Replaced Rear Wheel Bearings - Problem / Question

[JimmyZ]

Carl,

Just curious. Does your '72 FSM have any mention of using a fish scale on the rears? RE the earlier post I thought you were asking ME about the fish scale. (You were asking Julio)

FWIW If you go by the Haynes manual the 25-30 oz spec equals 1.5-1.8lbs of tug at the wheel stud. Really curious to see what the FSM says.

Here's my understanding of the deep groove ball bearing assy in the rear hubs. The tapered rollers up front are a completely different animal.

1.The issue is in the rigidty and fit of the bearings to their bores and shaft.

2."Preloading" or compressing of the ball bearing assembly which reduces internal tolerances is detrimental to the bearing. For instance, a spacer that's too short for one reason or another will cause the bearings outer race to shift relative to the inner race = bad. A spacer too large will allow the bearing to shift in it's bore. Tightening to reduce end play will cause inner race to crush reducing the bearing's internal clearances. They bearings will be too tight and bind. =bad

2a Using a scale on the axle simply checks that the bearings internal clearances are spot on.

3.It's highly likely that the designer specified the internal clearances of the bearings to jive with the the compression of the nut torqued to 200 ftlbs. (The races take on the right tolerances under compression otherwise they are "sloppy") This is why they reccomend tightening to achieve proper "preload". (Manual says preload to simplify things for the layman)

4. 200 ftlbs isn't much torque for a "fastener" of this size. You aren't going to get the stretch in the male member needed to reliably secure the nut in service. It's not long enough to have stretch. That's why it's staked. The torque exists to create a rigid assembly given that all of the parts are within tolerance.

The reason I'm writing this isn't so much for Julio but for the next guy who is searching the archives. We might also get lucky and have a resident engineer chime in.

2c

Jim

Edited October 17, 2008 by JimmyZ

[Carl Beck]

Carl,

Just curious. Does your '72 FSM have any mention of using a fish scale on the rears? RE the earlier post I thought you were asking ME about the fish scale. (You were asking Julio)

Hi Jim:

No problem - I was asking Julio or anyone that perhaps understood his first Post better than I, and I'm glad you answered.

Below are copies of the pages from the 72 Manual... my 73 Manual is in the garage right now - so it was easier to scan the 72 Manual in the office.. It is most likely the same as the 73.. No mention of the fishscale in the rear..

FWIW,

Carl B.

[doradox]

Hi Jim:

No problem - I was asking Julio or anyone that perhaps understood his first Post better than I, and I'm glad you answered.

Below are copies of the pages from the 72 Manual... my 73 Manual is in the garage right now - so it was easier to scan the 72 Manual in the office.. It is most likely the same as the 73.. No mention of the fishscale in the rear..

FWIW,

Carl B.

Bearing end play is given as 0 to .0057 in and bearing preload as 3.9 in*lbs or less. If you have more than 0 end play you will have no preload as there must be play in the bearings to have any end play. At 0 end play you must have no more than 3.9 in*lbs of preload. Since you can't

measure if you have less than 0 end play you use the bearing preload to make sure have not loaded the bearings too much.

Steve

[Oiluj]

After readng the post indicating it needs the 200 ft-lb torque, I went back last night and torqued both down to spec. No significant change in rotational resistance noted.

As a process check, I then removed the axle nut and inner hub to see of the rotational resistance was different from before. It was, but only very slightly, as the bearings have been driven onto the shaft into thier proper locations.

Based on what I've read in this post, I'll go with the 200 in-lbs torque and check for excess heat after a few miles, then again after 100 miles. I'll finish-up tonite with the shafts and the rear disc brake install.

BTW, the rear disc brakes installed easily, except that I had to "free" the frozen slide pins on one caliper.

[John Coffey]

Using a copper washer would be a poor choice for the long haul. It would compress and eventually give excessive slop.

The copper washer was/is a common dealer fix for hub bearing issues and I've seen them in probably half of the few dozen S30 rear hub assemblies I've torn down and rebuilt. Copper does not continue to crush once the nut is tightened and staked. I've also seen a couple aluminum washers.

[Nigel1943]

Three possible issues here. In a couple of axles I've stripped, instead of the correct stepped outer bearing there was a plain bearing and a spacer washer and also as far as I know there are at least two different length spacers between the bearings the most common one being the "B" spacer. I have also come across the copper washer.

[beandip]

My '73 has the copper washer, and my friend's '71 did also. When I finished assembly on both wheels they were stiff as Oiluj has stated. I had packed with the same grease he had as well. I figured it was likely the grease that caused the resistance. I had packed them well. I watched for any signs of heat , indicating a problem and didn't find any. After driving the Z for some the resistance is gone and they spin freely. I admit this is the first time I have done the rear bearings on a Z, but I have packed at least 100+ on other cars and trailers over the years with no problem. Gary

[JimmyZ]

RE washers/shims. If you've got proper tolerances with the shim after torque you're in pretty good shape. Later down the road the copper or aluminum may introduce some slop though. (If you call .001-.0015 slop) Since the OD of the bearing bores is a "loose" fit the designer would have wanted the faces of the bearings to register at the bottom of each bore. This would help keep the bearings aligned. Antifriction bearings are very sensitive to misalignment.

We're only talking about a service life reduction of several years if a poor fit is used. It's not like your wheel is going to fall off in a year or two.

I've got a brother in law that is an A&P for an airline. Although the school he and his co-workers went to was pretty good they manage to do some things that would make an engineer cringe. We were discussing the use of an air chisel on 4130 steel engine mounts once. Apparently no one educated them about the need to not create notches. (There were other things discussed which were equally distressing) Somehow the planes manage to keep their engines attached and several home and shop mechanics manage to keep their wheels on. :)

Edited October 20, 2008 by JimmyZ