firmer shifts can be the result of higher line pressure.
I do not like firm shifts, the faster you stop a rotating part the more stress there is on the part
make a 700 trans in a gm shift too firm from 1st to 2nd and you will break the splines on the sun shell.
you can have smooth shifts with high enough line pressure to eliminate slippage as long as the accumulators are working properly.
when the pressure gets too high you break things like the servo apply strap, the pump has to work harder, it is hard on the seals ect.
the problem with these transmissions is not that the clutches inside the trans burn from too low a pressure, most of the time they burn because of leaks, low fluid levels, pressure does not rise properly in relation to throttle opening (the tv is set wrong).
amoung other things.
the big reason i see that the pressure is turned up is to hold the converter clutch from slipping----we get a lot of these units that the only problem is the converter clutch, the inside of the trans if fine, cut open the converter and the only thing wrong with the converter is the lining is bad and the cover is burned black, the rest of the converter is ok----just because the cover is burned from heat does not mean the rest of the converter is bad, seldom is it the case where the entire converter is bad.
get the pressure too high and you will break things, we fix the problem at the problem, we put in a big enough converter clutch to handle the load with reasonable pressures.
you can also get a firm shift with low pressure, if the accumulator piston strokes against its spring and bottoms in the bore b4 the shift is complete it will be a bump and the end of the shift
if you have bind up you will get a firm shift
a bind up is when there is more elements on than need be example----in 2nd gear on a 727 trans the front band is the holding member and the rear clutch is the driving member-----the band is holding the drum stationary----when it shifts to 3rd the band is released by the same oil that applies the front clutch, (front clutch is inside the drum that the band is holding).
if the band holds the drum stationary too long and the clutch is coming on trying to turn the drum the band and clutch are fighting each other, one trying to hold and the other trying to spin the drum. can't have it both ways someone has to give,SLIP.
this bind up feels like a good solid shift because when the band finally does release the drum the clutch is already trying to spin the drum and you get a very fast bang shift----not good for anything.
if you change the 3. 8 ratio apply lever to a higher ratio, especially the 5. 0 it will give bind up unless properly set up, which involves more that just the band adjustment.
so there are several things that can cause a firm/harsh shift, not all are related to high line pressure, there has to be a balance between firm and soft, to soft you can burn clutches but factory calibration seldom burns clutches unless something else is wrong also, too firm a shift is not only hard on shafts and splines it is hard on the clutch lining itself.
a proper shift will be completed in . 3 to . 5 seconds and you can have a nice feeling shift that takes . 3 second
a shift that takes longer than . 75 second is way too long, check it with a stop watch. if we sent a trans out with a 1 second long shift we would get it back before the customer got out of town, our town has only one stop sign.
on a chrysler 604/606 computer controlled trans the computer times the shifts and if a shift takes longer than . 75 second the computer will set a slip code. these transmissions are found in mini vans and intrepid cars among others.
dave
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