A833OD Binding in 4th Gear

Hi everyone,

I am finally reviving the 4-speed overdrive swap that I started 5 years ago now that the engine is finally out of my car. All I am missing now is a flywheel and the floor hump!

I inspected the A833OD that I rebuilt in 2018, and found that it will spin freely in every gear except 4th. With the box in 4th, the whole thing will spin clockwise (looking from the input shaft) with some resistance, and when I go to spin in counterclockwise, it locks up. It looks as though the slider/shift collar is crashing into 4th gear on the countergear. I read through this thread here (833 OD sticking in 4th, chipped synchro), but am not sure if I am having the same issue as the fellow in it. Furthermore, I am not sure what he did to correct the issue.

• The overshift happens in 4th gear with the side cover on or off. It is incredibly difficult to get it back out of 4th once it has shifted.
• This gearbox had new bearings from Brewers put in it back in 2018. The rebuilt kit was a Christmas present, but I am 75% confident it was the right one.
• The gearbox is from a 1976 slant 6 Dart, now going behind an almost stock 360. Yes, I know, take it easy in 4th :)
• The gentleman I bought it from said the synchros were new when it was rebuilt in 1995, but I have no way of verifying this. I had to replace the bearings in it because it sat in a field for 20 years after being rebuilt.

From the linked thread, it seems as though there are a couple things that can cause an overshift. My question is, what is the primary method that is supposed to stop the slider in the first place for 3rd and 4th? The detent springs help push the slider and the synchro towards the gear being selected, but do the shift fork detents in the side cover locate the shift, or the spacing between the synchro cone, sycnchro, and detents? From what I can see, 1st and 2nd gear shifts are stopped by the slider contacting the selected gear, which isn't an issue because the gear is a bigger diameter than the slider. The linked thread made it seem like the synchronizer was too worn, allowing the detents to open rock too much on their springs and pushing the slider too far forward.

I will provide more pictures when I get home, but I have already disassembled the gearbox and found that the thrust bearings for the countergear were damaged. Here are some photos of the 3-4 shift hub, freshly removed from the mainshaft. Let me know if I can provide any more information!