4 Speed Owners Must Read!!!!!

Discussion in 'U-shift em' started by bostongsx, Mar 16, 2009.

  1. bostongsx

    bostongsx Platinum Level Contributor

    DO NOT RUN GL-5 Gear Oil in your tranny it kills the syncros. Read the info below.

    REDLINE Synthetic Manual Transmission Lubricants

    Most manufacturers of manual transmissions and
    transaxles recommend an 80W or 90W GL-4 lubricant.
    GL-5 gears oils which are required in hypoid differentials
    are not used in most synchromesh transmissions
    because the chemicals used to provide the extreme
    pressure protection can be corrosive to synchronizers,
    which are commonly made of brass or bronze. Typically,
    the use of a GL-5 lubricant in a synchromesh
    transmission will shorten the synchronizer life by one
    half. The extreme pressure requirements of spur gears
    and helical gears found in transmissions are not nearly
    as great as found in rear-wheel drive differentials. A
    GL-4 lubricant provides adequate protection for most
    manual transmissions, unless a unique design
    consideration requires the extra protection of a GL-5.
    The reason that many manufacturers have made
    recommendations of motor oils or ATFs is that petroleum
    80W gear oils frequently do not shift well at low
    temperatures. Motor oils and ATFs are much more fluid
    at lower temperatures and they are not corrosive toward
    synchros, but they provide very poor gear protection.
    These lubricants provide almost no extreme-pressure
    protection. In addition, petroleum multigrade motor oils
    and ATFs have very poor shear stability. The shearing
    action by a manual transmission on thickeners is much
    worse than in an engine or automatic transmission.
    Within 5,000 miles the thickeners can be rendered
    ineffective and the transmission will be operating on a
    much reduced level of protection, as shown in the graph
    below. In hot weather these transmissions will whine
    and rattle because of poor vibration dampening and
    metal contact. Red Line MTL and MT-90 provide the
    excellent gear protection of a GL-4 gear oil in a synthetic
    lubricant which spans hot and cold temperatures and will
    not shear or oxidize with use.
  2. SpecialWagon65

    SpecialWagon65 Ted Nagel

    Interesting, thanks Herb.
  3. PaulGS

    PaulGS Well-Known Member

    Great post Herb.

    I run Amsoil Sythetic gear Lube (75-90, GL4) in my rebuilt Muncie M21.

    Works and shifts perfectly.
  4. bostongsx

    bostongsx Platinum Level Contributor

    I am glad I found out before I filled my tranny, just had it done over with the overdrive, it looks like amsoil or redline is the way to go.
  5. Davis

    Davis Moderator

    I checked last night and the Valvoline Syn gear oil in my trans is GL-5.

    I wonder if that occasional rattle I hear is as described in the Redline article?

    Time to drain it out and make a change, luckily it doesnt have to many passes or street miles with this oil.

    Thanks for the heads up Herb.
  6. shamone

    shamone Well-Known Member

    this should be a "sticky" post :Smarty:
  7. bostongsx

    bostongsx Platinum Level Contributor

    Definitely a costly mistake for someone that doesn't have this information.
  8. Davis

    Davis Moderator

    Stuck it now is.
  9. Tim

    Tim Silver Level contributor

    I wonder if this is why my trans is acting up, I bought my 72GS455 4 speed used and rebuilt the motor rear end but did not touch the trans because everything seemed Ok when I bought it. I replaced the trans lube with Valvoline 85 weight gear lube. I have driven the car approximately 600 miles and this problem has occurred several times. I will be driving and all of a sudden the trans will come out of gear, it seems to happen more frequently when I am cruising in fourth gear and let off of the gas, it has not happened under acceleration. I checked the gear lube contents tonight and sure enough it is the GL-5. I will change the gear lube with the GL-4 before I drive it again. Is there something else that can be causing the trans to pop into nuetral???
  10. skylarkroost

    skylarkroost skylarkroost

    My m-21 does the exact same thing. Upon deceleration in 4th it occasionally, actually more often than not, pops into neutral. I always thought I just had a syncro that was getting a little feeble. May have to check into this lube issue as I can't recall which type I changed it with when I had the motor out for rebuild. Great sticky Herb.
  11. Todd69GS

    Todd69GS Silver Level contributor

    This is good info. I just went through this a few weeks ago when I bought parts to convert my M21 to an M20. The guy that rebuilds and sells Muncie parts locally told me the same thing. Stay away from anything that is GL5 rated or mentions that it is safe for hypoid gears. It will literally eat the synchros. He also had the opinion that synthetic should never be used in a Muncie. Too slippery for the synchros and can cause shifting problems down the road. Maybe an old school opinion but he's rebuilt probably thousands of Muncies so I will take his word.
    Problem is finding the stuff thats only rated GL4. What I have seen is some of the GL5 stuff will say it's safe for GL4 apps but on the description on the bottle it will say for use with hypoid gears. So be careful.
    The only GL4 I could find around here was the cheap no brand stuff.
  12. 70sLark

    70sLark Well-Known Member

    This comes up allot on TGO as factory GM said to use ATF in the T5, some still use 80-90 but its suppose to be to thick, some like me run straight 30w oil, not a multi oil. Some use a mix of both ATF and oil.

    Now some may know the T5 was or is considered a bit weak but in my searches into the subject. I found the folks who had a normal T5 behind some power and were able to make it last changed the trans fluids with every oil change.

    There were guy with stock 305s who could blow them out daily.
    And guys with built 400 with several race seasons with no problems.

    The ones that had the fewest problems changed it with the oil.

    Id say regardless of what you use, change your tranny fluid in your stick more often then ever 10-20 years like folks do for automatics and you will be cool.
  13. moleary

    moleary GOD Bless America

    GL-4 is obsolete isn't it?
  14. Todd69GS

    Todd69GS Silver Level contributor

  15. moleary

    moleary GOD Bless America

    So, If I plan to run AMSOIL Severe Gear SAE 75W-90 SYNTHETIC EXTREME PRESSURE LUBRICANT bar code ----97012 25601 should I be prepared to rebuild the trans in a year?.
  16. GSX-PKV

    GSX-PKV registered user

    Over 15 years ago, we were driving the GSX to the Nationals in Bowling Green from Northern Illinois. Near Indy on I-65 we smelled smoke coming up through the shifter boot. It turns out that the bearing in the tail shaft extension housing must have been slightly out of round and our 70+ mph cruising for 250 miles was the final straw for that bearing and it popped out, leaking trans fluid on the exhaust. In effect, we drove the car for miles with no fluid in that trans until we could find a place to get help.

    When I returned home, I took the trans to a 4 speed expert for repair and we were amazed to discover that other than it needing a new tail shaft extension housing, all the gears all were in great shape thanks to the Red Line fluid we had in that trans. Paul
  17. bostongsx

    bostongsx Platinum Level Contributor

    I believe both redline and amsoil have a gl4 specific fluid.
  18. moleary

    moleary GOD Bless America

    I have checked a couple sources who say that the AMSOIL doe snot make GL-4 anymore and most lube mfgr's just make products that meet multiple applications specifications. I talked to a roundy round racer pal that runs AMSOIL ATF in his MUNCIE and he does not have any issues.
  19. Tim

    Tim Silver Level contributor

    Does anyone know what the cause of my trans slipping out of gear is, and how to fix it?
  20. bostongsx

    bostongsx Platinum Level Contributor

    Here is the amsoil product

    Attached Files:

Share This Page