Manual Transmissions and Lubricants

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MolaKule

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Used by Permission of the Author for BITOG Protection-wise, most Manual Transmisson Lubes are rated with an API protection rating of GL-4 because of the type of gearing used as will be explained later. I think manual (or Stickshift or Standard) transmissions are more fun to drive than automatic transmissions. Manual transmissions require more driver interaction than do automatic transmissions. You can’t talk on the cellphone, or eat, or text when you have to shift gears. In this paper we examine the internal mechanisms of the manual transmission and the effects of the lubricant’s viscosity and additives. We are discussing light truck and passenger vehicle manual transmissions only. We will not discuss OTR or heavy-duty transmissions which use a different type of lubricant. A modern gearbox is of the constant mesh type, in which all gears are always in mesh. The exception is the reverse idler gear which will be explained later. This constant mesh and the cut of the gears insure a rather quiet transmission. In any one gear, only one of these meshed pairs of gears is locked to the shaft on which it is mounted. The others are being allowed to rotate freely; thus greatly reducing the skill required to shift gears. Most modern cars are fitted with a synchronized gear box, although it is entirely possible to construct a constant mesh gearbox without synchromesh, as found in motorcycles for example. Some manual transmissions are integrated with differentials to form a “Transaxle.” The differentials here are usually NOT the hypoid types found in larger vehicles, but are of the spider gear configuration. Going from the top of the transmission case downward, we have the shifter mound which contains the shift lever and linkages. The shifter will have a seal or boot at the top with an additional gasket to keep the lubricant from flowing out when slung by the gearing. Below that are two shafts, one the input shaft and the other being the output shaft. The input shaft is splined to the clutch for power connect or disconnect. The output shaft goes to a universal joint, then to the driveshaft (a hollow “torque” tube), and the driveshaft connects to the differential via another universal joint. An illustration of a basic manual transmission is found here, so exercise the shifting as we discuss the mechanisms (not a perfect illustration but makes the point): http://auto.howstuffworks.com/transmission4.htm Shifter Assembly: The gears resting on the top shaft, the input shaft, are locked onto that shaft and rotate at the same rpm as the engine. The bottom output shaft has synchronizers “splined” to this shaft, so they can move around as the gear ratio is changed. The gears on the output (bottom) shaft are allowed to rotate freely on the output shaft or on small roller or “needle” bearings, depending on the horsepower transmitted and the design. The output shaft will rotate at various rpms depending on gear selection. In first gear, for example, you want low output shaft rpm and high torque. The shifter moves the associated linkage which connects to the shifter forks. The linkages position the shifter forks, and effectively “programs” the shifter forks in order to select the required gear ratio. I.E., for each shift lever position, the shifter forks are moved around to drive the splined synchronizers on the output shaft. The shifter forks have a bore so they can slide on the guide rods. There is a specified clearance between the shifter forks’ bore and the shifter fork guide rods. Lubricant effects: Too high a viscosity lubricant and the shifting will be hard and sluggish. More force will be required to go from one gear to another. Too thin an oil and the forks will wear, the clearances will increase, and the shifting will become sloppy and uncertain. The correct mix of base oil viscosities is needed here to insure good cold weather and hot weather shifting. Synthetics excel here because of their high viscosity index. Synchronizer: The locking mechanism for any individual gear consists of a collar on the shaft which is able to slide sideways so that teeth or “dogs” on its inner surface bridge two circular rings with teeth on their outer circumference; one attached to the gear, one to the shaft. (One collar typically serves for two gears; sliding in one direction selects one transmission speed, in the other direction selects the other) In our illustration from above, the bottom or output shaft has splines that mate with the synchronizer “collar.” The synchronizer collar moves transversely on the splines, positioned by the shifter fork. When the rings are bridged by the collar, that particular gear is rotationally locked to the shaft and determines the output speed of the transmission. In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone-shaped brass clutch which is attached to the gear, which brings the speeds to match prior to the collar locking into place. The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings also called blocker rings. Notice, before locking and speed