Hot lug nuts and hub after Syncro front end rebuild [SOLVED]

[T3TRIS]

[MarkWard]

I was referring to the scoring on the inner surface of the bearing race. Especially since you thought it pressed apart pretty easily. You don't want to change the diameter of the stub shaft, but maybe some 320 might clean off some of the high spots so that when it goes back together it doesn't score the inner races.
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[T3TRIS]

[Zeitgeist 13]

Syncros, like most FWD/AWD VAG vehicles come with sealed front bearings, so there's no need to add extra grease, other than a light assembly coat to aid the hub stub into the inner race bore. Speaking of, that hub stub looks kinda scored up, but it's hard to tell. As mentioned, try cleaning them up with a light grit emery cloth. You should also clean the outer seal surface on the hubs.
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Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
'01 Weekender --> full camper
y u rune klassik?

[T3TRIS]

[MarkWard]

Talking about the race in this picture.

It looks distressed to me.
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[T3TRIS]

[MarkWard]

Well, that's certainly looks fresher. Carry on.
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[Sodo]

I think those scored surfaces main function is to center and support the races.
Sanding it with 320 etc would not reduce the diameter if you don't sand the scratches off.
All you want to do is remove any high spots - so they done cause additional galling and more scratches.
Be sure to "wash down" and float all the carborundum grit (or steel woll) off.


Discoloration of the grease is alarming.
Hard to tell in pics, but grey means steel, right?
And orange color changing, perhaps due to temperature?

Something is strange here and prob good you took it apart.
Not being there, it's difficult to offer ideas.

Can you put that grey grease hanging on a very soft thread, and check if a magnet 'pulls' it?
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'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[T3TRIS]

I wasn’t able to learn anything from a magnet and the grease... it’s just too messy for me to tell if there’s enough metal in the grease that it’s magnetic.
I also used 600 grit (didn’t have 320 grit) on the hub. Used a sheet of sand paper around the shaft and spun it. I couldn’t feel any raised surface catching, but it looks cleaner. Here’s how the other side looks by the way (the original one that had the loose axle nut). The lines are interesting. It seems that there is definitely damage from the loose axle nut, hopefully not enough that a new bearing will have issues.

Not sure what these marks mean... maybe that the bearing spun a fraction of a mm, breaking loose, before it starting pulling upward?
In any case, I wonder how much it would be to have this part machined... seems like a good contender for a machine shop out there.

Since I removed this side, we’re able to see the difference from side to side. Here’s the passenger side again, the one that was overpacked with grease and running 20° hotter than the other side:

Here’s the driver side, which had less grease packed into it and was running cooler:

To me the differences are obvious. The problematic one had its red grease turn dark gray and the grease inside the bearing seemed like some metallic fudge. The other side had its red grease still red and clean looking ball bearings. Here’s another photo with the ball bearings only comparing sides. As a reminder, there’s only about 140 miles on these and the right side wheel hub was running at least 20° hotter when testing.

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Guillaume, Jennifer & T3TRIS
87 2-knob Syncro
- 94 Subaru EJ22, 225/70-R16 CLK 16x7 ET37
- Transaxle rebuild, Mexico paint job, Front end rebuild, 320Ah LiFePO4 Battery

[Sodo]

[T3TRIS]

[T3TRIS]

New update: I just finished pressing the bearings back in. I only used the thinnest film of grease to coat the outer seals. I installed the steering knuckle on the passenger side (the problematic one), without the axles and without brakes. In this exact scenario, when I tried spinning the wheel by hand, the wheel would stop within 2 seconds. Now with the new bearing, the wheel stops spinning at 6 seconds.
I installed the CV joint (without the axle) and torqued the nut, the wheel stops spinning just after 2 seconds (used to be just 1 second).
None of this is very scientific but it was clear to me that the wheel was much easier to spin without all that grease than it was when I overpacked the bearings.
I’ll keep installing everything and I’ll try to take that same drive tonight or tomorrow, without using the brakes and measuring hub temps. I’ll measure rotor temps too.
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Guillaume, Jennifer & T3TRIS
87 2-knob Syncro
- 94 Subaru EJ22, 225/70-R16 CLK 16x7 ET37
- Transaxle rebuild, Mexico paint job, Front end rebuild, 320Ah LiFePO4 Battery

