Auto box issue, not wanting to change from 3rd to 4th

[R3SSSPECT]

hi guys

just need an idea where to start troubleshooting with this issue

i have never worked on auto boxes and dont know where to start looking to resolve this issue

basically its a 300zx auto gearbox with quick shifter kit, a couple of weeks ago i noticed there was a delay in the shift change from 3rd to 4th, as in the box was changing gear at higher Rpm(off load), this is gotten worst to the point now that i wont be able to get into 4rth unless i rev up to 5-6000 RPm and it wont change to 4rth unless its under load.
other gear changes are normal and there is no issues with them. have checked over drive and this is not the issue either....
oil level seems to be normal aswell.

i have heard something about vacuum pipes in the gearbox?? where abouts are these and how easy is it to replace these??


any help would be appreciated

thanks

[2LV8ETR]

Sounds like it could possibly be a shift valve.
Basically the valve body is the control center of the automatic transmission. It contains a maze of channels and passages that direct hydraulic fluid to the numerous valves which then activate the appropriate clutch pack or band servo to smoothly shift to the appropriate gear for each driving situation. Each of the many valves in the valve body has a specific purpose and is named for that function. For example the 2-3 shift valve activates the 2nd gear to 3rd gear upshift or the 3-2 shift timing valve which determines when a downshift should occur.
On computer controlled transmissions, you will also have electrical solenoids that are mounted in the valve body to direct fluid to the appropriate clutch packs or bands under computer control to more precisely control shift points.
If you've never cracked an automatic transmission open, I would strongly suggest that you don't start now. Manual transmissions are a breeze to work on due to their simplistic nature, but with automatic transmissions there is a myriad of components that need to be precisely positioned in order for the box to work.
I would take the car or box to a competent transmission specialist if I were you. This is not a job for someone who has never performed this kind of work before. Attempt it with a workshop manual if you must, but be prepared for the consequences if it should all turn south.

[SLYSIL]

oie it helps if u put the clutch in!!!!!

[R3SSSPECT]

thanks for the info mate. yea i have done some reasearch and it seems a lot more complicated that it sounds.

sounds like its going to be a costly fix.
any recommended places that i could take the car in for a look and estimated cost?
i have been thinking bout going manual for a while, might aswell do it if the cost is going to be the same i guess....

[2LV8ETR]

A manual conversion would make more sense in a performance car. It really comes down to what you want though.
As for recommended repair shops, I'm not sure what state you're in so I would advise you name your area, then see if anyone else can post a reply. I've never gone to one as I do all my own work, so I cannot give a recommendation.
Sorry.

[MrMayhem]

I have a manual Z32 front cut Im bringing over for the engine so the rest would be for sale box/ hydraulics/ tailshaft/ pedals / flywheels clutch etc pm me if you're interested