I have a 1970 455 & TH 400 in my 1971 convertible. i am thinking to 1-2 up shift happens way too quickly; also when coming to an intersection it seems that unless you come to a complete stop it doesn't shift back to first at all. I've read a bunch of threads about this same condition and the general sense i get is that the down shift function needs to be working correctly and then if that checks out then look to the vacuum modulator and then if everything else is in good shape then the next step is messing with the governor fly weights. The engine is a pretty much stock SF 455 with a Poston GS 116 cam and the engine makes 20 Inches of vacuum at idle and runs pretty well; the converter is a stock unit to the best of my knowledge. I just feel like if i could get it to stay in each gear longer it would perform much better. If i am driving normally in 3rd gear and mat the accelerator the transmission will down shift into second and take off pretty well, if i stay in it it will bark the tires on the 2-3 shift so the down shift function is working and the engine seems to make decent power. My first concern is the wiring to the transmission. I have a new M&H 1971 engine harness which is set up for the TCS and thermovac which i do not have on my engine so i have just left these coiled up and tucked out of sight. Presently there is a wire that has been tapped off the down shift switch on the accelerator linkage under the dash which runs to the transmission to control full throttle down shifts. Is there something I am missing with the 71 harness and the 70 transmission? What else i should be looking at in terms of wiring in order to slow down the 1-2 up shift? if my present set up is correct what would the next trouble shooting step be? I assume the modulator first then the governor but maybe i am overlooking something obvious. Thanks in advance for the help
Tom, There are 2 types of down shifts, hydraulically actuated and electrically actuated. The later valve bodies have a 3-2 valve, something the earlier switch pitch VB lacked. I can get my transmission to downshift without the gas pedal switch connected at about 40 MPH, by just pedaling it some. You can read more about this in Mark DeConti's article on George N's site. When I bought my car, it had a stock 67BT SP transmission. While I could get my 1-2 to 5500 RPM, it would short shift into 3rd no matter what I did to the governor weights. It would also not down shift until full throttle. I switched my VB to a 71 unit, and I gained that Part Throttle downshift and was able to raise my WOT shift points to 5500 and 5400. http://www.buickperformanceclub.com/SPTrans.htm If I read your post right, your electric kick down is not connected, and that will cause your transmission to short shift. You have to connect that up, and then evaluate the shift points. The modulator can adjust the minimum throttle and part throttle shift points, but the adjustment range is small. Changing the governor weights is the way to adjust full throttle shift points, but first, you need the electric kick down hooked up.
Ok i guess i didn't explain this too well. there is an electrical connection from the accelerator pedal switch to the transmission case on the drivers side. Is this the only connection or is there another one i am missing? Is there a difference between the electrical connections on a 71 vs a 70 transmission?The connection i am presently not using is a 2 conductor connection but the only connection i have seen is a single conductor connection that is presently connected to the accelerator linkage switch. If there is another one that i am missing where might i find it?
No, no other connection. SP cars used a two prong connection. The vertical prong was the kick down, the horizontal one was the stator control. Later transmission also used the 2 prong connector, but it was for the TCS Emissions system, and led to a pressure switch on the valve body. So your single connector is more common, and all that is necessary for proper function. But, just because it is there, and connected, doesn't mean it is functional, and the presence of a part throttle kick down, doesn't mean the electrical system is in fact working. What you need to do is follow the wiring and check for voltage at the gas pedal switch, and down near the transmission. Then check the down shift solenoid inside the pan. Apply 12 volts to the prong on the side of the transmission (I just use a jumper from the + battery terminal). When you touch the prong with the 12 volt wire, you can hear a click from the solenoid if it is working. Evaluate those things first.
