off the assembly line (well worth it's weight in Au).

A naturally aspirated ICE (Internal Combustion Engine) draws air into the cylinders w/o the aid of electronic fuel PCM/ECM/FYI management devices. The engine relies on intake pressure of the surrounding atmosphere to draw in air, which is then mixed with fuel for combustion. Vehicle manuals are written to accommodate engines which normally operate @ MSL (Mean Sea Level) +/- 1,000 ft. I don't know what mountain it is you're referring to, but "in general" you should expect to advance the timing ~0.5°/1,000' - 1.0°/1,000' increase in elevation for naturally aspirated engines as the air becomes less dense w/ altitude. Try increasing your timing & use a vacuum gauge to establish your highest vacuum reading during your tune-up with your carb. idle mixture screws. This would be the second area to evaluate besides functionality of the ATMV.

 

Thanks for the thorough research and response. I solved the cannister issue and have a 72 service manual, tnx. I did inspect the ATVM and replaced the short rubber hose at the VM. I am using manifold vacuum off a Quickfuel carb that went in last year. Drove Sat. and coming up mountain (2900-3900 elevation change), I did not get the stutter/hesitation as before but my RPMs were going up higher than usual and felt like I was losing torque or trans /TC was slipping. I will bring up the timing and check the vacuum. On another (unrelated) note, the TH350 had no issues until now, but ever since I installed the rebuilt unit (2006) I can't get the floor shifter to manually shift into 1st gear (it will when in automatic). The service manual shows what looks like a slot /pin adjustment (fig 2) but mine doesn't look like that- plz see pics and diagrams below, tnx!







Tnx again for your expertise!

 

I am not a transmission expert by any stretch. Worked on several (of my own), gotten by, know "some" things but there are FAR more knowledgeable members here.

Not really familiar w/ the Holley Quickfuel carburetors.

Before I mention a couple things, what you're saying is the only item you addressed was to R&R the short rubber vacuum hose between the ATMV & the hard steel pipe, drove it up the mountain you did not get the stutter or hesitation as before, except that you felt like you were losing torque or trans /TC was slipping & your RPM was higher. If all you did was replace that piece of vacuum hose & it no longer stuttered or hesitated it might suggest you better evaluate your overall vacuum on this engine. You should be able to develop a steady 17"Hg vacuum. Use a vacuum gauge & measure your vacuum.

As you noted previously, and I'll reiterate, you have a TH350 behind a 455 BBO + a reman. torque convertor with slightly higher stall & shift kit. Here's the extent of my knowledge. I know the TH400 sat behind the 455 from the factory, not the TH350. I know the TH350 is a direct bolt-in behind a 455 BBO. I've followed, heard, read about folks who bullet proof a TH350 when sitting behind a 455 BBO w/ no issues. I've also heard the exact opposite. Shift linkage differs between TH400 & TH350. That's about all I'm good for, unfortunately. Suggest you patiently await other members w/ more knowledge than myself regarding your latest questions. Again though, I'd measure your vacuum w/ a vacuum gauge to ensure you're developing a solid steady vacuum which could be part/parcel especially while under load (1) increasing in elevation (2) a TH350 sitting behind a 455 BBO (although, to this point I'd think if you matched up the TH350 correctly this wouldn't be an issue as long as it was done right) - there's obviously going to be more torque required during mountain climbing - will the TH350 handle that worse or better than the TH400 I am not the expert to help on this. Check your vacuum. Good Luck!

 

Are you sure it is not an ignition misfire? Ignition misfires usually occur under heavy load (like climbing a mountain).
misfires will feel like a stutter under load. First use your squirt bottle oscilloscope with the engine running (take a squirt bottle of water and spray each plug and plug boot and look for arcing to the head). Next pull each plug and inspect for any fouling or any carbon tracking on the porcelain. Next inspect both ends of each plug wire, a plug wire with a bad connection at the terminal will have black carbon looking soot inside the boot. Hope this makes sense

 

Yes. What is described strikes me more as points failure rather than transmission issues.

 

You definitely want to make sure your points are in good shape and properly adjusted. This is the primary ignition. Making sure you have a good hot spark from the coil is also a good test. You can do this with a cheap spark tester. Then you want to diagnose your plugs and plug wires for any issues. This is the secondary ignition.