Topic: GL-5 or GL-3?

[Jeffy]

In the Owners Manual and the Factory Service Manual it states, "The recommended lubricant is Mopar 75w-90, API Grade GL-5 gear lubricant, or equivalent".  When GL-5 first came out there were some problems.  A typical GL-5 contains  approximately twice the amount of Extreme Pressure (EP) additive as that of an API GL-4 gear oil.  What does this mean?  It means soft yellow metals like your transmission's syncro's will degrade over time.  Because of this, they went back and reformulated GL-5 and added MT-1 to it's designation.  This means it will work in Manual Transmissions.  So what's out there?

AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) http://www.amsoil.com/

AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) is specifically designed for manual transmissions and transaxles with synchromesh systems that require light viscosity, non-extreme pressure fortified oil. It is formulated with advanced additive technology to provide proper friction characteristics for smooth shifting without grinding or bump shifting, while providing the ultimate in gear and bearing protection. MTF provides far better protection in these manual transmissions than gasoline or diesel motor oils.

Superior Hot and Cold Temperature Performance
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) outperforms conventional oils and protects internal components at extreme temperatures from -40°F to 300°F. It controls the thinning effects of mechanical shear for stable viscosity and superior film strength, providing better anti-wear performance than conventional oils.

Customized Additives
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) contains friction modifiers for superior synchronizer compatibility and smooth shifting. It is non-corrosive to yellow metals, and its outstanding anti-wear properties protect gears and bearings under severe duty. MTF is anti-foam fortified and contains oxidation inhibitors to resist high temperatures, oxidation, acid buildup and varnish deposits.

Applications
AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) is recommended for automotive and light truck applications that require synchromesh transmission fluid. Applications include manual transmissions and transaxles such as New Venture NV T350, NV 1500, NV 2550, NV 3500, NV 3550, NV 5600 and Tremec T-4, T-5, T-18, T-176, TKO-500, TKO-600, TR-3450 and TR-3550. Replaces Honda Genuine MTF Fluid for manual transaxles, and MTF-94 as used in some Land Rovers, MGs and Mini Coopers. MTF is SAE 5W-30, however, it is not for use in engines or wet clutches.

AMSOIL Synthetic Synchromesh Transmission Fluid (MTF) replaces GM part # 12345349, 12345577, 12377916 and 1052931 as well as Chrysler part # 4874464 and 4874465. It meets GM specifications 9985648, 9986105 and 9985535 and Chrysler MS-9224 and MS-9417.

Pennzoil® Synchromesh Fluid (aka: Quaker State Synchromesh (Quaker State is part of Pennzoil), Texaco Synchromesh, GM Synchromesh, or AC Delco Synchromesh) http://www.pennzoil.com/

Pennzoil® Synchromesh Fluid is a synchromesh transmission fluid designed for certain manual transaxles and manual transmissions used by General Motors or Chrysler. Pennzoil® Synchromesh Fluid is formulated with high quality paraffinic base stocks, a fluidity modifier, multifunctional performance additives, corrosion inhibitors, a foam suppressor and a shear stable viscosity index improver additive. It provides excellent oxidation stability, low temperature performance, excellent synchronizer performance and compatibility with yellow metals, such as bronze, brass and copper components found in manual transaxles and transmissions. This product will satisfactorily lubricate General Motors or Chrysler manual transaxles and transmissions from -40°C to +150°C.

Redline MTL & MT-90 http://www.redlineoil.com/

Red Line Oil's MTL and MT-90 are designed to provide excellent protection and improved shiftability for manual transmissions and transaxles, having cured the problem of hard shifting in thousands of transmissions with shifting troubles. How? They have the appropriate coefficient of friction for most manual transmission synchronizers (many gear oils, engine oils, and ATFs are too slippery for proper synchro engagement). And, the wide viscosity of MTL and MT-90 allow proper shifting over the entire temperature range which the transmission will experience. The synthetic base oils used have a very high viscosity index which provides relatively constant viscosity as temperature changes. MTL is a low 70W at very low temperatures and a high 80W, nearly an 85W, at elevated temperatures, providing adequate viscosity to prevent wear and deaden gear noise. MT-90 is a thicker 75W90 version of MTL. The shear stability and oxidation stability of these products are excellent, thus the physical characteristics of Red Line MTL and MT-90 will change little with use.

Royal Purple Syncromax http://www.royalpurple.com/

Synchromax® is recommended for manual transmissions that specify an automatic transmission fluid or motor oil. It is also ideal for 4x4 transfer cases and / or 2-cycle and 4-cycle motorcycle gear boxes.

Synchromax® is formulated with Royal Purple's synthetic, proprietary Synerlec® additive technology, which offers 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.

Now there are other's out there but these are the ones people recommend.  Just remember to check for the GL-5/MT-1 or else go with a GL-3/4.  If you're still in doubt contact the manufacturer.

[Jeffy]

Amsoil: A Study  of Automotive Gear Lubes

This comprehensive study of gear lubricants will undoubtedly shake up the marketplace. Fourteen of the most popular brands of gear lube were tested at an independent laboratory in areas such as pour point, 4-ball EP weld point, 4-ball EP  load-wear index, Falex extreme pressure and many other tests used in meeting API GL-5 performance requirements and SAE J306 viscosity requirements.

The purpose of the Gear Oil White Paper is to inform consumers about the increasingly severe conditions under which differentials operate and to provide data reflecting the quality and cost differences of many popular synthetic and petroleum gear lubes. With this information, consumers are better prepared to make informed decisions when purchasing gear lubricants. All performance testing was conducted by an independent laboratory. Physical-property testing (viscosity, viscosity index, pour point and foaming after oxidation) was conducted in-house. Gear lube pricing was obtained from the manufacturers or distributors.

This no-frills study is designed to help consumers make informed decisions when selecting  gear oils. There is no hype and no sales pitch -- just facts. Never before has so much information on gear oils been delivered in one easy to understand source.

Download the PDF version of the Gear Oil White Paper by clicking this link:  Printable PDF Version (2 MB) This paper is also for sale as the G2457.