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Technical 1939 transmission fault

Discussion in 'Traditional Hot Rods' started by Jukenut13, Jan 1, 2019.

  1. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Hi, I finally fitted a '39 trans in my 1930 4 banger coupe. I used a Clings adapter and all went well but had a slight buzzing noise in third only, I could alter the noise by lifting or pulling the gear lever slightly. Pulled trans out and dismantled. All looked good.
    This is a 1939 Canadian unit with the 81A shifter tower, 78 main case, all helical teeth, small syncro. I replaced the 2nd gear bush and mainshaft as these were sloppy (on the splines). Also fitted a new syncro sleeve and hub - has the 48-7106 sleeve (although the one I replaced looked good). 2nd gear end play at limit. I have Mac Van Pelts book.
    Mainshaft is 68-7061B. . Main drive gear marked T-191-16A. (std 16 teeth) . The cluster (std 28 teeth) has the oblong hole, 2 part thrust and 3 ribs around between front large and second gears (51A-7113 ?) . Although all brgs looked good, replaced front and rear brgs.
    Had hoped all would be good, but noise still there - even louder!
    Gearbox shifts ok, detents firm, little play in swan lever etc. Up on stands, I select 3rd and sometimes ok. but if I move the lever slightly the noise kicks in - a wirring / buzzing noise as if the hardening has gone or sloppy meshing between teeth, if I shift to 2nd, (no noise) and back to 3rd , sometimes ok but mostly noisy. I can ''feel'' the noise at the shifter tower.
    I put it into 3rd and carfully removed (when noisy)the top and found the syncro sleeve hard up to the main drive gear and the balls very close to popping out!
    It looks like the synro sleeve is traveling too far (checked 2nd gear - sleeve moves very close to 2nd gear teeth). Selectors all look good, detents -lever wear good etc.
    Any help most welcome
     
    stillrunners likes this.
  2. The 39 guy
    Joined: Nov 5, 2010
    Posts: 2,587

    The 39 guy
    Member

    I have nothing to offer but that was best, most complete description of a 39 transmission problem I ever read.
     
    Last edited: Jan 8, 2019
  3. King ford
    Joined: Mar 18, 2013
    Posts: 1,175

    King ford
    ALLIANCE MEMBER
    from 08302

    If you mix used gears with new or different used gears the wear pattern on the teeth can cause a slight " howling" or " singing " noise.....
     
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  4. WB69
    Joined: Dec 7, 2008
    Posts: 651

    WB69
    Member

    Had one professionally rebuilt, works great but has that slight singing sound. Was told it was normal and not to worry about it. 10 years later still working good, also still singing...….
     
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  5. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Hi, the noise previous to installing the new syncro etc. was annoying but now a lot louder. Maybe I need to stop the selector traveling past the detent? When 3rd selected, I can pull the lever back a little ( can feel the detent lock in and out), this kicks off the noise .
     
  6. alchemy
    Joined: Sep 27, 2002
    Posts: 13,690

    alchemy
    Member

    Doublecheck the actual shift lever is straight from the pivot ball down to the tip ball. I've found bent ones before.
     
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  7. VANDENPLAS
    Joined: Dec 14, 2009
    Posts: 1,673

    VANDENPLAS
    Member

    I have never done it in automotive
    But working on forklifts I do a lot of drive units ( a cross between a gearbox and a diff)
    Parts are astronomical so I do a lot of mixing and matching of gears from scrap and old units and would get a howling or whining noise from the mix matched gear sets.
    What I do now is assemble the drive unit and put lapping compound on the gears and run the run the unit for a bit
    Then disassemble clean everything out, replace bearings and bushings ( if they are contaminated) and reassemble .
    Poof! Noise gone, probably not the best way to do it but when parts are either “ no longer available” or cost 10X what the unit is worth this is a great alternative.
     
  8. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Gear lever ok,
     
  9. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    This sounds more like you would get with completely worn out teeth, but I think its in the syncro - noise stops if I lift the gear lever a little..
     
  10. jimvette59
    Joined: Apr 28, 2008
    Posts: 677

    jimvette59
    Member

    Have you tried other leavers ? Add some gaskets to he trans. case. JMHO
     
    flatford39 likes this.
  11. xix32
    Joined: Jun 12, 2008
    Posts: 426

    xix32
    Member

    Do you have this type of syncro drum ? with the fork slot to the rear, that requires the 91A , 3" shift fork .
    Either one of the early ( 2 7/8"), or late ( 3") forks will fit in the 81A shift tower. I ask, because it is possible for the late (3") fork to straddle the early syncro ( with the slot in the center) then it would push the drum too far toward the rear. ( edit) My mistake here, that would push it back too far in second gear, not third. Since third gear is when the drum is pushed forward, not back. sorry.
    `39 trans view of gears.JPG
     
    Last edited: Jan 5, 2019
    stillrunners likes this.
  12. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Hi, I mean when I push the lever back towards neutral a little (moving the detent position slightly). Unfortunatley only have a spare '35-'36 top .Parts here (NZ) hard to get, new ones expensive. Trying to locate spare top to compare /try.
     
