I have a 1968 Buick Lesabre 400 which has the 350 4bbl and TH400 trans. The car appears to have the original 70k miles on it and still has the factory exhaust back to the muffler which made it fun getting the front trans pan bolts out. Any way my problem is that my 1-2 shift and 2-3 shift occur at exactly 35/60 mph regardless of throttle and it won't shift back down until I come to a stop or darn near stop. I have replaced the switch on the gas pedal and the kick down solenoid in the trans which has has zero affect on my problem. Changing the fluid and filter in the trans helped shift quality but not the problem. Any ideas on what to do to this thing next.
Have you checked the vac. modulator or the vac. line going to it? I have even seen the vac. fitting on the intake get plugged with carbon.
Your problem is most likely the governor. Remove the cover, which is on the right rear of the trans, and has 4 bolts. Slide the governor out, pin the moving parts closed with your fingers, and hold the unit pointing up and then down several times. The barrel valve inside should slide freely in each direction. If not, drive out pin holding gear on bottom, and pull barrel valve and polish on wire wheel slide it back in and see if it moves freely now. Reinstall gear and put back in trans, and road test. Or just drop in new governor. Note the lighter the springs in the governor, the later it will shift. Rich
Check the Downshift Soleniod Sounds like the car isn't downshifting. It could be the downshift soleniod that attaches to the valve body. Over the years the insulation on the wiring that attaches to the terminal on the case from the soleniod becomes brittle and falls off. if this bare wire touches the inside of the case (ground) the transmission will not downshift. I seen this happen and it does not always blow a fuse. You can repair this by soldering on another wire or by using heat shrink tubing over the wire, depending on the condition of the wire itself. I would also pull the cover off of the soleniod and clean the sludge out of it that accumulates from years of use. You can check to see if the soleniod operates by using a 12 volt battery charger as a power source. I would check this after you check out the modulator. Hope this helps. Ken
I put in a brand new solenoid $18 from NAPA but I haven't checked to see if the old one blew a fuse or not.
I agree with Rich. This sounds like a governor problem. It may be sticking. I would try taking it out. Spray it down with some gumout, dry it, and dip it into some ATF. Make sure the valve is moving freely. The governor is located behind a cover(secured by 4 bolts)on the passenger side rear of the trans. You'll lose about 1/2 quart of fluid. The transmission should shift at about 10 MPH(1-2), and 20 MPH (2-3) at minumum throttle. The more you are into the gas, the higher it should shift. WOT, it could take 1st gear as high as 50 MPH (depending on rear gear), and 2-3 at around 80 MPH. As far as the detent solenoid goes, does the car downshift from 3-2 or 2-1 at full throttle?
Currently it doesn't appear to be downshifting during WOT but that is not near as important to me as fixing the upshift problem.
Unless the detent system is hooked up and working, the transmission will not upshift correctly. First things first. You need to make sure that 12 volts is reaching the downshift solenoid in the pan, and that the solenoid is activating. If you turn the ignition switch on without starting the engine, and activate the gas pedal switch, you should be able to hear the downshift solenoid click. Do that first. Without the downshift system connected and operational, the trans will short shift.
For those that may search one day for this particular problem. I did find the problem ou: I was doing to much :3gears: and blew the vacuum line out of the top of the intake which fed the modulator on the side of the transmission. So sometimes it is the easiest problem and I didn't need to replace the kickdown switch on the accelerator or the kickdown solenoid in the transmission or pull the governor and clean and scrub the little beast. A simply vacuum line caused my woes. I guess at least I don't have to worry about those other parts causing me any issues for a while. Thanks for those that were willing to share their knowledge in helping me find my trouble.
