TheSamba.com :: View topic - Wheel Bearing Grease in the Brake Rotor Hub

Wed Oct 29, 2014 6:59 am

Hello

I just purchased new Centric disk brake rotors, together with new bearings and grease seals. The Bentley is not very descriptive on the need for wheel bearing grease in the void space between the bearings in the rotor hub.

When I grease and install my new bearings, should I add additional wheel bearing grease inside the cavity in the rotor hub, or should I leave this space empty to avoid changing the balance of the assembled rotor?

Thanks

Wed Oct 29, 2014 8:24 am

I always pack that area too, If anything you get some bleed over grease over time. I have no proof that it works but grease is cheap....

Wed Oct 29, 2014 10:02 am

I've always done like Bentley says on page 14 of Section 5, Lubrication and Maintenance:
"Do not pack large quantities of grease inside the hub; just coat the interior lightly to prevent corrosion."

Wed Oct 29, 2014 11:52 am

Thanks for the reference, I had missed that when I looked over the section.

Wed Oct 29, 2014 2:12 pm

VWporscheGT3 wrote: I always pack that area too, If anything you get some bleed over grease over time. I have no proof that it works but grease is cheap....

I have proof that it works....you are spot on.

Bentley and other automotive manuals tell you not to pack the hug because they cannot control the "degree" to which one will pack the hub....or how well they do it.
If large voids re left, the expansion can push grease out and get on the brake rotor if you are not careful.

However....its simple to get around that problem. And....over a 300,000 mile driving span in my 412 in Texas, Oklahoma, Arkansas, Louisiana and New Mexico over about 8 years....I had to replace front wheel bearings in the first 120K miles about 3 time.

This failure is mostly due to poor lubrication from grease pressing out in cold weather and from grease flow in hot weather (usually over 100F and highways speeds).

Grease is always Mystik JT-6 high temp and pre-load is set by dial indicator.

When an old school mechanic told me to pack the center core of the hub....wheel bearing wear and replacement ceased. Same set for about 200K miles with regular grease replacement at 30-40k miles.

The issue is that when grease gets squeezed out of the bearings....and you have no grease in your center hub.....there is nothing backing up the squeezed out grease....which means nothing forcing it back in.

The grease gets squeezed out of the bearing when its stiff in cold weather.

Then...if you drive long distance at high speed in hot weather in the summer (highway surface temps in Texas at 100-105F ambient are typically over 120F)....the remaining grease even wwith high drop point greases like JT-6...will flow.
Add braking heat to this mixture from high speed hot weather traffic...like in Houston.....and you will eventually have metal to metal usually from the roller bearing corners. It eventually starts grooving the race.

Having back up grease with a packed hub eliminate this.

The trick to do this correctly is to pack bearings separately. Install races. Then install the packed inner bearing. Then the inner seal.

Pack grease around the sides of the inner core of the hub so its about 3/8"-1/2" thick leaving a hole through the center.
Dont just fill it up. If you do...it will push grease back out both ends when you slide it onto the spindle. This is the reason Bentley does not want you to fill it up. The problem is that they are too lazy to tell you how to pack it properly.

Coat the spindle with a smooth coating of grease about 1/8" thick. Slide the spindle on and keep it at level as possible. The thick coating inside will blend with the thin coating on the spindle.
Install the packed outer bearing. Holding the outer bearing against its race....before you install the flat washer......rotate the rotor through several complete rotations...and you will distinctly see it "burp" out the excessive air as the grease in the hub and the grease in the spindle merge.
Also ant excessive grease will pump out through the outer bearing while you turn it.
Install the washer and spindle nut and set pre-load. Ray

Wed Oct 29, 2014 2:35 pm

Yup what Ray said

A completely packed bearing will run as hot and fail as fast as an ungreased unit. Grease churns while in operation and settles when cool, without space in the housing for it to move around it generates heat and causes a failure when things get cooked.
With no grease in the housing the existing grease in the bearing gets pushed out when it's warm with the churning, and there is no reserve to draw back in when it needs it.

industrial applications spec around a 3rd of the housing filled with grease to allow for flow and air space for expansion.

Wed Oct 29, 2014 3:04 pm

I also follow the method Ray outlined... pack separately and then after final assembly. Leave slight voids to avoid pushing it out the inner seal on installation. Sometimes it pushes out the outer bearing and makes a little mess if it gets flung out on the outer wheel surface, but that is rare. What you DON'T want to do is pack the little bearing cover on the disc (like where your speedo cable pokes out). That will make an awful mess one hot drive.

Thu Oct 30, 2014 7:05 am

Thanks Ray, good to know I've been doing it right all these years :lol:

Thu Oct 30, 2014 11:01 am

VWporscheGT3 wrote: Thanks Ray, good to know I've been doing it right all these years :lol:

:D .....I dont know if its right.....but it sure works a damn sight better than what the factory recommended! Ray