Manta Auto Trans Issues

[ephillippe]

Greetings All,
Just the other day, my auto trans. starting acting up and now it won't shift from first into 2nd or 3rd until I reach a ridiculus RPM (Like 5500 or 6000)
Since I was driving around 75mph all day long on new synthetic fluid and filter for months before this happened all of the sudden, I'm inclined to think its the modulator or vacuum line that just went.
The big questions is, I can't seem to find the vacuum line connection to the carb/manifold/valve cover. The Haynes and Saturday mechanic books I have dont even show a modulator on the trans or a vacuum connection to the engine compartment (I know there's a modulator, I can see it on the trans)
Does anyone have any thoughts? (1973 manta Luxus)

Best and Thanks, Evan

[MikeyOne]

The modulator is on the passenger side of the rear of the trans and faces towards the rear of the vehicle. it is near the passenger rear corner of the transmission pan. THere is usually a short section of rubber vacuum line connecting to a steel line that runs along the transmission to the fuller tube and then follows the filer tube to the area where the filler tube gets near the exhaust manifold. From there the steel line generally goes wide of the exhaust manifold and comes around to the intake manifold just below the carb. Another section of rubber line connects the steel line to the tee on the intake manifold.

Failure to shift can indeed be due to this line being disconnected or leaking, the modulator failing, or a loss of fluid.

Since the shifting is vacuum controlled any vacuum leak can also cause the automatic to shift badly. If the line looks good and the fluid level is good then look for typical vacuum leaks around the carb base or brake booster. These will also cause the engine to run irregularly.

The TH180 trans is common and you can usually find a modulator at a NAPA or at any trans shop.

[ephillippe]

This actually makes sense now, thanks very much!

[GTJIM]

The "Kick-down" cable MUST be correctly adjusted as it has considerable effect upon the internal oil pressures in the trans when it is in the relaxed state even when not activated to force a kick-down.

When the rubber bearing, at the firewall where the accelerator linkage end fits in, wears (or falls out!!) the linkage drops enough to put the cable completely out of adjustment - this can destroy the trans by forcing to high or too low pressures in the control circuits.

Replacing this bearing makes the carb linkage work sooo much better as well.