when was the last time you checked your manual trans fluid

Discussion in 'transmission and Drive train' started by Grumpy, Nov 12, 2017.

  1. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

    I recently got a request to diagnose a problem a guy was having shifting his manual transmission, on his 1967 GTO,
    (similar to this but his car is light metallic blue)
    the car was put up on jack stands and I carefully checked and adjusted the linkage , but when I checked
    the transmission,by removing the LOWER lube plug and stuck my finger in it came out dry,
    I strongly suggested we buy and fill the transmission with fresh lube.
    (he had not driven the car for about 6 years)
    until trying to drive it around his block a couple days ago.
    we filled the upper plug until it leaked out,
    I don,t know what if any damage to the gears or internals has been seen yet,
    as adding the lube improved the function very noticeably,and the car still driving means the owner has chosen to not check it out.
    but just the idea that he was running the transmission with very low lube levels indicates that wear potential.
    I suggested we check further as it looked like the rear seal around the drive shaft yoke might be leaking.. but the cars owner declined... so I strongly suggested he verify the lube level in a week to see it it was still leaking and loosing lube...hopefully he will decide to correct this, issue then, as it should be rather obvious at that point that the seal's needs to be replaced.
    most people will check an automatic transmission fluid level if there's a dip stick to accurately measure the fluid level, but getting under the car is required on many manual transmissions and that generally means only the more dedicated hot rodder's will check a ,manual transmission.
    the fact the transmission gear lube was low in a car thats 50 years old, and rarely checked, is hardly rare.
    I've seen this happen rather often in the c3- c4 and c5 corvettes using manual transmissions or auxiliary over drive transmission units

    yes youll need a manual fluid pump to get fluid into the transmission as you can,t get access to pour the trans lube with the trans fluid containers, along side the transmission in the car












    Last edited: Nov 12, 2017
  2. Mark Bradley

    Mark Bradley Da guy in Newbury

    I’m a manual trans guy myself and I find that I check trans fluids once a year although I am pretty observant of leaks.

    Looking at your photos of Muncie trans I want to point out that (as you know) there are several versions of cases for the M-20/21/22 series transmissions. The common rumor was that having a lower drain plug was an M22 (not!).

    I feel that any individual who owns a Muncie trans should invest in this book. Even if you don’t ever rebuild it you will appreciate what you have, what the strength and weakness of the design are and how to care for it.

    I have upgraded to a Tremec TKO since the standard Muncie is really only reliable up to about 450hp when in top factory state. Yes they can receive significant upgrades and handle more power although after spending all that time and money I still have a 50 year old Muncie.


    Attached Files:

    Last edited by a moderator: Nov 12, 2017
  3. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks for flagging. I definitely need to check this as well.
  4. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

    All the newer synthetic gear lubes are NOT always an improvement over the better older mineral oil based lubes.
    but some of the better brands of manual transmission gear oils do work very well.

    ID suggest this dino lube
    Sta-Lube SL24239 API/GL-4 Multi-Purpose Hypoid Gear Oil - 1 gal

    the synthetic version costs about 45% more and I doubt its really worth the extra cost


    buy a gallon, youll save money in the long run as three quart bottles cost more than a gallon in most stores and youll need a bit over 2 quarts
    you'll need a manual fluid pump and some ideally clear hose to reach and see what your doing

    having 20 feet of vinyl hose on hand helps make this easier, and you,ll want
    some double end barb fittings to adapt the hose[​IMG]

    Last edited: Nov 22, 2017

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