First, the issue...on gears with spiral cut, end play allows the thrust of power against slanted gear teeth to translate into axial movement. On the application of power, as in letting out the clutch either from rest or after a shift, the gear skitters away from the load til it runs out of endplay, then takes the load BANG as well as pounding whatever part is at the end of the endplay...this is how your case got to be too long! Play in middle, where input and output shafts meet, allows wobble of both shafts, prevents full engagement of those tiny synchro teeth, AND puts endplay into the general stack of parts around synchro and second gear... This wobble plus any play radial wise in main bearings allows gear CLIMB...gears with play try to ride apart 90 degrees to shafts, climbing each other's teeth til something breaks, even splitting the case in some instances. Note that not just main 2 bearings and cluster bearings are involved, but also the bearing in middle of top and the pilot bearing... End play in cluster is obvious on trial fitting. Upper shafts require more ****ysis...proper bearing retention involving the front and rear retainers, snap rings, U-joint, etc. can pull the ends up tight so there is no play to feel, yet leave a gap at middle allowing all the ills mentioned above. Best way to see problem is to mount entire upper ***embly in a lathe and measure distance enclosed by the big snap rings that locate bearings against case, then measure the length of case surfaces, using one of those gigantic micrometers you can't afford... A more doable way is to ***emble the whole mess into case without the rear snap ring and see if groove for said snapring can be pushed into case...that way you can see the critical difference. The slop is not only slop, it is subtracted from your synchro engagement! There is also a select fit shim at second gear with an endplay spec....004-.008...go to or beyond LOW end of that!! Now, my info is from an article by Ch***is Research, about 1960--the dragster factory! They blueprinted and otherwise reworked Ford transmissions (usually reduced to 2 speeds) for use on dragsters. The role of endplay had never occurred to me til I saw this...I have since seen it fully confirmed by 1960's dragster and stock car people. They essentially built to ZERO play, even slight drag on cluster. Second gear play is dealt with by Ford manual. Any extra needed will require adding more shim. Upper shaft play: They milled the rear of the case, max milling is .080 in their highly experienced opinion. Another or supplemental way would be shimming--look at the rear slinger. What would happen if you put in more than one of those?? YES! Go for zero play. On cluster, they give no clues...try some stock thrust washers and see. My considered opinion would be to shim on non-wearing side of the thrust washer with a shim cut to full surface. Other stuff from their bag of tricks: They cadmium plated case before going to work...perfect cleanliness, slight buildup of all surfaces. They will sell you a complete done transmission for only $76.80 outright...but of course you'll need a time machine. Blasted calendar done slipped... For dragster use...this does not sound like a recipe for the street...they copper plated (to avoid accidental case-hardening during treat) and then heat treated gears to 35-40 Rockwell C scale, softer than stock, to increase gear ability to withstand shock loads...just as builders do now for 9" Ford R&P for really fast drag cars. Stock bearings are adequate (note that you can buy INADEQUATE bearings from the resto places, especially the cluster bearings), but they recommend "precision Torrington replacements" just in case...anybody here deal in/know the modern bearing business? Up top, they call for New Departure ND 306 and ND 477508...do those still exist? Now, that's the gospel from 1960, confirmed to me by a couple of old racers heavily engaged once in the breaking '39 transmission industry... It is book-learning from my research, not from my own experience directly--I have built happy and successful Ford transmissions, starting with messing with a '36 when I was 13, but all before I knew to think about endplay...my work just by regular Ford rebuild with mostly used parts has been happy and durable, but this endplay business makes a LOT of sense, explaining the differences between the transmissions that ran at the drags into very low numbers and those that blow up weekly. Also note that car weight is a big factor...OHV swappers were forced to go to LaSalle by the early 1950's in big street cars, but dragsters ran the same box into the '60's...
Dayum! It sure got quiet in here pretty quick.... LMAO!!! Let us know how the swap goes this weekend!
End Play and Overall Clearances: Bruce is exactly right as far as his post on the different things to consider in setting up a ******. When I rebuilt mine for my stroker motors as well as a blown stroker, I used to buy small parts kits that had all the pieces. I also used to go to ****** shops and see if I could find thicker cluster end-play shims than stock. I'd then put them on my surface grinder and surface them to fit. As Bruce noted, I'd slowly take them down until the cluster would just fit - no slop at all. If I remember, the end-play washers had a "tang" that kept them from turning (hope I'm right on early Ford!) - so I would surface the bearing material side. I paid the same kind of attention to where the main drive and main shaft met - making sure that things were tight, that the synchros were new, all bearings new or in good shape, etc.. These early ******s (modern ones are no different) need to have tight/correct clearances to be able to withstand much abuse. I used to drop the clutch pretty hard and shift to 2nd at about 6,000 RPM - which would break the rear tires loose - which were about 8 - 9" wide. I can't tell you how long and how much abuse a properly setup one will last -- all depends on the weight of the car, how hard it hooks up, the clutch, engine horsepower, etc --- but I ran mine pretty hard.
Somebody whao ran dragsters around 1960 wrote on the barn that they were forced to switch to T85's, then discovered end play was a factor and were able to switch back to early Ford...
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