Loose Rear Wheel Bearings. Help!

[Scott Clarke]

About two thousand miles ago I installed aluminum trailing arms on my '70. I assembled the arms with new bearings, heating the arms and freezing the new SKF bearings to assist in installation. I used the hubs from the aluminum arms (they came assembled) and the original drive flanges from my car. Everything was spotlessly clean and meticulously assembled. There were no suspicious, poorly fitting components. I was completely confident that everything had gone together absolutely correctly. If I remember correctly, the torque spec for the nut that holds the drive flange to the hub is in the order of 250 ft pounds. As my torque wrench doesn't have that capacity, I tightened the nut, essentially, as much as I could with a 1/2" breaker bar and a 2' pipe extension. A lot of torque.

Now, in the process of installing new rotors, I discovered that the passenger side bearings are loose enough that I can rock the hub assembly back and forth with my hands. The driver's side assembly seems fine. On the passenger side I checked the big nut to see if it was loose, and it is not.

So, what are the possible sources of this play? I'm sure not looking forward to taking all of this back apart again, but realize that I will probably need to. I'd just like to dive in only after really understanding what the possible sources of the problem are.

Thanks!

[DRACO A5OG]

Try re-torqueing it. I the FLAPS will rent a 250-300 torque wrench for free. Ask.

HF has them pretty cheap and they are guaranteed for life. I just got one for this purpose.

[stlrj]

I had the same problem and had to re-torque mine too. I can only assume they did not fully seat when I first installed them.


Cheers,

Joe

[Scott Clarke]

Gentlemen-

Wow, do I like what you are saying. I'll gladly spring for a HF 3/4" torque wrench if that solves my problem. I need to get to RRIV! Thanks for your perspective. I'll re-torque and post back the results.

[dad911]

1/2" breaker may be flexing before you can apply enough torque. I'd use 3/4 breaker/sockets.

[Grady Clay]

Here is a Factory cutaway diagram from a prior thread.


© 1969 Dr. Ing. h.c. F. Porsche A.G.

This is for the steel LWB trailing arm but the principal is the same.
The red arrows are pointing to the two rows of balls in the bearing assembly.

You need to decide if the hub/stub axle assemble and the two inner races are loose, causing the play or the bearing is loose in the trailing arm.
The former is related to correct torque on the stub axle nut that compresses the two race haves together with the hub on one side and the stub axle on the other side.

It is possible that the parking brake backing plate was deformed. This locates the bearing outer housing axially in the trailing arm.
If the bearing can move axially, it tends to enlarge the ID of the aluminum trailing arm producing some radial clearance.
This can allow the entire stub axle / hub / bearing assembly to ‘rock’.

As a first step, correctly torque the stub axle nut with a ¾”-drive torque wrench.

If the bearing is loose in the trailing arm, inspect the parking brake backing plate for deformation where it contacts the bearing outer race.
It is possible to deform the backing plate slightly to better contact the bearing.

If you have the bearing out of the trailing arm, inspect the bore with a precision bore gauge (as used for an engine cylinder).

Best,
Grady

[Canada Kev]

A couple years back, I had the same issue. I did some research here and some said that with the torque requirements, it is very difficult to over torque the nut. On my Carrera, the spec is for 348 lbs-ft or something like that (Yup, that much). I just went to a Canadian likeness of HF and bought a 3/4 inch drive 32 mm socket, a small extension and a four foot breaker bar. I figured that with a four foot bar, and my 180 pounds standing in the middle, it would be right around that 350 lbs-ft area. In retrospect, I probably should have sprung for the proper wrench, but with the amount I would use it, it seemed kind of silly.

Edit: I think I would listen to Grady on this one. Just throwing some more torque on the nut might not be the correct answer...

[Grady Clay]

There are two stub-axles and two different nuts: The early version (’65-late ‘80s) has M20 threads and a castle nut with cotter pin. This nut uses a 30 mm socket.
The later version (begins mid-Carrera production I think) has M22 threads and a self-locking nut.

The torque specs are:
M20x1.5 300-350 Nm (221 ft-lbs – 258 ft-lbs) or 300-320 Nm (221 ft-lbs – 236 ft-lbs).
The reason for the range is to accommodate tightening more to install the cotter pin.

M22x1.5 460 Nm (339 ft-lbs) self-locking nut. Is the wrench size 32 mm?

Best,
Grady

[Canada Kev]

Sorry, Grady, I don't recall. It's either 30 or 32 mm. I bought both at the time. I wasn't sure at that point and they weren't expensive.

[Scott Clarke]

Thanks for all of your input. I went to HF tonight to get the 3/4" torque wrench and 3/4" drive 30mm socket. Boy, it's nice having the right tools and not having to improvise (even if it's HF quality). I torqued the nut to 250 ft/#, and yes, it was very slightly loose. I'd say I turned it about 1/8 of a revolution. Bad news. Still some play. I removed the rotor to check the tightness of the parking brake backing plate bolts. They were not particularly loose.

