why spacers in c2 rear wheel bearings?

[Vintage Racer]

Hello all,

Both of my vintage race cars (1964 McKee mk3, 1965 Corvette) have the Corvette rear wheel bearings that are adjusted with shims and one large spacer between the bearings.

I'm curious, why do you actually need the spacers? The inner races can't come together, because the bearings are on opposing tapers.

Can't you simply not use the spacers, tighten the nut to the appropriate bearing play, put a cotter pin in it, and call it a day like other cars?

Has anyone tried this?

Your input is appreciated, thank you.

Casey

 

[BADBIRDCAGE]

Shims/spacers are to set proper end play. Bearings are not preloaded, they have a clearance on assembly.

Rich

 

[Vintage Racer]

not the case here

I just got done looking at cross section views of the Corvette rear hub/bearing assembly as well as in comparison with the front.

While "Badbirdcage" is correct that shims are nessesary to set clearance such as in setting up a differential, our Corvettes do not use any kind of spacing shims on the front bearings and simply rely on you tightening down the nut until the correct clearance is reached and then use a cotter pin to secure that setting.

With the exception of the front inner and outer bearings being of two different sizes, the bearings are the same in concept as the rear and orient their tapers in the same directions.

I cannot see any engineering reason why we need to use the shims in the rear. Why wouldn't it work to simply tighten the nut until the desired clearance is reached. I mean we don't in the front and everything is fine.

All I can figure is that if you overtighten the rear nut, you can't just loosen the nut to give more clearance without drawing the bearing back.

Any thoughts?

 

[BADBIRDCAGE]

When you mentioned shims I went to the rear wheel bearing assemblies as they are set without a preload.

When I adjust front assemblies I set them with a slight preload.

I don't know the consequences of assembling rear assemblies without the shims/spacers but GM engineers concluded that the clearance was necessary.

Rich

 

[Vintage Racer]

I see your point. However, I pose that one could adjust the rear bearings to give the same clearance and setting that you would with shims.

All I can figure is that the shims and spacers have to do with the fact that there is torque being applied and that it is also a suspensions link. However, I haven't thought of a scenario that there would be trouble particularly.

Any engineering thoughts?

 

[67HEAVEN]

Any engineering thoughts?

The answer is on its way.

"Paging JohnZ. JohnZ to the C2 Lounge please."

 

[Vintage Racer]

I think I have it figured

The spindle nut is to be torqued to a set amount. Without the spacers you would not be able to achieve this torque spec if you simply tightened down the nut to the proper bearing clearance.

I imagine that between the torque and the fact that it is a suspension link, the splines would eventually wear out and the whole assembly would perhaps wear its self loose.

Thoughts?

 

[Tom Bryant]

Torque is also applied to the front under braking. The big difference is that on the front the hub turns while the spindle is stationary. Braking torque is applied to the hub. On the rear the hub is stationary while the spindle turns. Engine torque is applied to the spindle. I don't have any idea how this plays out from an engineering standpoint.

It will be interesting to see what John has to say about this.

 

[JohnZ]

Can't you simply not use the spacers, tighten the nut to the appropriate bearing play, put a cotter pin in it, and call it a day like other cars?

Hi, Casey - welcome to the forum!

Nope, you can't do that - referring to the cross-section of the rear spindle below:

The key characteristic of low-friction tapered roller bearings is that they will carry huge radial loads, but they can't be axially preloaded at all, or they'll fail. Front wheel bearings aren't preloaded, which is why the adjustment procedure is to tighten the nut up to 12 ft-lbs. while spinning the hub to seat the bearings, then back the nut off one flat and insert the cotter pin (that will set axial clearance at .008" or less).

The tapered roller bearings on the Corvette rear spindle are no different - they can't be axially preloaded either or they'll fail.

The outer bearing inner race is a press-fit on the spindle, and the outer race is a slip-fit in the spindle support; the inner bearing races are a slip-fit on both the spindle and in the support. The tubular bearing spacer and select-fit shim (fitted to ensure that there is at least .001" axial clearance between the two bearings, and called the "bearing preload spacer" in the cross-section below) are required in order to maintain the clearance after installing the drive flange, which bears against the inner race of the inner bearing, and whose attaching nut is torqued to 100 ft-lbs to retain the flange on the spindle.

The spacer and shim create a solid stack from the inner race of the outer bearing to the inner race of the inner bearing and the drive flange, while maintaining the necessary axial clearance in the bearings.

If you left out the tubular spacer and shim and torqued the drive flange nut, that would pull both the inner and outer bearing rollers against their race tapers into interference, and the bearings would fail almost immediately. Tapered roller bearings CANNOT be preloaded in any way or they'll fail, and if they have excessive clearance they'll fail; the design must provide for the required axial play, and must not allow the clearance to be reduced or increased during operation in order for the bearings to operate reliably, and that's what the spacer and shim do.

 

[BADBIRDCAGE]

You are, of course, right John. I misstated when I posted that I adjust my front bearings with a slight preload. I do just like you said; I spin the wheel assembly while tightening up the nut until I get my resistance (stated preload) and then back off to the first opportunity to insert the cotter pin.

Rich

 

[Sky65]

John
I've built a bunch of differentials on Porsche and Audis. They use tapered roller bearings for the pinion and carrier bearings. On a new set up with new bearing you do preload the bearings a specific amount. The final check for proper preload is turning torque. No preload on those bearings and they will fail. What is the difference for wheel bearings? The lub? Grease instead of oil? Bearing hardness?