LuckyLuke

Hi,
I don't know if I like 3 gears, at a speed of 45mph I find the engine speed high (according to the speedometer 3,000 rpm) from 1 to 2 gears I like beautifully in the speed range 25-30mph .. at what speed I like 3 gears (when driving quietly)
Oldsmobile 88 1966 original engine and trans TH400
Engine 425cui originally 2bll now 4bll Edelbrock
Rear ratio: 2.93
Tires: 26.1 inches (235/60 / R15)

thanks for helping

BangScreech4-4-2

3000 RPM at 45 MPH with a 2.93 rear? Sounds like you only have two gears.

Koda

Downshift to second when you think you are in top gear. If there is no change, you are not in top gear.

Sugar Bear

How many times does the transmission upshift from a full stop? A three speed like a TH400 must shift twice to reach third/high gear.

LuckyLuke

I need to check the vacuum line and modulator.
Is the vacuum correctly guided to the automatic transmission from manifold (see photo ) or should it be guided from the carburetor.
The second question has this TH400 gearbox in my Olds 88 1966 car a kick-down sensor (I found the sensor at the firewall and there are 2 cables leading to the gearbox) and can it be settings ?

Thanks for the advice .. sorry my english is bad :-) I am from Czech Republic Europe





Thanks for the advice

Vista67

Before you take anything apart check the function of that throttle position switch on the firewall. Unless the transmission was changed you have a variable stall torque converter (also known as switch pitch) that was used in the Oldsmobile TH400 for 1966 and 1967. The throttle switch on the firewall controls both the downshift function and the switch pitch function. The wires at the transmission connector provide 12V to downshift and 12V to switch into high stall depending on throttle position. It is possible that the contacts in the switch are malfunctioning or the solenoids in the transmission are not working properly. Either one could make your rpms high. It is easy to test the switch pitch wiring and functions (the solenoids make a click when energized). Testing can be done without running the engine and without taking anything apart. Do a search on "switch pitch" and read all about it. If you get the switch pitch running right it will help move that big car.

cfair

Dig around under my username and you’ll find some further instructions on the Switch Pitch / Kickdown switch for these cars.

sysmg

Here are the instructions for adjusting the switch.

LuckyLuke

I replaced all the hoses as part of the maintenance and the vaccum line from the sled to the modulator was inside a bit of transmission oil, but the car does not smoke at all, the transmission oil does not disappear. a new modulator came to me on Friday so I will replace it. Q: When replacing the modulator on the TH400, does the transmission oil leak out of the modulator position or simply lift and tilt the car? Thanks

oldcutlass

You will lose transmission fluid when you change the modulator. I jack the car up and secure it on the modulator side only to limit this loss a bit.