My 71 daily driver has an annoying problem. The wipers and blower motor work fine when the car is in 1st and 2nd, but both quit when the car shifts into third. It is a 350TH auto transmission. I figure it is a vacuum problem. The tranny has had a shift kit put in it by the previous owner. Any ideas or shortcuts? Which vacuum line/supply should I look at? Any help would be greatly appreciated.

 

Are you sure you have a TH350, the 71 originally came with a TH400. As far as I know the standard run of the mill TH350, doesn't have any of electrical kickdown, it uses a combination of TV-cable from the carb linkage and vacuum modulator.
The TH400, on the other hand uses an electric kick down that is activated from a switch on the accelerator pedal linkage. Neither the TH350 or TH400, should have anything to do with the failure of your blower fan or windshield wipers.
If the wiper door is opened and electrically power is going to the wipers and blower, then they should remain working. Vacuum has no effect on the motor speeds, of either. There is a relay on the wiper door that could be effected by loss of vacuum, and stops the wipers from working if it thinks the door is closed. But the gear that the car is in should have that much effect on the vacuum that you have if cruising at a steady speed.
As far as vacuum and the A/C-Heating system, there is an acutator that opens and closes by the means of vacuum to introduce fresh air into the car, but it will not stop the blower from working. It can change the amount of air that is coming out of the vents and the sound of the blower, when it is open or closed.
This is a really wierd problem! Good luck on finding a fix.

 

TX, if anyone changedworked on the starter motor, find the black wire with large loop on it, I bet it on the battery post on the solenoid....
it should go go ground....IE...bellhousing or whatever....ME, I move the damn confusing thing up top of the engine where it belongs....
it's abotu 10-14 ga wire, black with a 3/8" loop on it....

GENE

 

I looked in the assembly manual and found a vent tube that was plugged coming off the acutator on the right side wiper. You are correct about the blower motor, it continues to run, but the volume decreases. That must be the door closing due to loss of vacuum. The car has had a sorted past and was pieced together with a '74 engine. The tranny was probably replaced at some point as well. It is a TH350 with a vacuum acutator on the passenger side, according to the shape of the pan. The hoses appear intact all over. I'm hoping for this vent tube to be the miracle cure. I will take it for a drive later today to see if anything has changed. Thanks

 

TX, see that the blower motor is not running backwards.....that black wire I referred to.....;-)))

GENE

 

Still no solution. I think it is definitely a vacuum loss. Is the valve above the filter that is on the main vacuum supply line a one way valve (the one above the filter). I found out that the wiper door actuator is leaking, but haven't tried to bypass it to see if it makes any difference. What if I jump across the switch under the dash to bypass the vacuum line altogether? Has anyone tried this? My wiper door stays open all the time anyway because of the bad acutator. I just changed the bypass valves under the dash, and rebuilt the switch. There is a line missing from the headlights to the electrical/vacuum valve that might contribute. I just want the stupid wipers to work in high gear. Help!