Rear Spherical Bearings Conversion on Stock Arms

+1 on toe arms + lockout kit. M3 is very sensitive to rear toe and toe arms are a great investment.

Redd wrote

+1 on toe arms + lockout kit. M3 is very sensitive to rear toe and toe arms are a great investment.

It drives fine with the rear toed out lol.

yeah that'll help turn in

So what’s the verdict? If we have the original custom washers are we good? Someone mentioned needing to also either get new hardware or upgrade the hardware to ARP?

I just found out the inner non modified side of my arms had the bolt back out. Dunno if the installer didn’t torque things properly? (He did leave the front control arm loose too) Did I need to replace the hardware? Or upgrade to ARP hardware? Luckily Ace hardware had the same grade 10 nut that came off.

I have custom washers on the spherical bearing side… do I need to replace all the hardware?

Bolts backing out on that spot seem to be common even for stock arms. I think the bolt/nut just losing it's tightness. They are suppose to be replaced every time they are removed anyway. Suggest u get new bolts and nuts, or at the very least use Loctite.

Since replacing my hardware with the ARP listed above and using a dab of medium loctite everywhere, everything has stayed right where it should be. I have a set of custom washers.

The arp bolts with loctite seem to be a good idea! 774-1009 might be a better fit as they are stainless. Same strength as the black chrome Moly. They seem to be the same strength as 12.9 bolts, which is stronger than the stock 10.9.

Long term update - So far I've got almost 3 years / 20k kms on the spherical conversion. My car has had no issues with broken bolts or bolts backing out, or any problems with the bearings themselves. I'm using new stock bolts with Loctite. I dont track but do drive pretty hard in the hills.

Anyone know the best source to get the coned washers?

houtan wrote

Anyone know the best source to get the coned washers?

Email spikenipple at ow_dont_pull_that@hotmail.com. He makes them and has them for sale almost all the time.

I've updated this info into the first post also.

Gathering the parts to get this done on my 135i.

Is ARP 774-100 stainless, 664-1009 chrome moly, or new factory bolts recommended?

houtan wrote

Gathering the parts to get this done on my 135i.

Is ARP 774-100 stainless, 664-1009 chrome moly, or new factory bolts recommended?

yeah I'm confused as to the issue. Was it the cheap washer alternatives causing the issue since the conical face didn't match up right?

The other thing I am seeing is bolts backing out which I Can see causing them to then break... maybe just don't re-use stock bolts? BMW says they're one time use... Do these other bolts have a higher shear strength? When I was snapping diff bolts the only thing I found that worked was drilling out and moving to a thicker bolt... higher tensile strength bolts didn't help much in shear.

I ran a batch of custom washers a few years ago and I have not had any issues with bolts backing out or shearing. car has had 285 hoosier A7 on it in autocross... Should I be swapping bolts out?

I think it really comes down to the workload. The guys who've had bolts break are track cars with pretty quick drivers. Then again, even SPL bolts break at track.

If you're a street driver I think new stock bolts are sufficient. If you track the car heavily then upgraded bolts won't hurt.

bbnks2 wrote

yeah I'm confused as to the issue. Was it the cheap washer alternatives causing the issue since the conical face didn't match up right?

The other thing I am seeing is bolts backing out which I Can see causing them to then break... maybe just don't re-use stock bolts? BMW says they're one time use... Do these other bolts have a higher shear strength? When I was snapping diff bolts the only thing I found that worked was drilling out and moving to a thicker bolt... higher tensile strength bolts didn't help much in shear.

I ran a batch of custom washers a few years ago and I have not had any issues with bolts backing out or shearing. car has had 285 hoosier A7 on it in autocross... Should I be swapping bolts out?

Thanks. I agree and always replace then suspension bolts that say one time use.

Redd wrote

I think it really comes down to the workload. The guys who've had bolts break are track cars with pretty quick drivers. Then again, even SPL bolts break at track.

If you're a street driver I think new stock bolts are sufficient. If you track the car heavily then upgraded bolts won't hurt.

Do the stock bolts break on heavily tracked cars with stock arms? Or does the bushing soften things?



My rear m3 arms have been installed for 35k miles and the bolts have never come loose (knock on wood). So I’m leaning towards factory bolts unless the bearing places more load on the bolt.

