Another 930 rear wheel bearing replacement saga

DaytonaCoupe66 · 01-02-2022, 07:30 AM

Hello and happy 2022!

I'm unravelling a rear vibration issue. One of the potential remedies involved replacing the left rear trailing arm when the toe eccentric mount was found to be broken. The axle was put on a lathe and found to be out 65/1000", so either offroaded at some point, or perhaps a CV joint let go and beat the edge off the trailing arm.

Having bought a shiny new control arm from the local P dealer, and the bearings, seals, and crush sleeve from our host, I brought the package with the workshop manual to a local mechanic who is experienced. We followed the gospel to the letter when doing the install. Used a press.

However, when the races, bearings and seals were in place, the trailing arm was back in the car, and the hub was put back together, the brake caliper will not centre over the disc. Note from the photos that the outside of the disc is snug against the outside edge of the caliper. It's as if the hub isn't in far enough.

We went as high as 340 ft lbs on the nut, but no change. As noted earlier, the script in the manual was followed exactly, and before inserting the bearings, we confirmed that the races were seated. The crush sleeve is on correctly. Once back together I took it out for short drive, ever hopeful that it'd seat itself (I know, dumb hopefulness), but no go.

I'm in the process of removing the trailing arm...again. I don't know whether to take another crack at the press, or pull it apart and start over. I expect the inner bearing and seal will be destroyed if dismantled.

Any thoughts on what's going on? Has anybody else been plagued with going backwards in this manner?

Cheers!

DaytonaCoupe66 · 01-03-2022, 05:29 AM

I've read sooo many rear bearing threads. The arm is off the car. I'll remove the hub and investigate what happened. I'm thinking that 'something' has obstructed the hub from fully seating. Round 2.

timc · 01-03-2022, 07:44 AM

If you are just trying to get the bearings out, just heat up the trailing arm with a map torch, two people make it more consistent, then the bearings almost fall out. Look for my thread. I struggled to get them out, and install one, then I decided to try heat and it made it so much easier. You don’t have to remove trailing arm, that just adds to the work. Good Luck!

T77911S · 01-04-2022, 04:08 AM

when I did mine I found that angle torqueing worked for me.
torque it up to 320 or 340, then continue to angle torque.
I think I marked the nut as a reference
you need to check crush sleeve with a dial gauge.
from memory, you have to loosen the nut back up and torque to around 220 to check it.

looking at the pic and to make sure I am seeing this correctly, the outer edge of the rotor (where the vents are) is hitting the caliper (between the pads).

that would not be a hub problem. it would be either the mounting holes on the arm or the screw holes on the caliper. by any chance is that a front caliper on the rear? don't know if the mounting ears or tabs are different but I know the piston size is smaller in the rear.

show us the mounting tabs or ears on the caliper.
I think you need a new bearing and crush sleeve if you take it apart.

I helped tim do his and I did mine myself on the car.
there is a good thread on here showing you how.

aschen · 01-04-2022, 07:00 AM

Jeeze dude, I feel your pain especially with a new trailing arm. I thought those were NLA.

I don't have anything productive to add except the only Thing I can think of is the bearing races not being fully seated like you said. They should definately seat themselves with 300ftlbs of torque on the axel nut though. Any chance of wrong part # bearing?

Is there any end play after torquing?

DaytonaCoupe66 · 01-04-2022, 07:58 AM

Quote:

Originally Posted by timc

If you are just trying to get the bearings out, just heat up the trailing arm with a map torch, two people make it more consistent, then the bearings almost fall out. Look for my thread. I struggled to get them out, and install one, then I decided to try heat and it made it so much easier. You don’t have to remove trailing arm, that just adds to the work. Good Luck!

Trailing arm is out. I'm getting good at this with practice so didn't take long

. I have a set of bearings, new crush sleeve and grease seals in the garage so it's going to come apart for a lookie.

DaytonaCoupe66 · 01-04-2022, 08:15 AM

Quote:

Originally Posted by T77911S

when I did mine I found that angle torqueing worked for me.
torque it up to 320 or 340, then continue to angle torque.
I think I marked the nut as a reference
you need to check crush sleeve with a dial gauge.
from memory, you have to loosen the nut back up and torque to around 220 to check it.

looking at the pic and to make sure I am seeing this correctly, the outer edge of the rotor (where the vents are) is hitting the caliper (between the pads).

that would not be a hub problem. it would be either the mounting holes on the arm or the screw holes on the caliper. by any chance is that a front caliper on the rear? don't know if the mounting ears or tabs are different but I know the piston size is smaller in the rear.

show us the mounting tabs or ears on the caliper.
I think you need a new bearing and crush sleeve if you take it apart.

