TH400 shift patterns - NOW I NEED HELP !!! I have a fresh rebuilt 400 behind my 455. It shifts very quickly. Is this determined by the modulator? What is the purpose of a modulator in a 400? And what (if any) adjustment are made via the modulator? Also, I had a new 2 wire kickdown switch put in, and the kick down is not working. I have not got down and checked the switch for continuity yet, but how does this kick down work exactly? I know the switch is being made, as far as adjustment. But I do not know if there is supposed to be a voltage there or not. This was all done for me in NY by a Buick guy who put my motor in during my move to GA. Thanks for the help, Mike
Mike, The 400 will shortshift if the kickdown is not working. The transmission determines proper shift point and feel from 3 inputs. The governor(vehicle speed), modulator(engine vacuum indicating engine load), and kickdown signal(throttle position). The kickdown is very simple. The gas pedal switch has 12 volts with the ignition on. When the switch is activated by the gas pedal, it passes the 12 volts down to the vertical tang on the drivers side of the transmission. This activates the downshift solenoid in the pan. The downshift solenoid controls hydraulic pressure to the detent valve in the valvebody. You can apply 12 volts directly to the transmission, and listen for a click, from the downshift solenoid. If you hear the click, look at the wiring between the switch and the trans. Determine where you are loosing the 12 volts. Use a test light or ohmeter to check. The modulator can be adjusted for minumum shift points, but only within a range of 2-4 MPH. Fix the downshift system first, then evaluate your shift points.
Larry, Are you out on LI? If so, you must know who did the work for me... Thanks for your answers. But it seems that I may have another problem. Like I said, a Buick guy put my motor in for me and had my tranny rebuilt during my move to GA. The tranny had a 1 wire solenoid in it origonally and he told me it needed a 2 wire setup. He had it put in during the rebuild. What you told me makes perfect sense, but I now have 2 wires going to the tranny. What is this situation I now have? And can I overcome its not currently working at the time without pulling the tranny out? I take it the governor shift setup is performed during rebuild, correct? Thanks again...
Mike, Could be any number of guys. Do you have his name? In any case, there are 2 tangs on the side of the transmission. One runs vertical, the other horizontal. The horizontal one is used either for a switch pitch or in the later transmissions, for a smog switch.(Part of the Transmission controlled spark advance). It is possible you have the wires reversed. Use a test light to determine which wire has 12 volts when the gas pedal switch is pushed, then connect it to the vertical tang. After you get the kickdown working, see where your WOT shift points are. If they are not where you want them to be, you can remove the governor and modify it with the B&M shift point modification kit. It has weights and springs. The governor is easy to remove, it's behind the 4 bolt square cover on the passenger side of the trans.
Could I have a stuck valve now? Here is what I found. The switch had 12V on one side, and was working when detented with 12V out. But he had the 12V through the switch going to the horizontal tab. And the other was connected to ground. I switched them around. I heard a click one or two times. So I went for a ride. Now it will not shift until I hit the WOT shift point. I even disconnected the connector from the downshift switch and it was still the same. I removed the ground to the horizontal tab before removing the connector. Here is another description that is going on. When I let off the gas before I shift, it is like in a neutral if I am in drive or second. But will rev up if I downshift into first when rolling and no gas given. Kind of acting like a manual valve body when in drive by being in a coast mode. What have I done here??? Help please !!! Mike
Mike, Sounds like the downshift solenoid is stuck open. I would drop the pan, and take a look. The solenoid is bolted to the case right next to the valvebody. Two bolts, and disconnect the wire, and it comes out. You can get a replacement at a transmission shop. You can test the solenoid when it is out, by applying, and removing 12 volts.