The play is radial, and not axial. With the rotor off I can rock the hub back and forth and hear the contact being made between loose parts. It's not really enough to see, but I sure can feel and hear it. It seems to vary a bit as I rotate the hub, getting slightly tighter at one point of rotation and getting a little bigger when rotated 180 degrees from that point.

A couple of questions:

1. Should there be ANY play in an assembly that is right?
2. Is there the possibility that the new bearings are defective in some way?
3. How bad of an idea would it be to drive the car in this condition?
4. Am I correct in assuming that removing the stub axle and hub will require the bearings to be replaced?

Grady- point well taken about the parking brake backing plate. I did check tonight to insure that it was tight. It was. I can certainly see how it could become distorted and allow the bearing to back out. I did clean and paint those items when I installed the arms, so I'm confident that they were flat at that time. Sure seems like a weak part of the system, though.

Thanks again to all,
-Scott

[DRACO A5OG]

Damn, you had a choice of SKF or FAG bearings. Is there a reason besides price that you chose SKF. I bought the FAG bearings to replace my rears.

[Scott Clarke]

SKF was the more expensive choice. Forum research suggested that SKF were of higher quality that FAG, so I spent the extra money. Do you think FAG are better?

[will hung]

I've actually read recently that the FAG's have been regarded as having less "trouble" new ones.

[Grady Clay]

Scott,

Now that the stub axle nut is torque to spec and the play is still there, some measurements are in order.

Bolt a straight wheel (no tire) in place.
Measure the ‘play’ by pushing & pulling the wheel rim with about the same (hand) force.
Measure the peak-to-peak deflection.
Most important is the 3 – 9 O’clock position.
How does this measurement compare to the toe-in?

The problem with the bearing loose in the trailing arm is that it will only get looser.

When you installed the bearings, did you test-fit with everything at room temperature or did you assume that it would be tight and heat/cool the parts?
If not test-fit first, it may be that the bore in the trailing arm was already too large.

It may be prudent to expend your good (new) bearing and measure the bore. (I know – pita & $.)
After removing the axle assembly with stub axle, it may be possible to unscrew the parking brake backing plate and remove the assembled hub/backing plate/bearing (if loose) from the trailing arm.
If loose, there may be a Loctite (bearing retainer) product that is suitable for this use.


Now, if there is still some play in the 4-point bearing, there is a manufacturing ‘defect’ where the two inner races can touch each other before the bearing is tight.
I have never tried, but have been tempted to remove (by lapping) a small bit of metal from the inside end of an inner race.


You are doing very well with this.
Our cars respond positively to this kind of attention to detail.

Best,
Grady

PS: It might be useful to email the engineering departments at FAG and SKF about their quality control and enclose the (many) Pelican and other forums’ links.
G.

[RWebb]

if worse comes close to worst, and Loctite won't work, is there any way to source an oversize bearing from an industrial supply house?

[Scott Clarke]

Grady-

When I installed the bearings in the arms I attempted to do so with press I made from aluminum disks and all-thread. No way that was going to work. Since the arms were off the car, I realized I could pop them in the BBQ, which is the perfect size for an arm, and was really unlikely to piss of my wife! I heated up the arms and froze the bearings. The bearings dropped in and make went clink when they hit the stop at the other side. When temperatures normalized, they were tightly in place. So, I'd be surprised if the trouble was with the arm.

A quick search, interestingly, found this:

Loose SKF rear wheel bearing

This sounds exactly like my experience. I think an FAG bearing is worth trying. I'm scared to death of trying to get it pressed in place while on the car, however. If I hit the arm with a propane torch and freeze the bearing am I likely to get it together?

Grady-

What were you getting at with the idea of measuring the play relative to toe?

[Brando]

Originally Posted by Scott Clarke

[...] If I hit the arm with a propane torch and freeze the bearing am I likely to get it together?

I have done this method numerous times without issue. It is a good idea to inspect the inner bearing carrier of the hub for any burrs or gouges that could later create issues. A very, very fine smearing of anti-seize compound isn't a bad idea either.

As for pulling the bearing... Worst experiences with the 'slam' pullers. I've broken a few. The best puller is one of these:

Wheel Bearing & Hub Kit for Porsche-SIR Tools B90-P | eBay

[bazar01]

Originally Posted by Scott Clarke

Grady-

I'm scared to death of trying to get it pressed in place while on the car, however. If I hit the arm with a propane torch and freeze the bearing am I likely to get it together?

I tried heating my 964 rear arm with a propane torch and froze the bearing, and the SKF bearing only went in 1/3 of the housing. I had to use all threaded rod and properly sized steel disc to fit bearing outer race OD to push it all the way to the back stop. It's 8k miles and still very tight and quiet. I used SKF on both sides. Good luck with the FAG bearing and be ready when the bearing only goes 1/3 of the way.