I helped tim do his and I did mine myself on the car.
there is a good thread on here showing you how.

We were uber diligent in following the service manual script. We torqued to 340 ft lbs before backing off after this issue was realized with the caliper. End play with the dial guage was < 1mm. The outer edge of the disc was right up against with the outer lip of that rotor so the rotor wasn't centered. Retorqued to 340, then back off. Short drive and no change. For the old trailing arm the rotor had been properly fit with the disc in the exact centre. I'm thinking that either the hub is hung up, which would cause the rotor to be further out than it should be, or the mounting boss for the rotor is not exact to the original as you mention. Then I think, naw, it's a new part from P (albeit a 'superceded part #) and I've been of the view that they don't make engineering mistakes.

I'll post a photo of the caliper.

DaytonaCoupe66 · 01-04-2022, 08:23 AM

Quote:

Originally Posted by aschen

Jeeze dude, I feel your pain especially with a new trailing arm. I thought those were NLA.

I don't have anything productive to add except the only Thing I can think of is the bearing races not being fully seated like you said. They should definately seat themselves with 300ftlbs of torque on the axel nut though. Any chance of wrong part # bearing?

Is there any end play after torquing?

I had purchased a rear bearing kit X 2. The races and bearings appeared to be the right configuration/size and they went in OK as far as I could tell. Cranking to 340 ft lb didn't appear to make any difference in seating the hub.

DaytonaCoupe66 · 01-04-2022, 09:03 AM

I appreciate the comments. I've made an appointment with the local P car service dept and will bring them the old arm, new arm, full bearing kit, rotor, caliper, axle, nut. The old arm had been tragically broken at some point at the toe eccentric capture. Not my first choice but P sold me the new arm so I think it's wise to involve them in the problem solving.

T77911S's comment about the mounting boss for the caliper has me thinking that perhaps this superceded 'newly manufactured' part isn't exact, although I'd be surprised to hear that Herr P would make an engineering faux pas. The material in the new arm appears to be slightly thinner, whereas the mounting bosses for the caliper and the spring plate surfaces are reinforced and raised higher than the old unit. Time to confirm with the calipers (the old arm has been at a machine shop for an attempted repair so I'll pick it up this afternoon).

I'll pass on what I learn. I've been chasing the cause of a vibration in the rear that I arm chair diagnosed as a bad CV joint and I'm finding all sorts of extra things that need attention. The transmission is also out for a rebuild. Fortunately we enjoy 5 months of winter here so there's time to catch up on the things that need obvious attention.

Cheers

T77911S · 01-04-2022, 10:11 AM

I don't understand the caliper alignment issue.
if you are facing the caliper, as in looking towards front of car, if the caliper is out of alignment left to right then you forgot the spacers, if it is front to rear then its something else.
again, trying to remember if both front and rear have the spacers.

T77911S · 01-04-2022, 10:14 AM

again, angle torque for the crush sleeve. turn about 45 degrees then check play. trying to determine WHEN it starts to crush is what makes it hard, that's why angle torqueing worked for me.
first one took hours, other side maybe 20 minutes.

DaytonaCoupe66 · 12:39 PM

No spacers for the rear just the front. The alignment problem is left to right as when the disc is on the hub and secured with the 2 screws so it’s tight and the caliper is affixed to the arm the outside face of the disc is snug against that face of the caliper where the pistons apply pressure to the pad. The caliper is not hovering over the centre line of the disc so it looks like the disc / hub are not in quite far enough. So putting in the pad on the inner faceof the caliper is roomy, whereas it is too tight on the outer face. I’ve measured the trailing arms and the mounting points seem to be identical. I’ve cranked up to 340 ft lbs, went for a drive, then cranked again to 340 before backing off to spec. I don’t want to crank higher on an aluminum part. For the cost of the bearings and crush sleeve it’ll be taken back apart and we’ll start over. Chit luck for me on this job.

DaytonaCoupe66 · 01-04-2022, 01:22 PM

Here's a photo looking down through the caliper at its' positioning vis-a-vis the disc....exaggerated slightly for the purpose of illustration. It's closer to one face/side of the disc than the other. Hoping this clarifies what I may have confused with words.

Also looking into the back of the new trailing arm vs the old arm, the inner grease seal is flush with the face of the hub as one would expect on the old one.

On the new arm the grease seal is pulled into the hub 1/8" of an inch in, and the bearing doesn't look like it's flush up against the seal but I'm not sure how far onto the hub shaft it should be or how far into the hub the bearing should sit. I'm thinking that the hub isn't pressed in enough. Maybe my paranoid preoccupation with damaging the hub caused an overabundance of caution at the press.

