delta88_frankfurt

Fellow Olds Friends,
maybe some of you can spare me a lot of trail
and error. My car doesnt shift down, it just revs
higher and higher and melts another transmission
fuse.
Any guesses or advice how to diagnose this?
Thanks in advance!

delta88_frankfurt

...sorry, 1966 Delta 88, TH 400

Octania

Sounds like the vacuum line to the modulator came off or the modulator is bad.

Modulator is a round canister, RH side, near the aft end of the pan, above the pan. Steel line runs from intake to it. Ck for vacuum at the modulator end of the steel line while engine is running. Look for oil inside the tube, indicating bad leaky modulator. IF you have a hand vacuum pump you may test the modulator so ensure it holds vacuum.

Failing to shift until RPM's are very high sounds like a bad modulator.

Then again your kickdown switch may be sticking ON
It's the roundish switch in the throttle linkage.
Ck the service manual for when the wire to the trans is supposed to have voltage- I think it is 1) at idle and 2) at oh about 3/4 to wide open throttle. If it is feeding power to the kickdown solenoid ALL THE TIME then the trans is being told that you are running wide open throttle and please never upshift until very high rpm. Easy test with voltmeter, light, or an old seatbelt buzzer.

droldsmorland

Im trying to understand your question...
Did you do the basics? Check fluid level & condition? Hows the modulator line from an intake manifold vacuum source (not from the carb) to the trans modulator? If it has the steel line that runs down to the trans make sure its not blocked up. As mentioned a bad modulator will have some of these symptoms too. How many miles (kilometers) on the trans?

I think what your describing is it will not "up-shift"?
Down-shift is when your in 3rd gear (above 35MPH (56KM/H)) and it needs to go down into 2nd or 1st. Will the car move on its own power in Drive, but simply wont up-shift into 2nd & 3rd??? Thats likely the modulator or its lines.

Specifically what fuse is blowing? The passing gear or down shift feature is electrical in a TH400. It works off of the gas pedal position switch. If this circuit has a open or a short it will either stay in 1st (short) or wont down shift when you need it to passing gear (open). Check that switch and all the wiring down to the trans.

Tell me if I interpreted you problem correctly?

delta88_frankfurt

Thanks a lot for your elaborate answers. I must apologize, I should have been more detailed, but I gave it a try that it might be a very common malfunction.

And honestly, I needed some vocabulary. :-)
So "passing gear" is my problem.
The electrical down shift doesnt work.
So you helped me with that, already.

My modulator should be allright, At least it is installed correctly, the steel line is clean and tight. The only flaw might be that I dont have a pre-curved hose to attach to the modulator but my "normal" hose is fixed in a nearly similar curve.

When I kick down, nothing happens. Car revs up higher and higher in the gear it is in and I can do nothing than let go the gas and then it shifts revs down in the same gear.

I can't cause a down shift.

And during the attemot, I burn my 9A fuse in the "Transmission" socket.

Unfortunately I can't watch the fuse-box or test the wires while driving...

delta88_frankfurt

...that sounds very likely!

Thanks a lot.

75cutty455

This is right on time. I am looking at this same issue.

Octania, This electrical line you speak of...... Mine is not even connected. I have the TH400 transmission manual from wild about cars and I dont see that in there.

Hmmmm.

Let me look again.