I have a 1967 GS-340 with a ST-300 transmission, which I have had since new. When I first purchased the car, the transmission had a shift problem. From a dead stop,it would shift from 1st to second with no problems, but if you were slowing down to about 12 to 15 mph and stepped on the gas, the engine would rev as if in neutral, then slam into gear. The dealer never did totally fix the problem when under warranty. I learned to drive around this problem over the years and over 100,00 miles. During my restoration of this car, I had a transmission shop rebuild it. I had no idea when it would be on the road, so the owner said the warranty would start when I registered the car. That was maybe 5 years ago, and the shop is no longer in business. Well when I first used the car, everything shifted ok. Now, with less than 100 miles, it's back to it's old tricks. This time it not only slips at 12- 15 mph, it has a long shift between 1st and 2nd when starting from a standstill. It also shifts worse when cold.I have no idea what all was replaced during the rebuild, but obiviously something is still out of wack. I have or have had 3 other A-body Buick's with the ST-300 transmissions in them, and they all shifted fine. Now I'm wondering if it's maybe in the case itself. Any information as to how to correct this ongoing problem would be greatly appreciated. Tom
Check your governor. Sounds like it could be sticking. Also, check your switch on the throttle linkage that controls the switch pitch functions.
George: Thanks for the info, I will check both items, but how do you go about checking the switch? At what throttle position should it make or break? Is there an actual set-up procedure? Tom
At idle, you should be in high stall, once moving, the stall changes to low stall by applying volatage to the top tang on the side of trans. Use a volt meter and measure the voltage on the top tang receptacle in your trans wiring. You want to verify the top socket is getting +12v. If not, you have a bad switch and/or wiring. You can also run a "hot" wire to the top tang and listen for the solenoid inside the trans to activate low stall.
I'll take a shot at it, and see what happens. If I have any other questions, or run into problems, I'll get back to you. Thanks again Tom
George, Isn't 12 volts required for high stall? Take away the 12 volts, you get low stall. At least that's the way it is on my ST400 switchpitch. Factory setup had high stall at idle,(within 6* rotation) low stall up to half throttle, then high stall again at over half throttle. So the horizontal tang should be hot at idle, and over half throttle. Vertical tang should be hot at or approaching WOT.
George: I removed the governor cover and inspected the weights. Everything appears to be moving smoothly and easily. Next I tackled the switches and solenoids. Powered both solenoids and I could hear both click. Next, I rang out the switches and those both checked out ok. After putting my service manual under a magnifying glass, I could read the set-up for the linkages. I reset to factory specs. (I'm now getting a hang as to what takes place) Started her up and took her for a ride. SAME THING !!! If I increased throttle after slowing to 12- 15 mph, the transmission slips then engages. From a dead stop, it has a long shift going from 1st to 2nd. I did however fix so it goes into passing gear. That's what's funny. Why doesn't it slip when it drops into first gear then? One of the guys in our car club thinks it may be in the modulator. What's your thoughts, and how would you check it? Remove it from the case, suck on the hose and see if it moves internally? I could be wrong, and probably am, but it seems to me that the modulator is what the dealer changed way back 30 years ago. That fix only lasted a couple of weeks maybe,and my problem was back. As I stated earlier, I dealt with the slip, during slow down, for 20 years and learned to drive around it, but the long shift from start bothers me. It would however be great to eliminate both problems. :rant: :rant: So put on those thinking caps boys and girls, and hopefully we can correct this problem. Thanks for your help so far. Tom
Ok, sounds like everything checked out. If your fluid is clean and you have low miles on the trans, sounds like your valve body has a problem. Your 1-2 spring could be weak or one of the check balls could be sticking in the valve body. So, you will probably need to take it to a trans shop for inspection/review if you are not capable of doing this work.
Not what I wanted to hear. Boy, I hate the thought of taking things apart when I just finally got things back together, but if that's what has to be done, then I guess that's what somebody will be doing. At this time I'm still a little gun-shy about tackling a transmission tear down, o No: so I guess the car sits until spring at which time I can locate a reputable rebuilder.This valve and spring you mentioned; is that something that would normally be checked and rebuilt during a transmission overhaul? As I mentioned earlier, I had this redone several years ago, and just now put it in service. When it was re built the guy said that because it would be sitting, he would reassemble it using vaseline. Then, when I was ready to install it, that was the time to put fluid into it. I didn't seem to notice the problem when I first started driving the car up and down the street ( without a registration) but after everything was legal and I could take it 20-30 miles, that's when the problem came back. What's your thoughts about putting more miles on it and see what happens, or do you think I could do more damage than good? I do appreciate all of the info. Tom
Tom, Before you take the trans apart, I would get another governor, and sustitute it to see if it makes a difference. A governor can appear to be OK, but still be sticking or worn. Also, try pulling the stator(horizontal) connection off, and take it for a ride. Does it still do the same thing?