synchronization, a lot of shearing takes place at the interfaces and for the reasons given above. Most synchronizer materials are of brass, but newer synchronizers can be made of strengthened graphite composites. Lubricant effects: A special Friction Modifier (FM) additive is incorporated into the base oil to allow just the right amount of friction before engagement. I.E., the FM gives rise to a specific coefficient of friction (COF) to allow engagement without “crunching.” Automatic Transmission Fluids (ATF) DO NOT have these specialized FM’s. Note, the specialized FM used in manual transmissions is NOT the same FM used in Limited Slip Differentials, nor is it the same FM used in Automatic Transmissions, nor is it the same FM used in engine oils. It is important to understand that there are different FM chemistries for different automotive applications! Bearings: Lubricated bearings are used to reduce friction between rotating parts. The older Munice transmissions, for example, used brass or sintered brass sleeve bearings or bushings. Most modern transmission bearings today, as can be seen by the links given below, are of two main types 1) Roller or needle bearings, and 2) ball bearings. Ball bearings or tapered roller bearings are usually used at the shaft ends to resist radial and transverse loads. Smaller roller or pin bearings are used inside the driven gears that reside on the output shaft. Lubricant effects: Depending on the horsepower transmitted and the size of the bearings, the lubricant’s kinematic viscosities range from 7.5 cSt (ATF-range) to 14.5 cSt (equivalent to a light 75W90 gear lube) given at 100C. The anti-wear/Extreme pressure additives keep wear in check as they rotate in their races. Anti-corrosion additives keep the anti-wear/Extreme Pressure additives from attacking the synchronizers, and anti-rust additives keep any moisture from creating rust on the steel components. For lower horsepower drive trains, the lubricant must be thin enough to penetrate the cages in the pin/roller bearing areas. For higher horsepower drive trains, the lubricant must maintain a thick film in order to protect the bearing surfaces. Too thick a lubricant will cause poor cold weather performance and loss of mpg, while too thin a lubricant will cause undue wear. Of course, the lubricant is also used for cooling. The lubricant transfers heat from the bearings and gearing to the case where it is transferred to the air. Gearing: Most gear types in manual transmissions are of the helical type, which because of the cut, reduce noise and vibration. Due to their angular cut, thrust loads are transmitted to the shafts on which they reside. The gears on the input and output shafts are usually produced in one integrated piece, called “gear clusters, “ or the cluster gear assembly. You will notice the only gear that is actually moved is the reverse idler gear. This is moved into position to mesh with the small reverse gear on the input shaft so you can “back up” or reverse direction. At higher reverse speeds, this gear will usually give off the familiar “reverse” whine. Lubricant effects: Being in constant mesh, they are dipping in the oil bath and slinging the oil up to the shifter assembly. Since they transmit torque, they must have an anti-wear/Extreme Pressure additive in the lubricant in order to reduce wear. The slipping and rolling action of the gear teeth causes localized high pressures and heating. The anti-wear/Extreme Pressure additive forms a protective but complex ferrous film at the contact surface to protect from galling and other wear mechanisms. Other components such as thrust washers, flat thrust bearings of the roller type, and shims may also need cooling, lubricant film, and anti-wear additives as well. Rebuilding manual transmissions usually require only a modest rebuild kit consisting of bearings, synchronizers, and seals unless the transmission has been abused or the wrong lubricant has been used. In that case, gear teeth need to be examined for any chipping, galling, breakage, or other signs of problems. (Transmission Kits). http://www.manualtransmissionkits.com/nv4500_bk308ws_bearing_kit_rebui.htm Here are some individual transmission parts layed out for Jeep transmissions but is typical of others. http://www.4wd.com/Transmission-and-Transfercase/Manual-Transmissions.aspx?t_c=69&t_s=239 Images of Manual Transmissions, both external and internal: http://www.bing.com/images/search?q=manu...ORM=IGRE#x0y810 If you are going to modify or rebuild your Manual Transmission, I highly recommend this book or equivalent:: http://www.mre-books.com/transmissions/rebuild_and_modify.html Passing Thoughts One variation on the Manual Transmission is the “Automated Manual” using a dual clutch. Some people consider many of the Honda Automatic Transmissions simply automated manual’s as well. http://www.allpar.com/corporate/auto-manual-transmission.html A long winded History and Summary but without the in-depth knowledge of internal mecahnics-vs-lubricants: http://dictionary.sensagent.com/Manual_transmission/en-en/ I like this link; it contains online MT manuals for classic Chevy’s: http://chevy.oldcarmanualproject.com/trans/index.htm
 
