'flare' between 2nd and 3rd

[pixelpusher]

Michael,
Thanks for your detailed explanation. Automatic transmissions have been a mystery to me. I appreciate your input.

I,ve owned this 92 since it was new. At about 30,000 miles the upper gears went out. Sounds like it was that high clutch you mentioned. A year later the same thing happened. The third tranny has been going strong for over 100,000 miles. It seems to me that all three trannys had the same flare at low speed. Sounds like it may well be the TPS.

Thanks, Mike

[B 4 You]

Originally Posted by longassname

That sounds like your line pressure is low at that time. You probably just need to adjust your throttle position sensor.

If the adjustment of the brake band allows it to be fully applied by the servo at one throttle position it allows it to be fully applied at any throttle position. You just have more hydraulic pressure available to hold it at different throttle positions.

Line pressure is specified by a value looked up in a map in the TCU according to throttle position. The maps aren't smooth at low throttle positions. A little difference in throttle position can make a big difference in line pressure or barely any difference at all depending on just where you happen to fall on the map. Here is a graph of one of the maps controling line pressure: http://www.ecutune.com/images/3rd&4thDutyControl.gif You can see at 6% throttle (15/255) the solenoid has a 60% duty cycle ((20000-8000)/20000) bleeding off most of the line pressure. At just a little more throttle the map jumps up to 30% duty cycle ((20000-14000)/20000) that's half as much bleed off of line pressure. A missadjusted throttle position can have you sitting just on the wrong side of one of these cliffs.

There are other possibilities like the line pressure on your transmission might just be a little low. It's also possible your brake band is just out of adjustment enough that it can barely tighten at high line pressure and low line pressure isn't enough to quite get it there but that is stretching it--excuse the pun.

It is important that the brake band be in propper adjustment but once it is it usually stays that way. The travel on your brake band servo, that's the piston that open and closes the brake band around the reverse drum, is very long. The lining on your brake band is very thin. There are always exceptions around the margins but in general if the band wears enough to need adjustment it needs replacement. They always wear the most at the ends where it is sinched together by the servo application. The hardware on the band is riveted here so there are rivets which start digging into your reverse drum as soon as the band is this worn. From there the friction material starts flaking away from the ends so you have an increasing amount of metal on metal contact. The brake band will keep functioning like this but it will behave more erratically and is destroying the reverse drum.

well at least it isn't my transmission slipping.. i always thought it might be a bad TCU, and it's confused when to shift gears at low speeds. anyway, how difficult is this to adjust? can i do it myself or should i take it to a shop?

[pixelpusher]

Originally Posted by B 4 You

well at least it isn't my transmission slipping.. i always thought it might be a bad TCU, and it's confused when to shift gears at low speeds. anyway, how difficult is this to adjust? can i do it myself or should i take it to a shop?

Look in the how to documents under "engine"

[longassname]

If you can get an ECUtune TCU it will prevent high clutch burn out. It's the solution to SVX transmisison failure.

Originally Posted by pixelpusher

Michael,
Thanks for your detailed explanation. Automatic transmissions have been a mystery to me. I appreciate your input.

I,ve owned this 92 since it was new. At about 30,000 miles the upper gears went out. Sounds like it was that high clutch you mentioned. A year later the same thing happened. The third tranny has been going strong for over 100,000 miles. It seems to me that all three trannys had the same flare at low speed. Sounds like it may well be the TPS.

Thanks, Mike