Homemade Thrust Arm Bushing Monoball Upgrade

[KinkedChrome]

Update 8/31/2020:

There has been a lot of interest in these lately. I have these in stock and ready to ship for E38 and E39. I have them for both the thrust arm and control arm. The price is $200 per set or $175 per set if you buy the control arm and the thrust arm at the same time. That includes shipping and installation if you have arms shipped to me, most people just have them dropped shipped from their favorite supplier. I recommend installation into brand new arms. Try to avoid the very cheap parts, but I'll install them in anything you ship to me. Feel free to contact me directly at 208-577-0635 if you have any questions or are interested in purchasing.


Orignal Post:

I have been driving my E38 now with a bad 45mph shimmy all summer, which I attributed to bad thrust arm bushings. I have been putting off fixing it since almost all the miles I put on the thing are on the highway where it doesn't shimmy. Not to mention the will power required to work on cars outside in a Phoenix summer exceeds the amount of will power that I have.

I didn't just want to replace the bushing or the arm because I am of the opinion that the suspension setup has a design flaw that causes premature wear of the bushing. I feel as though these bushing wear prematurely because of the direction that the suspension travels. That is, it won't let the bushing rotate along the axis it was designed about. The hub wants to follow the travel of the strut and the spring along their linear axis towards the strut tower, not backwards along the axis of rotation of the thrust arm. Thus, every time the suspension travels the thrust arm bushing is trying to twist itself apart. If a guy were to replace the bushing with a spherical bearing, the thrust arm could than follow the travel of the hub without it's pivot point wanting to bind on itself. I briefly considered going with a polyurethane option, since I believe that poly urethane would be robust enough to handle it, but frankly it's just makes for a less fun project.

A few company's offer a monoball solution, some are even conveniently offered installed in a thrust arm. However, as a self-proclaimed circle expert, I decided to reject all those options and just build some myself.

I started off by trying to figure out what bearing to use. I have a lot of QA1 bearings around, and initially that is what I was going to use. A big beefy 1.00in spherical bearing and some misalignment spacers to match. Then I saw some of the other options out there that use a sealed OEM bearing. Even though the QA1 stuff does ok for everyday use, I really liked the appeal of a sealed bearing. I browsed realoem.com until I found an OEM bearing that had a 14mm bore. I ended up with PN 33326792553, it is a rear control arm bearing from later model BMW's.

I found some suitable 6061 stock and went to town. A few hours later I had a few parts in my hand and I'm pretty happy with the way they turned out.

[Sobek]

That looks fantastic, awesome work! I was reading about these and had a similar thought myself a year or so back, but I don't have the ability (or willpower, currently) to put them together like this. Let us know how they ride and if that sorts your shimmy out!

[Old525i]

Outstanding!

[haynes740]

Very nice setup, I’m going to follow this post for updates.


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[KinkedChrome]

Thanks for the kind words guys! I have about 100 miles on them so far. They did completely eliminate the 45mph shimmy which is so nice.
I did not realize how much stress that issue was causing me. Other than that, my experience thus far is consistent with other monoball reviews that I have read.

They definitely make the car have a much tighter feel during heavy turning and heavy braking. Although I use those terms lightly since I can't really
drive that hard on the street, but I can tell a difference. However, you also feel bumps, rough road, etc more than a bushed setup.
I feel like it is akin when you make the change from 16in wheels to 18in wheels. It is not unbearable, but you notice it. On the other hand if you didn't notice a change
in NVH switching from 16in to 18in, you probably won't notice this change either. I would say that the people who are very sensitive to the comfort that a
stock, well maintained, non-sport e38 provides, this would not be a good upgrade for you. But if your the type of dude that gets on the highway at 5am every morning
just so you can blast around a trafficless freeway interchange way faster than you should, which is not actually on your way to work, this is a worth while mod to do.

[Old525i]

What's the purpose of the four conical shaped devices?

[KinkedChrome]

What's the purpose of the four conical shaped devices?

They are spacers to make up the difference in width between the bearing and the bushing.

[racer2086]

Wow this is one of the best upgrades I've seen on this forum...and I've been on here a good while. The look of this is just simple and beautiful, not to mention functionally superior to the rubber bushing that is squeezed between the subframe so it can't rotate and instead shred itself.

I have that 50mph shake and hate it. Worse some days than others. I only seem to get a year or two out of arms before it comes back.

