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the problem is every time I down shift into 2nd and 3rd it grinds but it doesn't grind when down shifting into 1st. up shifting is not a problem smooth as ever. here is the history, 1963 Galaxie 500 xl 427 and a t-10 4 speed. trans was just rebuild, new syncros, slider assemblies, and new bearings. new clutch was installed when trans was installed.
 

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I have a similar issue with my T-10 behind my 390. Once it warms up, 4-3 shifts are increasingly hard to achieve, but 2-3 and 3-4 are smooth as silk. 4-3 when cold is fine, the issue is when it warms up...

Any thoughts?
 

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yep. when cold, the thick oil connects the blocker ring so the gear spins up. when hot, the oil is thin and doesnt help the connection. parts are not matching up
 

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Normally, I would say it needs a rebuild kit with a new 2nd and 3rd gear. Be a good time to upgrade to a Toploader or a 5-speed. This would be for a transmission that was previously shifting cleanly, but gradually got to the point it would grind the gears.

Since your trans was recently 'rebuilt', this may... or may not be the case. It depends upon the quality of the rebuild. There are four main gears in the trans, 1, 2, 3 and 4. The gears have small teeth on the ends that the synchros slide onto to engage that gear. These snyncro teeth that the sliders engage to are normally sharp and well defined, making it easy for the slider to slide onto. These get rounded off and flattened over time... keeping the gear from engaging properly.

I rebuild a lot of toploaders. Normally, a rebuild consists of a rebuild kit, along with a new 2nd gear, and usually a new 3rd gear as well. You almost always replace 2nd gear, and usually 3rd. If your rebuilder did not replace these gears, it's likely why they are grinding. Downshifts are the first to grind. Upshifts are usually less of an issue.

One thing you could do, is to ensure you are getting proper clutch disengagement. I'm assuming you are using the stock bellcrank linkage. This gives tons of clutch movement... lots more than a hydraulic setup, which is GOOD. However, make sure it is adjusted correctly. The pedal should only have around an inch or so of freeplay at the top of its travel before it starts to disengage. This will give you plenty of disengagement for gear changes.

If the clutch is disengaging properly, the first place I would look is replacing 2nd and 3rd gears in the transmission, as their syncro teeth are likely worn out. If you have photos of them before/during the rebuild, that would be helpful.

For the guy who says his trans works best when cold, changing to 85w140 oil can help. May buy some time before a rebuild is needed. Plus, do not use synthetic in a toploader. May also help the original poster to band-aid things until it can be repaired or replaced.

Good Luck
 

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Sounds like the second gear is worn or the brass is bad . The brass is tapered on the inside to go with the taper on the gear and this is where the "speed up" ( in the case of downshifting) or slow down ( in the case of upshifting ) is done . The brass has to work much harder on a downshift and it's common for a "crash" to happen then. Your rebuilder should have inspected the gear and brass to make sure the brass had enough "bite" into the gear at assembly time. I will also warn you that there is some poor quality brass out there. The only brass that is worthwhile using is that sold by Autogear Manufacturing. Sadly not every rebuild kit uses it. The only other source for this problem is IF you used a GL5 specification gear oil. This is THE most common spec gear oil being sold now and is DEATH to brass synchros. you MUST use GL4 spec fluid ONLY in a transmission with brass synchros. You should have been warned of that when your trans was rebuilt.

When the "crashing" is less when the oil is cold , it is proof that the brass is worn and not doing the job after the oil heats up and gets thinner.
 

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Sounds like the second gear is worn or the brass is bad . The brass is tapered on the inside to go with the taper on the gear and this is where the "speed up" ( in the case of downshifting) or slow down ( in the case of upshifting ) is done . The brass has to work much harder on a downshift and it's common for a "crash" to happen then. Your rebuilder should have inspected the gear and brass to make sure the brass had enough "bite" into the gear at assembly time. I will also warn you that there is some poor quality brass out there. The only brass that is worthwhile using is that sold by Autogear Manufacturing. Sadly not every rebuild kit uses it. The only other source for this problem is IF you used a GL5 specification gear oil. This is THE most common spec gear oil being sold now and is DEATH to brass synchros. you MUST use GL4 spec fluid ONLY in a transmission with brass synchros. You should have been warned of that when your trans was rebuilt.

When the "crashing" is less when the oil is cold , it is proof that the brass is worn and not doing the job after the oil heats up and gets thinner.
As was said, the brass colored blocking rings are not all created equal. The better ones have a good fit, and are more bronze than brass... as bronze is a much tougher, longer lasting material. I know how to guide you with toploader stuff, but not so much with the T10. The above advice with sourcing is likely good info.

As for oil, some has a dual rating... but GL-4 and GL-5. Some GL-5 oils can be corrosive to 'yellow' metals such as brass and bronze. I've always used Valvoline (which has a dual rating) and have never had an issue. Summit also sells Penn Grade. It's a GL-4 80w90 made for classics. It's green in color, and cost $8.99/qt. https://www.summitracing.com/parts/bpo-77296/overview/ For racing, I'd use the dual rating Valvoline. If you want to use a straight GL-4 in your classic, the Penn Grade is not a bad choice. It's also the oil David Kee Toploaders sells. (Toploader Specialist) https://www.4speedtoploaders.com/
 
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