Transmission grind

1984 JEEP CJ7
74,000 MILES • 2.5L • 4 CYL • 4WD • MANUAL
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ARUN NAYAK
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Hello. I have a question on gear grind with the transmission of my vehicle.

Shifting is good but there is a mild grind when I shift to fourth after driving for a few minutes. If I shift very slowly, or wait a second between 3rd and 4th, then there is no grind. Could this be a synchro issue? It only starts happening after driving for some time. Could it be the oil as it thins when it warms up?
Jul 18, 2020 at 7:26 AM
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ASEMASTER6371
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Good morning,

I will address the transmission for you.

For the front end, you will need to start a new question. Site rules are 1 subject per question.

As far as the grinding, it sounds like a synchro for 3-4 is the issue. The brass ring wears out and grinds when changing.

https://www.2carpros.com/articles/how-a-standard-transmission-works

I would change the oil and inspect for any meal debris in the oil. It will look like shiny brass in the oil.

Roy
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Jul 18, 2020 at 8:31 AM
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ARUN NAYAK
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Thanks, Roy.

If there is any metal debris, I guess the only way to fix it is to rebuild the transmission. Am I right in understanding that?
Also, can you guide me on why the grinding starts only after driving for some time? It’s fine for a few miles before it starts.
Jul 18, 2020 at 8:43 AM
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ASEMASTER6371
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The oil is thicker and slows down the gears to match RPM. They turn much easier with thin oil.

Yes, that would be a rebuild.

Roy
Jul 18, 2020 at 8:52 AM
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CJ MEDEVAC
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Hey ARUN NAYAK,

My transmission guy says you can run 80W-90 GL-5 in a T-4 or T-5,

Which is what I run in my 1977 CJ-5 T-150 transmission, Dana 20 transfer case, and both of my differentials (Nowadays, it is used instead of 90 wt, which is what I used back in the 1980's and 1990s).

I can comprehend doing this! It's a gearbox! I see no special materials in there that mine does not have.

Worst case? A rebuild? Sort of maybe headed that way, in time, anyway?

The Medic
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Jul 18, 2020 at 11:49 AM
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ARUN NAYAK
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Thank you. I will consider that.
Jul 21, 2020 at 12:17 PM
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ASEMASTER6371
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I do not think the oil will make a difference. I think you still have a syncro issue.

Roy
Jul 21, 2020 at 12:20 PM