My transmission is shifting way too early and I'm thinking it has a faulty vacuum modulator. Looking at replacements online I see that some are adjustable with a set screw inside the vacuum port. Have not looked at mine yet, are the stock ones adjustable? What is the best one to buy?

 

I just replaced mine in my 67 442, TH400 with an adjustable B&M modulator. Stock ones are not adjustable as far as i know. This one will allow you to change your shift points a bit.

 

Mine is a switch pitch as well but i had the opposite issue. 2nd to 3rd was shifting at 3K RPM which was to high with 3:90's. After replacement it shift smooth and early. If i manually shift the shift kit is very noticeable and shift on command.

 

Did you play around any with the adjuster?

 

No, i was happy with the stock setting under normal driving conditions. If i need it to shift harder the manual shift seems plenty hard enough. There are some vids out there but i think clockwise gives a bit later, harder shifts, whereas counter would do the opposite.

 

If im just cruising casual im in 3rd gear at about 15/20 MPH with no hard shifts. 3:90 gears so is expected. If i step into it a bit my shift ranges spread out to higher RPMs. What is you shifting conditions? Did it change suddenly to early shift points? When you shift manually does it hold until you manually shift between gears? The vacuum modulator adjustment may be what you need if you want to extend shift points and firmness a little under normal driving conditions.

 

Car did this when I purchased it several months ago. Though not desirable it is drivable so I addressed some other issues first. It absolutely shifts way early whether normal driving or aggressive throttle. Will be in 3rd by 50mph at WOT, but it will hold the gears manually. I'm going to try a new modulator this week.

 

Does the kickdown/downshift work?

 

Yes

 

Would you describe the shifts as stacked, practically right after each other? If yes, first confirm good vacuum to the modulator and if that is good I'd try a new modulator.

 

You want full & constant vacuum established via manifold vacuum only. Could there exist the chance the automatic transmission modulator line is connected to a carburetor ported vacuum source instead of manifold vacuum source? I don't believe a '67 has a TVS or any other emissions nonsense which might interfere so ensure you're direct to a manifold vacuum source.

 

It's connected to an intake port and has good vacuum at the modulator. As soon as it starts rolling it starts shifting.

 

If it holds/maintains gear when shifting manually, it appears to suggest the modulator is suspect.

 

Tried a new adjustable modulator today with set screw one turn out. Still no change to early shifting. Pulled the governor out and let my transmission man take look at it. He said it had medium to light springs so we removed the spring on one side to see what effect that had. It still shifts early and I ran out of time for today. Had to free up my lift for tomorrow. Tomorrow I'm going to try it with vacuum disconnected from modulator.

 

Turning the screw in raises the shift points.

Keep in mind, at most you can change shift points 2-4 mph with the modulator adjustment. If you need a bigger change it’s time to start playing with the governor. Before attempting governor modifications, it’s very important to make sure the kickdown solenoid works correctly. Without the kickdown working, the trans will always tend to “short shift” at wot.

 

I'm thinking about adding a hand switch temporary on the kick down because it is hit or miss due to thick carpet at the accelerator. But first I need to get part throttle shifting in the ball park.

 

Tried it with vacuum disconnected from modulator and it would not shift out of low gear. Went ahead and bottomed set screw out and that helped some. At WOT now it shifts to 3rd at 60 instead of 50. That confirms modulator valve is not stuck and firmness felt pretty good. My next move is to get the B&M governor kit and start playing with weights.

 

Got a chance to work on the governor again today. Added the 2 lightest springs from the B&M kit but the weights would not fit..go figure. Anyway, I took one of the factory weights and ground 2 grams off of it. Tried it out and bingo, almost exactly what I wanted. Next chance I get I will remove 1 gram from other side and it should be spec on.

 

Great to hear. I will tuck this knowledge in my bag of tricks.