[T3TRIS]

I put everything back together and went for another test ride doing the same loop as before, stopping in the same spots (without using the brakes) to measure temperatures. Conditions were similar though about 5º cooler (43º to 44º instead of 47º to 49º the first time around).
I measured temperatures on the rotors, which is a bit finicky with an IR gun but the rotors never got over 70º. I only had to brake briefly once on the second test in order not to turn right without stopping at a red light as a car was coming!
Here's a graph of my measurements.
The dotted lines represent the first test, before replacing both front wheel bearings.
The solid line represents this latest test, after replacing wheel bearings.
The blue lines represent the passenger side (right side).
The green lines represent the driver side (left side).

It would seem that replacing the bearings fixed the hot wheel hub issue. Our right side wheel hub used to run 20º hotter than the left side when I performed this short, low stress test. I imagine the difference from side to side was much more significant after extended highway driving (which I didn't get to measure). Though it was a few degrees cooler outside, both sides seem to run cooler and both sides are the same temperatures.

Another thing I noticed was that the cage of the outer front CV was cooler on the passenger side by 15º to 20º (from about 115º at highway speeds down to 99º), however the driver side was running about 10º warmer than before (from about 115º at highway speeds up to 124º). I'll have to keep an eye on this, though I do intend on replacing those outer CV's eventually.

I'll keep an eye out on things but I'm thinking (hoping) this one is solved. Bottom line is:
Don't pack the sides of your syncro front wheel bearing with grease!!!

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In case this image of the graph disappears, here's the temperature the data:

0.4 mi, max speed 10mph
Right side before wheel bearing swap (RB): 66º
Right side after wheel bearing swap (RA): 57º
Left side before wheel bearing swap (LB): 59º
Left side after wheel bearing swap (LA): 57º

1.4 mi, max speed 35mph
RB: 90º
RA: 72º
LB: 70º
LA: 72º

2.8 mi, max speed 35mph
RB: 100º
RA: 75º
LB: 80º
LA: 78º

5.6 mi, max speed 60mph
RB: 126º
RA: 92º
LB: 100º
LA: 91º

7.8 mi, max speed 60mph
RB: 123º
RA: 95º
LB: 100º
LA: 94º

10.3 mi, max speed 40mph
RB: 119º
RA: 85º
LB: 97º
LA: 95º
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Guillaume, Jennifer & T3TRIS
87 2-knob Syncro
- 94 Subaru EJ22, 225/70-R16 CLK 16x7 ET37
- Transaxle rebuild, Mexico paint job, Front end rebuild, 320Ah LiFePO4 Battery

[4Gears4Tires]

[jimf909]

Nice work. I love science!

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- Jim

[MarkWard]

There's an old trick for removing VW pilot bearings. You pack the bore with grease and then using a spare input shaft, you force it into the grease and it walks the pilot bearing out.

In other words, you probably did develop some pressure with the added grease that wasn't playing well with the other parts.
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[korkwood]

It sure is a very long discussion. Just wanted to chime in
I am sure heat was caused by improperly installed bearings.
Nothing to do with extra grease, if there was too much of it would easly escape thru the seals. Nothing to do with torque as more torque doesn't do anything to bearings except squeeze hardened inner race more.
I have seen "professional mechanics" installing bearings wrong way
These bearings have to installed carefully and in certain order.

[T3TRIS]

[korkwood]

I always put grease next to bearing and never ever had the "hot hubs".
Too much grease escapes thru seals but keeps dirt out of bearings
Just replaced bearing on one side, not because it was worn but 2 studs spun after taking my Syncro for tire work.
Dirt roads really mess up Vanagons...but also lead to better life