93 J30 shudder help!! Infiniti Technicians pretty technical.....

[Danz32tt]

Hope you guys can help me out.

93 J30 with a bad shudder at 22- 2400 rpm 3 or 4th gear but only at around third to half throttle. Standing start with full load it will go all the way up reasonably smooth even if you hit the brakes at the same time to hold it around that 2200 range but if you let off on the gas at that rev area and then continue the shake starts instantaneous.Stall tests are fine and smooth.Car runs and shifts perfectly fineDead stop hold the throttle at 1500 or when its started cold on fast idle and ride the brake as soon as the car moves ever so slowly the vibration comes in although much less agressively but at the same frequency or so it seemsand seems to be only when the car physically starts to move

Brand new aftermarket drive shaft including center bearing and quadruple checked and balanced and .010 out of round of rear shaft from my dial. trans overhauled just over a year agonew plugs irridiumsI have swapped all 6 coils with used ones just to see if any differenceConsult came up no fault found on trans or engine codes (go figure)

I was thinking possibly lockup circuit in torque converter malfunction?? or internal trans failureThis is a weird one as it feels just like a center bearing failure

Any help guys??Thanks,Dan

[Q45tech]

When Nissan rebuilds transmissions they always install a new remanned TC because the lock up clutches have short life [but this has nothing to do with acceleration].

The central facility in Tennessee always tests every unit on a transmission dyno something mom and pop even good sized companies skip.

Try some Lubguard Red additive in ATF look for a change even a minor one.

How is engine compression, just a10% drop in power can make things interesting especially at low load.

[Danz32tt]

Thanks for the reply I will give it a quick comp test when I will swap out the plugs this time and the coils once again. I am going to shut off cylinders one at a time with the consult on the road to see if any change or lack thereof as well. This one is pretty hard to isolate to me for some reason......... engine or trans??. It really seems too aggressive for it to drop out one cylinder and power doesn't seem to fall off. I did disconnect the throttle sensor thinking it would boost up the line pressure and shift points went up and so it seemed that the vibration went up a couple of hundred rpm as well.Sorry for the bookDan

[Q45tech]

Line pressure increases as TPS voltage increases [so called load factor] so dicoing TPS is the wrong way to go as a failsafe occurs.............throws a code in transmission [tcu] when TPS is missing.

Lock up in TC only occurs in 3rd and 4th gear so this is a clue!