Ok I'll check make the checks you are describing. One more question, if my engine harness is set up for the TCS should i be using that wiring or can i continue to use the extra wire that one of the previous owners installed directly from the accelerator linkage switch? I have none of the other TCS or thermovac pieces installed presently and i am going to guess that with out them the voltage isn't going to reach the transmission connector and that is why I have the added in wire between the linkage switch and the trans case. I am looking through my 71 chassis manual right now trying to see if there is anything i can pick up but with the 70 transmission i think i am comparing apples and oranges.
No, the TCS system shouldn't have anything to do with the kick down. The kick down wiring is really very simple. The gas pedal switch has 2 prongs and 2 wires. One side of the switch gets 12 volts with ignition key on. The other side goes directly to the transmission. 5 minutes with a multi-meter or test light and you can check the system for continuity. Then make sure you hear the click from the solenoid inside the pan, Done.
Ok I'll climb under the dash and then under the car tomorrow afternoon and see what i can find out and get back to you . It sounds pretty straight forward, thanks for the help :beer:
You shouldn't need the kick down to hold off shifts at max throttle. That should be controlled by the governor & vac modulator. Might take some trial & error, but a governor weight/spring kit, an adjustable vac modulator, and possibly an extra experimental governor should help a lot. Failing to downshift to low at a stop sounds like a defective trans. If it hasn't been at least resealed before, you are wwwwaaaaaay overdue. Bruce Roe
Bruce, the trans was rebuilt less than 3K miles ago, the problem may be that the rebuild was many years ago and the car has very few miles on it since then. As far as your advice on the 1-2 upshift I am not talking about full throttle upshifting the problem i am seeing are during normal around town part throttle driving. Once i get the part throttle driving sorted out then I'll get to fine tuning the full throttle shifting:Brow:
Larry, I got under the dash and fopund the accelerator switch was stuck in the full throttle positiono No: I eased it back to where it should be and ran through the electrical trouble shooting and every thing checked out OK. The switch opened and closed as it should and there was power at the transmission end of the conductor. When i re connected the conductor to the transmission connector i could hear the soleniod cycle as it manually operated the switch on the fuel linkage. I test drove it and it seems to be improved, there was a bunch of traffic so i really couldn't beat on it close to home and as rain is threatening i didn't dare to go to "Deserted Road International Raceway" for a full throttle testing for fear of getting trapped in a down pour. I did get into the throttle a bit and got it to bark the tires on the 1-2 shift and the 2-3 shift so we are heading in the right direction. Now i guess my focus would have to be on increasing the RPM at which part throttle up shifts happen. Right now if i stand on it a bit, not enough to get into the secondaries, it will up shift at 2000 RPM 1-2 and the 2-3 is happening at around 2500. I think the next step is the Vacuum modulator I'm not sure if mine is adjustable but if it is which way should i adjust to increase the shift points?
To make the shifts occur later, run the adjusting screw in clock wise. Keep in mind that the adjustment range is only 2-5 MPH. At light throttle, the transmission is supposed to shift quickly. As you get into the throttle, the shift points should increase with increasing throttle openings. The full throttle shift points are controlled by the governor. Changing the weights and springs (Get the B&M kit) is the way to tune that.
Thanks Larry, I'll slide back under there and see if my modulator is actually an adjustable unit. If not I'll get one on there and then move on to the governor if needed. It will probably be a few days/ weeks before i get into it as I'm just about to get the correct Big Block carb on there and I don't want to make too many changes at once. Many thanks for your assistance!
High years will hurt you regardless of the mileage; rubber dies. High heat speeds it. The only way the trans knows the output shaft speed, is from the governor. So both the governor & modulator will affect ALL shifts. My rule of thumb is, adjust the weights more for the high rpm, the springs more for the low rpm. Try to find the right balance. I had a 67 Buick trans that would shift out of 1st at 15 mph with the throttle to the floor. By modifying the gov, and somewhat the mod, got it to work right. Write down every change, and drive each for a while, to home in on your right combination. Bruce Roe
will do Bruce, thanks for the tips. I like the idea of getting a second governor to make the changes quicker.
