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drag co-efficient question | 23 comments (23 topical)
Re: drag co-efficient question (3.00 / 0) (#15)
by xymox on Tue Sep 06, 2005 at 07:31:40 PM MST

Allan, Here is a good article on how much force it takes to actually remove the bearings
http://www.rangerovers.net/repairdetails/drivetrain/hubs.html#bearingonly
given that, it seems pretty unlikely that this process could happen on its own.
I still dont feel quite at ease about using this hub design, but given that its fairly easy to replace and will require no welding to attach to a frame(given the 3 bolt flange), I think it is a good trade off.

Also while thinking of it. The force will probably 99% of the time be focused in towards the mounting flange, so I can imagine, if anything it will tend to tighten itself, I say this in jest of course ;)
Beat the system, do as much as you can do.
[ Parent ]



Re: drag co-efficient question (3.00 / 0) (#16)
by kitno455 on Tue Sep 06, 2005 at 08:14:21 PM MST

you are not using an off-road spec hub from a solid axle rover 4.6 (with 32x12 tires), you are using a cheap rebuild from a chevy FWD with some half the tire weight for on-road use :) yes, it takes a big press, yes i have seen presses bent trying to do this. that does not mean that corrosion and vibration and yaw precession will not eventually loosen this thing. a big bolt or the actual end joint of a CV and the appropriate washers are cheap insurance.

oh, and they most DEFINATELY should touch. dont leave a gap, cause that defeats the purpose. follow the axle nut torque specs of the manufacturer, minus a quarter turn since you want a little less friction and have less load.

i think perhaps you are missing the intended location of the inner washer- it should only cover the inner portion of the hub, not the outer, three-bolt flange. take a look an an actual half-shaft at the auto parts store. see how it fits into your hub. replicate that, or just get the outer joint and nut at your local junk yard.

allan

[ Parent ]



Re: drag co-efficient question (3.00 / 0) (#17)
by maker of toys on Wed Sep 07, 2005 at 12:33:16 AM MST

preload is important to the longevity of this sort of bearing system.
prevailing torque is not sufficient to lock the nut.
never rely on a press fit to hold things in place.
things can come unraveled frightfully fast.

anecdotal evidence:

I had occasion to change the wheel bearings twice in one month in a CV equipped car. . . after the mechanic had his try, the nut worked loose because it hadn't been staked over properly. so the new bearings lost their preload and ate themselves by running on the wrong part of the race. the hub also worked its way about 1/3 the way out of the bearing. (this only took about 1000 freeway miles in a very light car. . .  I guestimate about 6 months at 250 rpm for a windmill.)
I had caught the lack of staking a couple of days after getting  back the car, but hadn't thought to retorque the nut.  (it didn't spin by hand, and I didn't have a big enough socket or torque wrench at that point. . . could have bought both for what the job cost. always doublecheck anything someone else has done to your car . . . .)  

so, no longer trusting that mechanic, I undertook the task myself.

it turned out that it actually was a pretty light press fit. . . I managed to remove and replace the bearings using some creative bracketry and a 1/2" bolt. the hub was a similar light force-fit in the bearing.
I never got above 40 ftLb torque on the bolt.   (I think that's about 60 Nm to those of you who use a real measurement system. . .) I've since done some research, and I figure the 'press fit' was about 6 tons force.  

There was a special 'external thread nut' sort of a thing to hold the bearings in place in the hub carrier. . . . seems the engineers at Fiat didn't trust a press fit either. . . .

moral: vibration and impact can undo anything that a press can do.

so:  preload those suckers, and at lease use a staked nut or cotter pin if you're going to double-think the original engineer. . .  washers alone won't cut it in this application.


It's not a case of 'Save the planet,' it's a case of 'Save the humans.'
[ Parent ]



Re: drag co-efficient question (3.00 / 0) (#18)
by kitno455 on Wed Sep 07, 2005 at 07:57:01 AM MST

preload is important, yes. though more important with ball bearings than tapered roller, though that is mostly due to the 'ramping' effect of the weight of the car in the races. in this case, with no appreciable vertical load, i bet the rear/inner bearing will take most of the force in compression, and the outer/front bearing will be largely unloaded (until vibration or precession starts)

i recommend highly that you use the outer part of a cv, instead of a bolt and washer. it has radiused corners, case hardening, and is cross-drilled for a cotter pin. it is also self-centering, and not fully threaded (less stress raisers). you can cut the birfield cup off, as long as you leave the flange under it.

if you insist on using a bolt and washers to do this, find a way to keep the bolt centered in the hole, and use grade 8 hardware, not the crap from the home improvement store, and try to find a properly made bolt, with threads only at the tip, and a narrowed shank, like a good cylinder head bolt.

allan

[ Parent ]



drag co-efficient question | 23 comments (23 topical)

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