I'm puzzeled by the upshifts in the Turbo 400 in my Riv. If I leave it in Drive, upshifts happen at around 5,200 1 - 2, and 5,000 2 - 3. It'll automatically downshift from Drive to 2nd at full throttle and run back up to around 4,800 before it shifts 2 - 3. But if I start in manual low it'll hold low at least until I hit the rev limiter at 5,600 and then again in 2nd gear, right up to the rev limiter. I haven't tried it with the rev limiter set to 5,800 or 6,000, but that's next. I just don't understand why it'll hold each gear when I'm manually shifting, but appears to be shifting off the governor (or something else?) when it's in Drive. I thought the governor overrode everything else. Any thoughts??
Governor and electric kick down switch at WOT, but at part throttle it's the vacuum modulator. Your kick down switch might not be working properly to override the vacuum modulator.
I'm no transmission expert, but I believe the actual mechanics of how each shift is accomplished, is different when you shift manually, or simply leave it in Drive.
You're shifting the lever before the RPMs max out, and it shifts later? Maybe a dumb question, but I have to ask, just to be clear. It may take some time for the transmission internals to move the fluid where it needs to be, at WOT with a manual shift. I do recall the "Dual Gate" Pontiacs. While I realize that this may be a different story, maybe it's related. Just a thought, though I think I've experienced the same thing, and made the above assumption about shift delay based on a manual shift. FWIW, I had a B&M built 350 trans in my '56 Chevy wagon with their "slap shifter", and when I hit the handle it shifted, now, leaving rubber, both upshifts. I didn't have a rev limiter, though...and I may have had it wound up a little above the preset governor shift RPMs, it being a 'Vette motor and all. :laugh:
The trans should hold the gear when manualy shifting as long as the lever or selector is not moved. L shold stay in L till you move to 2 no matter what the RPM's are. the electric kick down will hold it in gear till it reaches the set RPM limit or vac setting when in D. I like to run the brackets in D. Green light and hold it on the floor. The car shifts itself at the same time every time.
SteeVeeDee, nope, it shifts immediately when I move the shifter. I have the shift lite set for 5,600 rpm, and the rev limiter there also, just coincidence, didn't even realize it until I saw the tach hit 5,600, shift lite came on, and rev limiter came in at the same time. I was planning to run it up to 5,800 to 6,000 to see if it'd hold low that long. So then I just ran it up to 5,600 in second and shifted, which it did immediately. What I don't understand is why it'll short shift (relatively speaking) when I run it WOT in Drive, but it'll hold whatever gear is selected manually to well above where it shifts in Drive. See, I thought at WOT it was going to shift off the governor in Drive, and that it wouldn't make any difference by shifting manually. It's not a full manual valve body. Probably doesn't make any difference really, since I'd prefer to shift manually, and it seems to be shifting when I tell it to, at least up to 5,600. But I'd just like to understand what's happening. Just routine driving I use Drive and let it shift when it wants.
Briz, You must have posted while I was typing the previous response. OK, what you said is what it seems to be doing, and I'm fine with it working that way. It's just not how I thought it worked, I thought that the governor would override the shifter. But I'm happy with being able to hold it to a RPM higher than I get in Drive. Gives me something to do on a run, if I ever get some other issues worked out so I can get it to Cordova dragstrip in the spring.
First is first and second is second. If you use the trans the way it was designed than you'll understand that the gear you choose is the gear that's available. Selecting first means it'll only be in first and never anything else. That helps with engine braking and with low traction situations. If you choose second than you have both first and second available to you. If you bump it from first to second and it shifts instantly than that means it was already meeting the requirements to be in second but wasn't because that gear wasn't an available option. If the car decided that it could shift to whatever gear it wanted when you select first than people could potentially die. Drive a 4x4 in the snow and you'll understand why it'll allow you to stay in first no matter the rpms. It's all about torque multiplication and not top speed. Generally I find that manualy shifting an auto on dry pavement just slows you down or causes things to break.
Hmm, I'm pretty sure the governor overrides my manual shift on my Centurion. It shifts at 5200rpm no matter what, which I figure is because the governor. I put it in 1st and leave it there and it's quite jarring. It chirps the right rear at 45mph!
Yep, that's what I was expecting, that it'd shift to second and I suppose eventually to high even though the shifter was in Low. And that's the way I understood these things to work unless a manual valve body was installed. But now I've heard it both ways, so I don't know any more. All I do know is that it shifts when I move the shifter at 5,600 and hopefully it'll hold low and second to around 6,000 or a little less.
In a stock TH400 all W.O.T. shifts are a balance between the governor & line pressure. If you select manual low gear, line pressure is increased for improved clutch holding ability. That is why it shifts approximately 300 rpm higher than when the shift lever is in drive.(same governor weights & springs) 1-2 is also a "forced" shift. You can leave the lever in low but it will still shift to second gear when the governor overrides the line pressure. You can FEEL how much harder a TH400 shifts to 2nd with a "forced" shift. With a stock TH400 it is wise to ALWAYS use "manual low" when racing-like with sticky tires, because of the line pressure increase. You can shift out of "low" anytime after the forced shift to second gear. It will stay in 2nd gear forever. This applies to a STOCK TH400 transmission.
RDK, thanks, excellent explanation. So, hypothetically speaking, I can keep running to a higher RPM in manual low until I get to where I want to be (say a max of 6,000) and, unless it does a forced shift to second first, I can shift manually to second. If it does a forced shift to second before I hit 6,000, I need to modify the governor to raise the forced shift point, right? So ideally I'd be able to manually shift at the track at the RPM I want (I'm using Mickey Thompson ET Streets), but still maintain automatic shifts at other times? Right now I know I can manually hold Low and Second to 5,600 RPM, so I'll see if it'll hold to 5,800 or 6,000 without a forced upshift.
You are correct, but I would not play with the governor without reading Ron Sessions "How to work with & modify the TURBO Hydra-matic 400 transmissions. The Bible.
I race shifting manually as well. My tranny upshifts at a good rpm at WOT in D "IF" I do not spin the tires at all and "IF" I can mash the throttle quick enough from a launch without spinning tires "before" it upshifts. I hope this makes sense. In other words, when the tires spin it is simulating a part throttle acceleration, so it upshifts fast (I think that's my vac. modulator adjustment at part throttle that causes that quick up shift) but if I can keep the throttle mashed from the start, then the 1st to 2nd upshift is determined by the governor. While racing, I cannot take that chance, so I shift manually and it has worked well. I have shifted manually since 1985 so I know by the sound of the engine where I am rpm wise. I do not even look at the tach half the time.
Ken, I've always manually shifted also, but in the past I was using automatics with manual valve bodies. I didn't realize that line pressures increased in manual low and second when compared to automatic shifts. That sorta makes me think that there are disadvantages to modifying the governor to get the shift RPMs you're looking for and then just driving it without touching the shifter. At least if you're doing it regularly on the track and using sticky tires, as RDK mentioned. Plus, I just like shifting myself. I think if I had it to do over again I'd go with a manual valve body, even though it's a predominantly street car. Hell, this transmission doesn't downshift to Low when I come to a stop anyway. Need to sort that out next I guess.
