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Old 03-25-2009, 11:44 PM   #7231
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Originally Posted by wingracer View Post
I have to disagree a bit. Normally what's good for a thrust bearing is a good grease like moly, wheel bearing grease, AE black grease, etc. These are not good lubes for the actual diff due to the torque being applied to it. This is not a normal operation for a thrust bearing so while a diff may be built just like a thrust bearing, it's operation is quite different. Greases will increase slippage which is not good on a diff and is why AE silicone is so good. A thrust bearing however, is not subjected to this torque that tries to slip it so a good grease (used sparingly) is perfectly fine for this.
I'm sorry, but the torque must be applied equally over both races, otherwise it wouldn't work!! If the torque were unequally applied, then the diff would operate and the car would steer off into the boards!!

I do wish people would do their homework before coming on here...
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Old 03-26-2009, 04:36 AM   #7232
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I'm sorry, but the torque must be applied equally over both races, otherwise it wouldn't work!! If the torque were unequally applied, then the diff would operate and the car would steer off into the boards!!

I do wish people would do their homework before coming on here...
Uhm no, do your own homework. Hold both tires still with your hands and turn the spur gear with your thumb. the spur gear will slip, the thrust bearing will not move AT ALL. The thrust bearing will not slip the way the spur will, it will only ever rotate. Therefore it does not require the use of the same less slippery silicone diff lubes that the diff does.
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Old 03-26-2009, 05:34 AM   #7233
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I dont want to step on toes or offend anyone but i figured i would add a little. The thrust bearing is under alot more load than the diff gear is because it is closer to the locking nut which makes the pressure exceed everything else in the assembly and it also is a much smaller diameter and spins at a higher RPM when the diff is rotating. In order to extend the life of a thrust bearing, a high lubercant grease is recomended. The silicon diff grease is used in the spur because it allows for some lubrication but does not let the diff slip. The thrust does wind up having more resistance than the balls in the spur because clamping force from the nut is reduced the further you get away from the nut. This is in both diameter and linear distance. The thrust bearing will need a grease with good lubrication properties. Please dont anyone take offense to my post. It is not intended to offend anyone.
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Old 03-26-2009, 05:59 AM   #7234
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No offense here, I agree with you. I would add though that while the thrust bearing is under more load, the diff still has to deal with slip which is why a loose diff will wear out quickly while the thrust bearing will be fine.
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Last edited by wingracer; 03-26-2009 at 06:11 AM.
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Old 03-26-2009, 02:24 PM   #7235
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Originally Posted by wingracer View Post
No offense here, I agree with you. I would add though that while the thrust bearing is under more load, the diff still has to deal with slip which is why a loose diff will wear out quickly while the thrust bearing will be fine.
Lets forget the grease argument for a minute and get back to basic mechanics. Correct me if I'm wrong, but...

Since there is only one load on both pairs of thrust races, and the mechanism between the nut and the fixed flange (on the axle) is floating, any load you apply to the nut MUST be equally shared between the two thrust races. There is no mechanism to distribute the load unevenly between the two races, so how can one race take more load than the other?

As far as my car is concerned, the whole diff rotates at the same speed when going in a straight line. When the diff action comes in, the wheel on the hub will either rotate slower, or faster, than the fixed wheel. However, one thrust washer from each pair will rotate at the speed of the slower wheel, and the other at the speed of the faster wheel. At no time is the thrust race rotating faster than the main spur gear because it physically can't! (Leave aside the fact that, as they are at a smaller diameter, the thrust race balls rotate at a slower speed than the spur gear balls!)

The spur-gear balls wear prematurely because they are taking the input torque, and if the diff isn't tight enough, that's what will slip first - the thrust race has no input torque to control. That's the cause of the wear. There's also the point loads to consider. The trust race has very small balls (!) giving rise to high point loads compared to the spur thrust race.

So, returning to the grease, the only reason one would want to use a different grease would be to provide a higher shear for use with the higher point loads. However, since we don't want any slip at all (and we agree we don't get it at the thrust race) the only thing we need lube for is the slip between the balls and the cage. As lubrication is only effective when we are trying to prevent friction between moving surfaces, and the only moving surfaces are the balls in the cage, can you see why I am saying that the higher spec grease is not necessary?

I hope that explains things OK, but if not come back to me.

