Technical Flathead transmission syncro blocker ring wear question?

My trany would grind going into 3ird. How does one get wear like this?

All 3 notches look like this. My blockers have nice square corners like they should. I hate just replacing the brass part and putting it all back together without understanding how this happened?


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How does the syncro hub , inserts , springs , balls look?seems like the inserts might be moving more than they suppose to maybe digging into the brass a bit . The reason I ask about the input roller bearing is if it is worn it could cause additional play and of course the main input bearing could be worn as well . I've only rebuilt 2 recently and don't have a lot of experience with these but have rebuilt several 5 speeds over the years so I am sure one of the inhouse experts will chime in soon but other than a foreign object, trash, bit of a tooth or something else I think one or all the areas I mentioned need to be checked.

 

I noticed later that all 3 of the rectangular shaped blocks that engage the brass blocker ring have damage on one side were they chewed down the blocker ring. What I can’t figure is how this happened.



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Those rectangular blocks are thr inserts I was talking about.

 

That ring isn’t worn a little bit......it’s not worn a lot.....it’s practically ground down into a silhouette of its original self! If the inserts or springs came apart (or out of position) they could interfere with the bronze rings. It can be aggravated by excessive end play between the mainshaft and the main drive gear. Besides replacing all the rings and inserts, you should find the underlying problem that may have caused premature wear like this.

 

That's just it. I can't find anything that would explain why this blocker ring look like this. The inserts and springs and balls are still there. All three inserts do have damage were they plug into the bad blocker ring. The history on this tranny goes like this. I bought a "78" case and put the guts from a junkyard side shift in it. The side shift tranny looked like it had been rebuilt before it got parked. When I transplanted the insides to the "78" case I did not know enough to recognize the blocker ring was bad. I just thought it was machined to be like that. When I got my car going, it would grind going into 3ird. When I pulled the trany back apart, there is no brass shavings in the case, so what ever happened must have happened before in the side shift case. The bearings are tight and good. I don't know what to do but replace the bad blocker ring and try again. I hate not knowing what caused this.

 

You say the bearings are tight, but how's the end gap? That's what Mac said will be a concern.

 

Do a push-pull test on the input shaft. With the front bearing retainer bolted tight there should be no perceptible movement in or out. The output shaft is a bit trickier to test for this same push-pull test....you must have the rear bearing retainer bolted tightly in place...AND you must have the universal joint bolted onto the output shaft (assuming this is a closed drive application). Grab the front half of the u-joint and attempt the push- pull test. Once again, there should be no perceptible movement of the output shaft.

Should you find any movement on either test, you’ve got an end play problem and you’ve got to resolve that before you run the transmission again. Most commonly the fault with end play in the output shaft is a missing rear oil baffle at the rear ball bearing. There could be other subtle faults in the gearset contributing to the issue, and this is where it gets complicated trying to identify the problem in a forum. You can get some good ideas and you can also find yourself chasing rabbits down holes.

If you want to resolve this problem through the forum, do the end play tests first and report back to the thread. After that you’re going to have to get the transmission apart and be prepared to take clear pictures of the relevant parts to post to the thread. You can also consider sending it to us and we can report back to the community on our findings.

 

To clarify my comments above, when the input and output shafts are correctly placed, the front bronze synchro ring will not be tightly held......it will be slightly loose. When the transmission is in neutral, you can wiggle it slightly with your fingers. If this area is too loose, the ring can flop around too much which can let it get slightly cocked. I suspect that the synchro inserts then don’t align well with the three slots in the ring.....perhaps causing the wear you saw. Bits of metal trapped in the area will also grind away at the bronze rings.

 

Thanks for the input Mac........

 

I understand. I will do the end play checks as described and post the results. Thanks for taking them time, I value your time.

 

I just wanted to post that I did the end play checks and everything was very tight. I replaced the destroyed blocker ring and now after driving it, I am happy to report it shifts great. Thanks for all of the good advice and help.