Front wheel bearings

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Front wheel bearings

Postby FV80 » July 31st, 2013, 7:56 pm

In the light of Brian's brake posts, I thought I'd post what I JUST learned earlier today.
I was QUITE surprised to find out that SKF and FAG front wheel bearings are (can be) SIGNIFICANTLY different! The INNER ID of the outer (small) bearing race (the one you slide in last before the washer) and the OD of it's mate (the one mounted into the hub) .. as well as the OUTER OD of the inner (large) bearing race (the one mounted into the inside of the hub) and the ID of it's smaller mate are all within 0.000x (TEN thousandth's) ... for a proper semi press fit - *HOWEVER*, the alternate dimension of each race is (can be) significantly different - in the order of 0.005 (WOW!).

That explains to me why, on occasion, I will change a hub .. NOT change the inner race and have GREAT difficulty getting the hub to seat .. sometimes NEVER. The inner race kinda 'rides' on the spindle and sometimes they are a PITA to swap .. so sometimes I don't.

I can now see why my Dad told me "ALWAYS" change races and bearings in SETS. Although I generally do that, anyway, I was shocked to find THAT much difference between 2 bearing sets that have IDENTICAL part numbers on them - only the mfr is different.

A word to the wise ?? :mrgreen:
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Re: Front wheel bearings

Postby fvracer27 » August 1st, 2013, 9:40 am

Thats funny Steve I remember my grandfather telling me the same and I never really thought about it. These days a lot of tappered bearings come seperate as a race and bearing and I always thought (what if they are not matched) but never looked into it as it was only for street cars and trucks. Good stuff to think about.
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Re: Front wheel bearings

Postby hardingfv32-1 » August 1st, 2013, 12:03 pm

I think you are getting the meaning of the 'grandfather' quote wrong. I would say they were concerned with mixing new with old, similar to lifters and cams.

I would say that bearings are standardized for a given p/n by type, outer dimensions, and seal configuration. A bearing that comes as a set must be used as a set within a given manufacture. There is no convention for the individual components of a set to be standardized for internal dimensions.

I would assume that bearings made up of individual p/n's would have standardized dimensions. A needle bearing with the outer assembly and inner race each having a different p/n for example.

Can anyone confirm?

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Re: Front wheel bearings

Postby smsazzy » August 1st, 2013, 2:21 pm

I agree with Mr. Harding's assessment that a given part number is a given dimension as long as we are talking the same manufacturer. They would be much more expensive if they were hand matched one at a time.

That said, if you actually run it, I would expect wear of the part to cause a new bearing and a used race, (or the other way around too) to cause problems due to not being 'matched' by running together.

Bottom line, I would recommend always swapping the race when changing bearings. Might not always be 100% needed, but the parts come together, spend the extra half hour to do it right.
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Re: Front wheel bearings

Postby fvracer27 » August 1st, 2013, 3:00 pm

smsazzy wrote:That said, if you actually run it, I would expect wear of the part to cause a new bearing and a used race, (or the other way around too) to cause problems due to not being 'matched' by running together.

Bottom line, I would recommend always swapping the race when changing bearings. Might not always be 100% needed, but the parts come together, spend the extra half hour to do it right.


This is what I meant maybe it came out wrong once bearings are used with a race they get changed together he never wanted us to use a new bearing with a old race. That being said I don't know why they sell bearings and race seperate. :roll:
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Re: Front wheel bearings

Postby FV80 » August 1st, 2013, 3:36 pm

FWIW - *ALL* parts - both inner and outer races all have the EXACT same part number. Just different mfr's.

Just an observation on my part.
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Re: Front wheel bearings

Postby hardingfv32-1 » August 1st, 2013, 4:16 pm

FV80 wrote:FWIW - *ALL* parts - both inner and outer races all have the EXACT same part number. Just different mfr's.


Because they are part of a set. I would say that any time more than one piece of a bearing assembly has the same p/n, you must maintain the integrity of the manufacture's set. Having assembled a large inventory of front 'ball' bearing, I can state there are at least two sizes of balls being used among the 3-4 manufactures that I have found. Some of the larger ball bearings in the transmission actually have different ball bearing counts relative to the same p/n bearing.

Some bearings are made from the grouping of different p/n's so the manufacture can make changes to the exterior dimensions or features without stocking many different assemblies.

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Re: Front wheel bearings

Postby hardingfv32-1 » August 1st, 2013, 4:33 pm

smsazzy wrote:I agree with Mr. Harding's assessment that a given part number is a given dimension as long as we are talking the same manufacturer. They would be much more expensive if they were hand matched one at a time.


There is nothing preventing a manufacture from using different internal dimension for a specified p/n bearing. In other words the sets do not have to be interchangeable among components. They only have to maintain the exterior dimensions. I am not talking about micro dimensions in this context.

The machining capabilities of the major bearing manufactures around the world are so good these days that you would not be able to differentiate the country of origin. There are no hand matched bearings. That is not to say that there are not different levels of tolerances that bearings are assembled to.

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