Acceleration problems: this thread is only for the gifted

[jetjock]

As torque increases throttle line pressure must modulated to prevent slippage. Many cars of this vintage did that with a vacuum modulator but on this car it's cam operated by the throttle cable. I'm not going to write it all out because it's too long and a bit complicated but maybe this will help. You may want to check basic line pressure because all other pressures (governor, throttle, etc,) are derived from it.

 

[3p141592654]

The line pressure cable controls the fluid pressure out of the transmission pump. That pressure is used to actuate the various clutches and bands, as well as push fluid around to lubricate and cool the various parts.

The more power you are putting through the transmission, the tighter you need to clamp the clutches, so you need more fluid pressure. During high power shifts you also need to shift faster to prevent something called "shift flare", where the engine speeds up between shifts roasting the clutches.

At lower speeds you want less pressure to soften the shifts and to reduce noise, pump losses, wear, and temperature rise. With the engine idling, pull the cable out and you'll hear and feel what I am talking about.

Since you have it disconnected, you can pull the cable fully out and fix it in place temporarily using a zip-tie. Go for a drive and you'll notice much harsher shifts at low speeds.

 

[jdub]

I edited post #39...look at the 2nd link for a top view of the cam/throttle valve.

You should be able to replace this part from the dealer....inspection should tell you if it's the spring, retainer, roller or or cam.

Edit: Damn JJ...another book I need to get my hands on

 

[dezthumper]

As torque increases throttle line pressure must modulated to prevent slippage. Many cars of this vintage did that with a vacuum modulator but on this car it's cam operated by the throttle cable. I'm not going to write it all out because it's too long and a bit complicated but maybe this will help. You may want to check basic line pressure because all other pressures (governor, throttle, etc,) are derived from it.

That was helpful as well. I am starting to picture the physical mechanics of this.

The line pressure cable controls the fluid pressure out of the transmission pump. That pressure is used to actuate the various clutches and bands, as well as push fluid around to lubricate and cool the various parts.

The more power you are putting through the transmission, the tighter you need to clamp the clutches, so you need more fluid pressure. During high power shifts you also need to shift faster to prevent something called "shift flare", where the engine speeds up between shifts roasting the clutches.

At lower speeds you want less pressure to soften the shifts and to reduce noise, pump losses, wear, and temperature rise. With the engine idling, pull the cable out and you'll hear and feel what I am talking about.

Since you have it disconnected, you can pull the cable fully out and fix it in place temporarily using a zip-tie. Go for a drive and you'll notice much harsher shifts at low speeds.

This is exactly what I am experiencing without the cable connected. Under soft acceleration, it almost drives normal.

During medium acceleration - specifically upshifts, it is experiencing a weird high rev (slippage) sensation just before going into the next higher gear.

During hard acceleration, it has the same feeling as if a clutch is going out with a manual - the engine revs but the power or engine to tranny connection is just not there and the thus the power is certainly decreased - power meaning RWHP...

 

[IJ.]

They also decrease the LP in the higher gears
(I run a LP sensor to my MoTeC)

 

[dezthumper]

They also decrease the LP in the higher gears
(I run a LP sensor to my MoTeC)

Is LP, line pressure and what is the MoTeC?

I might be interested in helpful electronics for the Supra.

 

[IJ.]

Correct

MoTeC = Expensive Standalone ECU.