  13. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Hi, mine has same box as yours but with the earlier small syncro and small fork.

    Will try to upload some pics later.
     
  14. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Here are the photos of my trans. 101_0795.JPG 101_0810.JPG 101_0795.JPG 101_0810.JPG 101_0803.JPG 101_0795.JPG 101_0810.JPG 101_0803.JPG 101_0792.JPG 101_0812.JPG
     
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  15. The 39 guy
    Joined: Nov 5, 2010
    Posts: 2,587

    The 39 guy
    Member

    [​IMG]
    Did you say you replaced the main shaft? It looks like it is pretty chewed up. Not say that is the cause of your noise, just wondering.
     
  16. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Thats the factory cutouts to assist dismantling lock slide.
     
  17. 5280A2
    Joined: Sep 8, 2014
    Posts: 102

    5280A2

    I think you need to use the 68 shift tower on that synchro sleeve. I believe the sleeve was changed when they went to the 91 tower with the 2-7/8 fork. If you compare the two towers you will see that the fork is farther forward in the 81 top so it is pushing the sleeve too far forward when you shift into high gear. I have a 1938 transmission and the gearset and synchros look exactly like your photos and uses the 68 top.
     
  18. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    I just got a reply from the person I got it from, he said it worked ok for him- no noise etc.
    From what I've read, the late 81A top could come with either the small or large forks, depending on the syncro used?
     
  19. 5280A2
    Joined: Sep 8, 2014
    Posts: 102

    5280A2

    Which fork is in your 81A top? It should be the narrow one (2-7/8) to be compatible with your gearset and synchro sleeve. The 3-inch 91A fork is offset further toward the front of the gearcase and would cause the synchro sleeve to move too far forward and potentially contact the front gear on the cluster to get the noise and vibration you feel.

    I suppose that could also be caused by the cluster being too far to the rear in the gear case. Is there an extra shim on the cluster and is it perhaps on the front side? I have seen gearboxes with an extra shim to resolve cluster and play and these should be installed at the rear of the case. You might also try asking on the early V8 section of Fordbarn, I see Mac Van Pelt post there on transmission questions quite often.
     
  20. xix32
    Joined: Jun 12, 2008
    Posts: 426

    xix32
    Member

    Do you have this type of shoulder bolts that hold on the shift tower ? These are meant to hold the tower in position.
    The other type ( full threads) can allow the tower to move. Maybe you could try to loosen your bolts to move the tower in the direction where it won't make the noise.
    shoulder bolts for `39 trans tower.jpg
     
  21. Yes xix32. The correct shoulder bolts are a Must. They index the Lid to the Gear box. It's kind of like having dowel pins to locate heads or a Bell housing correctly. Same with Clutch pressure plates. There is a solid reason Ford did this.
     
  22. rusty valley
    Joined: Oct 25, 2014
    Posts: 682

    rusty valley
    Member

    i also think your 35 top will go on that trans since you have the early "center slot" type syncro, and not the later "side slot" type that needs the 3" fork. easy to try, and eliminate one possibility of bent forks or shift lever. it has the symptoms of the detent not putting the syncro in the right spot when in gear
     
  23. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Thanks everyone for your input. It has the small 2 7/8 fork.
    The cluster has the std thrust in front, 2 part in rear.
    The Clings Kit comes with new longer top bolts, tried moving top back but virtualy no slop in holes.
    When 3rd selected carfully, removed top, syncro sleeve had clearance from MDrive gear. Usually no noise untill I pull back on lever, then noise starts --- the lever can be pulled back past the detent, allowing nearly 1/16'' fork travel past detent--- I think this allows the syncro balls to almost eject and produce the noise by touching the cluster? When the noise is there, I carefully remove top and find the sleeve hard up to the main drive gear.
    The spare shifter top 40-7222 has smaller 1st fork than 81A top.
    Is the extra travel past detent normal?
     
  24. 5280A2
    Joined: Sep 8, 2014
    Posts: 102

    5280A2

    There should be enough spring tension and positive contact between the shift rail and detent ball to keep the fork from moving past the detent under normal conditions. I wonder if you have a badly worn shift rail or broken spring on the detent for 2nd and high gear. Did you disassemble the top and inspect or restore the components? If not I would take it completely apart and see what the detents and shift rails look like. The edges of the detents on the shift rails should be nice and crisp and not rounded over, and the springs should be about the length as shown below (new from Van Pelt). Your problem may be entirely in the shifter top.