PS - Chris, hold the RH wheel and the spur in one hand, and turn the fixed wheel in the other - both races slip. It's a different way to check a diff, and it checks the condition of both races, not just the large one at the spur gear. HTH
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Old 03-26-2009, 02:37 PM   #7236
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Originally Posted by SlowerOne View Post
PS - Chris, hold the RH wheel and the spur in one hand, and turn the fixed wheel in the other - both races slip. It's a different way to check a diff, and it checks the condition of both races, not just the large one at the spur gear. HTH
I have to disagree with this statement. Hold the right wheel and spur, turn the left wheel, the diff slips, the thrust bearing rolls. Only way to make that thrust bearing slip is if you somehow could grab the cage...
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Old 03-26-2009, 03:13 PM   #7237
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Hold the right wheel and spur and turning the left wheel does not mean slip!!! Hold both wheels and try to turn the spur, if it turns, thats slip (NOT GOOD)
Holding one wheel and the spur and turning the other wheel is basically the operation of the diff. The tighter the diff. the harder it will be to turn the other wheel. If the diff. slips the backend will slip out coming out a corner, because it will spin and when it catches there will be a sudden burst of power to the rear wheels. This is why there must be no slip. Same as touring cars only even more important. You need the diff. to work smoothly with no slip
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I have to disagree with this statement. Hold the right wheel and spur, turn the left wheel, the diff slips, the thrust bearing rolls. Only way to make that thrust bearing slip is if you somehow could grab the cage...
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Old 03-26-2009, 03:57 PM   #7238
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If you are getting no slip at all when holding the wheels and turning the spur you are running too tight. You do want no slip but you want no slip under track conditions. Your fingers can put a lot more torque on the spur then your motor can.
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Old 03-26-2009, 05:22 PM   #7239
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How did the team do at the Nationals?
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Old 03-26-2009, 09:46 PM   #7240
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Originally Posted by InspGadgt View Post
Your fingers can put a lot more torque on the spur then your motor can.
you must have a grip like a monkey... That, to me does not seem right. I'm not challenging you... I just sayin' and trying to make a joke
E
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Old 03-26-2009, 10:44 PM   #7241
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You are right
If I try to turn the spur it will turn, but not easily. Basically I check it on the track as well. Put the car down, hammer throttle and adjust until no slip on the spur/diff.


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If you are getting no slip at all when holding the wheels and turning the spur you are running too tight. You do want no slip but you want no slip under track conditions. Your fingers can put a lot more torque on the spur then your motor can.
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Old 03-26-2009, 11:03 PM   #7242
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Man where's that can-o-worms picture when you need it. Hey Eric I'll be running here tomorrow night, are you going to CH this weekend or next?

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Old 03-27-2009, 06:07 AM   #7243
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Originally Posted by PHI/BMI racer View Post
You are right
If I try to turn the spur it will turn, but not easily. Basically I check it on the track as well. Put the car down, hammer throttle and adjust until no slip on the spur/diff.
If you knew what he did for a living you would have know he was right from the start

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Old 03-27-2009, 06:25 AM   #7244
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Originally Posted by SlowerOne View Post

The spur-gear balls wear prematurely because they are taking the input torque, and if the diff isn't tight enough, that's what will slip first - the thrust race has no input torque to control. That's the cause of the wear. There's also the point loads to consider. The trust race has very small balls (!) giving rise to high point loads compared to the spur thrust race.
You make my point for me. I guess you read something into my post that was not intended. My point is that the diff can slip, while the thrust bearing cannot. We use AE silicone on the diff not because it's the best thrust bearing grease but because it's the best that doesn't allow too much slip. Something better may not be required on the thrust bearing but why would you not use something better? I can tell you from experience that if you use AE silicone on a 1/8th Centax style clutch thrust bearing it will not last very long. Use wheel bearing grease and it will outlive the car.
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Old 03-27-2009, 12:51 PM   #7245
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you must have a grip like a monkey... That, to me does not seem right. I'm not challenging you... I just sayin' and trying to make a joke
E
Did anyone laugh???
If you track set it just to the point where it does not slip under hard acceleration from a dead stop then pick it up, hold both wheels in your hand and turn the spur with your fingers you'll find it does still slip, not easily but it does. But since it does not slip on the track this gives you the most free diff possible. This brings up another point that your diff settings may even change depending on motor.

I haven't tried the Corally but I have tried the Slapmaster. Jason pointed out the difference between the Slapmaster and the stock setup at the Birds which I had not noticed. For club parking lot racing the Slapmaster was working just fine for me but at the Birds I wasn't getting enough turn in because my diff wasn't free enough. I looked it over when I got back home trying to figure out why that was...one thing I thought of was the washers...with the slapmaster running concave grooves in the washers more of the thrust ball makes contact with the metal which is going to increase the amount of drag on the diff. Additionally if it has to do more with the direction the force is applied on the thrust bearing vs the outer hub bearing maybe something like a conical thrust bearing would work or it could be as simple as using a larger bearing race in the hub to increase durability.
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