ATX downshifting protocal

[tommyturbo]

So I have only had this car a few weeks, and have some questions about the atx. I've had a few regular tauri, so know kinda what to expect.

noticed tonight that at fwy speed the car will not downshift from 4th to 3rd by flooring the gas, unless your below about 60. at 70 it will just unlock the torque converter. if you hit the lockout on the shifter it will kick down fine. Is this normal? is the downshift cable operated? It is agressive with downshifts at lower speeds like 2-1 with just a touch of throttle. never had an issue getting my 92 vulcan to downshift out of overdrive with the throttle.

next question. if the overdrive lockout is on, car seems to only upshift from a stop from 1st to 2nd, but just holds 2nd and never hits 3rd. if overdrive lock out is off it seems to shift through all gears normal. yes it is in the drive position not second.

sometimes downshifts from 2-1 are runaway and jerky, but most upshifts are ok, sometimes I feel a slip on 1-2. car has 144k.

No faults as of now, but there was a code in mem 647 incorrect 3rd ratio, but hasn't come back since I cleared codes.

I expect that I will need a rebuild and can live with that, but wondered if there is something I can do to correct the above issues for now.

 

[whiteguy3]

As a precautionary I would ALWAYS replace the TPS, VSS and change the filter and fluid. Sometimes shifts can get tricky when a TPS has deadspots or a failing VSS.

 

[tommyturbo]

I figured I would try replacing the vss. But what i was really hoping is that some folks with atx's could tell me if not downshifting out of od is normal at 70, or holding second and not shifting to third with overdrive lock out is normal, or if that too is related to vss.

 

[rubydist]

lots of very strange shifting things can result from sick vss. a dead vss will result in upshifts at way too low of rpm.

the downshift strategy does not depend on any cables - it is all controlled by the pcm based on the various inputs it sees.

a properly operating trans will shift from 1st to 2nd to 3rd with the o/d off.

my atx cars will all shift down at 70+ mph if there is enough load or throttle - generally, there is very little time between the tc unlock and the downshift to 3rd, so you may be getting the downshift and not realizing it.

 

[tommyturbo]

I will get a vss. I can tell it is only unlocking 4th at fwy speed,but if i hit the od off button it does downshift to 3rd. I know enough to be able to see the differences between unlock and downshift in rpms.

I played around a little on my way home, and if i stab throttle over 60 i just get torque converter unlock, no downshift. under 60 if I stab it i get second, and the car pulls hard shifts to 3rd, pulls and once i back off shifts up to 4th.

if i am moving and am around say 50-60 cruising and hit the od off, i notice that the torque converter unlocks but it takes a sec or two and then it shifts down to third kinda hard sometimes.

 

[whiteguy3]

Either some of your clutch packs are worn or you have got one of the above mentioned parts that are faulty. I had a bad TPS once that did not read accurately from 3/4 to full throttle causing inaccurate downshifts based on my pedal input. The TPS and VSS do not always throw a code either.

If you floor it at 70mph on the highway it should downshift to third and pull to about 114mph at full throttle.

 

[tommyturbo]

got a new speed sensor, trans range sensor, and tps. so far it seems to have corrected the problems, shifts better, and downshifts like it should. also it will upshift 1-3 in d with the od cancel, where as before it would only go 1-2. thanks for the suggestions.

 

[whiteguy3]

Glad that fixed it