QuestionDick--
Thanks for the blazingly quick reply! Can the vacuum modulator be bad even though there are no signs of ATF in the vacuum line to the carb? I'll check againt to make sure there is no ATF in the line.
Also, the kickdown linkage will be routed from the carb down to the transmission? Like I said earlier, I'm no transmission expert, especially automatics.
Thanks.
Mark
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Followup To
Question -
My 1968 Cutlass "S" with 350 Rocket and 2-spd Jetaway automatic transmission (ST300) will not shift into second automatically. It will however, shift nicely into second gear if I do it manually. In other words, If I start off in "D" it will not shift to second but if I pull it down to "L" while still crusing down the road and then put it back to "D" it will shift nice and smoothly into second gear every time. It also downshifts normally at stop signs. The transmission rebuild is only 8,000 miles old and appears to be very solid. I don't think it is anything serious but I am not knowledgeable enough to troubleshoot very far.
So far my troubleshooting has involved checking to see if their was a problem with the vacuum modulator on the transmission. Sure enough, the rubber hose from the vacuum line to the modulator was sliced so I'm guessing this would surely be the cause of my troubles and I'd be up and running in no time. Must to my surprise, a new rubber hose did nothing. I then took the entire metal vacuum line off of the car (from the carb to from the transmission) and blew compressed air through it. I found no leaks and nothing was blocking air flow. I found no transmission fluid in the line either which I belive would indicate a worn out modulator allowing transmission fluid into the vacuum line and ultimately the engine.
I'm no transmission expert but I believe the vacuum modulator on the Jetaway controls the upshifts. Perhaps not. The car runs great and I'm looking forward to getting this problem fixed. I have not looked at linkages or anthing else yet simply because I'm not exactly sure what I'd be looking for. I'm mechancially-inclined and not afraid to do the work myself but I lack the expertise to diagnosis it properly.
Thanks! What a great website.
Mark
Columbia, MO
Answer -
You've got the right ideas, (Yes, the modulator definitely controls the upshift!) and I think there are only a few other things you can do for yourself. One is to use a clean hose routed to where you can suck on it yourself to see if the modulator diaphragm is leaking - you should be able to pull a vacuum on it and it should hold the vacuum, no leak off.
If that is OK, next check the kickdown linkage to make sure it is all hooked up - and if you have the manual for the adjustment, make sure it is set right, although if this is a sudden problem, most likely it has either become disconnected, or else there is some other problem.
If none of those things lead to a cure, then I think there is probably a particle of dirt stuck in the governor that controls the upshift, and it is going to have to go back to the transmission shop to have them sort it out. The trans doesn't have to come out to fix that, the governor assembly can be checked and cleaned on the car.
You should get this taken care of, as you can cause rapid wear in the transmission by driving this way for a lot of miles.
Good luck,
Dick
AnswerYes, it can be bad even with no fluid in the lines, so check it for vacuum leaks also.
Yes, the kickdown linkage is attached to the accelerator linkage. On your car, I believe it is a cable kickdown linkage, so there is no adjustment to do, but make sure the cable is good and is connected at both ends - have someone mash the gas pedal while you watch the cable end at the transmission to make sure it is moving the transmission control lever.
Normally, you wouldn't get such a fast response - I just happened to be sitting here tonight when the question came in.
Dick
