Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties speedo drive leaking?

speedo drive leaking?

Post Thu Jul 04, 2013 7:27 pm

Posts: 109
even'n folks, got an oem 4 speed case with vent in top of case between kicker cover and jockey top ( 42 or 52, forget the date code but it was a 2 ), it pushes a fair amount oil up thru drive and leaks out through the unjacketed cable housing.... never had a 4 speed do this before. the drive is the late style, fine teeth, 1to 1 i think, anyhow it's the late shovel style, tried another drive and gasket today and this one is worse? now i have never tried to pull one apart but are they sealed somehow when they are assembled? i did not check the vent yet but i'm sure it's open, just put tranny together this past winter and vent was fine, would a shovel lid vent screw help at all, venting would be to inside case instead thru kicker cavity. not a big deal but if i can dry up this leak i'll have 39ul that is really tight oilwise. and it seems to only leak during extended 50 to 70 mph rides. around town and back roads it settles down and stays dry. both drive seem tight and not loose and worn, thanks for any insight and ideas, ......and yes i'm going to pull the vent and double check that it's open....mark

Post Thu Jul 04, 2013 7:48 pm

Posts: 109
okay i just pulled vent screw out and it's open just fine, also noticed that vent is in gear compartment and not on the kicker cavity.

Post Thu Jul 04, 2013 8:21 pm

Posts: 391
Is the gearbox overfilled? Bottom of filler threads when vertical? Is the hole for the screw clear into the box cavity?

Post Fri Jul 05, 2013 7:01 am

Posts: 109
i put 3/4 of a quart in the tranny a few days ago. now that amount did come above the filler hole on the kicker cover so less than 24 ozs is what i'll have to figure out, on my shovel i just dump a quart in there and she's fine with that. thanks Robbie

Post Fri Jul 05, 2013 4:17 pm

Posts: 391
Factory spec is 5/8 qt. If overfilled even with a breather it will come out. Primarily out the MDG into the clutch, but also anywhere else it can.

Post Fri Jul 05, 2013 8:53 pm

Posts: 109
well i'll try 5/8 of a quart and see if that will help. i do have a new old stock gary bang kicker cover with the solid kicker boss, so the fill may not be the same as oem. drive gear has ray's o-ring spacer, so drive gear is pretty tight, another damp spot is at the shifter shaft in the jockey top, that has the leather washer. thank robbie......always spooks me to come up short on lubrication, but 5/8ths seems reasonable, will just have to check the level more often til i get comfortable with it....mark

Post Mon Jul 08, 2013 9:24 pm

Posts: 109
well i went and got a new speedo cable, new style repop with vinyl sheathing.....but while i was searching for a nos cable i came across the old sportster cables.....the old tranny drive type on the K's and xl's thru 1972. now why did not all the oil in the primary/tranny just seep out onto the ground? these cables had to be sealed somehow? so maybe my old oem cable housing is just shot and leaks.
i took the flathead for nice 30 mile ride to the the area i'm from and went to see my old boss at laughermans HD down the road from the york HD factory, we're talking 35 yrs ago when i worked for him, i know he keeps a fairly good stock of older items (1970's) and we were rummaging thru speedo cables when we came across the old xlch type, now he said my vent must be blocked and i said no it ain't , he suggested also using the lid vent screw to create more venting, while i unwound this long speedo cable........old xlch...yeah forgot about those, then it hit me.....dang thing comes out on the very bottom of the tranny case, any thoughts on why they didn't leak?

Post Tue Jul 09, 2013 12:20 pm

Posts: 391
Speedo drives use a labyrinth type seal, a reverse spiral and close tolerances keep them from leaking. The same system used on left engine main bearings, Tranny main drive gear bushings, etc. They do not leak because there is no pressure against them. And speedo cables are not sealed, again because they do not have any pressurized lubricant trying to get out.

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