Evening project: custom 128/135 control arm bushings

John V · 11-08-2016, 12:50 PM

A local autocrosser asked me how hard it would be to make some custom front bushings for his E82. The lower control arm on these cars has a very stiff rubber bushing from the factory, but he wanted to move the pivot point to gain negative camber.

The E90/E92 M3 control arms are compatible but slightly longer which achieves the same result, but they're not legal for his prep class.

There is an aftermarket polyurethane offset bushing available as well, but he's found that the adjustment slips. Polyurethane also sucks as a bushing material. I had some 2" diameter Delrin so I whipped up a prototype.

The bushing will be a shrink / force fit into the control arm. This bushing will see some off-axis loads and has the potential to turn. If it does that we can pin it, but I wanted to have him try it with just a force fit to see if it will hold. The center hole is 3/4".

The center sleeve is made in two parts out of 7075 alloy aluminum for strength. They're sized to allow free movement of the bushing around the sleeves. The bosses on each end are to constrain the fore-aft movement of the bushing and control arm. The minimum wall thickness is 0.2" and the center bore is 12mm to accommodate the stock bolt to mount the control arm.

Pretty easy parts to make, and allows a gain of about 0.75 degrees negative camber. The completed assembly ready to shrink and press into the control arm:

rumatt · 11-08-2016, 05:22 PM

That's awesome

Jeff_DML · 11-08-2016, 05:32 PM

Quote:

Originally Posted by rumatt

That's awesome

bren · 11-08-2016, 06:47 PM

Very cool.

So you shrink them by freezing?

John V · 11-09-2016, 05:36 AM

Yes. Delrin grows and shrinks a lot with temperature.

I didn't need to, though. They pressed in at room temp with no problem.

Biggins · 11-14-2016, 02:26 PM

Do you know how much camber would be gained from this? It looks like a cool project.

JST · 11-14-2016, 02:46 PM

Quote:

Originally Posted by John V

Yes. Delrin grows and shrinks a lot with temperature.

I didn't need to, though. They pressed in at room temp with no problem.

if they press in at room temp, what keeps them from pressing out?

John V · 11-15-2016, 05:41 AM

Camber gain should be about 0.75.

The force it takes to press them in is far more than they'll see in use on the car.

Biggins · 11-15-2016, 02:16 PM

Awesome, would this be a similar creation to the "offset bushings" that are sold for E36s?

John V · 11-16-2016, 05:49 AM

Similar, but because the E30/E36/E46 has a single control arm in front where the inner front pivot is a ball joint, the offset bushing in those cars adds caster rather than camber.

The 1 series and 3 series from the E90 onward has a two-arm front suspension with outer ball joints but inner bushings.

11-08-2016, 12:50 PM	#1
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	Evening project: custom 128/135 control arm bushings A local autocrosser asked me how hard it would be to make some custom front bushings for his E82. The lower control arm on these cars has a very stiff rubber bushing from the factory, but he wanted to move the pivot point to gain negative camber. The E90/E92 M3 control arms are compatible but slightly longer which achieves the same result, but they're not legal for his prep class. There is an aftermarket polyurethane offset bushing available as well, but he's found that the adjustment slips. Polyurethane also sucks as a bushing material. I had some 2" diameter Delrin so I whipped up a prototype. The bushing will be a shrink / force fit into the control arm. This bushing will see some off-axis loads and has the potential to turn. If it does that we can pin it, but I wanted to have him try it with just a force fit to see if it will hold. The center hole is 3/4". The center sleeve is made in two parts out of 7075 alloy aluminum for strength. They're sized to allow free movement of the bushing around the sleeves. The bosses on each end are to constrain the fore-aft movement of the bushing and control arm. The minimum wall thickness is 0.2" and the center bore is 12mm to accommodate the stock bolt to mount the control arm. Pretty easy parts to make, and allows a gain of about 0.75 degrees negative camber. The completed assembly ready to shrink and press into the control arm:

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11-08-2016, 05:22 PM	#2
rumatt Mugwump Join Date: Oct 2003 Carmudgeonly Ride: E46 330i, Chevy Colorado, Tesla Model 3 Location: NY Posts: 17,475	That's awesome

11-08-2016, 06:47 PM	#4
bren lawn boy Join Date: Oct 2003 Carmudgeonly Ride: e46m3, f25x3,C5 Z06, C4 Vette, 06 CTD Ram, and a trailer Location: Maryland Posts: 14,029	Very cool. So you shrink them by freezing?

11-09-2016, 05:36 AM	#5
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	Yes. Delrin grows and shrinks a lot with temperature. I didn't need to, though. They pressed in at room temp with no problem.

11-14-2016, 02:26 PM	#6
Biggins Crotchety Join Date: Aug 2007 Carmudgeonly Ride: 22 Tiguan, 11 328i Posts: 912	Do you know how much camber would be gained from this? It looks like a cool project.

11-15-2016, 05:41 AM	#8
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	Camber gain should be about 0.75. The force it takes to press them in is far more than they'll see in use on the car.

11-15-2016, 02:16 PM	#9
Biggins Crotchety Join Date: Aug 2007 Carmudgeonly Ride: 22 Tiguan, 11 328i Posts: 912	Awesome, would this be a similar creation to the "offset bushings" that are sold for E36s?

11-16-2016, 05:49 AM	#10
John V No more BMWs Join Date: Apr 2005 Carmudgeonly Ride: Ram, MS3, CX-5, RX-8 Location: Glenwood, MD Posts: 14,753	Similar, but because the E30/E36/E46 has a single control arm in front where the inner front pivot is a ball joint, the offset bushing in those cars adds caster rather than camber. The 1 series and 3 series from the E90 onward has a two-arm front suspension with outer ball joints but inner bushings.