95maxrider
95maxrider Reader
2/24/19 8:25 a.m.

I've been trying to replace the spherical bearings at the bottom of my "custom" Bilstein rear shocks on my rally-x 1998 M3 for a while now, and I'm having a hard time finding the correct replacement parts.  I'm unable to get in contact with the guy who built these for me, and the two replacement bearings I've ordered have been slightly off.  If anyone can point me in the right direction, I would greatly appreciate the help!

I was pretty sure the second set I ordered were going to work, so I pressed out the originals:



Here's what I'm working with.  The original is on the left, the Bilstein bearing is in the middle, and the most recent one from RE Suspension is on the right.





Unfortunately, when I went to press in the new ones from RE, they just dropped right in the hole with no need for a press.  Turns out 0.6 mm is a lot when it comes to this stuff!  Also, the outer race is too wide, making it impossible to reinstall the second circlip.

So here's my problem: the bearing dimensions for the bearing from Bilstein (center) are incorrect, and the outer race dimensions for the bearing from RE (on the right) are incorrect.  Here's a chart summing up the problem areas:



Making things more complicated are these spacers for each side of the bearing:





I have no idea if these were custom made or if they're an off the shelf part, but I need to use them.

I'm going to reach out to Bilstein and RE Suspension again tomorrow when they open, but I wanted to put this out here in case anyone knew of other places I should check.  Please let me know if you have any advice on how to proceed.  Thanks!

rslifkin
rslifkin UltraDork
2/24/19 9:36 a.m.

Is there any reason you can't use the Bilstein bearings with different spacers and bolts?  Bilstein offers spacers for their off-road shocks that serve the same purpose as the ones in your picture.  Worst case, your shock mounts might just need slight modification to get solid mounting with a different size bolt. 

Dr. Hess
Dr. Hess MegaDork
2/24/19 9:56 a.m.

That looks like some serious Aggie Rigging there.  If McMaster-Carr doesn't have it, it's got to be some custom made part.  What is the bolt diameter?  I'm thinking:  Make a sleeve for the shock end with the ID to fit some actually available spherical bearing.  Make a new spacer for the rest of that.

rslifkin
rslifkin UltraDork
2/24/19 10:14 a.m.

Wait a second...  Do those spacers insert into the bearing and shrink the bearing ID down to the bolt size?  If so, the Bilstein bearing and spacers might be pretty easy to adapt. 

95maxrider
95maxrider Reader
2/24/19 4:13 p.m.

Sorry, I should have included some other info in my original post!  So here's how it looks installed on the car with the spacers on either side:

The bolt there is an M12x1.5, with a diameter of 11.75mm/0.462".  The ID of the spacers is 12mm/0.475".  The ID of the Bilstein bearing is 12.72mm/0.5", which would allow too much play around the bolt if the reducing spacer wasn't used.  When I showed it all to the owner of a local BMW racing shop, he mentioned that milling down the existing spacer wouldn't leave enough material on the lip where it goes into the bearing for necessary strength.

 

rslifkin: To answer your first question, I don't know.  I wasn't aware Bilstein made spacers like this that I could just buy.  Regarding your second question, the answer is yes.  The problem I'm concerned about is that the ID of the original bearing is 15mm.  The OD of the bolt is 11.75mm.  That leaves about (15-11.75=3.2 / 2) 1.6mm of metal thickness for the part of the spacer that goes into the bearing.  If I use the Bilstein bearing, with an ID of 12.7mm, that would leave something like (12.7-11.75=0.95 /2) 0.475mm metal thickness if I were able to find a new spacer to fit.  I don't think a spacer with metal thickness of less than 0.5mm is going to be very strong.

 

Dr. Hess:  I've never heard that term before, but I'll assume it's not a good thing!  Please see the info above regarding the size of the bolt, and how using the Bilstein bearing would necessitate a spacer with metal that would likely be too thin.  I looked through the stuff at McMaster-Carr, and they don't seem to have anything even close in the spherical bearing section.  Using the terms in their chart, my ID is 15mm and my OD is roughly 1-1/32".  They don't offer a single bearing with a 15mm ID.

 

Question: A friend mentioned removing the spacers and finding a shoulder bolt of the proper dimensions.  This would hard mount the shock to the spindle assembly, which is I guess how it was stock.  What benefits are there to having a spherical bushing there, allowing the shock to swivel a bit?  Would I lose anything by hard mounting it and basically bypassing the utility of the spherical bearing?

Dr. Hess
Dr. Hess MegaDork
2/24/19 5:11 p.m.

I think you need some movement there, not hard mounted. You could always go urethane or Delrin.  As I said, if McMaster doesn't have it, it probably doesn't exist.

It looks like that Bilstein bearing you have will press in the shock and work.  Shim it with some half MM something or other or make a sleeve so it is all tight and make new spacers.  When it is all bolted solid, it won't matter how thick the shim material is.

TurnerX19
TurnerX19 Reader
2/24/19 5:22 p.m.

There is definitely some angular movement at this shock bottom that needs a spherical bearing or a rubber bushing to accommodate it. The spacers you show are very common on formula and sports racing cars of the 1960s onwards. Do not be concerned about lack of wall thickness on the inside of the spherical, the load is taken by the step edges and the bolt itself. Use the Bilstein bearing and modify your spacers in the lathe for diameter and use a slightly longer bolt to take up the additional width. Might be easier to make new spacers  rather than modify what you have, then you can accommodate the original bolts as well. Do not worry about any eccentricity, it does not effect operation. The large O.D. of the spacer is a fail safe in case the spherical disintegrates, as required in some racing rules.

rslifkin
rslifkin UltraDork
2/24/19 6:02 p.m.

Use the Bilstein bearings and spacers.  Drill the mount holes a hair larger if needed and use a 1/2" SAE bolt instead of metric.  That'll be a tight fit in the Bilstein bearings. 

There are also poly bushings you can press in to those shocks in place of the bearings. 

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