trans issues reverse goes forward....

[kraus]

Well after my buick finally stayed together and put 1200 miles on of pure driving.Last night went for a lil ride left a stop side quickly car shifted fine etc.Went to buddies house to hang out,went to leave.Put car in reverse and it went forward,so i'm like what the heck.Jacked car up checked linkage for light rods all is correct.Checked fluid all is full and red.So what happened and is it something i can repair myself is the question.....
ihave a spare trans that could use for parts but not sure what it needs etc.

 

[SSedan64]

Is Neutral also forward? Would indicate Forward clutches welded together. Cross leakage.
Disconnect the Cable & Column linkage on the side of Trans and manually shift the Trans into gear. This will indicate if the Manual detents are positioned correctly when Cable/Column is connected.
Car on Jack Stands.

 

[kraus]

neutral also forward with trans in air.Reverse does nothing in air lights come on and stuff.I disconnect linkage nothing changes.

 

[SSedan64]

I should've said to apply the Parking Brake, when the Trans is in Neutral it will rotate forward just from the Engine spinning the TC & drag from Tran's internals.