1st Generation Dodge Cummins 89-93 Discussion of 12 Valve 5.9 Liter Dodge Cummins Diesels with Rotary Injection Pumps

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Old Jan 21, 2010 | 12:10 PM
  #1  
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1993 5 speed

I want to change out my fluid, is the 5w30 synthetic ok to use?

what should I use? I heard that if you use the wrong oil on these trans, it will cause damage to the bearings and raceways..


any thoughts?
 
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Old Jan 21, 2010 | 03:05 PM
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its a semi controversial issue on what oil to use. most say to use 5-30w synthetic. if you search a little ways back this same topic was brought up just a couple weeks ago and had a ton of results. try searchin for it you should find what you need
 
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Old Jan 21, 2010 | 03:43 PM
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5w/30 motor oil would have been the correct answer 15 years ago.
 
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Old Jan 21, 2010 | 03:57 PM
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don't forget to overfill! or at least that's what I was always told with the Getrags
 
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Old Jan 21, 2010 | 10:16 PM
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i run gear oil in mine and i have been told by several people to overfill it..... it's a little hard to shift when it's cold out. think i will soon be putting 5-30 in it soon
 
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Old Jan 22, 2010 | 08:00 PM
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i use 15w-40 in mine. it has worked great for the last 50k mi. the factory manual called for 30 non detergent, not to be confused with hd30 which contains detergents. i say 30 wt isnt heavy enough to keep the main bearings lubed proper as that is the only thing ive ever seen go bad in these tranys. other opinions.....?
 
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Old Jan 23, 2010 | 09:13 AM
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Heavier oils are one of the worst possible things you can do to a Getrag, right behind lugging it and towing in 5th. It ties in to why they need to overfilled. It is tallish case design canted down at the rear in the Dodge. This can result in oil starvation for the pilot bushing and front bearings.

Overfilling with lighter oil will enable proper lubrication. A modern Synchromesh is the single best fluid for the G360. It'll shift much smoother with Synchromesh as well.
 
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Old Jan 23, 2010 | 09:33 AM
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actually the failures ive seen are worst for the rear main bearing. i tend to find it hard to believe that that bearing was being starved for oil but rather the particular oil could not provide the necisary cushioning to prevent severe wear.
 
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Old Jan 23, 2010 | 09:53 AM
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Probably from lugging it. There's literally hundreds of possible failure mode combination, depending on what was done to it. I'm just telling you what the lube issues are.

Heavier oil will not necessarily provide better protection, contrary to the old wive's tale, and has a harder time getting into the front bearings. Add cold weather to not enough gear oil and your Getrag's days are numbered for sure.
 

Last edited by NadirPoint; Jan 23, 2010 at 09:58 AM.
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