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Originally Posted By: MolaKule
I think manual (or Stickshift or Standard) transmissions are more fun to drive than automatic transmissions. Manual transmissions require more driver interaction than do automatic transmissions. You can’t talk on the cellphone, or eat, or text when you have to shift gears.
+1 thumbsup I agree! Thanks Molakule for the great article! Very interesting!
 
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Reading this very informative post got me thinking. How can some transmissions get away with recommending motor oil as the lubricant? It's pretty obvious that gear oils and MTL's have specific additives for optimal performance that motor oils probably lack, but they're still listed as acceptable lubricants. Would motor oil produce more wear and reduce transmission life in the long run?
 
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Originally Posted By: KrisZ
Reading this very informative post got me thinking. How can some transmissions get away with recommending motor oil as the lubricant? Would motor oil produce more wear and reduce transmission life in the long run?
I am curious too. As 10w40 is nearly the same viscosity as 75w90, I am considering it as an alternative.
 

MolaKule

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Quote:
Reading this very informative post got me thinking. How can some transmissions get away with recommending motor oil as the lubricant? It's pretty obvious that gear oils and MTL's have specific additives for optimal performance that motor oils probably lack, but they're still listed as acceptable lubricants. Would motor oil produce more wear and reduce transmission life in the long run?
1. This is not a putdown, but while mechanical engineers are great at designing complex machinery, not all fully understand lubricant chemistry and the salient interactions of machine parts with lubricant components. 2. Sometimes PCMO's are listed as temporary alternatives for MT lubes. Historically, PCMO's were listed as MT lubes before Texaco, Delco and Pennzoil and others came out with the optimized synchromesh MT lubricants. 3. The PCMO does not contain the proper friction modifier so the synchronizers might wear faster. Then there is the question of the proper amount and type of Anti-Wear additive. The MT tranny won't fall apart with PCMO but it is not optimal, whereas MT lubes are.
Quote:
Lubricant effects: A special Friction Modifier (FM) additive is incorporated into the base oil to allow just the right amount of friction before engagement. I.E., the FM gives rise to a specific coefficient of friction (COF) to allow engagement without “crunching.” Automatic Transmission Fluids (ATF) DO NOT have these specialized FM’s. Note, the specialized FM used in manual transmissions is NOT the same FM used in Limited Slip Differentials, nor is it the same FM used in Automatic Transmissions, nor is it the same FM used in engine oils. It is important to understand that there are different FM chemistries for different automotive applications!
 
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Does anyone know if Red Line's D4 contains the manual gearbox type of FMs, since they recommend this over their MTL (as does Amsoil for their ATF over their MTF) for my car? shrug I may have to call Dave about this.
 
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Originally Posted By: dailydriver
Does anyone know if Red Line's D4 contains the manual gearbox type of FMs ...
I'd like to know this as well. I'm currently using Valvoline MaxLife Dex/Merc in a Suzuki 5-speed manual and it's working OK with the worn synchros but I don't think it works as good as the GM Synchromesh. I'll be rebuilding a tranny to swap in and I'll likely use Red Line MTL for the initial fill.
 
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Originally Posted By: dailydriver
Does anyone know if Red Line's D4 contains the manual gearbox type of FMs
We all know the plural of anecdote isn't data, but FWIW I know several folks running it in their VW manual transmissions for a very long time with no ill results. VW's own G060 & G070 have been excellent for me, so I was happy to switch away from the Redline MTL/MT90 mix I had in there previously.
 

