 Gearbox oil Minerial v Synthetic |
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| neilbardsley |
 Sep 9 2023, 06:42 PM
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#1
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Newbie  Group: Members Posts: 25 Joined: 11-October 20 From: England Member No.: 24,754 Region Association: Europe  |
I recently changed back to using mineral 80/90 GL4 oil from a synthetic 75/90. Seems to shift better with the mineral. I read something about the synthetic being too slippery for the synchro rings? Can someone explain that or point me to somewhere I can read? That isn't intutitive to me
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Replies(1 - 6)
| Shivers |
Sep 9 2023, 08:05 PM
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#2
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Senior Member Group: Members Posts: 2,373 Joined: 19-October 20 From: La Quinta, CA Member No.: 24,781 Region Association: Southern California |
This pic shows two rings. One is new with a rough bumpy surface and an old one that is smooth. As I understand it the new ring uses that rough surface to slow down the teeth so the gears can mesh. If it is too slippery the synchro rings can’t slow things down like they are designed to.
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| neilbardsley |
Sep 9 2023, 11:27 PM
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#3
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Newbie Group: Members Posts: 25 Joined: 11-October 20 From: England Member No.: 24,754 Region Association: Europe |
Thank you
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| BillJ |
Sep 10 2023, 05:42 AM
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#4
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Senior Member Group: Members Posts: 1,096 Joined: 4-March 13 From: charlotte, NC Member No.: 15,610 Region Association: None 
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QUOTE(neilbardsley @ Sep 9 2023, 08:42 PM)  I recently changed back to using mineral 80/90 GL4 oil from a synthetic 75/90. Seems to shift better with the mineral. I read something about the synthetic being too slippery for the synchro rings? Can someone explain that or point me to somewhere I can read? That isn't intutitive to me I thought was supposed to be 80/90 gl5? |
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| Superhawk996 |
Sep 10 2023, 06:56 AM
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#5
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914 Guru Group: Members Posts: 5,819 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch
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QUOTE(BillJ @ Sep 10 2023, 07:42 AM) QUOTE(neilbardsley @ Sep 9 2023, 08:42 PM) I recently changed back to using mineral 80/90 GL4 oil from a synthetic 75/90. Seems to shift better with the mineral. I read something about the synthetic being too slippery for the synchro rings? Can someone explain that or point me to somewhere I can read? That isn't intutitive to me I thought was supposed to be 80/90 gl5? Yes - GL-5 to protect the ring and pinion which needs an EP (extreme pressure) lube due to hypoid gearing. @BillJ 901 transaxle doesn’t use brass based synchros which would be the only rationale for GL-4. Even then, the need to protect the ring and pinion (non consumable) would trump protection of brass synchros (a consumable). Factory manual  Note for OP: don’t freak out that you’ve been running GL-4. Just switch back to proper lube. |
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| neilbardsley |
Sep 10 2023, 09:37 AM
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#6
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Newbie Group: Members Posts: 25 Joined: 11-October 20 From: England Member No.: 24,754 Region Association: Europe |
QUOTE(Superhawk996 @ Sep 10 2023, 06:56 AM) QUOTE(BillJ @ Sep 10 2023, 07:42 AM) QUOTE(neilbardsley @ Sep 9 2023, 08:42 PM) I recently changed back to using mineral 80/90 GL4 oil from a synthetic 75/90. Seems to shift better with the mineral. I read something about the synthetic being too slippery for the synchro rings? Can someone explain that or point me to somewhere I can read? That isn't intutitive to me I thought was supposed to be 80/90 gl5? Yes - GL-5 to protect the ring and pinion which needs an EP (extreme pressure) lube due to hypoid gearing. @BillJ 901 transaxle doesn’t use brass based synchros which would be the only rationale for GL-4. Even then, the need to protect the ring and pinion (non consumable) would trump protection of brass synchros (a consumable). Factory manual Note for OP: don’t freak out that you’ve been running GL-4. Just switch back to proper lube. Noted thank you. I was using gl 5 before. I will find a gl 5 mineral oil |
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| 930cabman |
Sep 10 2023, 10:06 AM
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#7
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Advanced Member Group: Members Posts: 3,061 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States
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I have been using this one from NAPA https://www.napaonline.com/en/p/SL_SL2473
seems to work well, but we need to remember these gearboxes are old technology and some level of care must be taken |
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