So I have to drop the pan to do this? If so, this really sucks. What a pain in the butt. What would have caused such a thing? Would a reverse polarity in the origonal condition before I switched it today? I am kind of curious. Thanks for the help, Mike
Mike, yes, you must drop the pan to get to the solenoid. Before doing that, try applying 12 volts directly from the battery to the detent (vertical terminal). If you can hear it clicking, I don't think it's stuck. Try doing that a few times, then take the car for a ride. Check all the simple things first. Make sure the modulator is connected, and has a leak free vacuum supply. The only other thing that would cause your problem would be a defective governor. If this transmission was rebuilt, everything should be good. The governor is behind a 4 bolt cover on the passenger side rear of the trans. You'll lose about 1/2 pint of fluid, if you remove it(very easy) Make sure the weights move freely and nothing is stuck (gummed up). BTW, unless your trans is a switch pitch, you don't need a wire connected to the horizontal terminal. In later years this was used for a pollution device. (I'm sure you don't need that.)
YEEEEE-HAAAAAW !!!!!!! I went out today and started to look at it. I used a battery and it was operating properly. I then chacked the output of the switch and it worked fine. I chacked the wire going to the connector for the tranny, and it had power all the time. The guy that put all of this in used a wire that was not the correct wire and had constant 12V with key on and ACCY. I tried to find the correct wire in the harness and I could not locate it. I ran a temporary wire for the time being. I went for a test run and it worked fine. It seems to be shifting a little earlier than I would lie to see it do. Next step is to put my tach in and then adjust the governor, hopefully. Does anyone know exatly where that wire comes out at? I checked in the harness that comes out above the fuse panel and runs above the brale booster and I did not see it in there, and even tested all of them to make sure. Thanks for the help. Mike
Glad to hear you found the problem. Depending on whether your car was originally equipped with a THM400, there may not be a wire. Just run your own, as long as it works, that's what counts. Stock governor will shift at about 4800 RPM. Just get the B&M shift point modification kit, and start experimenting. It took me 4 tries to get it right. It was fun though.
My car is a 350/350 car. But the harness is there with the two yellow wires together supplying the 12V on one terminal and the other terminal is the black with white stripe going into a harness. I guess using the wire I ran today is just fine, I need to clean it all up. I priced the kit at Summitracing at $29.99, and then the handling is around $8. I will check my local prices and if not any better, I am sure I will be able to think of something else to help divide the handling fee up. Went for another ride this evening with the wife. It sure feels good downshifting. Even when it will not downshift anymore, the motor lifts the front end up nicely. I am anxious to get out and see what I can do now. A guy that has a garage in town that we get together every Wednesday night asked me a few weeks ago what I thought I could do in a 1/4. I said I am pretty sure I have a 13 second car. He sort of chuckled and said that a lot of people think thier car is faster that they really are. He has a computer that you attach to the windshield and plug into the cigarette lighter. Once it is leveled, you can take off. It measures acceleration and gives a 1/4 mile time. He states it is very accurate. I am ready to give it a go now, after I put my tach in for shift points for now. I am sure I am at 13 seconds, with 1970 rotating assembly, 1976 block, 1970 heads with Stage1 valves, Performer intake, John Osborne balanced carb, 104 cam, manifolds through TorqueTech 2 1/2" with X-pipe and Dynaflows connected throuth the TH400 and 3.90 posi with P255/60R15's. My only problem is that I may top out before 1/4 mile with the gear/tire combo. What do you think? Thanks, Mike
Mike, I wouldn't worry about topping out in the 1/4 mile. With the 27" tires, your gears are a little reduced. You'll probably be around 5100 RPM. That's perfect, right at the horsepower peak. I have 3.42's. This past Buick Performance weekend in Sept, I used 275/60-15 Drag Radials which are 28" tall. I went through the traps at 4200 RPM. I need a shorter tire. I have a G Tech, but it is not accurate at all. I think I didn't have it mounted correctly/securely enough. I'll have to figure it out when it gets warm again. It was a second and 10 MPH off. The car went 13.585@ 99 MPH in the heat and humidity, and with those 28" tires. The G Tech said 12.6@109.
