C2 Front vs. Rear Spindle Bearing Question

[Dave Rossi]

Hello All,

I have my entire chassis apart for restoration and have been referring to the archives in many instances to help me along. I want to thank all who contribute information for the many useful posts. I have read various posts regarding front wheel bearings and the similar clearance numbers of .001"-.005" that they share with the rear wheel bearings. I absolutely understand that you cannot have preload forces on the roller bearings in these wheel applications like what is seen in a differential. My question is, why are the front wheel roller bearings allowed to slip fit on a front spindle, while the rears have to be interference fit. I'm not trying to stir the debate re: slip fit vs. press fit on the rears, I'm just wondering why its ok to allow the front roller cone to spin on its spindle if that were the path of least resistance. I ask this because I have noticed the metal surface on my spindles under the cone portion of the roller bearings appears polished and is .001" smaller than an NOS spindle that I have, and it got me wondering. Thanks Dave

[Joe L.]

Re: C2 Front vs. Rear Spindle Bearing Question

Dave-----

I can't explain the dynamics of it. However, bear in mind that the ORIGINAL 1963 design for the rear spindles was, basically, the same as the front (except that a spacer and shim were used for setting end play rather than just backing off the spindle nut). This design failed in use and was replaced, prior to the end of the 1963 model year, with the press fit bearing design. So, initially, GM engineers felt that the slip fit design would work ok. I'm sure they studied it. But, it didn't work out that way.

There can be all sorts of theories as to why the rear requires the press fit design. However, in this case we have what amounts to EMPIRICAL evidence of the need for it------the slip fit design resulted in premature failures and the press fit design worked well for the following 18 years without much more change in the system. I strongly suspect that the reason has to do with the fact that the rear wheels are the drive wheels and drive power is supplied through the rear spindle assemblies.

As I've mentioned previously, the change to the press fit design for the rear spindle assemblies had to have been a costly one for GM. The press fit design increased the complexity of assembly and, even more greatly, increased the complexity of the service procedures. So, I doubt that this change was made without much justification.

[Duke W.]

Re: C2 Front vs. Rear Spindle Bearing Question

I don't understand the mechanism that the caused slip fit rear design to fail, but I just want to remind all that with the change to the press fit design the 30K mile repack requirement that is in the '63 Corvette Shop Manual was ELIMINATED!!!

If you pack the rear bearings with a high quality, preferably a FULL synthetic wheel bearing grease, you should never have to work on them again.

Duke

[Dave Rossi]

Re: C2 Front vs. Rear Spindle Bearing Question

Joe and Duke,

Thanks very much for both of your replies. I was hoping you'd wiegh in on this one. I was however more interested in hearing your thoughts about the front spindles rather than the rears. I am already convinced of the neccesity of the press fit rear and will carry that through on my car. It is the loss of .001" of material, (NOS is 1.2490" and my current spindle is 1.2480" at the inner cone surface) and polished surface of the front spindle diameter that concerned me. Should I be concerned? Do you think that roller cone is spinning on the spindle, as it appears to be? Thanks again for your input. Dave

[Joe L.]

Re: C2 Front vs. Rear Spindle Bearing Question

Dave-----

There's nothing to prevent the inner races of the front bearings from "spinning" on the front spindles. However, the "path of least resistance" is through the roller bearings and that's where most of the "spinning" should occur.

The front spindles of my 1969 have 200,000 miles on them and, to that point, had the original bearings, too. There was no measurable wear on my spindles, although they were somewhat "shiny" at the inner race contact points.

The kind of wear you're talking about should not be a problem.

[Duke W.]

Re: C2 Front vs. Rear Spindle Bearing Question

By design the inner race is allowed to rotate, so some wear after many miles would be expected, however, I don't think the amount of wear you are measuring is enough to warrant a new spindle.

The other thing to observe is the spindle shoulder that the inner race bears against. This surface usually shows some galling because it takes all the lateral load, and is the reason clearance increases with time. Unless the surface is severely galled, it doesn't appear to be an issue, but make sure some grease is applied to this surface.

I like to keep wheel bearing clearances near the minimum. I notice better tracking and "tighter" steering when clearance is near minimum.

The spindle thread is 24/in. with six flats and there are two perpendicular cotter key holes so you can readjust the nut in twelveth turn increments, which will move the nut axially about .004" and this is the source of the one to five thou spec.

If you measure clearance of .004" you can remove the washer and dress it down about two to three thou using mineral spirits wetted 280 or so paper on a flat surface, like a piece of glass. When you reinstall, go one more twelve turn and the clearance should be about two thou.

IMO tight clearance may reduce wear/galling of the spindle shoulder that takes lateral loads.

It appears that the Chevrolet engineer's intuition told them a slip fit design was okay on the rear (mine too), but it didn't work. I don't know why, and don't know if they ever figured out the failure mechanism, but the press fit design appears to be very durable.

As a point of reference the front bearing clearance spec on my '88 190E 2.6 is .01-.02 mm, which is .0004 -.0008"! Maybe that's one reason why Mercs have a reputation for excellent steering characteristics, and there is no periodic repack requirment. Such a tight range cannot be obtained with a conventional castle nut. Mercs have a "pinch nut" with a set screw so it can be installed at any arbitrary radial location. The adjustment is VERY senstive. I've done it with a dial indicator, but found that tightening the nut to eliminate all the clearace and then just loosing until I could feel a first hint of "wiggle" (grabbing the top and botton of the tire and wiggling back and forth) got me in the range.

Duke

[Billy Olson]

[Billy Olson]

Re: C2 Front vs. Rear Spindle Bearing Question

I also should have added that the dynamic power and braking loads at the rear change where the contact point is located and the magnitude of the load transfered through it, for the case of a clearance or slip fit.

Billy

[Michael H.]

Re: C2 Front vs. Rear Spindle Bearing Question

Now THAT makes sense. Probably one of the best explanations I've heard in the last 40 plus years. Thanks.

That would be the exact same problem that front wheel bearings have when a wheel/tire assy is out of balance at high speed. Instead of the load being supported at one spot on the bearing race, the load area would rotate with each out of balance rotation of the wheel and this rotates the inner race.

[Dave Rossi]

Re: C2 Front vs. Rear Spindle Bearing Question

Hello Billy,
Thanks very much for your response. Nice illustrations! I took a look at my spindles and sure enough what I initially saw as a uniform polished surface around its circumference at the bearing contact point, was actually far more pronounced on the lower portion. The bearing is not spinning as I had imagined but probably rocking on the spindle as loads change. It took me a little while to see the contact point on the rear spindle changing as the spindle rotates, but I've got it now. Thanks again for your excellent explanation. Dave