Kinkedchrome, two questions:

Can that outer metal sleeve you fabricated for the outside of the bearing be replaced with a rubber or polyurethane material? Reason I ask is because that will reduce a whole lot of the NVH from bumps since it appears from the suspension design that the thrust arm does most of the front-to-back stabilization of the wheel when it hits a bump travelling forward. That would make your design superior to anything else I've seen -- long term durability with as much comfort as possible. (As an aside, I felt the difference going from the Meyle HD bushings to stock Lemforder bushings; notably softer, but not mandatory, so I know what you're describing. I have Bilsteins and lowering springs on my car, so it's not like I need to ride on a cloud, but I feel like having the stiffer set up magnifies bumps.)

Second, can I buy from you a set of this stuff to put in my own arms? Or send you arms and pay you to press them (since I don't have a press)?

A+ job.

[bigperm206]

Wow this is one of the best upgrades I've seen on this forum...and I've been on here a good while. The look of this is just simple and beautiful, not to mention functionally superior to the rubber bushing that is squeezed between the subframe so it can't rotate and instead shred itself.

I have that 50mph shake and hate it. Worse some days than others. I only seem to get a year or two out of arms before it comes back.

Kinkedchrome, two questions:

Can that outer metal sleeve you fabricated for the outside of the bearing be replaced with a rubber or polyurethane material? Reason I ask is because that will reduce a whole lot of the NVH from bumps since it appears from the suspension design that the thrust arm does most of the front-to-back stabilization of the wheel when it hits a bump travelling forward. That would make your design superior to anything else I've seen -- long term durability with as much comfort as possible. (As an aside, I felt the difference going from the Meyle HD bushings to stock Lemforder bushings; notably softer, but not mandatory, so I know what you're describing. I have Bilsteins and lowering springs on my car, so it's not like I need to ride on a cloud, but I feel like having the stiffer set up magnifies bumps.)

Second, can I buy from you a set of this stuff to put in my own arms? Or send you arms and pay you to press them (since I don't have a press)?

A+ job.

+1. Following and I'd be interested in buying this set up from you as well.

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[1999 540i m]

Time for a group buy, e38, e39 540i, m5, and e53 x5, i'm in for a set,

[KinkedChrome]

Wow this is one of the best upgrades I've seen on this forum...and I've been on here a good while. The look of this is just simple and beautiful, not to mention functionally superior to the rubber bushing that is squeezed between the subframe so it can't rotate and instead shred itself.

I have that 50mph shake and hate it. Worse some days than others. I only seem to get a year or two out of arms before it comes back.

Kinkedchrome, two questions:

Can that outer metal sleeve you fabricated for the outside of the bearing be replaced with a rubber or polyurethane material? Reason I ask is because that will reduce a whole lot of the NVH from bumps since it appears from the suspension design that the thrust arm does most of the front-to-back stabilization of the wheel when it hits a bump travelling forward. That would make your design superior to anything else I've seen -- long term durability with as much comfort as possible. (As an aside, I felt the difference going from the Meyle HD bushings to stock Lemforder bushings; notably softer, but not mandatory, so I know what you're describing. I have Bilsteins and lowering springs on my car, so it's not like I need to ride on a cloud, but I feel like having the stiffer set up magnifies bumps.)

Second, can I buy from you a set of this stuff to put in my own arms? Or send you arms and pay you to press them (since I don't have a press)?

A+ job.

To answer your first question. Yes, I think this is possible. I had the exact same thought a few miles into driving around on the parts I just made. lol, like why couldn't I had thought of it before I started this project. I think it's an idea worth pursuing, not sure when I would be able to get around to it.

+1. Following and I'd be interested in buying this set up from you as well.

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Time for a group buy, e38, e39 540i, m5, and e53 x5, i'm in for a set,

For the second question, yes I will make these available for purchase. I have had enough interest in them that I think it's worth doing. I ordered some material for them today and have enough to make 30 or more sets.

The price will be $175 shipped to lower 48. So tell your friends. You can send me your arms also and I'll install them for free and ship them back for the same $175. I'll ship international, but I have never done that before so I don't know how all that works, but I'm sure I can figure it out. This will include the two aluminum housings, two lemforder bearings, and four stainless steel spacers.

Lemforder thrust arms are ~$100 with free shipping from the popular websites. So you if ordered them and had them shipped to me, you would have two brand new thrust arms with the mono balls for $375 shipped to your door. Would be even less if you went with a TRW arm.

