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I am looking to change my transmission fluid in my 6 speed nv5600 and I went to napa and they gave me royal purple 75w90 synchro max, after doing a little research I learned that the nv4500 uses the 75w90 royal purple synchro max but that the nv4500 has brass synchros and the nv5600 has fiber synchros. I would like to know the absolute best fluid for my transmission, thanks
 

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that is the incorrect weight for the 5600 you must overfill the 5600 to lube some rail parts and lube and cool the rear bearing. we had amsoil give my person the 75w90 oil I did not check on it to verify the proper weight was used. it lasted about 150,000 and was trashed, we tore it down in our shop and seen how it was built and the wear points. a $1,000 worth of Chinese parts later we were back in business. we have trans- cools on ours now with a oil temp gauge. I am going to give you two oils to blend in a 50-50 mix for the 5600, fill until full then add four more quarts. the two lighter oils we have used is royal purple syncromax and amsoil mtf , the heavy 50 wt delvac 50 from ww granger delo, Castrol , and amsoil listed below
Delo Synthetic Transmission Fluid SAE 50 delivers exceptional all-climate, year-round performance in heavy duty truck transmissions. A unique additive package can protect gears without using the “active sulfur” agents commonly found in automotive axle oils. This results in little to no corrosion and long life for copper-containing parts, such as oil coolers, bushings, and thrust washers. Good pumpability in extreme hot or cold temperatures promotes smooth shifting and efficient power transfer. It is specifically formulated to meet the latest extended drain requirements for Eaton transmissions, with drain intervals of up to 500,000 miles.
Synchromax is recommended for manual transmissions
that specify an automatic transmission fluid or motor oil.
It is also ideal for transfer cases and 2-cycle motorcycle
gear boxes.
Synchromax is formulated with Royal Purple’s synthetic,
proprietary Synerlec additive technology, offering
improved shift quality over a wide temperature range and
reduced gear noise.
Synchromax is fully compatible with all types of friction
materials and offers excellent corrosion and oxidation
protection without affecting the soft metals commonly
found in manual transmission synchronizers.
Performance Advantages
• Greater wear protection
• Smoother shifts
• Excellent rust / corrosion protection
• Reduces friction for more power
• Lowers operating temperatures






Castrol 50 wt is syngear CD50 o’rileys p/n syn 50-5
Amsoil FT F05-EA
 
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So, you use 8 qts in the NV5600 and mix the oil you put in it??!?
 
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