I posted this in another forum and did not receive any responses so I thought I would also ask here. (sorry if you read it elsewhere)

I am just wrapping up a transmission rebuild (1980ZX - FS5W71B) and I had a question about the counter-shaft front bearing shim.

Backstory, the transmission needed to be refreshed because of a failed counter-shaft (center) bearing.

Disassembly revealed that the front bearing distance to the case was 3.92mm (Measurement A) and a 0.2mm shim was installed at the factory (assumed).

Looking at the diagram below, 3.92 mm is considerably off the chart and would require something like a 0.3mm machining of the front cover.

After rebuilding, the transmission case to counter gear front bearing (measurement "A") was 3.65 mm.

Logic tells me that the next increment past the 0.1 shim would be in the 3.52-3.61 range and would be a 0.0 shim (or nothing).

Now, I have no idea how many miles the transmission had on that previous setup (drove in my Z for almost 2 decades) but I wonder if the shim and measurement put too much axial load on that bearing that contributed to the failure.

Should I:

1. Slap it back together like it was using the 0.2mm shim? (Seriously, it lasted this long and you don't drive more than 500 miles a year anyway)

2. Leave all shims out because that is the closest to what the FSM states. (Who cares what the muppet before did, the FSM knows best)

3. Give up and buy an electric car.

Cheers

EDIT: I did try tapping the bearing back before measuring. The front counter shaft bearing is a slip fit into the case and the depth is set by being pressed back against the counter shaft drive gear snap ring. The shaft depth is set by being pressed into the counter shaft (center) bearing which is soft pressed up against the bearing retainer. The only way (I can see) to get that bearing to sit lower and thus use a thicker shim is to space the center bearing retainer plate away from the adapter plate, remove the counter gear snap ring and seat it against the front bearing or find a thinner bearing. It seemed like it wouldn't hurt too much so I tried it anyhow.

Edited 4 hours ago4 hr by DrFeelGood

Any chance the bearing is not fully seated on the gear?

16 minutes ago, Zed Head said:

Any chance the bearing is not fully seated on the gear?

Thanks for the reply. I suppose there is always a chance you know? I mis-interpreted or made a mistake, etc... I did check closely when I pressed this part on for two reasons. One, was to make sure it was al the way down (because the was the most obvious source of too much bearing projection) and the second was, I was a little worried I may have deformed the snap ring by "over-pressing" it trying to make sure it was seated fully. I did not go back after assembling the rest of the front to see if it moved.

As far as I can tell, it is seated. Also, why was the distance even greater (3.92 mm) originally? To me, the most obvious reason is that I am not measuring correctly. I checked against my 1-2-3 blocks and the calipers are good. I am using my square to make sure the caliper is perpendicular to the surface when I drop the caliper depth.

Shrug, I don't know.

I will have to make a decision and roll the dice though.

There are other possibilities. Maybe somebody overcleaned the case mating surface at the adapter plate. Maybe the countershaft drive gear isn't fully seated. Maybe the countershaft itself is not pulled back all the way by the nut. I don't know what stops the shaft when you tighten the nut. I didn't read through the assembly procedure to see how the various steps are checked. I've had some transmissions apart but have not rebuilt any. Just tossing some things out there to think about.

@Zed Head All valid points. I cant say anything about the case to adapter plate. It seats flush and I had to clean it well to make sure the sealant (no gasket there) surface was unmarred. The countershaft drive gear is a possibility I suppose. To be honest, I did not do anything with this part as there were no bearing in between.

`Some pics of the counter shaft forward and behind the adapter plate.

@EuroDat might have some thoughts.

Another curiosity is the spacer indicated in the picture below does not seem to appear in any of my service or parts documents. It is way beyond the 0.2 mm we are taking about here however.

Edited just now1 min by DrFeelGood