MolaKule

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Quote:
Does anyone know if Red Line's D4 contains the manual gearbox type of FMs
It does not. D4 is a DexIII/MERC universal ATF fluid.
 
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Originally Posted By: MolaKule
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Does anyone know if Red Line's D4 contains the manual gearbox type of FMs
It does not. D4 is a DexIII/MERC universal ATF fluid.
Yes, but Red Line lists it in their MTF tech-sheet as a GL4 oil suitable for manual transmissions and that's why I was curious. http://www.redlineoil.com/content/files/tech/Man%20Trans%20Lubes%20PDS%208-10.pdf I now notice that they list Dexron/Mercon as a 'recommended use' so that does make sense now (for transmissions not using brass synchros). The lightest dedicated MTF on that sheet would be the MTL product. Do carbon-faced synchros have any unique FM requirements?
 
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Hi, I realise this Thread is predicated towards car transmissions This may interest some here. In my Eaton Road Ranger 18 speed truck transmissions I used a synthetic SAE50 lubricant Eaton recommend: Synthetic SAE50 or, Engine oils to MIL-L-2104D SAE30 Below 10F SAE40 Above 10F SAE50 Above 10F or Gear oil API GL1 SAE90 Above 10F SAE80W Below 10F It was common practice here in Australia to use a SAE50 engine oil in these demanding applications I was one of the first to "buck the system" here by using a synthetic in this application It was a great success with no lubricant related issues over many many millions of kms and many years in all of my vehicles. Up to 300F operating temepratures are permitted and engine oil would have required regular OCIs I never changed the lubricant - it was whole of life - going out to 1.5 kms at sale of the Rig The UOA condemnation limits used were (never reached): Fe 1000ppm Sodium 50ppm Viscosity increase/decrease of 20% from new It is common practice nowto use a synthetic and I believe they are now used as FF
 

MolaKule

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Quote:
Do carbon-faced synchros have any unique FM requirements?
They have about the same requirements as metal synchronizers. They are simply carbon-fiber reinforced materials.
Quote:
The lightest dedicated MTF on that sheet would be the MTL product.
Yes, the MTF 70W80 is almost the same viscosity (10.5) as Pennzoil Synchromesh at 9.5 cSt.
Quote:
Yes, but Red Line lists it in their MTF tech-sheet as a GL4 oil suitable for manual transmissions and that's why I was curious.
Ask them how they determined the D4 to be a GL4 equivalent.
 
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Originally Posted By: MolaKule
Quote:
Do carbon-faced synchros have any unique FM requirements?
They have about the same requirements as metal synchronizers. They are simply carbon-fiber reinforced materials.
Quote:
The lightest dedicated MTF on that sheet would be the MTL product.
Yes, the MTF 70W80 is almost the same viscosity (10.5) as Pennzoil Synchromesh at 9.5 cSt.
Quote:
Yes, but Red Line lists it in their MTF tech-sheet as a GL4 oil suitable for manual transmissions and that's why I was curious.
Ask them how they determined the D4 to be a GL4 equivalent.
I did not ask Dave (at Red Line) this, but he explained that the Borg Warner/Tremec engineers actually designed the synchros in their gearboxes to work properly with a Dex 3 type, slushbox, FM, instead of the different, stated above, manual gearbox lube type of FMs. (I believe their claims to it being up to GL-4 specs have to do with the D4's inherent shear-stability, due to PAO/POE basestocks, and a stout addpack. wink ) Now I am REALLY confused. ??? Mola, others, comment on the probability of this being correct? Must I switch back to MTL/MTF/GM/Pennzoil Synchro once again?!?!
 
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If the "older" muncie transmission the Author was talking about are the m21 and m22, they are constant-mesh, with needle bearing supported gears! Not trying to start a fight, just saying.
 
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