REAR AXLE BEARING SHIMS

[Jay Darlington]

I'm setting up my rear axle bearings and have the bearing retainers bolted up. i come up with a measurement of 4.10 mm for the gap and 4.90 mm for the thickness of the backing plate a difference of .80mm. my book says .10 crush on the bearing, so that means I need to install 9 .10 shims. does that sound correct? I don't remember that many being on there I only had 4 in my box of parts for the rear axle. the only thing different is the new axle bearings and a light coat of epoxy paint on the backing plates.
Jay D.

[Vic Skirmants]

Jay; and EVERYBODY else who is listening. The factory manuals give a wrong impression on what needs to be done regarding the shims. If you clamp the bearing, the backing plate will be loose. You have to clamp the BACKING PLATE, and not have excessive movement of the bearing. Jay, you would need to install 7 shims; which does sound excessive. Re-measure everything, especially the backing plate. Take four measurements NEAR THE BOLT HOLES. That area is usually thinner than the space between. Average the four measurements and let us know what you get. I assume you are NOT using the improper VW gaskets. Porsche did not use paper, just the O-rings.

[Trevor Sewell]

Hi all, i'v had to clean paint or powder coat of the matting surface on the back plate to get back to steel
Went from about the 4.90 you got down to 4.75.

[Vic Skirmants]

I'd put in 5 max.

[Jay Darlington]

went out and cleaned the paint off the backing plates and like Trevor I come up with 4.70. so now im looking at .60mm, should I just add 6, .10 shims to take up the space? the bearing is in the housing quite tight I don't think a few thousands thrust is going to make much difference. you do need the clamping force on the backing plate. the bearing I have is a SKF 6306/c3 and specs to 19mm wide I don't have the old bearing to compare and yes I do have the o ring kits.
thanks Jay D.

[Eric Wills]

JD

If you have 4.1mm gap, measured correctly and 4.7mm width backing plates, your shim total will be .5mm. 5 .10 shims. Vic explained in an earlier post. Take the difference and subtract .10mm. No preload on the bearing. Tight backing plates are required to keep everything solid while braking.
EW

[Jay Darlington]

got it its a done deal. as Vic said the books lead one to think that preload of the bearing is necessary but it just the opposite.
thanks for all the input. Jay D.

[Jeff Adams]

I would agree with Vic on a 5 shim maximum. Sometimes the thickness of a repaint on backing plates can result in a ridiculous stack of shims, especially if powder coated. An excess of shims could produce a situation where the oring that goes around the outside of the bearing doesn't get preloaded between the bearing housing and outer cap. This area often seeps gear oil when things are correct, and worse if the oring isn't squished properly.

[Eric Wills]

We have our axle tubes, backing plates and bearing covers powder coated. The folks we use for that service, don't apply the coating as thick as some others I have seen. We have them mask off the bearing housing and cap where it contacts the backing plate, so bare metal on those two pieces. Our powder coater has a poster on the wall in their warehouse with a diagram we created to mask axle tubes and other 356/911 parts properly! 3-5 shims installed is the usual.....even with powder coated backing plates

EW