Transmission grind

Tiny
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?
Saturday, July 18th, 2020 AT 7:26 AM

6 Replies

Tiny
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
Tiny
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
Tiny
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
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Saturday, July 18th, 2020 AT 8:52 AM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,004 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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Saturday, July 18th, 2020 AT 11:49 AM
Tiny
ARUN NAYAK
  • MEMBER
  • 23 POSTS
Thank you. I will consider that.
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Tuesday, July 21st, 2020 AT 12:17 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
I do not think the oil will make a difference. I think you still have a syncro issue.

Roy
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Tuesday, July 21st, 2020 AT 12:20 PM

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