sam12345

iTrader: (1)

Yes newer cars use a pulse width modulated solenoid to adjust the pressure and ones with this type do not have as hard of a shift when cold because they use a look up table to compensate. Next generation of transmissions will have closed loop control for even better control of shifts. As far as the link it is in the post. Just click on it its in blue. BTW when the fluid is colder the line pressure is higher

3UZFTE

Ok. Can you adjust the PWM by hand or even scan tool for that matter? the A650e, or newer lexus V8 trans do not sense the temperature of the fluid and adjust accordingly, they simply do as they always do. It isn't as if the PWM ramps up the line pressure when it hot or cold, they simply adjust as far as the ECU needs to. As far as the future transmissions being closed loop... well aren't they already? They have been electronically controlled for sometime, which means that they take care of tolerances, fluid indexes, shift time, etc. If it were open loop it would be strictly reading from the ECU, instead it reads throttle position, coolant temp, etc, so isn't already in closed loop? The fluid has the same amount of pressure as what dictates the pressure in the transmission is pressure relief valve. The fluid requires more pressure to flow through the same surfaces, it doesn't mean the pressure is altogether higher than if it were when it is at operating temperature. The pump is what creates the pressure, the relief valve limits, it, it isn't as if the relief valve says wait a second I am a little colder than normal, I am going to stay closed to allow more pressure to build up... Anything else, this is fun.

sam12345

iTrader: (1)

No current transmission do not have a pressure sensor (expensive and you need one for each gear) so they are not closed loop. The ECU gets the information from all the sensors you mentioned and then uses a look up table to adjust. So the transmission only works as good as the testing that was used to determine the look up table. The transmission does have some feed back parameters so it does do some adjusting but it is not fully closed loop. Where I work we are working on a closed loop system in our R&D. There may be a closed loop tranmission out there but none that I know of. Due to the fact that it is not closed loop the solenoids have to be maintained to a very tight specification. With the closed loop system the ECU can adapt to the solenoid slop and does not have to be so precise. With the current system it can not compensated for differences from solenoid to solenoid (The pwm or VFS solenoid that regulates pressure not the on off solenoids)

The way to adjust would be to download different software (with a different look up table) So the manufacture adjust the look up tables for different types of cars to fit the customer type of that car. (Buick softer shift, Pontiac harder shift or whatever)


As far as the pump when the fluid is colder and more viscous the pump will have more pressure. When I tested at -30 C the test required X pressure. Since the pump we used for testing was not closed loop we would have to adjust to lower the pressure. If I remember correctly on a GM tranny (the 6 speed automatic) the pump pressure can vary from 70 psi to 300 psi depending on the conditions.

Also adjusting this cable gives you only a limited amount of adjustment. So it will not create more pressure than the pump can put out. I have not tried the other extreme but I think I will just to see the adjustment range. Also the danger in making the shift to soft is that you could be slipping the clutches even when you are not changing gears. That is not good.

sam12345

iTrader: (1)

One of the reasons that many fear the Transmission flush is that when you take it to a shop to do a flush they first add an additive to get all the junk out. This junk can plug up the filters that Each solenoid has. The filters are designed with excess capacity to allow some plugging up but if the limit is exceeded then you will have issues and the only way to fix the issues it to clean the filter. (symilar to the power steering solenoid issues). What some people do not understand is that if you simply remove the transmission cooler hose and flush this way without adding these chemicals then there is no danger to your transmission because you are simply exchanging the transmission fluid for new one using the same pressure that you transmission creates. (I guess the new fluid could have better detergents and therefore loosen up the gunk and plug up your solenoid filters but I doubt it) Also I personally (when I have a new car) change the transmission fluid at 25,000 or less because the gears let go of most of their junk at this time and I do not want the junk in my filters. So the theory that if the fluid looks good don't change it ignores the junk. The casting have flashing that are missed, the gears break in, ect. Sorry for being so long winded but there are 2 reasons to change tranny fluid. Lubrication and cleanliness, With the modern Electronically controlled trannies cleanliness is just as important.

sam12345

iTrader: (1)

I just finished doing a test with the cable at the almost as firm as possible setting. You could feel a harsh shift even at low rpms (under 1800 rpm shifts). Above 2000 rpm shifts car feels like it surges when it shifts. Above 3000 rpms feels nearly the same slightly harsher. Abover 4000 rpms about the same as the soft setting. RPM vs throttle shift points are the same. Kick down is the same amount of throttle. When you shift from reverse to drive or park to drive it slams into gear.

I set it back to the soft position only a little bit firmer than as the pick at the beginning of this thread. (maybe 2 turns firmer). Shifts below 2000 rpms are almost imperceptible except for the rpm gage and the change in motor frequency. Between 2000 to 3000 the shift is perceptible but barely. Shifts get firmer as rpms increase. Kick down the same. rpm vs shift points the same. Does not slam into gear when shifting from park to drive or reverse to drive

Amskeptic

And bringing up the rear of this discussion regarding the adjustment of the transmission cable by the engineers who designed and built the transmission, (great trepidation I am sure they must have had, when thinking of all the armchair engineers out there in Lexusland . . . )

"Adjust cable so the inner cable stop protrudes 1mm from the end of the sheath."

Thank-you,
Colin

(oddly enough, this things shifts soft under light acceleration and shifts deadnuts giterdone smooth under full acceleration . . .)

sam12345

iTrader: (1)

yes but a small adjustement so it shifts to your taste can be done to each his own.

python

iTrader: (4)

thanks SAM! woot, adjusted my cable and it shifts sooooo much better

sam12345

iTrader: (1)

Python did you adjust per spec or to your taste? did you go softer or firmer? just curious

python

iTrader: (4)

i loosened both nuts, then i tightened the one closer to the drivers side of the car a few turns and drove it, i wanted to get rid of the little bit of soft shifting.

sam12345

iTrader: (1)

did you notice a difference?

python

iTrader: (4)

yes i did...hence my post! thanks again.

1YUZFE

Bringing this back from the dead, this should be in the FAQ.


I just did this to my 94 and it shifts pretty firm now even with the cable adjusted properly. I guess I need to change all my mounts too? I don't think they were ever changed.

SpencerT

My 95 slips alittle when shifting out of first the first few time when it is cold out.

Fluid is correct and at the right level.
Will this help me?

sam12345

iTrader: (1)

Probably not