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LS400 will shift into every gear except reverse. Reverse only slips.


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Alright guys so a bit of a weird one here. I'll start at the beginning. So I bought this LS400 about a year ago and it was fine. 152000 km. Everything clean and mint. Was taking valve clearances one day and when I put the valve cover back on I forgot to reinstall the trans fluid dipstick. Low and behold some fluid leaked out and by the time I noticed the trans had been slipping and also stalling. (I know.. dumb..) So, filled it up and took the fluid level and it was normal. Tranny drove well for another couple days and then all of the sudden one day it started to stall everytime it was put into gear. (Even neutral unless I kept the RPMs up!) So my buddy and I replaced the transmission. Filled it back up put it in drive again and klunk it stalled. Every gear stalled once again even neutral. Did a bunch of research and came up with bad ecu capacitors. Had all those replaced (6 of em) last weekend and started it up and it ran. Put it in drive and it drove perfect and with extra power even in L 2 and D. Neutral was neutral and then reverse was... just... gone.... when put into reverse you can rev it but it just slips. With the car in the air on the hoist, reverse produces some backwards tire motion, but with 0 torque. I.E. when under load it will not move backwards and when given power from the accelerator the wheels don't speed up even in the air when its in reverse. They will slowly spin in reverse but even holding the wheel still with your hand is enough to stop it from spinning when in reverse. So we pulled the old valve body out ot the first transmission and installed it into the new transmission thinking it was a solenoid issue. Filled the tranny back up again and same thing. Still wont go in reverse. Only in L, 2 and D. Bottom line is this... the ecu fixed MOST of the shifting issues, except reverse... since the ecu fixed the biggest amount of problems we were thinking tomorrow we would switch valve bodies back and then swap the old tranny back in (seeing as it probably wasn't the issue and maybe its okay... there was no metal shavings in the original tranny.  so, in hopes that I somehow can avoid another tranny swap tomorrow, putting the old one back in and swapping valve bodies again, does anyone have ANY IDEAS as to why the heck my car won't drive in reverse? Fluid levels are optimal using type T-IV AISIN tranny fluid. Please please help. If I could avoid putting the old tranny back in I would love to but I think I may have to as when I went to pull the pan off the new tranny today to change the valve body, there was new metal in it (i had cleaned the pan when I installed the new tranny) (new is from a junkyard with 150000 km) so i am thinking MAYBE the clutch plates that shift it into reverse are just toast on the junkyard tranny i installed in it? Maybe the original tranny is completely fine and i spent 700 bucks for nothing.. (if i do the swap tomorrow i will return the junkyard tranny to the junkyard where it belongs and try to get my money back. I'm lost for  words and about to throw in the towel with this car. All I want is for it to drive, and back up. Any help is appreciated. Thanks.

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So it works! Swapped the old tranny back in. Turns out the ECU capacitors were the entire problem! Thank you all for your help and i hope this helps anyone else that has capacitors issues!

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On 3/11/2021 at 3:45 AM, Nate5517 said:

Alright guys so a bit of a weird one here. I'll start at the beginning. So I bought this LS400 about a year ago and it was fine. 152000 km. Everything clean and mint. Was taking valve clearances one day and when I put the valve cover back on I forgot to reinstall the trans fluid dipstick. Low and behold some fluid leaked out and by the time I noticed the trans had been slipping and also stalling. (I know.. dumb..) So, filled it up and took the fluid level and it was normal. Tranny drove well for another couple days and then all of the sudden one day it started to stall everytime it was put into gear. (Even neutral unless I kept the RPMs up!) So my buddy and I replaced the transmission. Filled it back up put it in drive again and klunk it stalled. Every gear stalled once again even neutral. Did a bunch of research and came up with bad ecu capacitors. Had all those replaced (6 of em) last weekend and started it up and it ran. Put it in drive and it drove perfect and with extra power even in L 2 and D. Neutral was neutral and then reverse was... just... gone.... when put into reverse you can rev it but it just slips. With the car in the air on the hoist, reverse produces some backwards tire motion, but with 0 torque. I.E. when under load it will not move backwards and when given power from the accelerator the wheels don't speed up even in the air when its in reverse. They will slowly spin in reverse but even holding the wheel still with your hand is enough to stop it from spinning when in reverse. So we pulled the old valve body out ot the first transmission and installed it into the new transmission thinking it was a solenoid issue. Filled the tranny back up again and same thing. Still wont go in reverse. Only in L, 2 and D. Bottom line is this... the ecu fixed MOST of the shifting issues, except reverse... since the ecu fixed the biggest amount of problems we were thinking tomorrow we would switch valve bodies back and then swap the old tranny back in (seeing as it probably wasn't the issue and maybe its okay... there was no metal shavings in the original tranny.  so, in hopes that I somehow can avoid another tranny swap tomorrow, putting the old one back in and swapping valve bodies again, does anyone have ANY IDEAS as to why the heck my car won't drive in reverse? Fluid levels are optimal using type T-IV AISIN tranny fluid. Please please help. If I could avoid putting the old tranny back in I would love to but I think I may have to as when I went to pull the pan off the new tranny today to change the valve body, there was new metal in it (i had cleaned the pan when I installed the new tranny) (new is from a junkyard with 150000 km) so i am thinking MAYBE the clutch plates that shift it into reverse are just toast on the junkyard tranny i installed in it? Maybe the original tranny is completely fine and i spent 700 bucks for nothing.. (if i do the swap tomorrow i will return the junkyard tranny to the junkyard where it belongs and try to get my money back. I'm lost for  words and about to throw in the towel with this car. All I want is for it to drive, and back up. Any help is appreciated. Thanks.

You need to replace your old tranny and test the ecu capacitors to make sure they are fine. I doubt very much that your original tranny was bad.

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