Larry: I assume you mean the wire connected to the horizontal spade on the transmission, powering the solenoid, right? I can take the governor from the extra transmission I have and try it, but I've got to wait for a decent day. I'll try anything before having to have the transmission pulled. Thanks Tom
Tom, Yes, the horizontal spade. I want to see if it makes any difference if the converter stays in low stall. Definitely try another governor, even another modulator. Do all the relatively simple things before yanking the trans. Good luck.
Thanks for all the ideas. I'll give each a try, as long as the weather holds out. Their forcasting snow by Thanksgiving, so things may have to wait until spring. I'll keep you informed whenever and whatever I find,good or bad. If I don't have it corrected by summer, do you think it will do any harm if I drive it? I plan on taking it to the Buick National in Batavia, NY. in July. It's about a 100 mile round trip. Tom
Tom, This may not be the news you want to hear, but I will give it a shot. My first 64 Skylark that I got in 1968 had the very same problem. The upshift was a bit drawn out and it would slip and bang into low at about 10-12 mph. All else functioned fine, but the "slip-bump" as I called it got annoying. Other 2 speeds I drove or rode in at the time never did it. A buddy had a 65 Skylark that worked flawlessly. At one point, the trans was rebuilt (not by me at the time) even though there was no evidence it needed it. There were no worn out parts and it still did the same problem after the rebuild. Modulators and governors were tried along with the band being adjusted several times. The problem was never corrected. Eventually, I replaced the trans with another one from a rebuilt unit from a 64 LeSabre 2 speed (same trans as Skylark) and never had a problem again. I took the orignal trans apart several times and could not find anything that could identify the problem. This trans was the reason I studied up on trannys in the first place and learned what I now know. Since you bought your car new, I assume it has the original 67 unit in it and was never swapped out. The 64 trannys used a slightly different shift valve setup than 65 and later. Buick released a service pack valve setup at one point which led me to believe the shifting problem was not an isolated occurance. This would not be the case on a 67 trans as it has the later valve already. Here as some of my thoughts as to what may be causing the problem. If the low servo return spring is too strong it would cause a timing problem with the band release and apply. It would come off too early on the upshift and apply too late on the downshift. This would cause a drawn out upshift and the slip/bang on the downshift. Another possible cause would be porousity in the case on the apply side of the servo. This would also cause the condition by not having enough pressure to hold the servo on until the clutch comes on when upshifting as clutch apply oil is applied to the back of the servo during the shift. Lower pressure on the apply side would cause the servo to release too early. The slip on downshift would happen as well since the apply of the servo would be delayed due to leakage. Can I prove any of this? In a word, No. But if all else is fine and there are no worn parts or other defects, it may be the cause of the problem. Changing the trans or the case is the only way to know for sure. Hope this gives you some idea. Good Luck, Mark
:grin: :grin: Well Guy's, I believe the problem is solved. Just so everybody knows. I removed the stator wire and took it for a spin. No change. Replaced the govenor with one from a used tranny, ran it, no difference. I finally removed the modulator and checked it. I was able to push against the bellows as per the service manual. I removed the modulator from my spare tranny, cleaned it up and installed it. Went for a ride, and lo-and- behold it shifted great and the slip was gone. I did notice upon removing the original modulator that the o-ring that seals it to the case was the wrong size. It did not fit the nose of the modulator tight. I'm wondering if it wasn't sucking air because of a bad seal. I don't think I'll go thru the trouble of putting on a new o-ring on the original modulator to see if it fixes the problem. I think I'll just locate a new modulator from a parts supply house and be done. I do want to thank all of you responders for allowing me to pick your brains, and sharing your knowledge with me. Without your help I'd still be scratching my head and wondering what to do. Thanks a million Tom And have a Happy Thanksgiving :3gears:
