Axle bearings

[Hib Halverson]

Here's a little anecdote which underlines the importance of preventive maintenance.

Way back in the early 90s, I had my rear axle bearings apart to set the bearing clearance at the ideal .0015, rather than the "acceptable" .001-.010. This is done by disassembling each axle and carrier, chucking the axle in a lathe to convert it from a heavy-press fit to a "slip fit" such that you can take the axle out with hand tools. While your at it, if you're really doing things right, press the wheel studs out of the axle then true the wheel mounting flange

Next, I surface-ground a bearing shim such that the axle/bearing/carrier stack has .0015 clearance. Then ordered Timkin bearings and packed them with Red Line CV-2 Synthetic grease and final-assembled each carrier.

They stayed that way for nearly 20 years.

This week, after almost two decades and about 40,000 miles, I disassembled each carrier to inspect the bearings and repack them. There was little or no wear on the bearings. The Red Line CV-2 was not dried out or comtaminated. In fact, the bearings probably could have gone another five years or so.

So, I ordered new inner and outer axle seals from Zip Products, replaced the parking brake shoes with relined stainless shoes from Zip Products, cleaned and repacked the bearings with fresh CV-2 and reassembled each axle/carrier.

Few people observe GM's recommendation of cleaning and repacking the rear bearings ever 36,000 miles or so because of the difficulty in disassembling the carriers the first time, but for those owning C2/3s with disc brakes, if you plan on keeping the car a long time, you're better to convert the bearings to a slip fit then cleaning/repacking the bearings ever so often.

 

[Vettehead Mikey]

My guess is that most owners are not familiar with the service interval, (it seems to be missing in most manuals) not aware of the car's history or conscious that it's been 10-20-30 years since the bearings were last serviced. :ugh

I prefer the concept of the tight fit of the bearings on the spindle having seen a few too many spun races but that's just me. My car sees very few miles each year so a new set every few decades doesn't bother me.

 

[Hib Halverson]

Well...objective testing indicates that a "slip fit" is the way to go.

Your front wheel bearings are a slip fit on the front spindle. The slip fit on the rear spindle is the same.

The only reason those bearings are a "20-ton" press fit was for the 63s and 64s with drum brakes. After disc brakes became standard, Duntov never spent the money to fix the bearings.

By going to a slip fit you also make the bearing clearance set up much easier to acomplish.

 

[Vettehead Mikey]

The spun bearings I've seen were all on disk brake C2 and C3.

 

[chuck]

Hib I agree. As the saying goes back in the day we always slip fit the bearing and never had a problem. It seems now they are more into the press fit. I will stick with the slip fit method.

 

[Hib Halverson]

The spun bearings I've seen were all on disk brake C2 and C3.

Engines "spin" bearings.

If you are talking about the axle bearing inner races rotating on the axle shaft...that happens because whomever set up the carrier/bearing/axle "stack", cut the axle down to far.

Note that I said "slip fit" not "loose fit". The fit needs to be the same as that between the front spindles and the inner races of the front wheel bearings.

Do that, and the system will last indefinitely as long as the bearings are repacked every so often.

That said, if you like the heavy press fit, stick with it.

 

[SVO]

I guess I'm a middle of the roader here. I have the Kent-Moore tool set up for servicing the rear bearings. I like to convert mine to light press fit. If the bearing fit is too tight, you run the risk of breaking the caliper mounting bracket using the Kent-Moore press. I set my end play a bit different also. I use a thicker shim and set the clearance by turning down the bearing spacer. I'm also into the bearings a little more often than 20 years/40,000 miles. But as you said, whatever you prefer.

 

[Vettehead Mikey]

Engines "spin" bearings.

If you are talking about the axle bearing inner races rotating on the axle shaft...that happens because whomever set up the carrier/bearing/axle "stack", cut the axle down to far.

Apparently GM got it wrong too. Spun bearing races were seen frequently enough on 63s and 64s for GM to change the fit to the press fit dimensions that existed right up to the end of C3 production. The introduction of disks brakes in '65 had no real impact on whether a race would spin or not.

I've always thought that the 100 ft/lb torque on the spindle nut would have been sufficient to hold the races in place- especially by comparison to the front wheel bearings where there are no means of securing the races in place and are a slip fit as well- but there you are.

GM's method of using a set up tool to quickly and accurately determine which spacer to use is virtually identical in methods I am familiar with and used in my own career in aerospace. Pretty good stuff for a 50 year old design.

 

[GTR1999]

Hib,
As you know I custom build T/A's,boxes, and diff's/ As you did I always machine the spacers,shims,and flanges BUT I'll never slip fit rear bearings. I turn those jobs away every time. I setup both the 17 spline stock axles and Tom's 31 spline all press fit.

Now I know this discussion has been on all the forums the past 10 years I'm aware of and there are a few that slip fit them.Like yourself, they never had a problem but again the early 63's did. I'm sure John H can shed more light on those early issues then I can.

Once properly setup they should not need to be torn down as the old manuals said at 36000 miles. The grease today is better then the old stuff. Pressing out or hammering out spindles will,in most cases, wreck the bearings anyway. Going through the trouble to do all that and not setup new bearings is not something I would advise.

Again this is not meant as a negative comment on your thread, just another point of view.

 

[Hib Halverson]

Rather than have this descend into a pissing contest:argue over heavy-press-fit vs: slip-fit, I want to move the discussion a different direction with a question:

Do these axle bearings fail and begin to "spin" on the axle shaft because of the slip-fit? If that's true, then virtually all axle/bearing/carrier stacks set-up with slip-fitted axles should experience failure in a short period of time in service.

Or...do the bearings "spin" because the bearing is defective, the lubricant fails or contamination enters the system, then the bearing begins to wear rapidly and, as this wear turns to bearing failure, the device becomes less a "bearing" and more a "bushing" such that the inner race begins to rotate on the axle shaft. Admittedly, at that point, a siip fitted inner race is going quickly destroy the axle shaft.

That said, the same bearing failure scenario can occur with a press-fit system but, instead of the inner bearing race spinning, the bearing wears until it fails completely. Once that happens, sometimes what's left can be pressed off and new bearings installed but sometimes the failure takes out the axle shaft, as well.

My belief is that slip-fitting is not the root cause of bearing failure.

My position is that bearing failure is either caused by defective parts, improper lubricant, overheated lubricant, other lubrication failure or the introduction of contamination into the bearing system. Once that happens, bearing failure is soon to follow and whether the bearing is slip-fitted or press-fitted is irrelevant.

My 20-year experiment with slip-fitted bearings began because I wanted both rear bearings at .0015-.002 clearance. Back when all the shims were available, they were .003 apart. Any math whiz can see that it's not always possible to get the minimum clearance with factory shims. If you can't get that with factory shims, the only solution is to work-up a shim selection which is .001-.0015 too large then surface grind it until the axle/bearing/carrier stack (assembled temporarily without seals) has .0015-.002 measured clearance. Once you have that, then the stack is disassembled, the seals are installed, the bearings are packed and the carriers are reassembled and put back on the car. To do all that with a press fit would be a total bitch for one without a hydraulic press, so that was one reason I converted to slip-fit.

This wasn't just some poorly-researched attempt to short cut proper service procedures. When I was really young, long before I acquired the 71 BBC Coupe I have now, I co-owned an SCCA B/Production C2 with a friend of mine, the late Rich Hearn, father of Indycar driver Richie Hearn. Now, Rich owned the roller and I owned the engines. For as long as we raced that car, it had slip-fitted rear bearings, but...I digress.

So why did I want the rear bearings on my 71 Big-Block hot rod set at .0015-.002 clearance?

Because of the rear brakes.

Those who understand the fixed caliper brakes on 65-82 Corvettes know that the OE-seal system can handle no more than about .010 piston movement due to any combination of rotor run out, axle flange run-out, bearing clearance and deflection of the caliper mounting during braking. With the OE axle bearing clearance tolerance of .0015-.008, if you are on the high side of that--remember .007 bearing clearance is multiplied by the radius of the rotor to a greater distance at the caliper--you're going to have rear brakes that suck air.

You're response might be, "Use o-ring sealed pistons".

Ok...that eliminates the air ingestion past the lip-type piston seals but, you still have the pad knock-back issue which means, the early part of every stroke of that brake pedal is going to first have to take up the distance the pads have been knocked back before you get any braking action.

It's unlikely this disertation will convince "GTR1999" and "Vettehead Mikey" to suddenly embrace slip-fit bearings, but I hope it explains my reasons for being an advocate of that assembly procedure.

And, Mikey, for my comment "Engines spin bearings" you can me.

 

[GTR1999]

Hib,
No problem on my end, I agree 100% on the brake issue. I've never used O-ring calipers nor needed them.

And yes, you won't change my mind or procedures on building arms. I simply trust in the engineers at GM who designed this system and the fact I've broken down many original arms with up to 80-100k miles that were pretty good. The original grease was dried out but I'm willing to bet that if the grease of today was used in some of them they could have gone farther. Of course this is not true with all setups. Driving condition, storage,and weather play a big part.

For example,
I just did a set off a 1970 LT1 car. These were never touched before & still had the rotors riveted on. Aside from the grease they weren't too bad. I could see where the rollers started to over heat so it was good to rebuild them. Before that I did a arm off a 1980 that sat outside for some time but had few miles on it. The rollers were rust-seized on the race and moisture ate into the race a good bit.

I have spoken with several people who slip fit their bearings and they are the guys that break them down for routine maintenance on a regular basis. They also swear by them, however most owners are not going want to do this.

Again I wasn't trying to take your thread off track and I certainly believe your findings with your setup. My concern is for the person who may consider doing these at home and consider polishing the spindles for an easier installation only to have issue later on.

 

[Vettehead Mikey]

It's unlikely this disertation will convince "GTR1999" and "Vettehead Mikey" to suddenly embrace slip-fit bearings, but I hope it explains my reasons for being an advocate of that assembly procedure.

And, Mikey, for my comment "Engines spin bearings" you can me.

Thanks for the write up Hib, I agree with all of your logic and it would be fun to turn back the clock to the early 60s and sit in on GMs engineering meetings to hear their thoughts on why they went from a slip to press fit.

My background involved working with 600-15,000 HP engines that each had dozens of low, medium and high speed rolling element bearings. 'High speed' would be in excess of 50K RPM and low speed would be comparable to the road wheels on a car. Not ONE of these bearings was a slip or light press fit- all were a tight snap or heavy press fit despite also having axial compressive loads that would make the C2/C3 rear bearing assembly look like a Tonka toy. Despite this we occasionally saw development engines on one particular program that had clear signs of the inner races having rotated on the shaft with no other damage what so ever. The cause was established as insufficient static preload not taking into account thermal changes at full operating speed. I can't help but wonder if GM got caught short also- not easy measuring dimensional variations of shafts and races while they're whizzing around at high speed.

As for the offer, nope. Have this instead

 

[Hib Halverson]

I have spoken with several people who slip fit their bearings and they are the guys that break them down for routine maintenance on a regular basis. They also swear by them, however most owners are not going want to do this.

"Regular basis" in my case was once every 20 years or 40,000 miles and looking at the bearings, seals and the grease, I could have left them alone for a lot longer.

Again I wasn't trying to take your thread off track and I certainly believe your findings with your setup. My concern is for the person who may consider doing these at home and consider polishing the spindles for an easier installation only to have issue later on.

I took that as you talking about those who reduce the spindle dia. simply to make the parts easier to assemble, may end up with too much of a "slip-fit" and don't observe the rest of the proper set-up procedure.

Thanks for the write up Hib, I agree with all of your logic and it would be fun to turn back the clock to the early 60s and sit in on GMs engineering meetings to hear their thoughts on why they went from a slip to press fit.

My understanding is the press fit existed from day one or maybe there were two different degrees of the press fit. Also my understanding of why the press fit exists in the first place was, on 63-65s with drum brakes, if an axle broke, to prevent the axle flange/wheel/tire from separating from the car.

The cause was established as insufficient static preload not taking into account thermal changes at full operating speed. I can't help but wonder if GM got caught short also- not easy measuring dimensional variations of shafts and races while they're whizzing around at high speed.

I doubt that in 1960-61 when the development of that system was taking place that the technology existed to measure diameter changes in rotating shafts.

I'm going to assume that given my car's duty cycle and the lubrication I use, I won't have any failures due to bearing temperature.

This has turned-out to be a very interesting exchange of ideas. No doubt both types of bearing installations will continue to be performed on disc brake 65-82s

As for the offer, nope. Have this instead

Ya know, my Wife sometimes does both. When I get drunk, she'll slap me.

Now, on to a different topic....what would you guys think of an aftermarket, C2/3 trailing arm which was stiffer than the OE arms, allowed for wide wheels and was made of aluminum?

 

[Peer81]

I think for the people that have the patience, technical skills and care for detail to make a slip fit bearing setup that is sure a good idea.
But on the other hand I don't think a destroyed bearing isn't a big problem for most people (with a press fit) as a destroyed axle is!

I also would like to know if a slip fit wouldn't still spung is the bearing clearance is the normal 0.01 to 0.05?

Greetings Peter

 

[JohnZ]

Just for the record, the original '63 design used slip fits for both the inner and outer bearings, and the drive flange nut was torqued to 50 ft-lbs.

As a result of a spindle failure at the Proving Grounds (which resulted in the wheel, brake drum, and part of the spindle coming off the car), the design was changed, and went into effect at Chevrolet-Warren between November 2 - November 19, 1962. The spindle was revised to provide a press fit for the inner race of the outer bearing, and a chamfer was added at the shoulder of the bearing seat area of the spindle to provide for tool (bearing separator) access.

The diameter at the inboard end of the spindle was revised to provide a .0005" loose to .0005" tight fit for the inner race of the inner bearing, and the thickness of the washer under the spindle nut was increased from .140" to .210"; the drive flange nut torque was increased from 50 to 100 ft-lbs.

 

[Vettehead Mikey]

Just for the record, the original '63 design used slip fits for both the inner and outer bearings, and the drive flange nut was torqued to 50 ft-lbs.

As a result of a spindle failure at the Proving Grounds (which resulted in the wheel, brake drum, and part of the spindle coming off the car), the design was changed, and went into effect at Chevrolet-Warren between November 2 - November 19, 1962. The spindle was revised to provide a press fit for the inner race of the outer bearing, and a chamfer was added at the shoulder of the bearing seat area of the spindle to provide for tool (bearing separator) access.

The diameter at the inboard end of the spindle was revised to provide a .0005" loose to .0005" tight fit for the inner race of the inner bearing, and the thickness of the washer under the spindle nut was increased from .140" to .210"; the drive flange nut torque was increased from 50 to 100 ft-lbs.

Now you know what got me curious and asking on the VH site.:L

 

[Vettehead Mikey]

Courtesy of JohnH, Mike McKown and Mike Hanson, here are pages 1 and 2 of the TSB issued by GM on this subject. Note that they do mention the occurrence of the races rotating (spinning) on the spindle which I believe is the primary fault. Mike Hanson further explained the mechanics of why a slip fit inner race can be used successfully on a fixed spindle (like a front wheel) but is not the best strategy in an installation where the spindle rotates. Similarly, this explains why a slip fit outer race would be disastrous for a fixed spindle. Neat stuff.

 

[SVO]

Interesting to note that with the spindle change that Chevrolet did away with the recommended 30,000 mile service interval and stated that no periodic maintenance was required. I would like to see the engineering drawing for the revised spindle to see what the shaft dimension and tolerances for the outside bearing is.

 

[Mac]

Now, on to a different topic....what would you guys think of an aftermarket, C2/3 trailing arm which was stiffer than the OE arms, allowed for wide wheels and was made of aluminum?

Hmmm... lower weight, stiffer t/a, narrower track but wider wheel allowance... Interesting...

-Mac

 

[Peer81]

If I want to change the trailingarms I would do a compleet rebuild. So away with the problems that the original TA's have. And build something like an improved 6-link.

Greetings Peter