Here's how I view the bolt issue:

The stock arms have the conical seat and when torqued that actually takes a lot of the sheer load so they're "single sheer" but the bolt never sees it. When you replace that with a bearing and washer you are creating a true single sheer plane that the stock hardware was never designed for, along with the bearing now inducing shock loads the stock system was never designed for.

The ARP bolts have a higher torque rating so you can crank them down to create more stiction between the bearing and the washer thereby creating less sheet force. I would also assume they have a higher sheer strength than the OEM bolts.

Also, I had OEM bolts loosen up on me twice, even with loctite and the ARP ones have been perfect for a whole track season so...

Lastly, they're not expensive and you're replacing the bolts anyway.

amg6975 wrote

Here's how I view the bolt issue:

The stock arms have the conical seat and when torqued that actually takes a lot of the sheer load so they're "single sheer" but the bolt never sees it. When you replace that with a bearing and washer you are creating a true single sheer plane that the stock hardware was never designed for, along with the bearing now inducing shock loads the stock system was never designed for.

The ARP bolts have a higher torque rating so you can crank them down to create more stiction between the bearing and the washer thereby creating less sheet force. I would also assume they have a higher sheer strength than the OEM bolts.

Also, I had OEM bolts loosen up on me twice, even with loctite and the ARP ones have been perfect for a whole track season so...

Lastly, they're not expensive and you're replacing the bolts anyway.

Like you said above, the bolt is just providing clamping force and the shear force is on the mating surface of the washer... much like a wheel lug bolt clamps a wheel to the wheel hub.

I don't see how the proper washers change anything vs a stock bushing. I don't see how it changes the shear plane. It's a single shear plane with or without a washer and since the washer doesn't change the surface area (if it's machined properly) then the shear load doesn't change. We aren't changing the bolt length or anything like that vs stock either.

I am leaning toward the re-use of stock bolts being an issue. I'll keep an eye on them but I don't think I am going to do anything preventatively. Really highlights the importance of following torque specs and measuring bolt stretch/fatigue if re-using hardware.

bbnks2 wrote

I don't see how the proper washers change anything vs a stock bushing. I don't see how it changes the shear plane. It's a single shear plane with or without a washer and since the washer doesn't change the surface area (if it's machined properly) then the shear load doesn't change. We aren't changing the bolt length or anything like that vs stock either.

The washer adds [strike]a true single sheer face[/strike] another slip plane that the stock bushing does not have.

Admittedly I'm an EE not an ME, but here's a simple drawing, stock on the left, washer on the right. Black is the bolt and the sheer force normal to the bolt which you can see ends up on the tapered face. On the left there is a sheer component (in orange) that is a true sheer force and doesn't end up anywhere other than the sheer on the bolt.

I think we should summon fe1rx I saw him brought up somewhere else around here recently.

amg6975 wrote

The washer adds a true single sheer face that the stock bushing does not have.

Admittedly I'm an EE not an ME, but here's a simple drawing, stock on the left, washer on the right. Black is the bolt and the sheer force normal to the bolt which you can see ends up on the tapered face. On the left there is a sheer component (in orange) that is a true sheer force and doesn't end up anywhere other than the sheer on the bolt.

I think we should summon fe1rx I saw him brought up somewhere else around here recently.

I did miss that the backside of the washer has less shear area compared to the conical face... I still don't think that's the issue but it's just my 2c. The broken SPL bolts had a similar failure point of installation torque causing bolts to back out and break.

bbnks2 wrote

I did miss that the backside of the washer has less shear area compared to the conical face... I still don't think that's the issue but it's just my 2c. The broken SPL bolts had a similar failure point of installation torque causing bolts to back out and break.

Yeah tons of people run OEM bolts without issue. I'm definitely in the minority but I guess hammering the bus stop at WGI is also not the usual use case.

So if APR is used, would you go chro moly again or stainless steel?

bbnks2 wrote

I am leaning toward the re-use of stock bolts being an issue.

I would not re-use stock bolts. Get new ones.

amg6975 wrote

The washer adds a true single sheer face that the stock bushing does not have.

I think we should summon fe1rx I saw him brought up somewhere else around here recently.

amg6975 is correct.

The following post is pretty sobering, if you are considering tapered washers:

https://www.m3post.com/forums/showpost.php?p=29083646&postcount=212

That failure looks like a fatigue failure to me, not a shear failure, but the fact remains that the conical washers fundamentally change the loading on the bolt, and any shear that makes it to the bolt is reacted on threads, not shank, which is bad.

Personally, I wouldn't use the conical washer solution.