If your interested send me a DM.

[Old525i]

Mmm, these should work with E34s. Some people used to install 750 bushings on E34 arms for longer life.

[KinkedChrome]

Mmm, these should work with E34s. Some people used to install 750 bushings on E34 arms for longer life.

If you send me e34 arms, id be more than happy to make them work for the same price.

[1999 540i m]

Do you have a rough estimate on when these will be ready to ship?

[KinkedChrome]

Do you have a rough estimate on when these will be ready to ship?

I ordered up a bunch of bearings and just received the raw stock for housings and spacers. I plan to machine the parts up over thanksgiving break. So they could ship next week as long as the bearings dont take too long to get here.

[racer2086]

I really want these, but I really want the poly housings with the bearings... What does it take to get/make those? Are they fabbed or ordered using dimensions from someone like Prothane? Seems like that is just a cylinder that you could give the width, OD, ID, and thickness (not even needed because of the OD and ID dimensions) and have someone make them? I wouldn't know where to start though.

[KinkedChrome]

I really want these, but I really want the poly housings with the bearings... What does it take to get/make those? Are they fabbed or ordered using dimensions from someone like Prothane? Seems like that is just a cylinder that you could give the width, OD, ID, and thickness (not even needed because of the OD and ID dimensions) and have someone make them? I wouldn't know where to start though.

I would just find a bushing with a barrel OD that would give me sufficinet wall thickness for the aluminum housing and maybe something like a 1.00in ID. Id then counter bore each bushing ID to fit the spherical bearing. The bearing would be captured between the poly bushings. The poly bushing would then have to be fixed in the thrust arm somehow. Id have to draw it up to see if there is enough meat on everything to make it all work out. Id probably need a bolt on flange on either side of the thrust arm to trap the poly bushings.

Bottomline is that it is probably a couple days of design time and researching hardware and then at least a full day in the shop building a prototype.

[1999 540i m]

Is this project still happening?

[racer2086]

I would just find a bushing with a barrel OD that would give me sufficinet wall thickness for the aluminum housing and maybe something like a 1.00in ID. Id then counter bore each bushing ID to fit the spherical bearing. The bearing would be captured between the poly bushings. The poly bushing would then have to be fixed in the thrust arm somehow. Id have to draw it up to see if there is enough meat on everything to make it all work out. Id probably need a bolt on flange on either side of the thrust arm to trap the poly bushings.

Bottomline is that it is probably a couple days of design time and researching hardware and then at least a full day in the shop building a prototype.

I was just thinking buy a sleeve with the same OD and ID as the aluminum sleeve you machined. Much like this:
Polyurethane-Bushing-for-Machinery-Buffering-and-Pressing-Reducing-Parts-Polyurethane-Sleeve.jpg

Then just press that in the thrust arm, press the bearing inside that and mount the thrust arm up with the conical pieces you machined. Would that not hold up you think?

[KinkedChrome]

Is this project still happening?

Yes it is happening. The first sets are shipping out this week. I have parts for e38 and e39, both 6 and 8 cyl cars.

[KinkedChrome]

I was just thinking buy a sleeve with the same OD and ID as the aluminum sleeve you machined. Much like this:
Polyurethane-Bushing-for-Machinery-Buffering-and-Pressing-Reducing-Parts-Polyurethane-Sleeve.jpg

Then just press that in the thrust arm, press the bearing inside that and mount the thrust arm up with the conical pieces you machined. Would that not hold up you think?

I dont think that would work the way you envision it. The poly has to be captured by the control arm to allow everything to pivot on the monoball. And the outer race of the monoball has to be captured by the poly. Other wise everything moves around under load. By definition, the poly cant hold a press fit since we are using it for its compliance to soak up some nvh.

[jjc034]

Yes it is happening. The first sets are shipping out this week. I have parts for e38 and e39, both 6 and 8 cyl cars.

How much for them?

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[bigperm206]

In for a set. Just sent you a DM.

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[KinkedChrome]

How much for them?

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$175 Shipped to you if your in the lower 48. $175 plus shipping anywhere else

In for a set. Just sent you a DM.

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I didn't see one come through so I dm'd you.

More parts shipping out this week.

A lot of these are already called for, but I still have a few left for anyone interested.

[1999 540i m]

Got mine today, looks good installs good thanks
IMG_1197.JPGIMG_1195.JPG