I'm going to hold off on that trip to the dealer and give this more thought. The input is helpful, thanks!

TurboKraft · 01-04-2022, 03:12 PM

Quote:

Originally Posted by DaytonaCoupe66

...perhaps this superceded 'newly manufactured' part isn't exact, although I'd be surprised to hear that Herr P would make an engineering faux pas.

I am sad to say we are seeing this more often than it should happen. Many new parts are simply not correct, not fitting properly.

I hope this is not the case for you, and it was simply an assembly error.

Also, be very carefully heating the trailing arm up with a torch, either propane or mapp gas -- they can make a flame of 3,600F+, while (pure) aluminum's melting point is only ~1,220F. Move the flame around a lot. You're looking to warm up the arm so the aluminum expands a minute amount.

DaytonaCoupe66 · 01-04-2022, 04:52 PM

Quote:

Originally Posted by TurboKraft

I am sad to say we are seeing this more often than it should happen. Many new parts are simply not correct, not fitting properly.

I hope this is not the case for you, and it was simply an assembly error.

Also, be very carefully heating the trailing arm up with a torch, either propane or mapp gas -- they can make a flame of 3,600F+, while (pure) aluminum's melting point is only ~1,220F. Move the flame around a lot. You're looking to warm up the arm so the aluminum expands a minute amount.

An interesting point on the newly manufactured parts. I’ll give it one more try and if the result is the same it’ll go to the dealer next.

T77911S · 01-05-2022, 05:10 AM

its hard to tell from the pics but the two arms don't look the same unless its just that one arm is angled different than the other
the inner mounts look different and cant tell because the old one is dirty but it looks like the new one has area machined out on the tabs where the caliper mounts.

DaytonaCoupe66 · 01-05-2022, 11:23 AM

Quote:

Originally Posted by T77911S

its hard to tell from the pics but the two arms don't look the same unless its just that one arm is angled different than the other
the inner mounts look different and cant tell because the old one is dirty but it looks like the new one has area machined out on the tabs where the caliper mounts.

There are a few slight differences as you’ve noted. Where material is machined off one face there a raised boss on the opposite face of the mounts to the spring plate. I did not have trouble mounting it as per the original and the 4 wheels were aligned within spec. The mechanic invited me in so no shortcuts. It’s the caliper that’s causing me the trouble. If too much was machined off the caliper mount I’d have a different problem where the other face of the disc would be against the other side of the caliper. I was going to tackle this again but we had been so careful that I can’t think of any steps we boogered up. I’m taking it to the dealer that sold it to me tomorrow with all the parts they need to put the bearings in round 2, including the disc and caliper, hub and stub axle for a trial fit of the caliper . We’ll see how they do. If they get an identical result I hope not to be told that it needs to be on the car and torqued fully to spec before the hub seats in. 125 ft lbs on the bench should get the bearings into the races. I’ll bring the original crush sleeve. It barely compressed, certainly not anywhere near the amount that my caliper is off. I’ll also bring the old trailing arm. I expect that if an anomaly is found with the trailing arm the dealer will be transparent about what the issue is. Unfortunately I don’t get away with a diy on this one. I’ll report back on the outcome. Thanks for the comments.

T77911S · 01-06-2022, 03:52 AM

just curious.
measure the old crush sleeve and the new one. I would think they should be very close.
if they are not you got the proper amount of end play then one of the races was not seated all the way in. i would assume the outer one.

Alan L · Alan L's Garage

You did mention earlier that end play was <1mm.
I am guessing you made a typo. I did mine earlier this yr - and posted it all up on the forum.
But from memory you are looking at end play of around 1 Thou, 0.001".
If you really did have end play in the mm range, things have not seated right.
We are feeling the pain. This would be the most stressful job I have done on the car - short of putting case halves back together.
Alan

DaytonaCoupe66 · 01-06-2022, 03:43 PM

Quote:

Originally Posted by T77911S

just curious.
measure the old crush sleeve and the new one. I would think they should be very close.
if they are not you got the proper amount of end play then one of the races was not seated all the way in. i would assume the outer one.

That is a great suggestion. I dropped the parts off at the dealer this morning. Fortunately business is slow so I had occasion to pull into the intake area and go over the parts and the predicament with the mechanic who will do the work, with both the Parts and Service Managers present. Best that the story come directly from me vs get passed on third hand to the mechanic. The Parts Manager had sold me the new arm. I hope to hear something tomorrow.