Steve69

Hey everyone, my name is Steve and I'm new to the forum. One week ago today I purchased my dream car, a 69 Cutlass S. I have the 2 speed "Jetaway" transmission and my problem with it is it shifts very harsh down from 2nd to 1st gear when I'm coming to a stop. It stays in 2nd until I'm down to 8-10mph then bangs down into 1st quite roughly. When accelerating it's fine, shifts into 2nd smoothly and everything is ok. I've been popping it into neutral when coming to a stop to avoid the harsh shift. Any ideas? The car has 59K miles and everything is original and working, even the AC! The tranny appears to have it's original vacuum modulator on it, could that be it? Fluid looks good and does not smell burnt, and is full. Any ideas would be greatly appreciated, thanks!!!

oldcutlass

Check to make sure your vacuum modulator line is connected to manifold vacuum. If that is connected pull the line off the modulator to see if its leaking. If its leaking, and/ or your line is connected to manifold vacuum, would say you had a bad modulator!

Steve69

Thanks for the quick reply! I forgot to mention that I checked the line and it was fine, no leaks or blockages, hooked up secure on both ends, no fluid coming out. NAPA has a modulator for $11 so I'm going to give it a try, I'll report back with results.

501Paratrooper

Welcome to CO.

Steve69

Thank you paratrooper. I installed the new modulator and no change at all. any other ideas?

oldcutlass

Have you made sure you have manifold vacuum to it??

Dapapadon

I had the same problem on the first 67 CS I had. I ended up buying the current 67 in the garage and swapped the motor to this car. But from what I remember from my research and troubleshooting the modulator isn't the problem. It controls downshift under hard acceleration. I did like you and replaced it with no change in the problem. Again this is from memory (and that's failing) but I believe there is a ball and spring associated with the governor that controls deceleration down shift. On my car it had sat for years and there was rust in the governor that was the problem. The trans worked fine when I first got the car running. But developed the hard downshift pretty soon afterwards.

Can't tell you how to fix the problem as another car came my way before I solved it. But if you're near the Portland, OR area I have a ST300 you could have. Not the one I had problems with either.

Don

Steve69

The modulator is getting vacuum. I also removed the governor and everything looked fine. so i decided to drop the pan. There were some small metal flakes in the pan similar to glitter. I've seen this in other trannys and had no problems. Fluid was slightly dark but didn't appear or smell burnt. I'll report back when I get the new filter and fluid in.

Steve69

OK, so far I've replaced the vacuum modulator, removed and inspected the governor and it was fine, dropped the pan and changed the filter, and added new fluid (about 3.5 quarts). AND, I still have the same problem. It's not as harsh as it was at first but still enough of a jolt to cause concern. It used to happen around 10mph now it happens around 3-5mph. Time for an upgrade.

oldcutlass

How much vacuum are you getting at the modulator?? The only time I ran across this is when I first bought my car and the PO had the vacuum connected to ported! As soon as I connected it to manifold it cured it! I went ahead and changed my modulator becuase it was weaping!

Dapapadon

Forgot to say: "Welcome to CO!" Now that you've decided to upgrade a turbo 350 will work w/o modifying the drive shaft. You'll just have to figure a way to hook up the detent/downshift cable to the carb. So while you're looking for a trans. how about some pictures of that 69? We like pictures!

Anybody that has never had this downshift problem wouldn't believe how hard it Bangs when it downshifts. I did like you and popped it in neutral till I stopped then back in gear. It was a pain, but I was afraid it would break something the way it banged into first.

Don

oldcutlass

Yeah it feels like you've been rear ended!!!!!

X2 on the welcome!!

Steve69

You guys are both right. It feels like something is going to break! The vacuum line goes into a plastic tee one end goew to the carb and the other goes to a thing toward the front of the manifold that has 2 other vacuum lines attached. Should the line be going somewhere else? Straight to manifold? Thanks for the welcome!

atkinsom

Perhaps post some pics if you can of the setup and questions that the fellas are asking about. Maybe there's something that you missed...a small thing...you never know. Alot of smart guys in here that can pick off things you'd never think of

oldcutlass

Run a line directly to the modulator from manifold vacuum and see if it corrects the problem. You may have a leak, from where its coming from now???

Steve69

Sorry about the delay guys, things got hectic at work. Yesterday I noticed I had a vacuum line going from one port on the manifold to another. So I put the modulator line on one and ran the other to where the modulator line was going. Car runs the same but the ROUGH DOWNSHIFT IS GONE!!!!!! I'm so glad, the car is driving great now. Thank you all for the help, it's greatly appreciated.

455man

I was going to mention that i had a vacuum leak on my line but it was the steel line that goes down to the tranny. I checked the manifold vacuum and the vacuum at the modulator and there was a 10 lb drop. Replaced the vacuum line and shifted fine afterwards. Glad you got it fixed but we still want pics

oldcutlass

Glad you got it fixed!!!