Hi team!! move got a TH400 in the coupe that is shifting 1-2 & 2-3 really quickly (by 30mph). The gearbox doesn’t shift down on a hill climb either. I have adjusted the vacuum modulator all the way in (no change), replaced the vacuum modulator with a known good one (no change). Is it time for me to play with the governor? Any suggestions would be great!!
Check your vacuum source for the modulator. Is the hose collapsing or plugged? Next step would be the governor.
Those do shift kinda early stock. Especially 1-2 The down shift is electric. Mine will shift into 3rd by 30mph if just cruising on a level road. It holds out longer if in the gas.
Does it shift early regardless of throttle position? A stock THM 400 shifts very early and softly at light throttle. Does it make a difference if you remove the vacuum line to the modulator?
Play with the governor weights. This is external and easy to "trial and error" with a governor kit OR the governor "plunger" night be sticking [and need a good clean out] https://www.motortrend.com/how-to/hppp-1203-recalibrating-turbo-400/
Maybe I'm thinking of something else, but wasn't there different vacuum modulators offered ? They had different colored stripes painted on them to adjust the shift points.
The vacuum line to the transmission is connected to manifold vacuum and not ported vacuum ? Normal vacuum to the modulator usually comes directly off the intake.
My lil truck has a 4L-60 with a shift kit. It has ALWAYS shifted early. Goes into OD by 40mph. Good (I guess) for MPG but I wish it would wind-up a little more between gears too! Several guys told me it's the governor (maybe vice president, not sure) Best thing to do is pull-it-out-&-play-with-it......to change the shift pattern. Been that way since 91............I guess it doesn't bother me tooo much. Drill some holes in the governor to make it wind-out some. 6sally6
I had a TH400 in a stock car, I was looking for a better rear, so ran it for a few races in 1st gear. What I did not know that even with the lever in 1st... it will up-shift to 2nd at a certain RPM, to keep the engine from blowing. That it did, at the end of the front straight at Islip one night, like being shot from a cannon. I had concrete dust in my eyes and gritting my teeth. After replacing 1/2 of the front end and a new radiator later, I pulled the governor and safety wired the flyweights closed. Rebuilts are like $55, new ones are $95 and up.
Hi all!! Thanks for the input so far. Vacuum to the trans is 17in/hg which is spot on. Vacuum modulator is working good and the pushrod/valve in the trans is free. Moving to changing out the Governor weights. Will update once I’ve increased the Governor weights.
Is was mentioned early on, but do you have an electric kickdown wired in? There’s specific kind of switches used, nothing like a push*****on with a dead stop. Some are used with the throttle pedal****embly and some as I recall, are bolted onto the intake and somehow hook to the throttle on the carb? But both kickdown before WOT and still allow more throttle movement.
passing gear is electric. The******* should shift down on its own anyway. If it were mine I would look to the governor first. You should be able to get a spring kit with instructions from your favorite catalog speed shop. If that don't cure it look at the valve body you may want to buy a shift kit when you order the governor kit.
Duh on my part. I brain farted We had 2 OD transmissions not shifting properly. A 700 and AOD. Bowler sent a guy to fix em. I was asked to weigh the cars before he showed up. He changed springs in the valve bodies based on the cars weight. Then installed their lockup solenoid stuff. Trans worked great. I think it was Squirrel that suggested I use a shift kit in mine to help the fast 1-2 shift. This was during my build stage. I guess that would be my only th400 complaint. With the 350 I was using the early shift kinda*****ed sometimes. With the 500 it doesn’t seem to be near an issue.
Unless the******* is built to the hilt T400s have a tendency to shift a little slow. All the internals are pretty heavy and that makes them a little sluggish. There is way more to tuning a******* then putting it in there and filling it with fluid. The guys that build 'em and know what they are doing to make one do everything but roll a joint.
Dang skippy. We had a fresh built car come in with a smoked trans. Car owner didn’t get to drive it far. I pulled the trans to find a very small race converter. This was a street car with overdrive. I’d imagine the trans died a very hot death. Our trans guy built one based on engine specs, weight……worked great.
Phoenix will do that for ya. We had them build a 700R for a 60 el camino several years ago. They wanted to know the vehicle, the cubes and the cam specs. The******* was plug and play.
I love 200R4 OD*******s gut they tend to shift early for stock grocery getters. Of course OD*******s only use the TV linkage for control and NEVER try to adjust shift points there. That will guarantee a fried box in a few miles. The shift points are controlled by the governor and i am sure the same goes for the earlier 350/400 series. The 200R4 governors are surprisingly inexpensive. Last time I got some they were $12 on the internet. That's cheap enough to ruin a few before getting the shifts perfect. To raise shift RPM, shave weight off the centrifugal weights. On the 200 I also remove a bias spring on one of the weights which is equivalent to weight shaving. Right shows stock governor with weight to be removed in black Sharpie. Left has the weights ground. Same thing just a different view. Here is the spring I remove. I braze a stub in the weight that keeps the spring to retain it. Unit throws these springs on hard shifts if this mod isn't done.
The Jalopy Journal
