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911 Monoball Installation
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Pelican Technical Article:

911 Monoball Installation

Bruce Herrmann


2 hours2 hrs






Propane torch, punch, hammer, snap ring pliers, torque wrench

Applicable Models:

Porsche 911 (1965-89)
Porsche 912 (1965-69)
Porsche 930 Turbo (1976-89)

Parts Required:

Elephant Racing weather-sealed rear monoball cartridge set for rear trailing arm, 10.9 spec bolt for monoball installation

Performance Gain:

Improved ride and designed to last for 100,000 miles of use

Complementary Modification:

Have your 911 professionally aligned at the alignment shop

Monoball Installation Photos

Maybe some of you have considered installing the Monoball cartridge replacement for the rear trailing arm inner rubber bushing. Here are some photos of my installation, it's a really easy job and a high-quality part. Pelican carries them or can get them.

1. Remove the old steel/rubber bushing from the trailing arm (the trailing arm must be removed, I can't see an easy way to do this with it still attached to the spring plate/axles- so this job will require a trip to the alignment shop when you are finished).

Here's a photo of the inner steel sleeve (2 pieces, they come out from each side). If you have the aluminum arms, be careful not to dig into the surrounding aluminum-it's soft. The early steel arms are a bit more forgiving. Either way, the old bearings come out without too much trouble. Clean up the bores so they are smooth, remove any sharp edges and polish.

2. Next install the monoball inside the cartridge. On the left is the empty cartridge with the monoball, the right side shows the monoball installed. Use a small amount of heat (gently applied by a propane torch works fine) and the monoball slides into place to the stop.

3. Next, slide the snap-ring down into the groove in the cartridge, chamfer facing away from the monoball (i.e. flat surface of snap-ring against the monoball).

4. Now, heat the bearing area of the trailing arm to expand it slightly, the directions say not to exceed 180 degrees. Just get it warm with a few seconds exposure to the propane heat. The cartridge will slide in to the stop quite easily. The shoulder of the cartridge goes on the transaxle side of the control arm. This fuzzy photo shows the shoulder ..

5. Flip the control arm over and install the snap-ring in the groove on the spring-plate side, chamfer away from the monoball.

6. Now install the tapered cones on each side.

7. Now the control arm is ready to go back in. I used a new nut for the 10.9 spec bolt, it's nylock and I figured it would be a good idea if that bolt did not back off. Torque it to 44 ft.lbs.

My 73S calls for a 14 x 77mm bolt. This seems a bit short to me as the thread do not protrude far out the other side of the mount. I assume this change was made in '73 to allow removal of the control arms without removing the transmission. I used a longer 10.9 spec bolt that I felt more comfortable with, slid it in from the trans side and will plan on a partial engine/trans drop if I ever have to remove the control arms.

It's an easy install, it will be some time before my car is back on the road to report on how they work, maybe somebody who has installed them can let us know. They will allow for easier fine tuning of the rear suspension, that much is certain.

If I've left anything out, please correct or add as you see fit.

Bruce adds:

The monoball pivots around an axis whose center point is roughly the middle of the control arm mounting area. It allows the control arm to move through an arc but not up and down in the mount. Will it transfer more noise?- probably. Will it wear out before 100,000 miles, I would say so. It's probably not intended for cars which will see high miles unless you are willing to service the monoball (i.e. change it). It's pretty new so not much data out there yet. I like the design. I think it's best for someone who wants to be able to dial-in rear alignment settings. Time will tell if it's just another gadget or a real plus. -Bruce Herrmann

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Comments and Suggestions:
89airhead Comments: It would be helpful to see some detail on how one goes about removing the old bushings.
July 16, 2012
  Followup from the Pelican Staff: You have to heat the factory bushing slightly, then pry out the metal spacers. Once spacers are out, pull out rubber part of bushing. Then using a punch, knock out the inner portion of the factory bushing. - Nick at Pelican Parts  

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