Transmission grind

ARUN NAYAK

MEMBER
1984 JEEP CJ7
2.5L
4 CYL
4WD
MANUAL
74,000 MILES

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?

6 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

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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Saturday, July 18th, 2020 AT 8:31 AM

ARUN NAYAK

MEMBER
23 POSTS

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.

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Saturday, July 18th, 2020 AT 8:43 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

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

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Saturday, July 18th, 2020 AT 8:52 AM

CJ MEDEVAC

MECHANIC
11,005 POSTS

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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