    IMG_2346.JPG
     
    The 39 guy likes this.
  25. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    Hi, I agree with what you say, was hoping it was in the top, did check the detents, springs and balls look good with firm action and rail looks ok. Previous owner turned up with a spare complete top so will try that and report results.
     
  26. wow...what a great thread.........
     
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  27. Jukenut13
    Joined: Feb 10, 2013
    Posts: 28

    Jukenut13
    Member

    We tried a different lever, two new (old) tops and swapped my origonal fork with another (small) fork , added washers to detent, no change. Problem still there.
    On start up, all seems ok , willrun for a while, but if you pull back on lever slightly it sometimes sets the noise off, other times is comes in on its own (sometimes it takes a while) - when this happens, the gear lever is pushed back firm (the ''extra small movement back past detent is lost). On removing the top, I find the syncro sleeve pushed forward and the ball bearings almost ejecting out....see photos.
    It looks like the syncro hub is moving back towards 2nd 101_0854.JPG 101_0855.JPG 101_0857.JPG 101_0853.JPG and forcing the sleeve forward as the balls try to come out?
    How much travel back and forth does the syncro hub normally have when in neutral?
    Maybe the mainshaft is too far back - although 2nd gear seems to line up with the cluster.
    Next move will be to pull the trans for closer inspection. Previous owner said he had no problems, came out of his 1939 coupe.
     

    Attached Files:

  28. rusty valley
    Joined: Oct 25, 2014
    Posts: 682

    rusty valley
    Member

    spec for the later style syncro is 4-8 thou after the whole stack on the main shaft is assembled. so, from the snap ring at the front of the main shaft back to the thrust washer behind second gear. i would guess the older style would be similar as the the point is to keep the stack of parts on the main shaft as close as possible, and yet allow enough clearance to get lube on to the thrust washers. if you can move your syncro hub around more than a few thou, thats the problem.
     
  29. It's been about 5 years since I did the gear box in my Roadster. It is a 39 unit also. Meaning top shift with Brass sincro rings so it shifts better than the 38 and earlier. Your calling yours a 39 unit yet I don't see the Brass rings. I guess I need to get out my book for a refresher as well as dig through my used stuff. I do believe there is something missing in your unit. Where are the Brass Rings? Look at the photo posted by XIX32 as well as mine.
    20150610_123526.jpg
    Notice the Brass Rings. Big fork or small fork are determined by the drum but as I remember things all 39 and latter had the Brass Rings then note the large space in your gear set. I understand your bolted up to a Model A motor but unless my Mind is out to lunch (that is a possibility) it looks to me like you have the wrong sincro unit coupled between second gear and the input shaft. I was also looking at photos in post 14 and it looks like your Cluster gear is ridding to the rear far enough to be an issue. If cluster 3rd gear is behind the face of the input gear of course the shift drum will make contact and noise. The cluster is turning opposite direction so it will sing for lack of better word when drum is dragging against it. You may need to move some shims around and shift the Cluster forward for proper gear alignment.
    The Wizzard
     
  30. 5280A2
    Joined: Sep 8, 2014
    Posts: 102

    5280A2

    This information is correct for the late style synchro with the brass blocker rings. However, the early style synchro hub is free to move back and forth on the main shaft in order to engage the friction surfaces on the hub with either the main drive for high gear or the front of the second gear for second. I think your synchro hub should be farther forward when the sleeve is engaged with the main drive for high gear. There may be an obstruction on the main shaft that is keeping the hub from moving forward when you shift; the result is that the balls become partially exposed on the taper of the sleeve and may actually push the sleeve forward due to the taper on the ID of the sleeve.

    As a starting point can you see, or use a mirror to see the front face of the sleeve to see if there are any wear marks that indicate it is running on the cluster gear? Secondly, can you duplicate the condition where the sleeve is fully forward with the balls partially exposed and attempt to pry the hub forward to see if it is hung up on the main shaft? Another indication that it may be hung up is if you are getting grinding upshifting into high gear indicating that the hub is not making contact with the friction surface on the main drive gear. It seems that you have eliminated the shift top as the potential problem if you are getting the same results regardless of which top you have installed.

    I have a 1938 transmission apart right now with the early synchros, so I will reassemble it enough to check how much movement there should be on the synchro hub and will report back. It is definitely more than the 4-8 thousandths that is spec'd for the late synchro assembly where the hub is essentially stationary on the main shaft.

    For the Wizzard and others I am posting a picture of the early style synchro in a 1936 transmission which is the same unit as in Jukenut13's transmission. It could be a 39 transmission but it has the earlier gear set that was used into early 1939

    IMG_3021.JPG
     
    rusty valley likes this.

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