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EFV-8 Club Forum / General Ford Discussion / Lapping Rear Hubs To Axle

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Posted By Discussion Topic: Lapping Rear Hubs To Axle     Oldad 09-12-2012 @ 2:45 PM reply profile send p.m. New Member Posts: 111 Joined: May 2012 I am refurbishing a 1937 Model 78 Ford. In the process I removed the rear hubs; checked the linings, cleaned, inspected and repacked the bearings, reinstalled and torqued the axle nut to specs. I ran the car on the lift, in gear, and noticed a small clunking noise in the right rear hub. Not good! I checked the lug nuts-they were all tight. I then checked for play in the axle-hub assembly and detected a slight movement. My diagnosis was a worn roller bearing or a poor fit between axle and hub. I have ordered a new roller bearing and have inside and outside micrometers but no idea what the specs are. In the dim recesses of my memory I recall reading that for a good fit the rear hubs should be lapped with the tapered portion of the rear axle. I have lapped valves in racing engines after a three angle grinding job but have never lapped an axle to a hub. I would assume that the procedure would involve removing the key,applying lapping compound rotating the hub and then checking fit with machinist blue. Any hands-on experience will be appreciated. supereal 09-12-2012 @ 3:07 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Be sure that the axle tapers are clean and free of any gouges or extraneous metal before you mount the hubs. The axles and hubs should never be lubricated before installation, and the keys and key ways should be intact without any signs of shearing. If you still detect any signs of looseness, obtain the tapered axle shims available from most good vendors. They will take up the slack, and are often used to fix your problem, Norris. Lapping isn't necessary, or advisable. Oldad 09-12-2012 @ 3:22 PM reply profile send p.m. New Member Posts: 111 Joined: May 2012 Thanks, Bob. I will follow your advice! Norris Stroker 09-12-2012 @ 3:39 PM reply profile send p.m. Senior Posts: 1460 Joined: Oct 2009 I'm with Super on this. In the 30's, some dirt-track racers advocated lapping-in rear axle tapers. I can relate, given the high stakes of competition, and extreme attention to detail to make things "perfect". Racers tend to do that. As a practical matter, if the axle tapers are in bad shape, it's time to think about axles. I have used shims in the past to salvage axles that had sheared keys and developed grooves due to abuse (drag racing). Neither lapping, nor shims are necessary in a stock, street-driven application if the axles are decent. When everything is working as it should, the axle will be tightly wedged into the hub, and the key is just there as "suspenders". Any marks on the key that indicate movement mean that the wedge isn't tight enough. Lapping won't hurt anything, but you could spend days making a minor improvement to the "wedging action". I often see questions on this Forum on just how tight the rear axle nut should be. It needs to be really-really tight! Properly installed hubs require a dedicated puller (such as the KRW) to break that wedge/bond. Obviously, you are familiar with the lapping process, so I'd say go-ahead if you have the time and patience. It won't hurt anything, and it will allow you to spend the fall,winter, and maybe even the early spring in the shop, rather than the house. Oldad 09-12-2012 @ 5:11 PM reply profile send p.m. New Member Posts: 111 Joined: May 2012 Thanks, I have a KRW type puller, since the hubs were recently installed it took a moderate effort to remove them. Been there, done that with the racing effort--now I just want a good ride! supereal 09-13-2012 @ 10:31 AM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 I should add that it is necessary to obtain genuine Ford axle keys if yours are not a tight fit. We find that some were homemade with ordinary key stock, which often is a tiny bit smaller than required. There also can be a problem with the hardness of the material. Only a 1000th lack of dimension can result in problems, particularly if you don't retighten the hubs after the first hundred miles or so. Oldad 09-13-2012 @ 7:50 PM reply profile send p.m. New Member Posts: 111 Joined: May 2012 Thanks for the help. I get the message loud and clear that the nuts need to be really tight. Any suggestions on foot-lbs with a torque wrency? supereal 09-13-2012 @ 8:15 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Use a big breaker bar with a piece of pipe on the handle. Mark the cotter pin hole on the end of the axle with a file or hacksaw. This is a big help in knowing how far the nut must go before a cotter can be inserted. If you need to move the nut to the next space, always tighten, never back off the nut. I've never twisted off the end of an axle, even standing on the wrench. At the shop, I use a big air wrench turned up to maximum.

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